EARLY WEANING IN SWINE: A BEHAVIOURAL ASSESSMENT

A Thesis

Presented to

The Facuity of Graduate Studies

of

The University of Guelph

by

ERlN KATHLEEN SOPHIE WOROBEC

In partial fuifilment of requirements

for the degree of

Master of Science

August, 1997

O Enn Worobec, 1997

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ABSTRACT

EARLY WEANING IN SWINE: A BEHAWOURAL ASSESSMENT

Erin Kathleen Worobec University of Guelph, 1947

The relationship between weaning age, pigkt and sow behaviour and performance was

investigaiai. Piglets weaned at 7 days of age had difficdty adapting to weaning. They

exhibited redkcted nursÏng behaviour (beily-nosing), dec-d social contacf Iess interest

in theu environment and had minimal growth. This evidence suggests th& weaning at 7

days of age is too eady. Piglets weafled at 14 days of age exhibited more behaviour

problems than 28day-weaned anirnais but had Iess skin abrasions h m fighting. This

suggests that pigiets weaned at 14 days have both wetfare advantages and disadvantages

cornpared to those weaned at 228 days. They had similar growth rates to piglets weaned at 28

days indicating that they codd compete commercially with initiai f e d encouragement. Sow

behaviour and pdomance were not affected by weaning age in this study. AU these results

suggest bat weaning piglets between 14 and 21 days will be the best compromise between

performance and welfare.

Table of Contents

Literature Review

..................... ....*.......................................... The trend towards Early Weaning l.. 1

Disadvantages of SEW ............................................................................................ 3

Behaviour Feeding behaviour in Pigiets ..................................................................... 4

.......................................... Weaning behaviour - When the Sow Decides 6 Weaning behaviow at 3, 4 and 6 Weeks ................................................... 8

............................................................... Weaning behaviour at 2 Weeks 10

Feeding the Early-Weaned Piglet .......................................................................... 11

The Conflict between Nutritional Requirements and ................................................................................................. Behavioural Needs 12

.................... How Does Environmental Enrichment Affect Weaning Behaviour? 14

Does the Shortened Lactation Length Associated with Early Weaning affect Sow Behaviour and Welfare? ................................................ 16

Weaning Behaviour in Other Species ................................................................ 18

Earty Weanhg: the effects on piglet behaviour .

Abstract ................................................................................................................. 21

............................................................................................................ Introduction 22

Materials and Methods ........................................................................................... 25

.............................................................................................................. Discussion 30

Does weaning age affect piglet performance?

Abstract ............... .. .............................................................................................. 40

........................................................................................................... Introduction. 41

Materials and Methods ........................................................................................... 43

........................................................................................ Results ..................... .. 45

.............................................................................................................. Discussion 48

Effect of segregated eariy weaning (SEW) on sow behaviour . ................................................................................................................ Abstract 58

............................................................................................................ Introduction 59

........................................................................................... Materials and Methods 62

.................................................................................................................... Results 64

Discussion .............................................................................................................. 66

Generai Discussion ............................................................................................... 75

............................................................................................................. References 79

............................................................................................................... Appendix 86

LIST OF TABLES

Pauer One: Earh Weaninn: the effects on tlidet behaviour

Table 1 : The mutually exclusive behaviour categories that were recorded d.yring the ....................... .................*. experiment together with their descriptions .... -3 5

Table 2: The percentage of the observed time piglets exhibited various behaviours ..... 36

Pauer Two: Does weanina age affect ~ ia le t uerformance?

Table 1 : Nutrient values and ingredients of the three diets ........................................... 52

Table 2: Mean feed disappearance ............................................................................... 53

Pawr Three: Effect of setrregated earlv weaning (SEW on sow behaviour

Table 1 : The mutuaiiy exclusive behaviour categories that were analyzed in the experiment together with their descriptions ...................................... ,. ............. 7 1

Table 2: The percentage of observational time the sows spent perforrning various behaviours ......................................................................................................... 72

iii

LIST OF FIGURES

Pa~er One: Earlv Weaninn: the effects on piglet behaviour

Figure I : The percentage of t h e piglets in the 3 treatment groups spent in various behaviours ............................................................................................... 38

Pa~er Two: Does weanine: age - affect pigIet mrformance?

Figure 1 : Bodyweight (kg) both before and after weaning over the six week experimental period ................... .... .............................................. 54

Figure 2: The mean skin integrity scores for each weaning age both before and after weaning ................................................................................................... 55

Figure 3: The percentage distribution of skin integrity scores one week after weaning for each treatment group ............................................................................ 56

P a ~ e r Three: Effect of semegated early weanina fSEW on sow behaviour

Figure 1 : The percentage of time the sows spent standing, lying ventrally and lying IateraUy ........................ .. ........................................................................ 74

The Trend Towards Eady Weaning

Over the last few decades weaning age in the mvine industry has been steadily

declining. Some of the proposed byefits of reducing weaning age include increased

facility utilization, increased numbers of litters per sow per year and a reduction in the

spread of disease. Brent et (1977) published the productivity results of the Cambridge

University sow herd in relation to weaning age. The nurnber of litters per sow per year

increased fiom 1.78 in wws weaned at 7&8 weeks to 1.98 in sows weaned at 5&6 weeks

to 2.24 in sows weaned at 3&4 weeks. In the last decade there has been a M e r decline

in the average weaning age on commercial pig farms. The catalyst for this recent decline

is the introduction of a management system know as Segregated Early Weaning (SEW).

SEW is a type of swine management system in which piglets are removed from the sow

at an eady age and raised in separate nurseries and grower-finisber facilities, away from

the breeding and farrowing areas.

In North America, before the introduction of SEW, conventionai weaning age was

21-28 days postpartum. This weaning age may be considered ''ear1y weaning" elsewhere

in the world. Most SEW f m s in Ontario wean their piglets between 14 and 17 days.

Some farms in the United States have average weaning ages of as early as 8-10 days

(Dial et al., 1995). There has been extensive research conducted regarding various

aspects of SEW. Researcti teams from the University of Guelph, Ridgetown College and

Agiculture Canada are currently coilaborating in an attempt to merge the knowledge

about SEW fiom rnany difFerent fields of study to formulate some genexal weaning

recornmendations. The project includes topics ranging from the econornic evaluation of

SEW, the anaiysis of immune and microbiological status, the evaluation of carcass

quality, the evaluation of reproductive performance, the assessrnent of nutritional needs

and an investigation into how early weaning affects piglet and sow behaviour.

Advantages of SEW

It is important to understand why SEW is emerging as a common management

practice in North America, and why this is happening before the specXc needs of the

anirnals have been established. The main goal of SEW is to limit the vertical transmission

of disease from the sow to her piglets (Clark 1995). SEW f m s attempt to wean the

piglets when they have received materna1 colostrum but have not yet received any

pathogenic organisms from the sow. The ideal weaning age of the piglet changes

depending on the potential pathogenic organisms (Dritz etal., 1994). Reduced weaning

age works in conjunction with more sanitary management practices (dl-in-dl-out

production) to produce healthier animals. All-in-dl-out production means that buildings

andior rooms are emptied, cleaned and disinfected before each new group of animais is

introduced. It helps to increase the health status of piglets by limiting the number of

pathogens present in the barn. This overall disease reduction may decrease the economic

impact of disease and may allow for greater exploitation of the genetic potential of lean

genotypes (Dial et., 1995). The anticipated higher health of auimals produced fiom

SEW units has been reported to result in increased feed efficiency (Clark 1995). This

proposed increase in feed efficiency wodd decrease the overall cost of production by

decreasing the total cost of feed on the f m .

Some of the disease benefits of SEW have been recently questioned.

Dionissopoulos et., (1997) compared the health status and feed efficiency of grow-

finish hogs obtained fkom a farrow-finish unit, an SEW nursery, and a specific pathogen

free (SPF) f m . The SEW pigs ranked the lowest in average daily feed intake (ADFE),

feed:gain ratio and contracted Mycoplasma hypopneumoniae @El) and Porcine

Respiratory and Reproductive Syndrome (PRRS) more often. One of the reasons that the

health status of the SEW pigs in this expriment was quite low may be because the

animais came fiom 6 dflerent sow herds. This means that piglets with many different

potentiai pathogens would be mixed together. Supplying piglets fiom several different

farrowuig herds for SEW nurseries is quite common in Ontario because Ontario's sow

herds are relatively small. This should be taken into consideration before the decision is

mzde to convert fiom a farrow-to-finish management system to SEW.

Disadvantages of SEW

The attainrnent of a hi& health status in a SEW herd requises superior

management skills, specialized food and housing and the CO-operation and CO-ordination

of pig producers. This speciaiized management system forces the mixing of piglets from

multiple sources, causes individual producers to lose their independence and results in

higher transportation costs (Ensrninger and Parker 1984). There has aiso been decreased

reproductive performance reported in sows that bave been weaned early. A decrease in a

sows' lactation length resulting fiom early-weaning may cause a drop in farrowing rate,

decrease the number of piglets born alive, decrease the number of piglets weaned per

litter and increase the number of non-productive sow days by increasing the weaning-to-

estrus interval (Deen 1994; Foxcrofi 1997). Field data based on 7-10 day weaning

suggested excellent piglet performance, but poor sow productivity (Dee 1995).

A possible disadvantage that is seemingly ignored in the overall cost-to-benefit

equation of segregated early weaning is the welfare of the aaimals. The welfate of both

the pigIets and tfle sows should be considered before SEW is accepted as a feasible mine

management system- An understanding of how the premature removal of piglets affects

their long term well-being and successful adaptation to their weaning environment should

be a critical step in the adoption of segregated early weaning.

Behaviour

Feedina Behaviour in Piglets

When weaned at an early age, piglets have to adapt to several changes in their

environment. The most critical of these is makuig the switch fiom sucking their mother's

milk to consuming solid food. An understanding on the ontogeny of sucking behaviour

wi11 therefore probably give indications as to how piglets h t learn to recognize and

consume food.

In fact, milk intake in piglets is dependent on the closely integrated behaviour of

the suckling sow and the sucking piglets. Suckling behaviour in swine is more complex

then in many other mammals because sows give birth to large litters of fairly precocial

Young. The sow m u t be able to assemble al1 of her offspring at the udder and adjust her

milk production for varied litter sizes. Research studies suggest that behaviour and

physiology help to dictate suckling patterns (Algers 1993). Sows change their suckling

behaviour as the piglets age. Irnmediately after parturition the sow has continuous milk

flow, allowing the piglets to suck mythe. About 10.4 4 4.5 hours after the birth of the

fht piglet, the sow has short bouts of mik availability (Lewis and H d 1985). When

the piglets are young (a few days old) the sow initiates most of the sucklings. The

initiation of these suckiings is signaleci by the sow gninting and rolling on her side to

expose her udder (Fraser 1980, Jensen et., 1991). A sucking bout is divided into four

phases: initial massage, an inactive phase, "me sucking", and a final massage phase

(Houpt 1982). The initiai massage phase (1 -3 min) is termed the "pre-ejection massaging

phase" which concludes with the release of oxytocin. Approximately 20 seconds &et

oxytocin release there is an increase in mammary pressure which causes miik let-down

(E l l endorE~ . , 1982). Fraser (1980) suggested that the massage period before milk let-

down allows the piglets time to assemble at the udder and find a teat to suck. The sow

speeds up her rate of gninting a few seconds before milk ejection as a signal for the

piglets. Newbom piglets "sample" a few dBerent teats before they find "the?' teat h m

which they will suck until they are weaned (Algers 1993).

MiUc letdown correlates with the "tme sucking" phase, which lasts about 10 to 20

seconds (Fraser 1980). The reason that miik is ody available for such a short t h e is

because the sow does out have a teat cistem to store the milk. Typical posture of the

piglets during milk let-down ("true sucking") includes a rigid stance with their ears back

and their tails tightly curled (Houpt 1982).

The h a 1 massage phase Iasts anywhere from 2-15 min, controversy exists

surroundhg its purpose. McBride (1963) suggests that the final massage scent marks

each individual teat as a type of "ownership". More recent research proposes the

"restaurant hypothesis", where piglets stimulate the development of the mammary gland

of their section of the udder. f i s would mean that piglets which performed more

forcefd pst-massage khaviour would receive more milk in their next sucking bout

(Algers and Jensen 1985). AIgers and Jensen (1991) observed that the duration and

intensity of the finai massage on a specific teat affected the mik production of that teat in

the first few days of lactation Spinka et., (1996) found that the length of udder

massage influenced hormone levels (prolacth, insulin, somatotropin) but did not affect

milk production.

Weaning Behaviour-When The Sow Decides

TJatural" weaning in M e is a gradual process. When housed in a semi-natural

environment a sow will seek out a favourable nest site one or two days before parturition.

The nest sites are usually isolated fiom where the main group activities take place (Stolba

and Wood-Gush 1989). During the first week postpartum the sow spends most of her

time with her piglets, Ieaving them ody for short spans of time (30 min on average).

Piglets as young as two weeks of age start to foliow the sow away fkom the nest. The

initiation of the weaning process starts, at the earliest, about ten days postparturn with a

decrease in suckling fiequency (Jensen et al., 1991). This decreased suckling time

corresponds to when the sow and her litter leave the nest to move closer to the group

(Jensen and Redbo 1987). When the piglets leave the nest with the sow they change fiom

"hiding" in the nest to "following" the sow when she leaves the nest. This "hider" to

"follower" shift causes a change in the interactions between the sow and her young. The

fiequency of nasal contact decreases and the frequency of auditory contact increases just

before nest Leaving time.

By weeks 3 and 4 the piglets are more active, engaging in ninning and playing

activities. Play fighting and aggressive behaviour between piglets starts to occur in weeks

5 and 6. Entire iitters are not completely weaned at the same time. By 6 weeks of age,

many unweaned piglets receive less than haif of their dry matter intake fkom mik

(English et., 1988). The strongest pigs in the Litter wean themselves before some of the

weaker animals in the litter. Weaning cannot be characterized by a specific point in time

but is a gradua1 shift fiom a reliance on the sow's miik to a reliance on solid feed. At 3

months postpartum, the sows in a Scottish study were suckling their piglets at 2 hour

intervals (Stolba and Wood-Gush 1989). There is some discrepancy as to when sows

have completely weaned their litters when they are housed in semi-natural environments.

For example, Stolba and Wood-Gush (1989) estimated this had occurred by 12.5 weeks

whereas Jensen and Recen (1989) thought that it was not completed until 17.2 weeks..

Similar weaning behaviour is seen in enriched pens (those with a separate area for

the sow and an area for the sow and her litter) as in semi-naturai environments. Sows

spend less time with their piglets and allow fewer sucklings as her piglets age. B0e

(1 99 1) found that the sow initiated 20% of the sucklings at 2 weeks postpartum versus

less then 10% of the sucklings at 10 weeks postpartum. Some sows started to stand for

nursing when their piglets were 4 weeks old. Standing for nursing could mark the

commencement of the weaning process because sows let down less milk while standing

compared with when they are lying (Gill and Thomson 1956). In one study, the final

stages of weaning were completed at 1 1-12 weeks in enriched pens ( B0e 199 1).

W d g Behaviour at 3.4 And 6 Weeks

The age at weaning in commercial pig operations has been steadily declining in

recent years. Weaning piglets at 4 or 6 weeks seems very late in cornparison to North

Arnerican "early-weaning" yet rem& quite young when compared with 'sow

controlled' weaning at 12-1 7 weeks. Abrupt weaning at any age causes the pigiets'

behaviour to change. They are moved fiom an environment where feeding and resting

behaviour of the litter is synchronized by the sow, to an UXLfamiIiar environment, with

strange pen-mates, and a novel food source where they have to initiate their own

maintenance behaviour. Weaning is a 'stressful' event at any age with indications that it

is more stressful at younger ages. Fraser (1978) noticed that piglets weaned at 3 weeks

showed an increase in overall activity and aggression, and appeared to have difficulty

lying together comfortably, compared with piglets weaned at 6 weeks of age. Wood-Gush

and Csermely (198 1) compared the diumal activity of a group of early weaned pigiets at

3 weeks and again at 6 weeks of age. They observed that the percentage of time that the

piglets spent lying, exploring, feeding, and drinking were essentiaily the same at 3 and 6

weeks of age. Only the scores for aggressive behaviour differed significantly between the

two ages. The piglets weaned at 6 weeks showed much less aggression than those weaned

at 3 weeks. This lower kequency of aggressive acts was most likely due to the piglets

being able to form a stable social hierarchy at 6 weeks and not 3 weeks.

As research to establish the relationships between weaning age and piglet

behaviour continued, the behaviour patterns studied becarne more specific. Researchers

began to measure the amount of behaviour that was directed towards the environment in

relation to the amount of behaviour that was directed towards pen-mates. The

performance of increased levels of redirected sucking-like activities in weaned piglets bas

been well documented (BIackshaw 1981; Bse 1993; Dybkjaer 1992; Worsaae and

Schmidt 1980). B8e (1993) found that sucking and massaging pen mates is seen

proportionately more when piglets are weaned at 4 weeks (sucking:O.l + 0.2% ;

rnassaging:0.7 f 1.6%) compared with 6 weeks (0.0 k 0.1% ; 0.1 + 0.2%). Other

beliaviours such as s ~ g / r o o t i n g pen-mates, chewing-nibbling fittings, and tail biting

are performed approximately the same arnount in piglets weaned at 4 and 6 weeks of age.

It is important to understand how to interpret the behaviourai dif5erences that

occur with early weaning. Dybkjaer (1992) attempted to identq behavioural indicators

of 'stress' in early-weaned piglets by exposing groups of piglets to two diEerent levels of

environmental and social stressors. Half of the piglets were placed in pens with eight

littermates (an area of 0.30 square metres per piglet) and given straw each day. The other

half were mixed with non-littermates (16 piglets in each pen with an area of 0.15 square

metres) and received no straw. Al1 of the piglets were weaned at four weeks of age and

the treatment groups were compared at two and four weeks after weaning. The

overcrowded, 'stressed' piglets performed more redirected oral behaviours such as belly-

nosing and manipulating ears, tails and other body parts in comparison to their less

'stressed' counterparts. It is important to recognize that some of these oral behaviour

patterns can aiso be seen in piglets housed in semi-natural environments but usually at a

much lower rate (Newberry and Wood-Gush 1988). The fiequency of redirected chewing

behaviour is substantially diminished in animals housed outdoors compared to intensively

housed animais (0.33 t i m d 30 min in a semi-natural environment; 2.2 timed 30 min in

'unstressed' treatment; 5.8 timesI30 min in 'stresse8 treatment).

BIackshaw (198 1) also studied persistent inguinal nose thnisting, and tail and ear

bithg in piglets weaned at 4 weeks of age. Biting was displayed by high ranking pigs and

may be fiinctional in the establishment of dominance hierarchies. Biting behaviour was

spread between pens where there was o d y visuai contact, suggesting that pigs imitate the

sight of another pig biting.

The motivation behind persistent inguinal nose t h d g (belly-nosing) is

unknown. Older studies have interpreted it as a displaced rooting urge ( Schouten 1986;

van Putten and Dammers 1976) or a resdt of hierarchical aggression (Blackshaw 1981).

More recent work has alluded to a possible association between nose-thnisting behaviour

and the initiation of feeding behaviour (Gonyou 1997). Further discussion about the

motivation behiad belly-nosing behaviour and its reIationship to weaning age is more

hlly expiored in the next section where it is related to 2-week-weaning.

Weaning Behaviour at 2 Weeks

As weaning age decreases, the proportion of abnormal and redirected behaviours

seems to increase. Few studies have examined the behaviour of piglets weaned at 2

weeks of age or younger. Metz and Gonyou (1990) compared the effect of age and

housing conditions on the behavioural and hemolytic reaction of piglets to weaning. The

behaviour of piglets weaned at 2 and 4 weeks were compared both after weaning and

while the piglets were with their dam. There were many différences in the feeding and

sucking behaviuur of piglets weaned at 2 versus 4 weeks when both were with the dam.

The 2 week old piglets spent significantly more tirne sucking than the 4 week old piglets.

The younger pigiets also had more contact with the teats after massage, often f a l h g

asleep beside i t The ciifferences between the behaviour of the 2- and 4-week-old piglets

were accentuated after weaning. Although the 2-week-weaned pigiets were younger and

presumably need more rest, the lying time of the 2-week-old pigiets was sigaifîcantly

shorter thau the 4-week-old piglets at both 4 and 6 days post-weaning . The younger

piglets also sbrted to beiiy-nose. The older piglets engaged in significady Iess belIy-

nosing behaviour. Any belly-nosing thai the 4-week-old pigiets did was less h t i c and

patterned d-erentiy than the belly-nosing of the younger piglets. The cause of the nosing

in the older piglets may be a rootiag urge rather than a sucking urge (Schouten 1986).

Belly-nosing and naval sucking in 2-week-weaned piglets does not start until about day 4

after weaniag. Gonyou (1997) suggests a connection between the initiation of feeding

and bely-nosing behaviour. This rnay have similar principles to the hding that veal

calves 'butt' more fiequently when artificiaiiy fed rr;ilk at a slow flow rate than at a

faster, easier to attain flow rate (Haley et., 1996). Research to establish the motivator

of belly-nosing and naval sucking behaviour must be conducted before proposed

soiutions to eliminate these behaviours can be established.

Feeding The EarIy Weaned Piglet

Before a relationship between the initiation of feeding and belly-nosing can be

postulated an understanding of how early-weaned piglets are currently fed must be

established. The nutritional requirements of the early-weaned piglet have been well

studied. C h e (1991) explains that early-weaned piglets have simiIar nutrient

requirements as growing-finishing piglets. AU young piglets require energy, amino acids,

fatty acids, minerais, vitamins and water. The objectives of the formulation of SEW dies

are expressed quite ciearly by Drïtz et (1997) as 1) the selection of ingredients that

stimulate feed intake 2) the provision of a substantial amount of highly available amino

acids in the proper proportions and 3) the preparation of pigs to utilize Iess expensive

diets in subsequent phases of growth. The feeding management system which is

recommended to achieve these objectives is a four phase diet including an SEW diet, a

transition diet, a phase two and a phase three diet. The shift from one feding phase to the

next brings a decrease in the amount of added fat in the diet, a decrease in the amount of

spray-dried plasma and an inmase in the amount of less digestible ingredients such as

soybeans and grain (Dritz et al., 1997). This ingredient shift causes the SEW diet to move

h m a highly palatable, easily -digested form to a coarser, less digestible, Iess costly

fom.

The Conflict Between Nutritional Requirements And Bebavioural Needs

It is essential to understand both what nutrients piglets require in different stages

of their life and what stirnuiates piglets to feed and establish feeding patterns. Piglets

establish their feeding cycles in their first few weeks of life fiom the vocal and

behavioural cues of the sow. The sow provides piglets with approximately 24 equally

spaced me& per day (Goodband et., 1995). Sow's d is highiy digestible and aii of

the piglets learn to feed at the same time and only when the sow allows them to eat. It is

important that nutritionists consider the development of this feeding behaviour when

designing feed and feeding schedules for the earty-weaned piglet Bark et al., (1986)

found that piglets weaned at 21 days and fed a dry diet either ad-libitum or at 2,4 and 6

hour meal intervals did not consume sufficient feed for maintenance during the first 3

days post-weaning. This suggested to the researchers that the number of meals provided

was not adequate. In a second experiment Bark et ai., (1986) compared the feed intake of

weaned pigiets that were allowed to consume food in a familiar environment via a

familiar method (sucking) 24 hours after weaning both with unweaned piglets and with

weaned piglets put into an unfamiliar environment and fed a dry diet. The weaned group

fed a dry diet consurned less and had signi£icantly higher plasma free fatty acid (FFA)

levels which may suggest a reliance on body fat stores during this period. The reduction

in feed intake which is seen directiy following weaning is likely caused by both an

unfaLniliar method of food acquisition and an unfarniliar food source.

Auditory and thermal cues are also very important in the feeding pattern of

piglets. Petrie and Gonyou (1 988) found that newly weaned piglets given the auditory

stimulus of a sow grunting spent more tirne feediag than did piglets without the auditory

stimulus (1 27.1 vs. 104.2 min, respectively). The initial seeking of a food source seems to

be in response to the surface of the udder. Welch and Baxter (1986) found that the body

temperature of sows rises before fmowing and when milk is present in the teats. The

researchers camed out preference tests with models using 3 different combinations of

temperature and 'sofhess' of udder. Piglets demonstrated a clear preference for a warm,

soft surface, both by the amount of tirne spent at the models and by the sucking actions

directed towards the models.

The development of feeding behaviour in young piglets bas been studied

intensively and a solid knowledge base has been established. The current irnplementation

of very early weaning practices on commercial swine f m s rnakes it al1 the more

important that this knowledge base be increased and used. Ignoring the learned feeding

behaviour of piglets may cause problems such as redirected sucking behaviour and

digestive discodort post-weaning. Both the nutritional and behavioural needs of the

early-weaned piglet must be met to achieve the maximum benefit fiom SEW systems,

How Does Environmental Enrichment Affect Weanhg Behaviour?

Piglets weaned at an early age may have many other behavioural needs apart from

those associated with feeding. One way that commercial pig producen may be able to

meet some of the behavioural needs specifically associated with abrupt weaning without

compromising overall productivity is through a concept known as environmental

enrichment. Many researchers have studied how different kinds of environmental

enrichment affect the behaviour of piglets following weaning. Schaefer et al., (1 990)

compared the arnount of aggressive behaviour exhibited by newly weaned piglets when

they were provided with objects such as a car tire suspended on a chah, a sugar-mineral

block suspended in a metal basket or a teeter-totter (metal bar with rubber belts on the

ends). Less aggressive acts were displayed when newly weaned piglets were given any of

the three "toys" in cornparison to the control (no toys provided) animais. The researchers

noted that the larger toys not only provided an aggressive outlet for the dominant anirnals

they also gave a hiding area for the submissive piglets. However, it is important to

acknowledge that familiarity with toy objects may reduce their effectiveness in

controlling aggression (Schaefer et., 1990). Waran and Broom (1993) studied the

influence of a galvanized metal barrier and two different housing systems (conventiond

flat deck; pen with straw) on the behaviour and growth of early weaned piglets and found

sindar results to the toy study. The provision of an opaque barrier both decreased the

fiequency of aggressive interaction by 40% the week after weaning and increased the

piglets' growth rate by 0.15 proportionately. Surprisingly, the piglets housed in a

conventionai flat deck demonstrated sunilar IeveIs of aggression as the piglets housed in

a pen bedded with straw. Btae (1993) used a 2 x 2 factorid design to compare piglets

weaned at 4 or 6 weeks with piglets housed in either a flatdeck or a farrowing pen

(bedded with sawdust). Piglets weaned in flat-decks spent more time rooting at objects in

the pen and chewinghibbling and tail-biting pen-mates than piglets weaned in the

farrowing pen. The fiequency of massaging and sucking pen-mates was higher amongst

piglets weaned at 4 weeks compared to 6 weeks and was also found to be higher among

piglets weaned in farrowing pens compared to flatdecks. FIat-deck housed piglets had a

higher fkequency of belly and tail lesious than animals in farrowing pens.

The behaviourd effects of early weaning are difficult to separate fiom the effects

of the weaning environment. Studies suggest that both factors contribute to the formation

of abnormal behavioural patterns post-weaning. The research to be described in this

thesis attempts to separate the effects of early weaning fiom the weaning environment by

housing al1 three weaning ages in identical environments and cornparhg the frequency of

abnormal behaviour exhibited.

Does The Shortened Lactation Length Associated With Eariy-Weaning Anert SOW

Behaviour And Welfare?

Previous research has established the patterns of nursing behaviour of piglets, the

behaviourai changes associated with the process of weaning (both sow controlled and

&ficial), the feeding systems of commercial SEW systems and how these feeding

systems relate to the behavioural needs of the piglets, and the use of environmental

enrichment to attempt to lesson the 'stress' of weaning. If early-weaning causes

behaviourai changes in piglets, how does it effect the sows?

Sows have complex social interactions with their Liners that govern the cycle of

piglet behaviour. They fom strong materna1 bonds with their piglets. Jensen et al., (1991)

observed that mothers and their young spent almost all resting time in close contact. As

the piglets aged, the sow spent less time in close proximity to them but the tirne she

spent close to her young during resting did not change. This suggests that the maternd

bond between a sow and her young continues until the completion of weaning. There is

practically no information available on how the early temination of this relationship

affects the sow. As previously mentioned, a disadvantage of SEW is reduced sow

reproductive performance. Lactation length seems to be inversely related to the weaning-

to-breeding i n t e d .

increase weanhg to

explains that one of

Each 10-day decrease in lactation length has been estimated to

breeding time by one day (Friendship 1987). Foxcrofk (1997) C

the reasons that sow productivity drops due to early-weaning is

because the reproductive system needs to recover fiom the effects of pregnancy. The

uterus has to r e m to its non-pregnant state and the brah and pituitary need to be

capable of producing the hormones (LH, FSH) needed for reproductive success. The sow

seems to have diffîculty adapting physiologicaily to early weaning. How does this lack

of adaptation relate to the animal's behaviour and weffare?

This question is reIativeIy novel and essentiaiiy uncharted, Pajor et ai., (1996)

studied the individuai difEerences and housing effects on the response of sows to

weaning. Sows were housed in either a pen confined with their litter or in a "get away"

pen where the sow couid leave her litter. They found a large variation in the amount of

tixne sows choose to spend with their young. Two categories of sows were defined based

on how much time they spent with their litters: "leaver" sows spent more than 50% of

their time away, "stayer" sows spent less than 50% of their time away. "Stayer" sows

were reported to vocalize more post-weaning, were more active, and investigated the

piglet creep area more often. These possible indicators of sow distress wouid be

important considerations in the design of an expriment attempting to establish the

relationship between lactation length and sow behaviour.

The identification of the signals that indicate the initiation of the process of

weaning are dso important. Boe (1991) postdates that the process of weaning is the

result of a confiict between mother and offspriag. If this is me, then an artificiaiiy

weaned sow is likely to never experience this conflict. This is not to say that such conflict

shouid somehow be induced or simulated at the same time the sows are artificially

weaned fiom their piglets. However, artificiai weaning practices such as SEW may be

depriving the sow of a stimulus which is essential to her recognition of the termination of

the relationship between her and her offspring.

Some may argue that the process of a sow suckiing her young is just as 'stressful',

if not more so, as t a h g ail of her young away relatively early in her lactation. Bse

(1991) opposed this theory by observing that given the opportunity for a sow to open and

dose a b&er which separates her fiom her litter, she wilI consistently and voluntarily

open this barrier and move to an area where she can suckle her young. AIthough suckhg

may be physioIogica.Uy 'sîresstùi' for the sow, she may have a behavioural need or

motivation to perform it.

The design of commercial management systems ofien ignores the animals'

behavioural needs. There is an obvious lack of information about how sows respond

behaviourdiy to reduced lactation length. Knowledge of this area may help us to

understand some of the reproductive failures of SEW sows and would also aid in an

assesment of the. well-being of early-weaned sows.

Weaning Behaviour In Other Species

Behavioural patterns associated with weaning across various species are similar.

The removal of young animals fiom their mother is understood to be a 'stressful' event in

many different species. The offspring of most animals that are artificially housed and

managed are abruptly weaned fiom their dam.

In anUnals f i e d for their fur such as mink, early weaning has been shown to

cause abnormal behaviour patterns. Mason (1996) found that mink removed from their

mother at 7 weeks compared with 11 weeks exhibited more stereotypic behaviour which

continued over the 9 month observation period. Laboratory mice weaned at 17 days with

a low weaning weight compared with 20 days with a higher weaning weight had higher

corticosterone levels 48 hours d e r weaning and developed a higher Level of stereotypic

wire-gnawing behaviour (Wurbel and Stauffacher 1996). Female hooded rats weaned

their litters eariy when they were food-restricted (Smith 1991). These early-weaned rat

pups exhibited more play behaviour than the controt animais- Martin and Bateson (1985)

observed that kittens aiso responded to early weaning by playing more and that diEerent

types of play behaviour were shown depending on when weaning occurred. The

researchers suggested that weaning age may affect the way that young kittens develop.

Early-weaning red deer calves at 3-4 months ( compared with the 7-8 months that occurs

naturally) aiso caused differences in the caifbehaviour. The weaned animals spent 12%

of their time pacing at the fencehe as opposed to the 1% pacing time seen in the

unweaned group (Pollard et., 1992). Human infants also exhibit changes in their

behaviour post-weaning. Prolonged crying, generai restlessness, and excessive pacifier

sucking are al1 possible results of the human weaning process (Gesell and ilg 1979).

In summary, weaning results in prolonged changes in behaviour in many different

species. The knowledge and appreciation of these changes is an essential part of strong

animal hus bandry skills.

Early weaning: The effects on piglet behaviour

To be submitted to Applied Animal Behaviour Science

Abstract

Piglets were weaned at 7, 14, and 28 days, housed in groups of ten and obsenred

until they were six weeks of age. Piglets weaned at 7 days spent much more time in

activities directed towards theu pen-mates, particuIarly belly-nosing behaviour @<O.OS),

showed more escape behaviour (j! <0.005), and less contact @ < 0.005), feeding

@<O.OS), and exploratory behaviour @<0.0005) compared with piglets weaned at 14 or

28 days. Piglets weaned at 14 days exhibited more belly-nosing behaviour than piglets

weaned at 28 days @<0.05) and spent less t he at the feeder directly foilowing weaning

than the 28 day weaned animals @0.05).

General aggression levels, aggression at the feeder and drinker and the

performance of social nosing and chewing behaviour were similar in piglets weaned at 7,

14 and 28 days of age. These results suggest that the welfare of piglets weaned at 14 days

and particuiarly 7 days is compromised. The welfare of early-weaned piglets must be

considered as part of the assessment of the feasibiiity of early-weaning systems.

Keywords: piglet behaviour, early- weaning, w e k e assessment

Introduction

[n North America, weaning age on commercial M e fanns has been steadily

decreasing. Recently, eariy weaning has been combined with a segregation of the piglets

fiom the sow in a system known as Segregated Early Weaning (SEW). Usually, several

sow breeding f m s attempt to synchronize fmowing. When aii the piglets on these

supply farms are about 14 days old they are weaned and transported to a growing f m

which has been thoroughly cleaned and disinfected. This unit is run on an all-in all-out

basis with strict biological security. Weaning ages in SEW systems range fiom 16-17

days to a s early as 7-10 days post partum. The main advantage of this system is the

decrease in vertical transmission of disease from the sow to her litter (Clark 1995). SEW

is being rapidly adopted by the swine industry in North America, suggesting that it works

well cornmercially. However, weaning piglets as early as 14 days raises questions of

animai welfare. Although their health status may be enhanceci, do piglets sufEer in other

ways when separated fiom their mother at 14 days?

Natural weaning in swine is a gradual process. When housed in semi-natural

environments the sow will seek out a favourable nest site one or two days before

parturition (Stolba and Wood-Gush 1989). During the first week postpartum, the sow

spends most of her tirne with her piglets, leaving them for oniy short spans of tirne (30

minutes on average) (S tangel and Jensen 199 1). The initiation of the weaning process

starts, at the earliest, 10 days postpartum with a decrease in suckling fiequency (Jensen

al 1991). This decreased suckling fiequency corresponds to when the sow and her litter 2-

leave the nest to move closer to the rest of the herd (Jensen and Redbo 1987).

Piglets graduaily become more independent. By weeks 34, they are more active,

engaging in ninaing and playing activities. Play fighting and aggressive encounters

between uiglets start to occur in weeks 5-6. Weaning cannot be defined as a specific time

but is a gradua1 shift Erom a reliance on the sow's miik to a reliance on other food. Entire

litters are not completely weaned at the same time. By 6 weeks of age, many unweaned

piglets receive less than half of their dry-matter intake f?om milk (English et al., 1988).

Descriptions of sows in semi-natural environments Vary with regard to when weaning is

completed. In a Scottish study, Stolba and Wood-Gush (1989) reported that aIi pigIets

were weaned by 12.5 weeks. In a Swedish population of pigs, Jensen and Recen (1989)

reported that weaning was not completed until 17.2 weeks. Bae (1991) found that with

sows and piglets housed in enriched pens, weaning was finished by 1 1-12 weeks.

The behavioural implications of abrupt artificial weaning at 3 weeks of age have

been weIl studied. Fraser (1978) observed that piglets weaned at 3 weeks showed an

increase in overall activity and aggression and appeared to have difficulty lying together

comfortably compared with piglets weaned at 6 weeks of age. This early work on the

behavioural effects of early weaning led into research about how piglets signal their

needs and what signals can be accurately used to assess piglet well-being (Weary and

Fraser 1995). Dybkjaer (1992) identified redirected oral behaviour in early-weaned

piglets, such as belly-nosing and oral manipulation of pen-mates' ears, tails and other

body parts, as possible indicators of 'stress'. There is, therefore, a good knowledge base

conceming the types of behaviour that may be useful in determining how disturbed,

distressed or frustrated early-weaned piglets might be. There are also a few reports on

the effects of very early weaning fiom 20 years ago (van Putten and Dammers, 1976; van

Putten, 198 l), but these studies pre-date advances in piglet nutrition and management and

so are less relevant.

Few studies have examined the behaviour of piglets weaned at 2 weeks of age or

younger. Metz and Gonyou (1990) compared the effect of age and housing conditions on

the behaviourd and immunological (neutrophiylymphocyte ratio) reaction of piglets to

weaning. The behaviour of piglets weaned at 2 and 4 weeks was compared both while

the piglets were with the sow and d e r weaning. There were many ciifferences in the

feeding and sucking behaviour of piglets weaned at 2 versus 4 weeks of age. The piglets

weaned at 2 weeks spent signiflcantly more time at the teat before weaning than those

weaned at 4 weeks. Weaning caused an increase in beily-nosing behaviour two days

post-weaning in both groups. More belly-nosing was performed by the early-weaned

animds. The authors suggest that nosing litter-mates in the weaned piglets acted as a

substitute for teat contact with the sow.

In order to gauge whether or not very early weaning leads to serious problems, ten

SEW nurseries in Ontario were surveyed and asked to describe any behavioural

abnormalities on their f m s (Dewey et al., 1997). Producers reported increases in the

arnount of belly-nosing, navel-sucking and aggression in piglets that had been weaned

early.

This study examines the effects in a controlled experiment of weaning at various ages on

piglet behaviour.

Materials And Methods

The 180 piglets used in this experiment were of pure-bred Yorkshire stock. Three

trials were conducted with nine litters in each triai. In each tri& three litters were

assigned at random to be weaned at 7 days, t h e at 14 days, and three at 28 days

postpartum. From each pool of three litters, two groups of 10 piglets were assembled by

weight and each group placed in a pen m e a s u ~ g 1.83 x 1.22 m, giving two pens per

weaning age per trial. Each pen had two nipple drinkers, two galvanized steel feeders,

two rubber mats, an infrared heat lamp and tender foot flooring. The temperature in the

room varied between 24 and 2 7 ' ~ and was monitored ddy. Ail of the pens were washed

and disinfected between each triai.

The study was approved by the animal case cornmittee at the University of

Guelph. Animals were cared for under the guidelines of the Canadian Council on Animal

Care ( CCAC 1993).

Three different types of starter feed were used in the experiment (Types 1,2 and

3) (TabIe 1, pp. 52). The piglets weaned at 7 days old were fed each type of starter for

two week periods in succession . The piglets weaned at 14 days old were fed Type 1

starter for one week, Type 2 for two weeks and Type 3 for two weeks. The piglets

weaned at 28 days old were fed Type 3 for two weeks. Type 1 starter was provided as a

creep feed in the farrowing crates to al1 of the pigiets fiom day 5 postpartum. Creep

feeders were used for the piglets weaned at 7 days for the fïrst week after weaning

because the animals were too smail to reach the feed in the large gdvanized steel feeders

used throughout the rest of the experiment.

The animals were d l weighed at birth and then weekly. Feed intake was

estimated weekly on a pen basis by measuring feed disappearance. AU piglets had their

teeth ciipped on &y 1 postpartum and were castrated and ear notched on day 4.

Observations

The piglets were videotaped for 48 h penods on different occasions. Piglets

weaued at 7 days old were videotaped on days 7 & 8,11& 12, 14 & 15,28 & 29, and 42

& 43. Piglets weaned at 14 days old were videotaped on days 14 & 15,28 & 29, and 42

& 43. Piglets weaned at 28 days old were videotaped on days 28 & 29, and 42 & 43.

The videotapes were scanned every five minutes to obtain an instantaneous behavioural

sample. Ten mutually exclusive behavioural categories were recorded and are shown in

Table 1 dong with descriptions.

S tatisticai Analvsis

The experimentai design was a completely randomized one-way ciassification

design. The number of piglets engaged in each of the ten behavioural categories was

counted for each scan, and adjusted for any missing piglets by determining the % of

piglets engaged in each behaviour at each sarnpling tirne. These percentages were then

averaged for the entire two-day observation penod. And fiom this, the amount of t h e

spent in each behavioural category was calculated and expressed as a least square mean

value. Analysis of variance was used to compare statistically the behaviour of piglets

weaned at 7 days of age with piglets weaned at 14 days of age on days 14 & 15,28 & 29

and 42 & 43. Piglets weaned at 7 and 14 days were compared with piglets weaned at 28

days old on days 28 & 29 and 42 & 43. The GLM (generai h e a r models) procedure was

used with SAS to perform the analysis (Statistical Analysis Systems Institute 1985).

Analysis of variance was also used to compare the amount of time spent performing each

behaviour for the fht 48 hours following weaning for each treatment group. The data

was aiso tested for normality (Statistical Analysis Systems Tiistitute 1985).

Results

The times spent by the piglets engaged in the ten mutually exclusive behaviour

categories are shown in Table 2. The most important of these, with regard to the amount

of time spent, were belly-nosing, feeding, general aggression, exploratory behaviour and

lying.

Figure 1 shows that in piglets weaned at 7 days, the incidence of belly-nosing,

although fairly low the day after weaning, had increased dramaticdy by days 1 1 & 12.

These piglets continued to belly-nose at a high level through to days 14 & 15 when it was

higher than that shown by piglets weaned at 14 days (PcO.0005) and through days 28 &

29 when it was higher than piglets weaned at 28 days (P<0.005). At 6 weeks of age the

piglets weaned at 7 and 14 days were still belly-nosing at a higher Level than the piglets

weaned at 28 days (Pc0.05).

Feeding Behaviour

Figure 1 shows that on the day of weaning and the foliowing &y the 3 treatment

groups spent varied amounts of time at the feeder. Pigiets weaned at 28 days spent 4.6 * 0.4% of their time at the feeder, piglets weaned at 14 days spent 2.8 1 .O% of their time

at the feeder, and pigiets weaned at 7 days spent 0.6 * 0.2% of their time at the feeder

ee0.05). At six weeks of age, the piglets weaned at al1 of the 3 weaning ages spent

similar arnounts of tirne at the feeder @O. IO).

Generai Aegression and Agmession at the feeder/drinker

The overall amount of generai aggressive encounters and aggressive encounters at

the feederldrinker did not m e r with weaning age. Figure 1 shows the general pattern of

aggressive behaviour in the 3 weaning ages.

Ex~loratorv Behaviour

During the fust 48 hours after weaning piglets spent significady different

amounts of time exploring dependhg on weaning age. Newly weaned 7 day old animais

spent 4.1 rt 0.71% of their tirne explorhg as opposed to 9.9 * 0.71% and 8.8 0.71% for

14 and 28 day weaned piglets respectively @ < 0.001). At two weeks of age piglets

weaned at 7 days spent less t h e exploring than piglets newly weaned at two weeks

@<0.0001). At 4 weeks of age, piglets weaned at 7 days spent less t h e exploring than

piglets newly weaned at four weeks @<0.001) (Figure 1). The pattern of temporal

changes in exploratory behaviour is similar across treatments. When piglets in al1 3

treatment groups were initially weaned into their pens, exploratory behaviour was at its

highest point and graduaiiy deched over the. This deciiie in exploratory behaviour was

sharper in piglets weaued at 7 days compared with piglets weaned at 14 and 28 days.

Social Nosinrr and Chewing

The piglets in al1 three treatment groups spent l e s then 3% of their time

exhibiting nosing and chewing behaviour during the six week observation period. Piglets

weaned at 7 7 28 days spent more tirne nosing and chewing pen-mates on day 28 & 29

than did piglets weaned at 14 days @<O.OS).

Esca~e Behaviour

Escape behaviour was seen almost exclusively in piglets weaned at 7 days of age.

Forty-eight hours following weaning, pigiets weaned at 7 days spent significantly more

time performing escape behaviour than piglets weaned at 14 @<0.0005) or 28 days

(P<0.005). On days 7 & 8 piglets weaned at 7 days spent 2.5% of the observed tirne

performing escape behaviour. Table 2 shows that as the piglets aged, the amount of

escape behaviour diminished.

Contact Behaviour

Following wedng, pigiets weaned at 14 and 28 days spent more time in social

contact behaviour than piglets weaned at 7 days @<0.005).

Drinkllig Behaviour

Pigiets weaned at 7 days spent siightiy more tirne at the nipple drinker than piglets

weaned at 28 days on days 28 and 29 (P < 0.10). PigIets weaned at 7 days spent 1.6 -1: 0.3%

of their time drinking on days 7 & 8. By week six, pigiets weaned at 7 days were spending

more tirne at the drinker than the later weaned animals (P4.05).

Lving Behaviour

Piglets in aii 3 treatments groups spent most of their time lying down (Table 2). Ali

of the animals in this study spent a p p r o h t e l y 70-80% of the observed time lying.

Discussion

Weaning age had a profound effect on piglet behaviour. The most ciramatic

ciifferences occurred in pigiets weaned at 7 days which spent much more tirne in activities

directed towards their pen-mates (belly-nosing and social nosing and chewing), more tirne in

escape behaviour, very smaii amounts of time at the feeder directIy after weaning, and

seemed to have less interest in their environment (decreased exploratory and contact

be haviour).

Piglets w m e d at 14 days showed simiiar behaviour patterns as piglets weaned at 28

days except that they showed more belly-nosing behaviour and they spent less time at the

feeder directly foliowing weaning. Other studies have found sirnilar results when

camparing piglets weaned at later ages. B a (1 993) found that sucking and massaging pen-

mates is proportionately more frequent when piglets are weaned at 4 weeks (sucking: 0.1 * 0.2% ; massaging 0.7 k 1.6% ) compared to 6 weeks (sucking 0.0 * 0.1% ; massaging 0.1 -1:

0.2% ). Mer behaviour such as sni£Eng and rooting at pen-mates, chewing and nibbling on

fittings, and tail biting, were performed at approximately the same rate by piglets weaned at

4 and 6 weeks of age.

Weaning at both 7 and 14 days was characterized by the occurrence of a large

amount of beiiy-nosing. This beiiy-nosing is undesirable since it can lead to skin lesions in

the piglets that receive it (Worobec et., 1997). However, before attempting to fmd ways

of eliminaîing or decreasing the belly-nosing behaviour, it is worthwhile to consider what is

motivating this behaviour to occur. The methods used to reduce the incidence of belly-

nosing may be very different depending on whether beiiy-nosing is part of the feeding or

social contact or escape motivational systems.

It seems most likely that belly-nosing is connected in some way to the feeding

motivationai system. The motor patterns involved appear very Sitnilar to the massagllig

movements that piglets direct towards the sow's udder both immediately before milk Iet-

down and for some tirne aîlerwards. In the case of feeding behaviour in calves, it has been

show that the appetitive element of sucking has become dissociated f?om the

consummatory element of ingestion of milk When a calf is aven milk fiom a bucket, it

stilI has a "need" to suck (Rushen and de Passillé, 1995). if it is provided with an artificial

dry teat, it will suck on it for some minutes afler drinking milk lÏom a bucket. Moreovei,

the performance of this non-nutritive sucking may have beneficial consequences for the caif

in that it stimulates secretion of certain digestive enzymes (de Passiiié et al., f 993). If belly-

nosing behaviour is some element of appetitive feeding in the piglet, such as redirected

massaging or pre-sucking behaviour, then it may be important for piglets to be abIe to

perform this behaviour. The solution may not be to prevent the occurrence of the motor

patterns but to direct them such that their perf0111lil~1ce does not cause injury.

The speed with which animds begin to feed on solid food is an important

indicator of how well they are adapting to weaning. Pigiets weaned at 7 days spent less

than 1% of their time at the feeder in the week following weaning compared with 5% of

their time when weaned at 28 days suggesting that the early-weaned piglets were not

adapting as well. Fourteen-day-weaned piglets spent 3% of their time at the feeder the

week of weaning. This suggests that piglets weaned at two weeks can adapt to dry feed

more easily than those weaned at one week but that work still needs to be doue to

motivate these animals to begin feeding. The prime Iimiting factor to performance

directiy after weaning is the delay of the initiation of feeding and the limited consurnption

of solid food in the week following weaning pettigrew et., 1994). Therefore, methods

of stimulating feeding behaviour directly following weaning will greatly contribute to the

welfare and performance of early-weaned piglets.

Reduced welfare would also be indicated by the performance of behaviour

associated with States of suffering. Escape behaviour may be an indicator of distress or

fear in young piglets. It is important to note that escape behaviour was seen only in

newly weaned 7 days old piglets. When it did occur, it was accompauied by high levels

of vocalizations. Over the last few years the analysis of piglet vocalizations has been

used as an indicator of well-being. Weary et al., (1996) found that piglets which were the

smallest and slowest growing (needy piglets) vocaiized at a higher rate and higher

kquency, and for a longer duration than "un-needy" piglets.

It has been suggested that animais that are stressed may pay less attention to theu

environment than animals that are relaxed (Wkpkema et., 1983). Therefore the amount

of exploratory behaviour and social contact that piglets show may be positively correlateci

with their weKare. Piglets newly weaned at 7 &YS spent only haif the time explorhg

compared with piglets newly weaned at 14 or 28 days. Social contact in this study is

defined as nose-to-nose contact with piglets in a neighbouring pen. Piglets newly weaned at

7 days performed seven times less contact behaviour than did pigiets newly weaned at 14

days and nine times less contact behaviour than did piglets newly weaned at 28 days. The

difference in exploratory and social contact behaviour seen in pigiets weaned at 7 days

compared with the later weaned piglets suggests strongly that very early weaned piglets

may be stressed, more apathetic, and less responsive to their environment. This

unresponsiveness or "apathy" was described by several SEW nurseries as ''the loss of the

will to iive" (Dewey et., 1997) and is a potentiai weKare concern.

The lack of establishment of stable dominance hierarchies in very early-weaned

piglets may also be cause for concern. Although general aggression levels were similar

when piglets were first weaned at different ages, the overall trend was different. The

piglets in al1 three treatrnent groups displayed similar peak levels of general aggression

when they were initially grouped together following separation fiom the sow. This

aggression decreased over time in the 14 and 28 day weaned animais. However piglets

weaned at 7 days did not show t h s steady decline in general aggression with age. The

resultant increased level of social fiction has the potential to reduce the welfare of these

piglets. More research is required to determine the exact age at which social mixing will

ailow the formation of a stable hierarchy.

In summary, it can be said tbat pigiets do not adapt weII to being weaned at 7

days. The merences in behaviour that were seen in these piglets cornpared with that

seen in piglets weaned at 14 and 28 days suggests that very eary weaning causes them

severe problems and greatly reduces their welfitre. Piglets weaned at 14 days seem to

adapt more easily to weaning, but still have some problems compared with piglets

weaned at 28 days. In fact, there has been a trend in SEW famis in Canada over the past

few years to wean slightiy later, at 16-17 &YS rather than 12-14 days. The present study

suggests tbat this trend to ctn older weaaiog age may have positive b e h a v i o d

ramifications and welfare benefits.

I f earIy weaning systems, induding SEW systems, are to become successfûl

commercially protect the welfare of the piglets, then the most pressing need is to find

a way to motivate the piglets to consume food as soon afkr weaning as possible.

Acknowledgements

The financial support of the Ontario Ministry of Agriculture, Food and Rural Affairs and

of Ontario Pork is appreciated. Many thanks to the staff of the Arkell Swine Unit,

University of Guelph.

TabIe 1. The mutually exclusive behaviour categories that were recorded during the

experiment together with their descriptions.

Feeding Dfhkin9;

--

General aggression

Aggression at the

feeder and drinker Escape

Exploratory behaviour

Social contact

Social nosing and chewing

Body weight not supported by legs Head in feeder Snout against nipple drinker A distinctive sequence in which one piglet

rubs a pen-mate's belly with rhythmic, up

and down rnovements of its snout (Fraser

Pushing, head-thnisting, biting and chasing (Blackshaw 1987). Forcetid displacement from the feeder or drinker

Jumping against the sides of the pen with

hind feet on the ground and fore feet on the

side of the pen.

Oral-nasal contact with parts of the pen or

objets in the pen

Nose-to-nose contact with piglets in a

neighbouring pen.

Nosing and chewing at the body of a pen-

mate (distinct fiom belly-nosing) (Fraser

Table 2: The percentage of the observed time (* s.e.m.) pigiets exhibited various behaviours

Days 7 & 8 I l & 12 14 & 15 28 & 29 42 & 43

Feeding Wean 7 0.6*0.5, 5.7 0.9 6.5 1 0 9 8.6 0.5' 6.1 * O S b

Wean 14

Wean 28

Expiore Wean 7

Wean I4

Wean 28

Belly-nosing

Wean 7

Wean 14

Wean 28

Drinking

Wean 7

Wean 14

Wean 28

Gen. Agg

Wean 7

Wean 14

Wean 28

Agg. FeedDrink

Wean 7

Wean 14

Wean 28

Days

Wean 7

Wean 14

Wean 28

Contact

Wean 7

Wean 14

Wean 28

Nose & Chew Wean 7

Wean 14

Wean 28

Lyhg

Wean 7

Wean 14

Wean 28

The letter supe-pts which appear in the columns and the numerid subscnpts that appear across columns ( boided

vaIues) indicate statistical differences (P< 0.05)

Piglets weaned at 7 days

Piglets weaned at 14 days

Piglets weaned at 28 days

- -

O Aggression Exploring Q Feeding Belly-Nosing

Figurel: The percentage of time piglets in the three treatment groups spent in various behaviours See Table 2 for statistical differences

Does weaning age affect piglet performance?

To be submitted to the Canadian Journal of Animal Science

Abstract

The average weaning age on many commercial pig farms has declined h m six

weeks to two weeks in the last twenty years. In the last decade, the catalyst for this decline

has been the introduction of a management system known as Segregated Early Weaning

(SEW). SEW involves the removal of pigiets fiom the sow at an earIy age and their

subsequent isolation to a separate site.

The objective of this study was to determine the relationship between weaning age

and piglet performance. Piglets were weaned at 7, 14 and 28 days of age. Three trials were

conducted with nine litters in each trial. At random, three litters were assigned to be

weaned at 7 days, three at 14 days and three at 28 days. Litters were mixed and the piglets

were grouped into pens of ten, giving two pens per weaning age per trial. Feed intake,

body weight and skin integrity scores were recorded weekly.

Early weaned piglets (seven days) consumed little feed during the week foilowing

tveaning (78.1 r 7.9 glpigletlday), gained minimal amounts of weight (42.4 r 8.7

g/piglet/day), had high mortality figures pst-weaning (8.7 r 2.8%) and diqlayed a higher

fiequency of skin markings one week f i e r weaning than piglets weanea at 14 and 28

days. By six weeks of age, piglets weaned at 7 days stiU weighed signifïcantly less than

piglets weaned at 14 or 28 days (P<0.05). The o v e d feed-to-gai. ratio of piglets weaned

at 7, 14 or 28 days was not significantly different over the last two weeks of the

experimental period @>0.1). Early weaning without off-site segregation did not result in

improved piglet performance.

Keywords: early weaning, piglet skin iesion score, weaning performance

Introduction

Weaning age on North American commercial mvine farms has been rapidly

declining in the last few decades. In the past, the purpose of reduced weaning age was to

increase the overail number of piglets per sow by reducing the farrowing interval and to use

the farrowingllactation facilities more efficientiy (Pettigrew et ai., 1994). The recent

emphasis on early weaning stems fiom heaith relaieci issues. A mauagement system caiied

Medicated Early Weaning (MEW) was developed in the 1980's based on the concept that

pathogens can be transmitted fiom the suckling sow to her piglets (Aiexander et al., 1980).

The MEW piglets were separated fiom the sow when they were a few days old, placed in a

nursery and quite heavily medicated to attempt to reduce the vertical transmission of

pathogens. The key to MEW was found to be the separation of pigiets h m the sow as

opposed to the heavy medication. The system was modified for commercial application and

renamed segregated early weaning (SEW). The arriva1 of SEW bas accelerated the trend

towards declining weaning ages on commercial farms.

An understanding of the specific needs of the young pig is an important step in the

development of early-weaning systerns. The nutritionai requirements and physiologid

attributes of the early-weaned piglet have k e n well studied. During the fkst few weeks of

life piglets undergo many digestive changes. The young piglet does not produce enough

hydrochloric acid to attain a low stomach pH. An alkaline pH can increase the chance of

bacteria reaching the small intestine which may cause scouring (Scholman et., 11996).

During the last decade the physiologid constraints of the young pigIet have k e n

considered in the formulation of diets for early-weaned piglets. Nuûitionists have developed

phase feeding systems which attempt to matçh the digestive capabilities of the pig at various

stages of its life (Tokach u. ,1994). Unfortunately, the overail "stress" asmciated with

weaning may affect the performance of eariy weaned piglets despite recent nutritional

advances.

There is very Little recent information about the relationship between weaning age

and piglet performance. Leibbrandt et., (1975) fomd that piglets weaned at four weeks

consumed more feed and gained weight more rapidly pst-weaning than piglets weaned at

two weeks. When the piglets had reached six weeks of age, the early-weaned pigiets

weighed the same as the later weaned animals. Most of the recent work in this a m focuses

specificdy on Segregated Early Weaning (SEW) management systems. Walker and

Wiseman (1994) examined split litters assigned to segregated early weaning (SEW) (10

days) or non-SEW weaning (27 days). The SEW piglets gained weight 20% faster than the

non-SEW piglets during the nursery phase. This increase in performance in SEW pigiets

may be due to a higher health status (Dritz et., 1994, Clark 1995). Wfiams et., (1994)

found that piglets with lower immune system activation grow 2942% more in the nursery

phase and deposit leaner tissue than piglets with higher immune system activation. The

management system can not always accurately predict the hedth status of the herd.

Dionissopoulos et al., (1997) compared the health status and feed efficiency of piglets

supplied fiom a farrow to f i s h unit, an SEW unit and a specific pathogen fiee (SPF) unit.

Al1 of these pigs were housed and managed in an isolation area where their health status and

performance was compared. The SEW pigs ranked the lowest in average daily feed intake

(ADFI), feed to gain ratio and contracted Mycop/asma Iyppneumoniae and Porcine

Respiratory and Reproductive Syndrome (PRRS).

The objective of this study was to detamine the effet that weaning age has on

pi& performance. This study examines the feed consumption, weight gain, feed to gain

ratio and skin integrity of piglets weaned at 7, 14 or 28 days and kept on-site.

Materials And Methods

Three trials were conducted with two pens of 10 pigiets per weaning age per trial.

The two pens per katment group were split into a "Light" and "heavy" pen based on

weaning weight. The a n i d s were weaned at either 7, 14 or 28 days postpartum. Each pen

rneasured 1.83 X 1.22 metres and contained 2 galvanized steel feeders, 2 nipple drinkers, a

mbber mat, a heat lamp and had tender foot flooring. Ail piglets were kept und six weeks of

age. Al1 sows used in this study were first parity animals.

The study was approved by the animal care cornmittee at the University of Guelph.

Animals were cared for under the guidehes of the Canadian Council on Animal Care

(CCAC 1993). A professional animal health technician was consulted about health concerns

and decided when humane euthanasia shodd be performed.

Feeding

A three phase feeding system was used in this study. Table (1) lists the ingredients in

the diets used in each of the phases. Feeding regimes were dependent on weaning age.

Piglets weaned at 7 days were fed each diet for two weeks. Piglets weaned at 14 days were

fed diet 1 for one week, diet 2 for two weeks and diet 3 for two weeks. Piglets weaned at 28

days were fed diet 3 for two weeks. The animals were fed pre-weighed amounts three times

a day. For the first two days after weauing some feed was sprinkled on the mat to stimulate

feed consumption. Feed intake was measured weekly on a per peu basis. Pigiets weaned at 7

days were given creep feeders for the first week after weaning because of the small size of

the animals. This feeder ciifference and the age differences between the piglets made it

diflïcult to quanti@ feed wastage, therefore feed data are described simply as "feed

disappearance".

Body Wei&

The animals were weighed at 1, 7, 14, 21, 28, 36 and 43 days of age. Piglets were

weighed weekiy both when they were with the sow and subsequent to weaning.

Skin inte&& Scores

At the time of weighing, the piglets were given a skin integrity score of zero, one,

two or three dependent on the numbers of marks on their skia A skin integrity score of zero

indicated that the animai was fiee h m scratch or suck marks on its body including the

beiiy, face, ears and tail. Score one indicated a few minor scratches, score two, a f& number

of visible scratches and suck marks and score three, severe marking on the skin of the piglet.

Statisticai Analvsis

The experirnental design is a one-way treatment classification in a completely

randornized design. Feed disappearance and weight gain were calculated weekly on a per

pen basis (experimental unit). The ratio of feed versus gain was then detenniaed. Analysis

of co-variance was used to compare the feed disappearance, body weight, weight gain and

feed to gain ratio across treatment groups. Initial bodyweight (day one postpaaum) was used

as a co-variate in the analysis.

A split pIot analysis of co-variance was then done with weaning age as the main plot

and pen as the sub-plot, This was done to determine if the "light" and "heavy" pens in each

treatment group performed differently.

Average mean integrity score values as well as linear and quadratic contrasts were

fitted to the data in a repeated measures d y s i s , to estabiish trends over time (Statistical

Analysis Systems lnstitutel985).

The skin htegrity scores of the piglets one week afkr weaning were analyzed

separately to determine if weaniag age has any effect on skin condition directiy &er

weaning. A Chi-square aaaiysis was done on the frequency distribution of skin integrity

scores one week d e r weaning for each treaîment group (Kuehl 1994).

ResuIts

Feed disa~~earance

Table (2) illustrates the ciifferences in feed disappearance as it relates to weaning

age. Piglets weaned at 28 days would be expected to consume more the week of weaning

than piglets weaned at 7 and 14 days simply because they are older and bigger. The

difference in feed disappearance following weaning for the three treatment groups was large

regardIess of the age and size factor. Age at weaning affected the amount of dry feed that

was consumed one week d e r weaning (P<0.10). Piglets weaned at 28 days consumed 241 .O

+ 50.2 g/piglet/day, piglets weaned at 14 days consumed 113.9 t 7.4 g/pigletlday and

piglets weaned at 7 days consumed 78.1 I 7.9 glpigletkiay. As the early weaned piglets (7 &

14 days) aged, the amount of feed that they consumed increased. By weeks five and six they

were consuming more feed than the 28day weaned piglets @<O.OS).

Weirzht Gain

Weaning age caused large diGerences in piglet weight gain (Fig 1). During the first

week afker weaning, the pigiets in ali three treatments had low weight gains. Again, the

pigiets weaned at 28 days have an advantage because they are older but the differences in

average daily gain one-week pst-weaning are notable. Animals weaned at 28 days gained

469.1 + 41.6 g/piglet/day the week foliowing weaning whüe piglets weaned at 14 days

gained 26.9 2 9.5 g/piglet/day and piglets weaned at 7 clays gained 42.4 t 8.7 g/piglet/day

@0.0001). At six weeks of age the piglets weaned at 14 and 28 days were si@cantly

heavier than the pigiets weaned at 7 days @<O.OS) (Fig 1). During the last 2 weeks of the

observation period piglets weaned at 7 days gained simiiar amounts of weight as piglets

weaned at 14 and 28 days @ >O. 1) but theu fimû weights remained significantly lighter @ <

0.05).

Feed: Gain Ratio

Weaning piglets at 7, 14 or 28 days did not affect theû feed-to-gain ratio over the

six-week experimental period (Table 3).

Performance ciifferences in the "li&tl' and "heavy" sens of each treatrnent m u p

The mean weaning weights for the "light" and "heavy" pens for each w&g age

were similar. Bodyweights for "light" and "heavy" groups respectively averaged 2.4 r 0.2

kg and 2.5 r 0.1 kg for piglets weaned at 7 days, 4.0 * 0.1 kg and 4.5 + 0.2 kg for pigiets

weaned at 14 days, 7.4 I 0.7 kg and 8.03 * 0.51 kg for pigiets weaned at 28 &YS. Due to the

fact that weaning weights were so similar, the mean performance of the groups was also

sirnilar. The only performance difference seen between groups was the amount that the 7

day weaned piglets in the two groups gained fiom ciays 7-43 (7.17 * 0.33 kg for heavy

group; 5.59 + 0.49 kg for light group) @ = 0.05).

Mortaiitv

Post-weanuig mortality was not significautly different among the three weaning ages

p0.10). Mortality rates were, 8.7 I 2.8%, 5.7 I 2.8 % and 0.0 t 2.8% for piglets weaned

at 7, 14 and 28 days respectively.

Skin Lesion Scores

Skin integrity scores were recorded on days 7, 14,21,28,36 and 43. Both the mea.

number ber pen) of scratches and suck marks averaged over the six week experimental

period and the fiequency distribution of skin integrity scores one week after weaning were

analyzed. The mean numbers of scratches and suck marks on piglets weaned at 7, 14 or 28

days were not statistically different averaged over the six week experimental period P O . 1).

The shape of the skin integrity curves for the 3 treatments were different (Figure 2). The

curve for piglets weaned at 7 days is more linear than the curves for the piglets weaned at 14

and 28 days @< 0.0001). Piglets in aii three treatment groups show an increase in skin

markings the week following weaning.

Figure (3) shows the kquency d i s t r i i o n of pigiet skin integrity scores one week

afler weaning for aU 3-treatment p u p s . Chi-square analysk indicated that the fkquency of

skin integrity scores were not randomly distn'buted for the three weaning ages (P<0.005).

There were no severe (score 3) skin markings on the pigiets weaned at 14 days one week

foliowing weaning. Twenty-five percent of pigiets weaned at 28 days had moderatdsevere

(scores two & three) markings, 9% of pigiets weaned at 14 days had moderatdsevere

markings and 39% of piglets weaned at 7 days had moderate/severe markings one week

aiter weaning.

Discussion

Weaning age afEected pigiet performance. Very early weaned piglets (7 days)

consumed less feed directiy after weaning, had a higher fiequency of skin markings and

gained minimal amounts of weight one week after weaning. By six weeks of age, the feed-

to-gain ratios were simila. for ail of the pigiets but the very early weaned animals weighed

significantly less than the later weaned animais. Pigiets weaned at 14 days consumed more

feed post-weaning, gained more weight and had Iower skin integrity scores the week d e r

weaning then the 7day-weaned animals. At week six, the leand 28-day-weaned piglets'

mean weights were simiiar.

An understanding of the type and cause of scratch marks is essential to the

establishment of the importance of these marks. This research suggests that piglets have

noticeable skin markings one week d e r weaning which decline over tirne. The percentage

of piglets with more skin marks one week after weaning is the highest among early weaned

piglets and pigiets weaned at 28 days (Fig 2). It would be interesthg to categorize the

marks into either marks made by sucking or scratches caused by aggressive encounters to

see if and how weaning age effects the type of markings fomd on pigiets. Pigiets weaned at

a younger age appeared to have more "suck" marks one week after weanuig and piglets

weaned at 28 days seemed to have more "aggression" marks one-week &er weaning

however these ciifferences were not quantifieci. These aggression marks include long

scratches on their flanks and lesions on their ears, which were probably more sevete in the

later weaned piglets because of their size and strength. The marked early-weaned piglets had

red, in-itated belly regions and oflen had bair loss on the beUy near the hind legs. Worobec

al (1997) observed that early weaned piglets perform significantiy more belly-nosing -9

behaviour (oral-nasal behaviour directed at other pigiets) than piglets weaned at 14 or 28

days. The "suck mark. that are seen on early-weaned piglets one week after weaning may

be related to the performance of beiiy-nosing behaviour. More research has to be conducted

in this area before conclusive results c m be obtained. Information about the relationship

between skin resilience and age would be important before more focussed research is

conducted.

In this study, early weaning without off-site segregation did not provide an

improvement in piglet performance. These results compare with a survey study done on 52

farrow-finish operations and 40 SEW operations in Ontario (Dewey et ai., 1997). There was

no significant difference between farrow-to-finish and SEW nursery pigs in average daiiy

gain (ADG) or feed conversion. The feed conversion for Farrow-Finish farms was 1.7 as

opposed to 1.6 on the SEW farms. The ADG for farrow-fmkh was 370 g/day cornpareci to

340 glday on the SEW farms. The ADG values are somewhat misleadhg because the

Farrow-finish pigs were older when they entered the nursery and therefore would be

expected to have higher ADG values. The @ormance values given in this stuciy would be

considered below average by industry standards. One explmation for this low performance

might be the fact that ail of the sows used in the experiment were purebred Yorkshire h t

par@ animals therefore iitter sizes and initial body weights were Iow. The main reason for

the poor performance of the very early weaned (7 days) pigIets was the delay in the

initiation of feeding directly foiiowing weaniug. The specificaiiy formulateci, highly

digestible diets that were used did not stimulate feed consurnption directly following

weaning. Piglets weaned at 7 and 14 days did not consume very much dry feed the first few

days after weaning (Jable 2). This delay in consumption may cause a lower rate of digestive

ce11 turnover in the mail intestine and the impairment of the intestines ability for digestive

ce11 production (Patience et., 1995). Enzymatic activity in the digestive system is also

affected by the amount of feed piglets consume. Decreased enzymatic (trypsin) activity may

1 s t the breakdown of protein in the diet (Schoiman etal., 1996).

Various studies have k e n conducteci to establish what motivates or stimulates

early-weaned piglets to feed directiy after weaning. Petrie and Gonyou (1988) observed that

piglets which were exposed to auditory playback of piglet and sow nursing vocaiïzations

spent more tirne feeding than the control group. Spraying the dry feed with 60 ml of

evaporated millr did not stimulate increased feeding behaviour. Csermely and Wood-Gush

(1981) also found an increase in both sucking and feeding behaviour when piglets were

exposed to nursing sow grunts and piglet suckling noises. The successful stimulation of

feeding behaviour in early-weaned pigiets would increase the feed efficiency of these

animais and may give the superior performance that has been suggested for early-weaned

animais. Countless other management factors also affect the motivation of piglets to feed

directly after weauing. Piglets should be fëcî at m e n t meal intervals (Ba& et., 1986),

given enough feeder space to eat simultaneously and pvided with proper sanitation, air

quaiity, temperature reguiation, floor space, feededdrinker design and feeding and weaning

management practices.

The important conclusions that c m be drawn h m this study include the realization

that piglets weaned at 7 days into standard management conditions do not adapt well, the

recognition that an extra week on the sow d t s in large d3Férences in piglet performance

and the acknowledgement that weaning age affects the skin lesion scores of piglets directly

after weaning. Decreasing the age at weaning without off-site segtegation does not resdt in

increased piglet performance.

Acknowledgements

The h c i a l support of the Ontario Ministry of Agriculture Food and Rural Affâirs

(OMFRA) and Ontario Pork is appreciated. We are gratefd to the stafîat Arkeii Research

Centre for their assistance, Dr. Tina Widowski for her comments on the manuscript and to

Dr. Ian McMillan and Margaret Quinton for their statistical guidance.

Table 1: Nutrient vaiues and ingredients of the three diets (Premiere Feed Company)

Crude Protein (%) Fat (%) Lys (%) Met (%)

M+C(%) Thr (%) TRP (%)

Calcium (%) Phoshorus (%)

Sodium (%)

INGREDIENTS (%) Corn

Dried Whey Infriinized ground oats

Blood Plasma Fat, pork

Herring Meal Soy conc.

Wheat rniddlings SBM 48%

Soy oiV lechithin Dicalcium Phosph.

Limestone Pellet Binder

Flavour L-Lysine

DL-methionine Vit + rninerals

Salt Medication, LS20

Table 2: Mean Feed Disappearance (gramsl piglet/ day SE)

Different lener superscripts within columns indicate statistical difference (PC 0.05)

D V Wean 7

Wean 14

Wean 28

Table 3: Feed-to-Cain ratio

7-14 14-21 21-28 28-36 36-43 14-43 28-43 78.1 rt 7.9 148.0 * 7.4' 2660 0 7,7 422.0. * 41.9 538.0k 13.7' 349.0 * 9.3. 478.0.k 14.0.'

114.0* 7.4.b 246.0k 7.7 417.0k45.9 620.0* l5.lb 354.01 9.3. 515.01 15.4"

24 1 .O k 50.2 455.0 k 18.7' 384.0 k 19,0b

Different lener superscripts within colurnns indicate statistical difference @< 0.05)

Dclvs Wean 7

Wean 14

Wean 28

7-14 14-21 21-28 28-36 36-43 14-43 28-43 2.0 * 0.4 1.4 * 0.2" 1.9 & 0.7 1 .O A O. 1 1.2 k 0.9 1.4 * O. 1 1.4 i 0.1

0.2 * 0.2 2.1 * 0.7 0,9 I O. 1 1.3 * 0.1 1.4 * 0.1 1.3 rt0.I

0.6 ,: O. 1 1.2 * 0.1 .. 1.3 * 0.1

-e- Wean 14

W e a n 28

Figure 1 : Bodyweight (kg) both before and after weaning over the six week experimental period. Different letter vertical superscripts indicate skttisticai difference: a b (P ~0.05); a* b @<O.OOS).

Arrows point IO the Lhree weaiung ages.

Figure 2: The mean skin lesion scores for each weaning age both before and afier weaning . Arrows represent the three weaning ages.

Wean 7

Score 3 Score O

Wean 14

Wean 28

Score 3

Score 1

Figure 3: The percentage distribution of skin lesion scores one week after weaning for each treatment group.

Effect of segregated early weaning (SEW) on sow behaviour

To be submitted to the Journal of Applied Animal Behaviour

Abstract

Segregated early weaning (SEW) is a mine management system in which

piglets are removed h m the sow at an eariy age and tmsported to a separate growing

facility. Average weaning aga in SEW systems range h m 16-17 days to as low as 7-

10 days postpartum. North Amencan commercial swine operations are rapidly shifting

to SEW systems with very little information about the behavioural and weIfare

implications of this switch. The behaviour and weKm of sows in early weaning

systems has been vimially ignored.

The objective of this study was to observe the behavioural effects of separation

from piglets and reduced lactation length on sows. The snidy was conducted on a

commercial SEW sow breeding and gestation f m . Two trials were conducted.

Twenty-four sows were weaned at 12-15 days of lactation (early-weaned) and twenty-

four sows were weaned at 19-22 days of lactation (Iate-weaned). m e r weaning the

sows were placed in pens in groups of six with two pens per treatment group per trial.

The sows were videotaped on days one, two, five and six pst-weaning. The weanhg-

to-breeding interval for each sow was recorded.

The behaviour of eariy- and late-weaned sows was very similar. The amounts of

time spent performing social behaviour (social grooming, nosing penmates, sniffing

penmates, mounting), feeding, drinkhg, aggressive behaviour (head knocking,

threatening, aitacking, fighting, escaping) and abnormal behaviour (bar biting, sham

chewing) following weaning were not affected by lactation length @ > 0.10). Reduced

lactation length led to an iacrease in inactive time five days after weaning @ < 0.05) and

a decrease in the performance of exploratory behaviour five and six days &et weanhg

@ < 0.05). These results suggest tbat the very early separation h m piglets and reduced

lactation length associated with SEW do not have any severe detrimental effects on sow

behaviour and welfare.

Key Words: Segregated early weaning (SEW); sow; behaviour; wean-to-breed interval

Introduction

Attention to the naturai weaning behaviour of pigs is needed in order to develop

husbandry practices which are in accordance with the biologicai needs of the animals

(Jensen and Recén 1989). To date, investigations into the effects of early weaning

practices in mine production have focussed on the behavioural and physiological needs

of the early weaned pigiets (e.g. Fraser, 1978) and the periparturent sow. Very Little

attention has been paid to the behaviour and welfare of the sow immediately following

early weaning. From a fiuictional point of view, an animai under naturai conditions wiU

need to perform certain behaviours in order to survive or for its offspring to survive.

Through the course of evolution, this "essentiai" behaviour may becorne controlled by

subjective emotional states (Duncan 1996). Thus in a natural setting, sows will have to

suckle their offspring and show a certain amount of other maternal care for many weeks.

By contrast, in production settings, the actuai need to perform such behaviour is

elirninated through early weaning and by providing highly digestible and nutritious diets

to the piglets. However, the sow may still be highly motivated to perform suckling and

other maternal behaviour and may suffer if the behaviour is prevented. Weary and

Fraser (1995) state that the fitness need, or what an animal requires to survive and

reproduce in natural conditions, is relevant to the welfare of that animai because,

although the f'uuctional need has been removed, the proXimate causes may still be

present. The animal may therefore be unable to perfonn higbiy motivated behaviour,

and this may resuit in a state of dering. This suffering may result in a change in the

behaviourai repertoire of the animal and the performance of a b n o d behaviour

patterns, such as stereotypes, vacuum activities, and redirected behaviour may be used

as indicators of reduced w e k (Duncan 198 1).

Under naturai, semi-naturai, and modined fatrowhg peu conditions, weaning in

swine is a graduai process, and depending on conditions, occurs between 70-88 days

pst-parturn (Be 199 1 ; Jensen and Recén 1989; Stolba 198 1; Stolba and Wood-Gush

1939). However, under modem production conditions, weaning is an abrupt event and

causes a sudden termination of the relationship between a sow and her piglets. The

effect of this abrupt and artincial end to the relationship, and to suckling in particuiar, on

the behaviour and welfare of the sow has yet to be quantüied.

Bm (1991) postuiated that the process of weaning is the result of a conflict

between mother and offspring. if this is true, then an artificidy weaned sow d l be

deprived of this con£lict, and the confiict may be necessary in order to d o w the sow to

terminate the relationship. Some may argue that the pmess of a sow suckling her

young is just as 'sfressfüi', if not more so,-on the sow as taking atl of her young away

relatively early in her lactation. However, given the opportunity for a sow to open and

close a barrier which separates her h m her litter, she will consistentiy and voluntarily

open this banier and move to an area where she cm suckle her young (Bm, 1991). Not

only did Bnre (199 1) find that the sow will do this regularly and on her own accord, but it

was also found that she wili suckie her offspring for an average of 11-12 weeks post-

partum. A study of &-range pigs revealed the proportion of sucklings initiated by the

sow was approximately 50 percent up to 10 weeks post-partum (Jensen and Recén,

1989). These observations suggest that the suckling 'stress' is either not avenive

enough to overcome the motivation of the sow to suckle her young, ensuring their

sumival, or it is not a 'stress' at aU. Stott (1981) maintained that measuting the

magnitude of stress often means measuring the degree of how weiI an animai adapts,

and goes on to emphasize the importance of management practices to avoid hamifiil

adaptations and capitalize on beneficial ones. Commercial swine operations do not allow

sows to leave the suckling environment therefore sows may develop strategies such as

stemal resting to prevent suckling in farrowing crates (de PassiiIé and Robert 1989).

This lack of control over the suckling/weaning process may be compounded by the

"stress" of early weaning.

Stolba (1981) suggested that both extemai and interna1 factors which together

cause behaviour to occur have been neglected in the design of swuie housing systems. It

could also be argued that these factors have ken ignored in the design of swine

management pmtocols such as SEW. This is not to Say that al1 current management

practices disregard stimuli and motivation for behavioural actions of animals. However,

without a critical review of the effects of management practices, specifically early

weaning practices, on the behaviour of animais, they can neither be accepted or refbted

as acceptable practices.

The objective of this study was to determine the effects of lactation length on

weaned sow behaviour.

Materiais And Methods

The study was conducted on a commercial SEW sow breeding and gestation

fann. Twenty-four sows were weawd at 12-15 days of lactation (early-weaned) and

twenty-four sows were weaned at 19-22 days of lactation (late-weatled). The sows were

housed in groups of six in pens measuring 2.3 x 4.0 m. There were two pens per

w e d g age for each of the two trials.

An attempt was made to group sows of d o m size together in order to

minimize fighting due to dominance effects. The temperature in f m w h g rmms and

post-weaning rooms was monitored daîiy and maintained at lg°C. AU sows were on a

14h Light: 10h darkness lightïng schedule throughout the duration of this study.

Pre-partunent and lactating sows were fed a conventional lactating sow

concentrate ration. Prior to parturition sows were fed 2.5 kg of lactation ration per &y.

On the day of parturition sows were fed the lactating ration to appetite; subsequently

they were fed 2.0 kg of ration on the &y foilowing parturition and this was increased

incrementauy by 1.0 kg per day until &y 6 pst-partum. Following day 6 pst-pmtum,

and prior to weaning, the amount of lactating sow ration fed remained at 6.0 kg per &y.

Once weaned, sows were floor fed the lactating sow ration until the first sow(s)

were bred. A conventional dry sow concentrate ration was then fed at a rate of 2.5

kg/sow/day mtil the conclusion of each trial. Water was available to both pre and post-

weaned sows ad Libitum via drinking nodes.

Behavioural Observations

A time-lape video recorder was used to record the behaviour of weaned sows

continuously on days one, two, five and six post-weaning. In order to obtain a

representative sample of behaviour during dayiight hows, the videotapes were sarnpled

h m 0800-1000h, 1200-1400h, and 1600-1 8OOh; previous studies @amet& et., 1984)

have s h o w that little activity other ttian resting behaviour occurs during darhess. The

behaviour of each of the six sows in a pen was noted every five minutes during the

observationai periods. This instantaneous sampling at five minute intervals aiiowed for

72 observations per pen per day. Behaviour was recorded under the broad categories of

Feeding and drinking, posture, social, exploratory, and abnormai (Table l), and M e r

designated to the specific sub-types of those categories.

Production observations

Sows were bred according to observable secondary signs of oestrus such as

standing response to be mounted, restlessness, ears "pricked and increased

interestlresponsiveness to the neighbouring boars. Wean-to-breed intervals were

cdculated as days pst-weaning to initiai breeding, and are presented as mean values for

respective treatment groups.

Statistical Analvsis

The expriment was designeci as a completely randomized one-way treatment

ckssification design with pen as the experimentai unit Behavioural and production data

fiom the two different treatment groups were compiled and analyzed. Analysis of

variance was used to test for treatment ciifferences for each of the behaviom on days

one, IWO, five and six days pst-weaning (Statisticai Anaiysis Systems institute 1985).

The behaviom were then grouped into main categories and linear models were fitted to

these categories.

The weaning-to-breeding interval was also compareci by d y s i s of variance.

Feedin~ and Dnnking Behaviour

The amount of feeding and drinking behaviour perfonned by the early- and late-

weaned sows was quite constant between weaning ages and over tirne @ > 0.10). The

sows in both treatment groups spent approxhately 2% of the observationai period

feeding and drinking for the first six days pst-weaning flable 2). The early-weaned

sows fed significantly less than the late weaned animais in the observationai period on

day six post-weaning @ < 0.05) This most Likely relates to a delay in feeding tirne.

Social Behaviour

The tirne spent nosing penmates, snifhg penmates and mounting was simiiar in

early- and late-weaned sows on days one, two, five and six post-weaning (Table 2).

Posture

Figure 1 shows the arnount of tune early- and late-weaned sows spent standing,

Lying ventraüy and lying laterally. Sows weaned earlier spent more time inactive (either

standing, sitting or lying) than sows weaned later (PC 0.05) but the overail tirne spent in

each posture was the same (Table 2).

Abnomal Bebaviour

Very little abnormal behaviour (sham chewing, bar biting) was exhibited in

either treatment group (Table 2).

ExpIoratorv Behaviour

For the fmt few &YS pst-weaning the amount of exploratory behaviour was

sirnilar in the two treatment groups (Table 2). On day six after weaning the late-weaned

sows explored significantly more then the early-weaned sows @ < 0.05).

Aggsessive Behaviour

The sows in both treatment groups spent approxMately 2% of the observation

time performing aggressive behaviour. Treatment did not affect the amount of attack,

fight, threat or escape behaviour exhibited one, two, five or six days pst-weaning

p o . 1 O).

Production observations

Wean-to-breed interval

The amount of time taken for behavioural signs of oestrus and subsequent

breeding to occur was not significdy d.erent for early- and late-weaned sows

p0.10). EarIy-weaned sows were bred 6.5 * 0.44 days after weaning as opposed to

6.3 k 0.46 days for late-weaned animais. There were two sows in the early-weaned

group that did not show any behavioural signs of heat on their first cycle after weaning

(hold-outs). There were no "hold-outs" in the late-weaned tteatrnent.

4.0. Discussion

The behaviour of early- and late-weaned sows was very similar for the fht six

&YS after weaning. Social behaviour, aggressive behaviour and abnormal behaviour

were not af5ected by time of weaning. Increased inactivity coupled with less exploratory

behaviour was seen in earlier weaned sows compared to Iate-weaned sows. The t h e

between weaning and breeding was not affected by time of weaning in this study.

Social behaviour of the weaned sow is not weil understood. The intensification

of swine production has limited the range of behaviourai patterns that sows are able to

perform. Stolba (1981) observed that when sows are aiiowed to maintain their family

groups, long-term bonds develop between mother and offspring as weii as "fnendship"

relations between certain adult members of the group.

The housing facilities provided in this study did not provide enough space for the

sows to M y express social behaviour. Behaviour such as nosing penmates, snifnng

penmates and mounting were performed for similar amounts of time in early- and late-

weaned sows in the week foilowing weaning. Mounthg behaviour increased five days

&er weaning in both treatment groups as the sows started coming into standing heat.

No mutuai grooming was seen at either weaning age although the sows spent

approximately 5% and 2% of the t h e observed sniffbg and nosing each other

respectively .

Aggressive encounta such as head knocking, atiacking, fighting and threat

behaviour were also observeci for approxhately 2% of the observational period for both

treatment groups. inter-sow aggression can be a weIfare problem and can also affect

productivity adverseIy. It has been demons&ated that the welfare of both the performer

and receiver of aggressive acts is compromisecl, however the receiver of such aggression

shows stronger indications of reduced welfare (Marchant et al., 1995). The amount of

tirne spent perfomiing aggressive behaviour had not decreased by day five pst-weaning

and was similar in both treaünent groups. This suggests that sows in both of the

treatment groups did not form stable domhance hierarchies. It was expected that when

the unfarniiiar sows were grouped together they would fight to establish dominance

directly after weaning and this aggression would decrease with tirne. The persistence of

aggressive behaviour six days post-weaning suggests that the spatial and environmental

requirements of the sows were not king met-

One way of determining how an animal is adapting to its environment and

management system, is in its performance of abnormai behaviour (Mason 1991). The

management system in this study involved a reduced lactation length. It was found that

lactation length did not affect the amount on sham chewing or bar-biting that sows

performed.. Sitting has also been identified as an abnormal posture for pigs. (Areiiano

& 1992; Dybkjaer 1992; Von Bord and Humik 1991). Again, the sows in each of the

treatment groups spent similar amounts of tirne sitting. This, in conjunction with the

absence of other abnormai behaviour, suggests that lactation length does not affect the

performance of a b n o d behaviour in sows.

Reduced lactation Iength did not affect the amount of thne spent standing, lying

ventrally or lying laterally foUowing weaning. Various studies have attempted to

understand the importance of lateral versus ventral lying. de Pasillé a., (1990) found

that lactating sows injecteci with thyrotropin-releasing factor (TRF:l or 9 @cggkg1)

exhibited more lateral recmbency than control groups and interpreted this as greater

stimulation of maternai behaviour. de Pasillé and Robert (1989) suggest that the change

from more lateral to ventral recumbency, in early and Iate stages of lactation

respectively, is a reflection of the sow's attempt to avoid the increased attention given by

their litter. The abrupt end to suckiing through artificial weaning does not allow the sow

to gradually alter her physiology by slowly weaning her litter, as observed under semi-

natural, free-range, and modified fxrowing environments (Bm 1991; Jensen and Recén

1989; Stolba 198 1; Stolba and Wwd-Gush 1989). Peak milk production in a suckling

sow occurs when her litter is approximately 3 weeks of age (Taylor 1988). We

postulated that abrupt weaaiog would cause a buildup of milk pressure in the sow's

udder. This pressure would cause udder discomfort and sows may lay laterally as

opposed to ventraIly in an attempt to relieve such discomfort. The general trend of lying

behaviour for both early and late weaned sows involves the sows lying predominantly

laterally for the first few days after weaning and shifting to ventral recumbency on days

five and six post-weaning. One explanation for this shift may be that as the udder

pressure diminishes sows begin to feel more cornfortable lying ventrally as opposed to

laterally. It would be interesting to do a more focused study to see if early-weaned mws

experience l es milk pressure than later-weaned sows because their lactation is

terminated before peak miik production.

Another explanation would be th& lateral fying is an expression of materna1

behaviour which diminishes a few days &er the piglets have been weaned. de-Pasillé

and Robert (1989) observed that SOM weaned into pens displayed more ventral lying

than weaned sows which remained in the fmwing crates. This suggests that lying

behaviour may be dictated by sow cornfort as opposed to residual m a t d behaviour.

Lactation length affected the performance of exploratory behaviour. Late

weaned sows spent approximately 20% of their t h e exploring on days five and six post-

weaning as opposed to 12% in the exly weaned sows. This decrease in exploratory

behaviour in conjunction with inçreased Uiactivity in early-weaned sows should be

exarnined more carefully to determine its rdationship to sow weLfare. One possible

explanation for the ciifference in activity level between early and late-weaned sows is

that the late weaned sows were in kat. External signs of heat may include restless

activity, sweliing and pink-red colouriug of the vulva, îiequent urination and occasional

loud grunting (Ensminger and Parker 1984). An average weaning-to-estrus interval for

sows is 7 days but early-weaned sows bave been reported to have Ionger weaning-to-

estrus intervals (Foxcroit 1997).

The analysis of performance data often helps to quantify and support

behavioural data. The time between weaning and subsequent breeding has been showi

to decrease with increasing length of lactation @ue et al., 1993). This study found that

tactation length did not change the weaning to breeding interval but that shorter lactation

tength resulted in more sows not retuming to oestrus. Failure of sows to return to oestrus

is one of the two major reasons for cuiling breeding females on commercial mine

farms. Therefore if SEW systems do affect retrrrn to oestrus swine producers may incur

significant economic l o s (Maurer et al., 1989).

Lactation length does not severely affect the behaviour of sows in commercial

breeding barns. This study will help to defend SEW systems in relation to sow weifare

and can act as a stimulus for the initiation of studies to more M y explore the concepts

intrduced in this paper.

Acknowledgments

1 would iike to thank Jeff Rau for his invaluable help and Tina Widowski for

ber advice on aspects of this research. 1 also gratefidly acknowledge Cold Springs Farm

Lirnited for their generous assistance in providing the facilities and aaimals for this

research and for the cooperation of Rob McDougall and Paul Bellanger.

TABLE 1 : Description of behaviours analyzed

Type of bebaviour Range of behavioural acts (sub-type)

Feeding Eating or manipulating feed with mouth or snout

Drinkhg Manipulating water nipple with mouth or snout

Posture Siandimg

Sitting

Lying - ventral lyïng : ventral or sternal part of the body

(udder) touching the ground with back and sides exposed

- lateral lying : side lying with udder exposed

Social Agonistic - threat, attack, fight, escape, avoidance

Non-agonistic - nosing, snBing, groorning or mounting

pen mate

Exploratory Envuonment-directed - sniffmglnosing inanimate

Abnormal Stereotypes - bar biting, vacuum chewing

Table 2: The percentage of observational tirne the sows spent perfoming various behaviours

Day 1 Day 2 Day 5 Day 6 FEEDINC Early Weaned Late Weaned

DEUMCWG Early Weaned Late Weaned

SOCLAL EarIy Weaned Late Weaned

Gmoming Early Weaned Late Weaned Nosing wnmates Eariy Weaned Late Weaned Snifiinp enm mates Early Weaned Late Weaned Mounting Early Weaned Late Weaned

POSTURE Early Weaning Late Weaning

Sitting Early Weaning Late Weaning Standing Early Weaning Late Weaning Ventral Lving Early Weaning Late Weaning Lateral Lving Early Weaning Late Weaning

ACGRESSION Early Weaning Late Weaning

Head knocking EarIy Weaning Late Weaning

Threat EarIy Weaning Late Weaning Attack Early Weaning Late Weaning Fight Early Weaning Late Weaning EXaE Early Weaning Late Weaning

ABNORMAL Early Weaning Late Weaning

Bar biting Early Weaning Late Weaning Sham Chewing Early Weaning Late Weaning

EXPLORATORY Early Weaning Late Weaning

The letter superscripts represent statistical diflkrences @< 0.05)

Standing

2 5

Days post-weaning

Ventral Lying

2 5 Days post-weaoing

Laterai Lybg

2 5 Days post-weaning

Figure 1 : The percentage of t h e the sows spent standing, tying venaally and lying laterally

GENERAL DISCUSSION

In the experiments d e s c r i i in this thesis, age at weaning affected the behaviour

and production of pigiets but not sows. Early weaned pigiets budgeted their time differently

than did pigiets weaned at 28 days, both directly after weaning and up to six weeks of age.

Piglets weaned at seven days of age spent 10% of their time beiiy-nosing a few days atler

weaning, spent Iess then 1% of their time at the feeder, performed a type of distress

behaviour named "escape behaviouf and spent oniy 1% of their time exploring their

environment At six weeks of age these early-weaneci piglets continued to spend more time

bdly-nosing than the 28-day-weaned animals. This dtered behavioural time budget in

conjunction with low feed intakes and weight gains suggests a weLfare problem for piglets

weaned at seven days of age. The time budget of piglets weaned at 14 days was different

h m piglets weaned at 28 days. Piglets weaned at 14 days spent more tirne exploring

directiy after weaning, less t h e at the feeder and p e r f o d more belly-noshg behaviour

than piglets weaned at 28 days.

The motivation behind beliy-nosing is still unclear, however this research suggests a

strong comection between age at weaning and belly-nosing. Piglets weaned at earlier ages

displayed greater amounts of belly-nosing. Beliy-nosing behaviour appeared when the very

early-weaned piglets (7 days) started to increase their c o m p t i o n of feed. Thetefore intake

of feed rnay be associated with the motivation of beiiy-nosing behaviour. n i e implications

of increased levels of belly-nosing are undetermined. There may be a relationship between

belly-nosing and the skin integrity of piglets. Piglets weaned at 7 and 28 days had a higher

frequency of skin markings one week &er weaning than piglets weaned at 14 days. The

type of markings found on pigIets weaned at 7 days seemed to be more "suck" marks as

oppsed to scratches resulting fkom aggression seen on the pigiets weaned at 28 days.

ûther performance indicators such as feed intake, weight gain and feed-to-gain ratio

were also affected by weaning age. By week six, piglets weaned at 7 and 14 days were

consuming more feed than the 28 day weaned piglets but the 7-day-weaned piglets weighed

significantly less than the later weaned animds. Piglets weaned at 7, 14 and 28 days and

kept on-site had simiiar feed efficiençies during the last two weeks of the observation period

(weeks 4-6).

Early weaned pigiets must be stimulated to feed directly d e r weaning to improve

their feed efficiency. Phase feeding systems have been developed to meet the nutritional

demands of the early-weaned piglet (Dritz et ai., 1997). However, the behaviouraI

abnormalities such as high levels of beUy-nosing and low feed consumption observed in

early-weaned pigiets suggest that even if their physiologid needs are king met their

behavioural needs are not.

This study demonstrated an inverse relationship between weaning age and altered

behaviour patterns. Piglets weaned at 7 days displayed the most severe behaviour

ciifferences foliowed by 14-day-weaned pigIets and the control28-day-weaned animals. B e

(1993) observed the same type of graded response to weaning with the amount of redirected

oral behaviours performed by pigiets weaned at four as opposed to six weeks.

If piglets display behavioufal abnormalities and poor performance as a result of

early-weaning, how does it affect the sow? Few studies have considered the behavioural

ramifications of the premature removal of piglets fiom the sow. Pajor et (1996) observed

the individual variation in sows weaning behaviour when given a chance to separate

foiiowing weaning. Pigiets' performance suggests again that 7-day-weaning is too young

and that 14-day-weaned piglets can compete with 28-day-weaned animais but they need

encouragement to feed directiy foiiowing weaning. Sow behaviour and performance were

not affected by weaning age in this study. Taking into consideration the cwrent knowIedge

of both piglet and sow behaviour and performance, weaning between 14-21 days is

recommended.

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Appendix One: ANOVA tables for feed data

2 1 day body weight

Pen

Treat

TreaPPen

E m r

Treat 537

28 day body weight Mode1

Mode1

B W I

1 BWI 1 1 1 3.67

8 1.97

1

2

2

9

1 1

I 1

Trial 12 1 1.08

8

1

0.12

5.37

0.37

0.22

I I en I I I 0.08

1.97

127

1 43 day body weight 1 Model 1 8 1 3.08

I 1 Triai 1 2 1 1.92

1 1 Treat 1 2 1 6.80

Emr 9 2.31

Weight Gain (kglldn~

1 1

1 1 Triai 1 2 1 0.06 1 1

1

I 1 I

Error 5 0.09 1

Mean Square

Source

8

1

1 4-2 1

Pen

Treat

DF

0.47

0.09

Mode1

BWI

I I 1

Error 9 039

1

2

1

BWI

Trial

Pen

Treat

Treat*Pen

0.07

0.68

1

2

1

2

2

-

1-45

0.36

0.37

1.11

0.24

Treat

Treat*Pen

1 3643 1 Mode1 ( 8 1 0.44

Trial

f en

l

Error

1 t 1 Triai

1

2

2 l

9 0.72

t 1

1 Emr 1 9 1 0.27

2

l

030

0.42

1.29

0.00

I I I 28-43 1 Mode1

.

Treat* Pen 0.33

Pen

Treat

BW1

Trial

1

2

1

2

Error

0.87

0.34

0.01

1.31

9 0.63

3643 Mode1 8 136

1 14-21 1 Model 1 6

1443

1 Trial 12

BWI

Trial

Pen

Tmt

Treat8Pen

E m r

Model

BWl

Trial

Pen

Trcat

Treat* Pen

Error

1 Pen 1 I

2 1-28 Model 6

BWI 1

I 1 en I l

1 28-36 1 Mode1 1 8

2843

I 1 en I l

Mode1

BWI

Trial

Pen

Treat

Treat*Pen

Error

8

1

2

1

2

2

8

2.87

0.08

228

1.46

14.0

0.74

0.31

Square

1 1 Trial 1 2 1 0.07

1 I

1 Error 1 8 1 0.07

1 I I

BWl 21-28 Mode1 6 3.55

BW1 1 1.88

1 Trial 1 2 1 6.89 1 1 1 I

Pen I 1 0.34

TreaPPen 2 2.50

Error 5 2.79 28-43

28-36 Mode t 8 0.16

BWI 1 0.02

Error

Model

BW1

Trial

Pen

Treat 1 en I ' I O.O0 1 1 Treat 1 2 1 0.32 1

5

8

1

2

1

2

1 Error 1 9 1 0.08 I

0.05

0.02

0.01

0.04

0.00

0.00

TEST TARGET (QA-3)

O 1993. Appaed Image. lm. W Rlghts R e s e M