Individual differences in responses of piglets to weaning at different ages

Individual differences in responses of pigletsto weaning at different ages

Sharon P. Mason, Susan Jarvis*, Alistair B. LawrenceAnimal Behavioural Sciences Department, Animal Biology Division, SAC-Edinburgh,

West Mains Rd, Edinburgh, EH9 3JG, UK

Accepted 11 September 2002

Abstract

Several studies indicate each piglet within a litter is affected differently by weaning and that these

individual responses may be altered by the age of the litter at weaning. In the present study, eight

litters of individually marked piglets (n ¼ 79) were randomly assigned to be weaned at 21 or 35 days

(four litters per treatment), and behavioural and physiological measures were used to elucidate the

relationship between age and weaning, and the within-litter variation in short-term responses to

weaning that is thought to occur. Weights, vocalisations, littermate directed behaviours, suckling

related parameters and salivary cortisol concentrations were recorded for individual piglets on both

treatments from birth to 37 days of age. The time piglets spent at the udder, massaging or suckling,

gradually increased over the preweaning period, as did aggression, nosing and chewing of littermates.

Higher levels of aggression were found on the day of weaning relative to the 2 days following, whilst

vocalisations did not peak until the day after weaning. Salivary cortisol was found to be lower for D35

piglets (day � treatment effect: F2;116ð38Þ ¼ 2:67, P ¼ 0:073) and ‘high vocalisations’ twice as high

on the day after weaning for D21 piglets compared to D35 (day � treatment effect: F2;146ð8Þ ¼ 3:93,

P < 0:05). Irrespective of weaning age piglets that suckled anterior teats during lactation were found

to be of heaviest relative weight throughout the preweaning and postweaning periods. Weaning

caused relatively heavier piglets to ‘high vocalise’ less, ‘low vocalise’ more and be more aggressive.

Anterior teat suckling piglets were also found to have high salivary cortisol levels postweaning. The

results provide evidence that weaning piglets at 21 days is detrimental to piglet welfare. Direct

support was also found for piglet teat choice to determine a piglet’s response to weaning. The increase

in low frequency ‘‘begging calls’’ by larger piglets along with the increase in high frequency

‘‘separation calls’’ by smaller piglets postweaning suggests that heavier, anterior teat suckling piglets

may experience more nutritional deprivation whilst smaller, posterior teat sucklers may experience

Applied Animal Behaviour Science 80 (2003) 117–132

* Corresponding author. Present address: Animal Behavioural Sciences Department, Animal Biology

Division, Bush Estate, PENICUIK, Midlothian, UK. Tel.: þ44-131-535-3214; fax: þ44-131-535-3121.

E-mail address: [email protected] (S. Jarvis).

0168-1591/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved.

PII: S 0 1 6 8 - 1 5 9 1 ( 0 2 ) 0 0 2 0 9 - 5

more maternal separation stress. Therefore, individual differences in short-term response to weaning

exist and are correlated with piglet weight and individual teat choice during lactation.

# 2002 Elsevier Science B.V. All rights reserved.

Keywords: Pigs; Weaning; Individual differences; Suckling related behaviours

1. Introduction

Much research has been carried out studying the effects of age on the responses of piglets to

weaning, showing levels of plasma cortisol (Worsaae and Schmidt, 1980), frequencies of

vocalisations (Weary and Fraser, 1995, 1997; Weary et al., 1999) and incidences of abnormal

behaviours (Fraser, 1978; Worsaae and Schmidt, 1980; Metz and Gonyou, 1990; Bøe, 1993;

Worobec et al., 1999) to be higher in early-weaned piglets. This work provides evidence that

the profound changes that occur during the weaning process cause considerably more distress

to animals the earlier separation occurs. In addition to this, there appears to be large within-

litter variation of postweaning behaviours, with the suggestion that these individual differ-

ences seen within litters are related to body weight and milk intake (Fraser, 1978).

Shortly after birth piglets begin to suckle from one or occasionally two adjacent teats

(Fraser, 1980). Piglets tend to develop preferences for specific teats that persist throughout

all of lactation (De Passille et al., 1988), a phenomenon known as the ‘‘teat order’’. Milk

production between different teats of the same sow can vary by as much as 200% and there

is, therefore, normally a large spread of piglet weights within a litter (Barber et al., 1955;

Gill and Thomson, 1956; Fraser, 1980). A small proportion of this variation in milk

production is explained by teat position (Fraser, 1984), with piglets suckling the anterior

end of the udder receiving up to 15.3% more milk than those at the posterior end (Gill and

Thomson, 1956). Small positive correlations between anterior teat suckling and relative

body weight have also been found in 3 week-old piglets (McBride et al., 1965; Fraser et al.,

1979; Cambell and Dunkin, 1982), suggesting the body weight of a piglet may be

determined, in part, by its suckling position along the udder.

Another possible reason for the wide distribution of body weight within a litter is that

piglets are thought to be able to affect the amount of milk received from the teat through the

amount of post milk let-down massaging performed. Piglet weight is, therefore, said to be

dependent on the productivity of the teat suckled as determined by the duration and

intensity of massaging given to the udder by the young after a suckling bout (Gill and

Thomson, 1956; Algers et al., 1990).

Due to the considerable within-litter variation of body weight frequently observed, one

might predict that the optimal timing for weaning may vary greatly between piglets

(McBride et al., 1965; Jensen, 1995; Bøe and Jensen, 1995). Evidence for this also comes

from research in semi-natural conditions, where some individuals tend to miss sucklings

before the weaning of the entire litter (Newberry and Wood-Gush, 1985; Jensen and Recen,

1989). Each piglet within a litter is, therefore, likely to be affected differently by

commercial weaning (Gill and Thomson, 1956), suggesting that perhaps smaller piglets

who have received less milk during lactation will be less able to adapt successfully to the

process of abrupt weaning than heavier littermates.

118 S.P. Mason et al. / Applied Animal Behaviour Science 80 (2003) 117–132

This study aimed to examine the effects of weaning, at two different ages, on the

behavioural and physiological responses of individual piglets within a litter with the

specific aim of assessing how short-term responses to weaning are affected by the relative

weight of piglets within a litter and by weaning age.

2. Materials and methods

2.1. Animals

The experiment involved eight entire litters from multiparous sows ((Large

White � Landrace) � Large White: Cotswold Pig Development Co., Lincoln, UK). During

pregnancy sows were group housed on straw and offered one meal of 2.5 kg/day (18% CP,

13MJ DE/kg) at 8:00 h. Approximately 5 days before the expected farrowing date, sows

were transferred to a farrowing house. The sex and number of piglets born alive was

recorded and no piglets were added to or removed from the litter at any stage. Piglets were

studied from birth to 37 days, after which they were returned to the original herd.

2.2. Housing and management

The piglets were housed from birth with their dam and littermates in a pen measuring

1:50 � 3:14 m fitted with a farrowing crate (0:54 � 2:22 m, 1.05 m high), and provided with

a heated area which the piglet could enter by choice in front of the sow (1:50 m � 0:64 m).

The crates were cleaned and fresh straw provided daily. Sows were fed to appetite (up to

6 kg/day) on a diet containing 13.75 MJ DE/kg and 18% protein at 8:00 and 16:00 h. Piglets

had access to water ad libitum via a nipple drinker and creep feed (Easiwean Startercare;

BOCM Pauls Ltd., Ipswich, UK) was introduced to all litters at 14 days old, irrespective of

weaning age. Artificial lighting was provided between 8:00 and 16:00 h.

Iron was administered by injection and the eye–teeth of each piglet clipped 2 days

postpartum. Sexing and marking, by painting large individual letters on their backs, also

occurred on day 2 postpartum. Marking occurred at the end of every day throughout the

experiment.

At weaning, litters were moved to a separate weaning room and placed in individual

straw bedded pens measuring 2:5 � 3:0 m, each pen containing a heated creep box, water

bowl and three-space-feeder. Piglets were supplied ad libitum water and a food appropriate

to their age (Easiwean Startercare; BOCM Pauls Ltd., Ipswich, UK) for the rest of the

experiment. The temperature in the room was monitored daily with a mean minimum and

maximum of 17:7 � 0:77 and 21:2 � 0:89 8C, respectively. Artificial lighting was provided

between 8:00 and 16:00 h. Pens were cleaned out daily with the provision of fresh straw.

All pens were washed and disinfected between each replicate.

2.3. Experimental treatments

Two replicates were conducted with four litters per replicate. In each replicate, two

litters were assigned at random to be weaned at 21 and 35 days postpartum (D21 and D35

S.P. Mason et al. / Applied Animal Behaviour Science 80 (2003) 117–132 119

pigs, respectively), resulting in 4 replicate litters for each treatment group. Litters of the

same weaning age treatment were placed in pens diagonally opposite from each other, with

rotation of the pen positions in the second replicate. Weaning was accompanied by ear

tagging and occurred around 1100 h. Piglets were allowed to suckle immediately before

removal.

2.4. Parameters recorded

2.4.1. Weight

Piglets were weighed on day 2 and 7 postpartum and continued at weekly intervals until

day 35. They were additionally weighed at the end of the experiment, on day 37. Weighing

always took place at the end of the day after all behavioural observations and saliva

samples were taken. Relative weights of individual pigs were obtained by dividing their

weight on a specific day by the average weight of its litter on that day.

2.4.2. Suckling behaviours

Teat order for each litter, taken during two milk-let downs, was recorded weekly from

day 7 and on the day before weaning. The preferred teat pair for each piglet was calculated

by finding the teat it used the most in all observations throughout the whole suckling period.

Teat pairs were numbered from posterior (1) to anterior (usually 7). Consistency of

suckling position was also calculated as the number of changes made by the piglet in

relation to all changes possible (Puppe and Tuchscherer, 1999), using the formula:

Stability ¼ 1 � number of changes made

observed sucklings � 1

� �� 100

Stability, therefore, ranged from 0 (inconsistent) to 100% (consistent).

2.4.3. Behavioural observations

Behavioural observations were recorded live using a Psion work-about mx hand-held

data recorder (Psion plc, London, U.K). Continuous observation periods (3 � 20 min) were

taken for each litter between 10:30 and 16:00 h on days 7 and 14 preweaning, the day

before weaning, the day of weaning after removal from the sow, and the following 2 days

postweaning. Seven behavioural categories were measured as shown in Table 1 along with

their descriptions.

2.4.4. Salivary cortisol

Weekly salivary cortisol measures were taken for each piglet at 16:00 h on day 14 and on

the day before weaning and the 2 days postweaning. Saliva was also taken at 16:00 h on the

day of weaning, with an additional sample 1 h after removal from the sow, to give a total of

two salivary cortisol measures for that day alone. Salivary cortisol samples taken at 16:00 h

occurred after all behavioural observations had finished and before the piglets were

weighed and marked.

Saliva was collected by allowing the pigs to chew on cotton buds until they were

thoroughly moistened. It was never necessary to restrain or handle piglets when obtaining


samples. The cotton buds were centrifuged for 5 min at 3000 rpm to remove the saliva,

which was then stored at �20 8C until analyses.

2.5. Radioimmunoassay

Concentrations of saliva cortisol were estimated by a direct solid phase 125I RIA

method (Coat-A-Count TKC05; Diagnostic Products Corporation, Los Angeles, CA).

All saliva samples were centrifuged again. 200 ml aliquots, assayed in duplicate (400 ml

per sample), were pipetted into label antibody coated polypropylene tubes. Radioactive

tracer was added and following incubation for three hours at room temperature, super-

natant was removed and the pellets counted. The minimum detection limit of the assay

was 0.500 ng/ml and the inter- and intra-assay coefficient of variation was 9.10 and

8.37%, respectively.

2.6. Statistical analysis

2.6.1. Treatment effects on behaviour and physiology

All data were checked for litter size and sex effects (proportion of males) between

treatments using two-sample t-test (Minitab, version 7.2). Data from all observation

periods were meant for each piglet for each day relative to weaning and mean cortisol

concentrations were calculated for each piglet each day. The meaned data were split into

two periods, preweaning (days 7, 14, 20/21) and postweaning (days 0, þ1, þ2) (Fig. 1).

Data were checked for normality and transformed if necessary; durations of behaviours

were transformed by arcsin and frequencies by log transformation. True means and S.E.M.

are reported in the results. Repeated measures analysis of variance (Genstat, Version 5,

Lawes Agricultural Trust, Rothamsted Experimental Station) were used to analyse the data

for the separate preweaning and postweaning periods. The data were blocked by litter,

piglet and day, with effects of treatment, day and day�treatment interactions investigated.

Relative weight, teat preference and teat consistency were fitted as covariates. When main

effects were found in the analysis of variance a least significant difference test was used as a

Table 1

Behavioural categories recorded in the experiment together with description

Behaviour Description

Presence at udder Oral–nasal contact with the udder of the sow.

High pitched vocalisation High pitched ‘‘squeal’’ from piglet.

Low pitched vocalisation Low pitched ‘‘quack’’ from piglet.

Chewing littermates Oral contact with the body of a littermate.

Nosing littermates Nasal contact with the body of a littermate (other than the belly), where

piglet pushes (with nose) in an upward motion.

Belly nosing A distinctive sequence in which one piglet rubs a littermate’s belly

with rhythmic, up and down movements of its snout (Fraser, 1978).

Aggressive interactions Pushing, head thrusting against, biting and chasing littermates in an

aggressive manner or in retaliation to an aggressive attack (McGlone, 1986).

Presence at feeder Piglet places their head in a feeder space.


posthoc test for differences between treatment or day means. Statistical significance was

accepted at P < 0:05.

2.6.2. Individual piglet effects on behaviour and physiology

The analysis was again split into two periods—preweaning (days 7, 14, 20/21) and

postweaning (days 0, þ1, þ2) period (Fig. 1), with the data meaned for every piglet for

each period. Data were checked for normality and transformed if necessary. Durations of

behaviours were transformed by arcsin and all frequencies by log transformation. The litter

effect was accounted for by producing residuals (one-way ANOVA, Minitab, version 7.2)

for each piglet for every behaviour, cortisol concentrations and relative weight. Correlation

analysis was carried out on residuals to examine the relationship between measures

(Minitab, version 7.2). Statistical significance was accepted at P < 0:05. To examine

the relationship between teat consistency and teat preference a regression (Minitab,

version 7.2) was performed using a quadratic function of teat preference as a predictor

for teat consistency.

3. Results

3.1. Litter information

Litter size at birth did not differ between D21 and D35 litters (mean litter size�S:E:M: ¼ 10:25 � 0:75 and 9:50 � 1:30 for D21 and D35 piglets respectively, t4 ¼ 0:49,

P ¼ 0:65). Similarly the proportion of males in the litter did not differ (mean proportion

of males � S:E:M: ¼ 0:565 � 0:11 and 0:595 � 0:058 for D21 and D35, respectively,

t4 ¼ �0:25, P ¼ 0:82). The weight of the piglets significantly increased over days

throughout the experimental period (Mean weight � S:E: ¼ 2:67 kg � 0:10 on day 7 up

to 11:05 kg � 0:34 on day 35, Day effect: F6;433ð28Þ ¼ 790:57, P < 0:001) however no

treatment differences in weight were seen on any day.

Fig. 1. Experimental treatments with defined periods of analysis. Day 0: birth; A: preweaning period—days 7,

14, 20/21; B: postweaning period—days 0, þ1, þ2.


3.2. Treatment effects on behaviour

3.2.1. Preweaning period

During the preweaning period, the performance of recorded behaviours did not differ

between D21 and D35 piglets at any time. However, all piglet behaviours increased over

the preweaning period. Frequencies of both ‘low’ and ‘high vocalisations’ gradually

increased over the preweaning period (‘high’, day effect: F2;151ð2Þ ¼ 4:40, P < 0:05; ‘low’,

day effect: F2;151ð2Þ ¼ 6:32, P < 0:01); (Fig. 2a), as did the number of aggressive

interactions (day effect: F2;151ð2Þ ¼ 16:99, P < 0:001); (Fig. 2b).

Fig. 2. Preweaning: (a) mean frequency/20 min observation of ‘high’ ( ) and ‘low’ ( ) vocalisations; (b) mean

percentage of time involved in aggressive interactions; (c) mean frequency/20 min observation of nosing ( ) and

chewing (&) littermates, for all piglets (days 7, 14, 20 for D21 and days 7, 14, 21 for D35 piglets). Error bars

indicate the S.E.


In relation to littermate directed behaviours, both nosing littermates (day effect:

F2;151ð2Þ ¼ 4:93, P < 0:01) and chewing littermates (day effect: F2;151ð2Þ ¼ 6:90,

P < 0:001) increased over days, (Fig. 2c). Interestingly, the time spent at the udder also

increased towards the end of the preweaning period (day effect: F2;151ð2Þ ¼ 5:79, P < 0:01).

3.2.2. Postweaning period

There was an increase in ‘high vocalisations’ over the postweaning period for both

treatments, but more so for D21 piglets on days þ1 and þ2 (day � treatment effect:

F2;146ð8Þ ¼ 3:93, P < 0:05; Fig. 3a). No treatment effects on ‘low vocalisations’ occurred

Fig. 3. Postweaning: (a) mean frequency/20 min observation of ‘high vocalisations’; (b) mean frequency/20 min

observation of ‘low vocalisations’; (c) mean percentage of time involved in aggressive interactions, for D21 ( )

and D35 ( ) for all piglets (days 0, þ1, þ2 correspond to days 21, 22, 23 for D21 piglets and days 35, 36, 37 for

D35 pigs). Error bars indicate the S.E.


postweaning, however, a significant increase was seen for both treatment groups on day þ1

(day effect: F2;146ð8Þ ¼ 10:33, P < 0:001; Fig. 3b).

Both treatment groups significantly decreased in levels of aggression (day effect:

F2;146ð8Þ ¼ 21:40, P < 0:001), however, D21 piglets tended to reduce levels of aggression

by day þ1, whereas this reduction was not seen in D35 piglets until day þ2

(day � treatment effect: F2;146ð8Þ ¼ 2:64, P ¼ 0:075; Fig. 3c).

The performance of littermate directed behaviours did not differ between D21 and D35

piglets postweaning although day effects did occur. Nosing of littermates was higher on the

day of weaning (day 0) compared to the 2 days postweaning (day þ1, þ2); (day effect:

F2;146ð8Þ ¼ 11:34, P < 0:001) as was chewing littermates (day effect: F2;146ð8Þ ¼ 10:77,

P < 0:001; Fig. 4), however, no day or treatment effects were found for belly nosing

behaviour.

Time spent at the feeder increased over time, with a significantly higher level of time

spent at the feeder on day þ1 and þ2 compared to day 0 (day effect: F2;146ð8Þ ¼ 7:86,

P < 0:001).

3.3. Treatment effects on physiology

There were no day or treatment effects on salivary cortisol concentrations during the

preweaning period. Postweaning, both treatment groups had higher salivary cortisol levels

on dayþ1 (day effect: F2;161ð38Þ ¼ 2:98, P ¼ 0:055), but for D21 there was a significant fall

from day þ1 to day þ2 and for D35 piglets a near significant increase from the day of

weaning to day þ1 (day � treatment effect: F2;116ð38Þ ¼ 2:67, P ¼ 0:073); (Fig. 5).

3.4. Individual effects on behaviour

3.4.1. Preweaning period

Piglets of heavier relative weight were found to be more likely to use anterior teats

(Table 2). Neither relative weight nor teat preference were correlated to consistency of

suckling position. However the regression analysis indicated that the relationship between

Fig. 4. Postweaning: mean frequency/20 min observation of nosing ( ) and chewing (&) of littermates for all

piglets (days 0, þ1, þ2 correspond to days 21, 22, 23 for D21 piglets and days 35, 36, 37 for D35 piglets). Error

bars indicate the S.E.


Fig. 5. Postweaning: mean concentrations of salivary cortisol for D21 ( ) and D35 (&) for all piglets (days 0,

þ1, þ2 correspond to days 20, 21, 22, 23 for D21 piglets and days 34, 35, 36, 37 for D35 piglets). Error bars

indicate the S.E.

Table 2

Pearson correlation coefficientsa between behavioural and physiological measures during

Behaviours Relative weight Teat preferenceb Teat consistencyc

(a) Preweaning periods of observations

Teat preference 0.352***

Teat consistency 0.002 0.075

High vocalisation �0.296** �0.141 0.204

Low vocalisation �0.023 �0.157 �0.084

Aggression 0.260* 0.218* �0.090

Nosing littermate 0.379*** 0.088 �0.084

Chew littermate 0.142 0.135 0.064

Belly nosing 0.106 0.132 �0.035

Cortisol (ng/nl) 0.072 �0.083 �0.149

(b) Postweaning periods of observations

Teat preference 0.419***

Teat consistency 0.081 �High vocalisation �0.312** �0.208 �0.000

Low vocalisation 0.331** 0.162 0.018

Aggression 0.295** 0.361*** �0.088

Nosing littermate 0.208 0.185 �0.115

Chew littermate 0.163 0.019 �0.044

Belly nosing �0.115 �0.214 �0.146

Cortisol (ng/nl) 0.058 0.227* �0.159

For (a) behaviours, relative weight, teat preference and consistency are measured during the preweaning period.

For (b) behaviours and relative weight are measured during the postweaning period with teat preference and

consistency being measured during the preweaning period.a Correlations are based on individual residuals, (n ¼ 79).b Teat preference is recorded on as (1) posterior to (7) anterior.c consistency of teat position is recorded as 0% stable (inconsistent) to 100% stable (consistent).* P 0:05.** P 0:01.*** p 0:001.


teat consistency and teat preference was not linear and was actually quadratic

(R2 ¼ 12:9%, F2;76 ¼ 5:64, P < 0:005). Therefore the change in consistency with increas-

ing teat preference is U-shaped (Fig. 6) with piglets at the most anterior and posterior teats

showing greatest consistency.

It was found that relatively heavier pigs ‘high vocalised’ less, nosed their littermates more and

were involved in more aggressive interactions (Table 2). Piglets suckling from the anterior end

of the udder were also found to be involved in more aggressive interactions (Table 2). Salivary

cortisol did not correlate with relative weight, teat preference or teat consistency. Piglets

that spent more time massaging the udder had higher counts of both ‘high vocalisations’

(r ¼ 0:272, d:f: ¼ 78, P < 0:001) and ‘low vocalisations’ (r ¼ 0:116, d:f: ¼ 78, P < 0:01).

Vocalisations were correlated well during the preweaning period with piglets that ‘high

vocalised’ more also having high levels of ‘low vocalisation’ (r ¼ 0:344, d:f: ¼ 78,

P < 0:001). Both measures of vocalisation were positively correlated with nosing of

littermates (‘low’: r ¼ 0:278, d:f: ¼ 78, P < 0:001; ‘high’: r ¼ 0:157, d:f: ¼ 78,

P < 0:001), aggressive behaviour (‘low’: r ¼ 0:164, d:f: ¼ 78, P < 0:001; ‘high’:

r ¼ 0:092, d:f: ¼ 78, P < 0:05), and chewing littermates (‘low’: r ¼ 0:176, d:f: ¼ 78,

P < 0:001). All littermate directed behaviours were positively correlated with each other

(nose littermate and aggression: r ¼ 0:507, d:f: ¼ 78, P < 0:001; nose littermate and

chewing littermate: r ¼ 0:585, d:f: ¼ 78, P < 0:001; aggression and chewing littermate:

r ¼ 0:402, d:f: ¼ 78, P < 0:001).

3.4.2. Postweaning period

Piglets that had suckled more anterior teats during lactation were also of heavier

postweaning relative weight after weaning (Table 2). All pigs made both ‘high’ and ‘low’

Fig. 6. The relationship between teat preference (1 ¼ posterior, 7 ¼ anterior) and teat consistency (percentage

of sucklings on preferred teat pair). Error bars indicate the S.E.


vocalisations, however relatively heavier pigs ‘high vocalised’ less and ‘low vocalised’

more than lighter pigs. Aggressive interactions were positively correlated with relative

weight, and piglets that preferred to suckle anterior teats during lactation were also

involved in significantly more levels of aggressive interactions (Table 2). Piglets that had

preferred anterior teats prior to weaning, however, had significantly higher levels of

salivary cortisol (Table 2). The time spent at the feeder during the postweaning period was

not related to the relative weight of the piglets (r ¼ 0:106, d:f: ¼ 78, P ¼ 0:367).

As was found for the preweaning period, piglets that ‘high vocalised’ more also ‘low

vocalised’ more (r ¼ 0:337, d:f: ¼ 78, P < 0:001), with these piglets also nosing litter-

mates at higher frequencies (‘low’: r ¼ 0:189, d:f: ¼ 78, P < 0:001; ‘high’: r ¼ 0:206,

d:f: ¼ 78, P < 0:001). All littermate directed behaviours were positively correlated with

each other (nose littermate and aggression: r ¼ 0:399, d:f: ¼ 78, P < 0:001; nose litter-

mate and chewing littermate: r ¼ 0:355, d:f: ¼ 78, P < 0:001; aggression and chewing

littermate: r ¼ 0:280, d:f: ¼ 78, P < 0:001).

‘Low vocalisation’ was positively correlated with aggressive behaviour (r ¼ 0:044,

d:f: ¼ 78, P < 0:05), as well as chewing littermates (r ¼ 0:161, d:f: ¼ 78, P < 0:001),

and the amount of time spent at the feeder (r ¼ 0:251, d:f: ¼ 78, P < 0:001). Piglets that

‘high vocalised’ more, however, were involved in significantly lower levels of aggressive

interactions with their littermates (r ¼ �0:170, d:f: ¼ 78, P < 0:001).

4. Discussion

The study provides evidence that the process of weaning causes immediate and

substantial changes in the behaviour of piglets, with these changes being affected by both

the age of the piglets at weaning and by individual characteristics including suckling

behaviour and relative weight at weaning. Following birth, teat order is established

within the first week (Fraser, 1975; De Passille et al., 1988). In the present study as the

piglets matured their time spent massaging or suckling at the udder increased. Aggres-

sion, nosing and chewing of littermates were also found to increase throughout the

preweaning period presumably as a result of piglets becoming active and explorative as

they developed.

Weaning did not appear to cause immediate distress to the piglets, as we did not

observe a peak in ‘high vocalisations’ until the day after weaning, as also reported by

Weary and Fraser (1995, 1997), and Weary et al. (1996, 1999). The increase in nosing

and chewing of littermates on the day of weaning could represent the onset of re-directed

suckling behaviour or that introduction to a novel environment initially led piglets

to engage in more exploratory behaviours. The rise in ‘high vocalisations’ did not

develop until the day(s) after exploration of littermates had diminished, and could be

a response either to maternal separation or to the onset of hunger, which would

also explain the increase in suckling associated ‘low vocalisations’ recorded on the

day after weaning and the sudden increase in time spent at the feeder over the

postweaning period.

Aggression was higher on the day of weaning compared to the 2 days after, similar to

results obtained by McBride (1963), Friend et al. (1983), McGlone and Curtis (1985) and


Algers et al. (1990). The higher levels of aggression on day 0 may be due to a general

increase in interaction with other piglets and/or exploration of the environment or to the

need for re-establishment of each piglet’s rank within the litter. Aggression was also higher

on day þ1 for D35 piglets relative to D21 piglets, which may suggest that piglets weaned at

older ages find it more difficult to reform a stable ‘teat order’. Although there was no

evidence of resulting increased physiological stress on D35 piglets. Instead it was the D21

piglets that had higher concentrations of salivary cortisol over the postweaning period, as in

the study reported by Worsaae and Schmidt (1980). ‘High vocalisations’ or ‘distress

vocalisations’ were also found to remain at higher levels for longer in D21 piglets

providing further evidence that the process of weaning provokes a greater stress response

the younger the piglets are at the time of removal from the sow.

In addition to the effects of weaning age, this study provides evidence that teat

preference, perhaps through affecting relative body weight, also has effects on the

behaviour of piglets in the postweaning period. Previously Fraser and Thompson

(1986) found no distinct individual differences regarding the relationship between animal

weight and teat order position, and Algers and Jensen (1991) also debated the association

of teat production and anterior/posterior teat position. The general assumption, however, is

that anterior teats are the more productive teats of the udder (Donald, 1937; Barber et al.,

1955; Gill and Thomson, 1956; Fraser, 1980; Rosillon-Warnier and Paquay, 1984/1985).

This study provides indirect evidence to support this assumption in that we found anterior

teat preference had strong positive correlations with piglet relative weight over both the

preweaning and postweaning periods.

Whilst finding many effects of teat preference on preweaning and postweaning

behaviour, we found no effect of teat consistency. We found that teat preference and teat

consistency were not linearly related, and of these two aspects of suckling style it appears

that teat preference is a better correlate of behaviour around weaning. Our finding that

piglets at the most anterior and posterior teats are more consistent in their teat use is in

agreement with De Passille et al., 1988, who also found a U-shaped relationship.

Following weaning, the present findings showed anterior teat sucklers to have higher

salivary cortisol levels suggesting that these piglets, which may also be the heavier

piglets, show a greater physiological stress response to the weaning process. ‘Low

vocalisations,’ thought to act as ‘begging calls,’ encouraging the sow to perform milk let

down (Weary and Fraser, 1995), were also higher for heavier piglets perhaps due to their

increased reliance on milk intake during the preweaning period. Weaning, therefore, may

cause them to be more nutritionally deprived than their smaller littermates. Time spent at

the feeder and ‘low vocalisations’ were also positively correlated with each other. This

provides further evidence of ‘begging for food,’ with the increased aggression seen in the

heavier pigs perhaps being as result of being unable to fulfil their nutritional demands, as

also seen by Algers et al. (1990). Aggressive interactions, however, may have been

aggravated due to the limited space of the three-spaced feeder used during the post-

weaning period.

Several studies have found temporary separation of piglets from the mother to result in

‘high pitched’ vocalisations, with smaller piglets vocalising more than their heavier

littermates (Weary and Fraser, 1995; Weary et al., 1996). A study carried out by Weary

and Fraser (1995) recorded the reactions of small ‘non-thriving’ and average weight


‘unfed’ piglets versus large ‘thriving’ piglets and average weight ‘fed’ piglets to isolation.

They found that all piglets including the ‘thriving’ and ‘fed’ piglets, made ‘high’ pitched

vocalisations suggesting that these vocalisations reflect a general need to be reunited with

the sow. However as ‘high’ vocalisations were greater in the ‘non-thriving’ and ‘unfed’

piglets these vocalisations most likely reflect the need for food in addition to a desire to

be reunited with the sow. The higher number of ‘high vocalisations’ and lower number of

‘low’ vocalisations recorded in this study by the smaller animals in the postweaning

period may, therefore, reflect a greater desire to be reunited with the sow (Weary and

Fraser, 1995). This may further indicate that unlike their heavier littermates, piglets of a

lighter weight are more responsive to the maternal separation rather than the nutritional

deprivation aspects of weaning. It could be argued that smaller piglets, perhaps due to

poorer development, are less physically able to make ‘low’ pitched vocalisations,

however all piglets in the study performed both types of vocalisations during the

preweaning period.

Performance of aggression, nosing and chewing littermates, belly nosing and both ‘high’

and ‘low vocalisations’ were interrelated throughout suggesting individuals who have a

tendency to engage in any specific littermate directed behaviour generally perform all types

and not just one specifically with these animals being more vocal too. The behavioural

evidence of the two stress effects suggested by this paper may, therefore, be more obvious

in more active piglets compared to quieter, subdued animals.

5. Conclusion

In conclusion, weaning was found to be more stressful the earlier separation occurred,

with several individual differences seen throughout the study relating to relative weight and

suckling behaviours. It was difficult to tell whether smaller, weaker piglets experienced

greater suffering than their heavier, stronger littermates as hypothesized. Instead, this paper

suggests that all piglets experience the stress of weaning with large piglets perhaps finding

it harder to adapt due to their nutritional demands, whilst smaller piglets, who received less

milk during lactation, may suffer more from maternal separation. Responses to weaning

are, therefore, to some extent dependent on body weight and the individual’s teat choice

during lactation.

Acknowledgements

All experimental work was carried out at Easter Howgate Pig Unit, Scottish Agri-

cultural College, Edinburgh. The authors would like to thank Sheena Calvert, Julie

Stevenson, Peter Finnie and Phil O’Neil for their help and assistance with animal

management, Fiona Gebbie of Scottish Agricultural College, Aberdeen for salivary

cortisol analysis, and Dave Allcroft at BIOSS for statistical assistance. The Scottish

Agricultural College receives funding from the Scottish Executive Rural Affairs Depart-

ment. Sharon Mason received studentship funding from The Royal Society for the

Prevention of Cruelty to Animals.


References

Algers, B., Jensen, P., 1991. Teat stimulation and milk production during early lactation in sows: effects of

continuous noise. Can. J. Anim. Sci. 71, 51–60.

Algers, B., Jensen, P., Steinwall, L., 1990. Behaviour and weight changes at weaning and regrouping of pigs in

relation to teat quality. Appl. Anim. Behav. Sci. 26, 143–155.

Barber, R.S., Braude, R., Mitchell, K.G., 1955. Studies on milk production of Large White pigs. J. Agric. Sci.

46, 97–118.

Bøe, K., 1993. The effect of age at weaning and postweaning environment on the behaviour of pigs. Acta Agri.

Scand. Sect. A-Anim. Sci. 43, 173–180.

Bøe, K., Jensen, P., 1995. Individual differences in suckling and solid food intake by piglets. Appl. Anim. Behav.

Sci. 42, 183–192.

Cambell, R.G., Dunkin, A.C., 1982. The effect of birth weight on the estimated milk intake, growth and body

composition of sow-reared piglets. Anim. Prod. 35, 193–197.

De Passille, A.B., Rushen, J., Hartsock, T.G., 1988. Ontogeny of teat fidelity in pigs and its relation to

competition at suckling. Can. J. Anim. Sci. 68, 325–338.

Donald, H.P., 1937. Suckling and Suckling preference in pigs. Empire J. Exp. Agric. 5, 361–368.

Fraser, D., 1975. The ‘teat order’ of suckling pigs. II. Fighting during suckling and the effects of clipping the eye

teeth. J. Agric. Sci. 85, 393–399.

Fraser, D., 1978. Observations on the behavioural development of suckling and early weaned piglets during the

first six weeks after birth. Anim. Behav. 26, 22–30.

Fraser, D., 1980. A review of the behavioural mechanism of milk ejection of the domestic pig. Appl. Anim.

Ethol. 6, 247–255.

Fraser, D., 1984. The role of behaviour in swine production: a review of research. Appl. Anim. Ethol. 11,

317–339.

Fraser, D., Thompson, B.K., 1986. Variation in piglet weights: relationship to suckling behaviour, parity number

and farrowing crate design. Can. J. Anim. Sci. 66, 31–46.

Fraser, D., Thompson, B.K., Ferguson, D.K., Darroch, R.L., 1979. The ‘teat order’ of suckling pigs. III. Relation

to competition within litters. J. Agric. Sci. 92, 257–261.

Friend, T.H., Knabe, D.A., Tanksley Jr., T.D., 1983. Behaviour and performance of pigs grouped by three

different methods at weaning. J. Anim. Sci. 6, 1406–1411.

Gill, J.C., Thomson, W., 1956. Observation on the behaviour of suckling pigs. Br. J. Anim. Behav. 4, 46–51.

Jensen, P., 1995. The weaning process of free-ranging domestic pigs: within- and between-litter variations.

Ethol. 100, 14–25.

Jensen, P., Recen, B., 1989. When to wean—observations from free-ranging domestic pigs. Appl. Anim. Behav.

Sci. 23, 49–60.

McBride, G., 1963. The ‘‘teat order’’ and communication in young pigs. Anim. Behav. 11, 53–56.

McBride, G., James, J.W., Wyeth, G.S.F., 1965. Social behaviour of domestic animals. VII. Variation in weaning

weight in pigs. Anim. Prod. 7, 67–74.

McGlone, J.J., 1986. Agonistic behaviour in food animals—review of research and techniques. J. Anim. Sci. 62,

1130–1139.

McGlone, J.J., Curtis, S.E., 1985. Behaviour and performance of weanling pigs in pens equipped with hide

areas. J. Anim. Sci. 60, 20–24.

Metz, J.H.M., Gonyou, H.W., 1990. Effect of age and housing conditions on the behavioural and haemolytic

reaction of piglets to weaning. Appl. Anim. Behav. Sci. 27, 299–309.

Newberry, R.C., Wood-Gush, D.G.M., 1985. The suckling behaviour of domestic pigs in a semi-natural

environment. Behaviour 95, 11–25.

Puppe, B., Tuchscherer, A., 1999. Developmental and territorial aspects of suckling behaviour in the domestic

pig (Sus scrofa f. Domestica). J. Zool. 249, 307–313.

Rosillon-Warnier, A., Paquay, P., 1984/1985. Development and consequences of teat-order in piglets. Appl.

Anim. Behav. Sci. 13, 14–58.

Weary, D.M., Fraser, D., 1995. Calling by domestic piglets: reliable signals of need? Anim. Behav. 50,

1047–1055.


Weary, D.M., Fraser, D., 1997. Vocal response to piglets: effect of piglet age. Appl. Anim Behav. Sci. 54,

153–160.

Weary, D.M., Lawson, G.L., Thompson, B.K., 1996. Stronger sow response to isolation calls associated with

greater levels of piglet need. Anim. Behav. 52, 1247–1253.

Weary, D.M., Appleby, M.C., Fraser, D., 1999. Responses of piglets to early separation from the sow. Appl.

Anim. Behav. Sci. 63, 289–300.

Worobec, E.K., Duncan, I.J.H., Widowski, T.M., 1999. The effects of weaning at 7, 14 and 28 days on piglet

behaviour. Appl. Anim. Behav. Sci. 62, 173–182.

Worsaae, H., Schmidt, M., 1980. Plasma cortisol and behaviour in early weaned piglets. Acta Veterinarica

Scand. 21, 640–657.


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Individual differences in responses of piglets to weaning at different ages