Extensiﬁcation of grassland use in the Welsh uplands: sheep … et al 2001.… · of national food security, contributions to the balance of payments and rural prosperity. Agriculture

Extensification of grassland use in the Welshuplands: sheep performance in years 1–6

M. Fothergill, D. A. Davies and C. T. Morgan

Institute of Grassland and Environmental Research, Bronydd Mawr Research Station, Brecon, Powys LD3 8RD,UK

Abstract

An experiment was established in 1991 on a 25-year-

old perennial ryegrass/bent (Lolium perenne L./Agrostis

capillaris L.)-dominated pasture in Wales to study the

effects of reducing nutrient inputs to previously ferti-

lized upland pasture. The effects of the removal of

applications of (1) N (denoted by CaPK) (2) N, P and K

(Ca) and (3) N, P, K, and Ca (Nil) were compared with a

treatment which received applications of all four nutri-

ents (CaPKN) over a 6-year period (1991–96) in a

randomized block design replicated three times. The

experiment was managed under a continuous variable

stocking regime (ewes and lambs until weaning and

ewes thereafter) maintaining a sward surface height of

4Æ0 cm throughout the grazing season. Although indi-

vidual liveweight gain of the lambs was unaffected by

the treatments, there was a significant reduction

(P < 0Æ05) in total lamb liveweight gain, ewe stocking

rate and length of grazing season as a result of the

withdrawal of nutrients. Over the 6 years total lamb

liveweight gain was reduced by 17%, 32% and 45%

and ewe stocking rate by 21%, 36% and 49% on

treatments CaPK, Ca and Nil, respectively, compared

with treatment CaPKN. The effect of withdrawing

nutrient inputs on ewe stocking rate was progressive

and by 1996 the Nil input treatment displayed a 63%

reduction compared with the CaPKN treatment and this

was also coupled with a 21-day reduction in length of

the grazing season. During the post-weaning period,

ewes from the Nil input treatment recorded a live-

weight loss in 1995 and only a modest liveweight gain

in 1996. This coupled with significantly lower body

condition scores (P < 0Æ01) of these ewes in the autumn

indicated that the Nil input treatment could lead to

reductions in reproductive performance.

Keywords: extensification, upland grassland use, Lolium

perenne/Agrostis capillaris, nutrient input, lamb live-

weight gain, ewe stocking rate

Introduction

Advances in technology and innovations in grassland

management, coupled with government incentive

schemes, encouraged reseeding of hill land throughout

the UK between 1940 and 1980. The intensification of

upland grassland farming was justified on the grounds

of national food security, contributions to the balance of

payments and rural prosperity. Agriculture was not

identified as a threat to the countryside and for 40 years

intensification and concomitant increases in output

from sheep systems in particular was embraced with

little regard for nature conservation objectives (Sheail,

1976).

At the end of the 1980s, grassland comprised

approximately 50% (12Æ8 million ha) of the UK agri-

cultural land area, with rough and hill grazing, perma-

nent grazing and silage grassland dominating the

landscape of much of western and northern Britain

(Alcock, 1992; Bunce et al., 1996). In more recent times

it has been appreciated that this policy led directly to a

substantial decline in the conservation value of upland

areas (Thompson et al., 1995) and a growing popular

concern over the destruction of sensitive landscapes and

habitats (Winter et al., 1998). The UK Ministry of

Agriculture Fisheries and Food (MAFF), thus, imple-

mented a series of measures designed to integrate

agricultural and environmental concerns and alter the

balance of the countryside by safeguarding rural land-

scapes and habitats.

There is a move to area-based payments, and with the

advent of agri-environment schemes, environmental

protection may be a precondition for the receipt of

payments (Waters, 1994). The idea of ‘sustainable

agriculture’ incorporates three equally important

components: environmental quality and ecological

soundness, plant and animal productivity and socio-

economic viability. Central to all these schemes is the

Correspondence to: M. Fothergill, IGER, Plas Gogerddan,

Aberystwyth, Ceredigion SY23 3EB, UK.

E-mail: [email protected]

Received 20 December 1999; revised 16 November 2000

Ó 2001 Blackwell Science Ltd. Grass and Forage Science, 56, 105–117 105

emphasis on lower stocking rates and reduction in

fertilizer use (Countryside Council for Wales, 1999).

Whereas much is known about the intensification of

grassland management, there is a scarcity of informa-

tion on the consequences of a reduction in nutrient

inputs on both animal output and sward dynamics.

Where long-term studies have taken place (Wind et al.,

1993; Smith, 1997), the main interest was centred on

the effect of extensification on pasture yield and

botanical composition. In these studies the grazing

animal was used as a means to effect changes in

diversity with little or no animal production data being

recorded. Richards and Evans (1993) compared lamb

production from re-created botanically diverse swards

with that of conventional reseeded pasture receiving

100 kg N ha)1 annum)1. However, that system was

monitored only during the establishment phase, which

was floristically dynamic compared with semi-perma-

nent or permanent grassland systems. These are known

to be more stable in response to management with

changes in grazing regime having only small effects on

floristic diversity (Bakker, 1989). Even when animal

production was assessed on semi-permanent grassland

(Treweek and Watt, 1993), the system was a careful

integration of sheep production and nature conserva-

tion involving only ewes grazing swards receiving no

fertilizer application.

The objectives of the present study were to examine

the effects of the withdrawal of nutrient applications

from previously well-fertilized, semi-permanent upland

pasture, on ewe and lamb performance. Animal pro-

duction per individual animal and per unit area from

four different nutrient treatments was assessed, when

the swards were managed according to common sward

surface height guidelines throughout the grazing season

for 6 years.

Materials and methods

The experiment was established in 1991 on a 25-year-

old perennial ryegrass/bent (Lolium perenne L./Agrostis

capillaris L.)-dominated pasture at Bronydd Mawr

Research Station, South Powys, Wales (51°58¢N,

03°38¢W). The experimental site was on an acid

brown earth soil of the Milford series overlying

Devonian Red Sandstone (Rudeforth et al., 1984) at

370–390 m above sea level on the south-east facing

slopes of Mynydd Eppynt. Soil analysis at the site in

1991 showed P, K, Na, Mg and Ca contents to be

0Æ007, 0Æ218, 0Æ058, 0Æ109 and 2Æ1 g)1 soil, respect-

ively, and the pH to be 5Æ6. No detailed fertilizer

records were available for the site prior to the

experiment. However, the area had received applica-

tions of 50–70 kg N ha)1 annum)1, maintenance ap-

plications of P and K (approximately 25 kg P ha)1 and

50 kg K ha)1 annum)1) during the 1980s and was last

limed in 1984 at a rate of 5 t ha)1 of ground

limestone. Over the period of study, average rainfall

was 1412 mm per year with a mean annual tempera-

ture of 8°C. Annual meteorological data for the period

1991–96 are presented in Table 1.

Treatments

Four experimental treatments were established, in a

randomized complete block design replicated three

times, to study the effects of reducing inputs to previ-

ously fertilized upland pasture. The effects of the removal

of applications of (1) N (denoted by CaPK) (2) N, P and K

(Ca) and (3) N, P, K, and Ca (Nil) were compared with a

treatment which received applications of all four nutri-

ents (CaPKN). Individual plot size was 0Æ4 ha.

Table 1 Summary of weather data (means of daily maximum and minimum temperatures, total sunshine and rainfall) in 1991–96,

together with the long-term means for the site.

1991 1992 1993 1994 1995 1996 1986–96

Annual

Maximum screen temperature (°C) 11Æ3 11Æ6 11Æ2 11Æ6 12Æ6 10Æ6 11Æ5

Minimum screen temperature (°C) 4Æ1 4Æ9 4Æ7 4Æ6 4Æ9 4Æ0 4Æ6

Soil temperature (°C) at 100 mm 8Æ1 8Æ4 8Æ0 8Æ3 8Æ7 7Æ5 8Æ1

Sunshine (h) 1029 1033 1005 1101 1416 1249 1194

Rainfall (mm) 1415 1471 1522 1657 1248 1160 1443

April–October

Maximum screen temperature (°C) 14Æ9 14Æ9 14Æ3 14Æ4 16Æ6 15Æ0 15Æ0

Minimum screen temperature (°C) 6Æ7 7Æ1 6Æ9 7Æ2 7Æ6 6Æ8 7Æ0

Soil temperature (°C) at 100 mm 11Æ3 11Æ3 10Æ8 10Æ6 12Æ1 11Æ0 11Æ2

Sunshine (h) 816 832 815 866 1121 1021 949

Rainfall (mm) 693 749 802 628 466 649 676

106 M. Fothergill et al.

Ó 2001 Blackwell Science Ltd, Grass and Forage Science, 56, 105–117

Fertilizer applications

Lime (in the form of ground limestone) was applied at

5 t ha)1 in September 1990 and 150 kg N ha)1,

25 kg P ha)1 and 50 kg K ha)1 were applied annually,

from 1991 onwards, to the appropriate treatments. The

N was applied as three equal applications of a 34Æ5% N

fertilizer; 50 kg N ha)1 in April, early June and mid-

August of each year. The treatments receiving P and K

were given a single application (in a compound fertil-

izer) in mid-June of each year.

Animals

From 1991 to 1996, the plots were stocked with

Brecknock Hill Cheviot yearling ewes and their single,

pure-bred lambs during the pre-weaning period. Each

year, the animals were allocated to individual plots at

the start of this period by selecting five ewes and their

lambs in a stratified random manner according to ewe

and lamb live weight and age. These animals represen-

ted the core group for each plot. In each year, there

were no significant differences (P > 0Æ05) between

treatments in initial ewe and lamb live weights.

Weaning took place in early August when the lambs

were removed from the experimental area. The core

ewes remained on the plots for the post-weaning

period. The extra animals used to maintain the target

sward height came from the same flock and so were of

similar type and age as the core group. Routine

veterinary care was carried out during the experiment,

which included periodic dosing with an anthelminthic.

Adequate clean water was available to the animals at all

times.

Grazing management

The dates and duration of the pre- and post-weaning

periods of the CaPKN treatment for each of the 6 years

are presented in Table 2. It was intended to commence

the grazing regime when the sward surface height

reached 4 cm in the spring. However, this was not

always possible as spring conditions for herbage growth

and availability of ewes and lambs did not always

coincide. Sward surface height was determined on

individual plots every week during the grazing season

by taking 40 measurements, at random, in a ‘W’

transect using the HFRO sward stick (Barthram,

1986). Once grazing commenced, ewe and lamb num-

bers (or ewe number in the post-weaning period) were

adjusted regularly to obtain and maintain a sward

surface height of 4 ± 0Æ5 cm on all plots. In the autumn

of each year, the core groups remained on the plots

until the sward height declined to 3Æ0 ± 0Æ5 cm at

which time grazing was terminated. During the winter

months (November-April) the plots were unstocked.

However, the pastures were observed regularly during

this period and the protocol allowed for removal of

excess herbage down to the 3 cm-sward height (by mob

stocking of ewes of the same breed) if the sward height

exceeded the 4 cm-target height. This occurred on two

occasions during February 1993 and 1995. Any increase

in sward height above the 4-cm target height that

occurred after 1 April was allowed to remain on the

plots. It was deemed that the increase in stocking rate

required to bring the swards down to the target sward

height would be a reasonable estimate of the early

spring production that otherwise would have been lost

to the system of measurement. This is the reason for the

high starting sward height on some of the treatments at

the start of grazing in the spring.

Measurements

Individual liveweight gains were calculated using data

from the core animals only. Total lamb liveweight gain

data were based on core and non-core animals which

were weighed when adjustments were made, i.e. either

adding or removing extra animals. All animals were

weighed and body condition score (Russel et al., 1969)

measured at turnout and at approximately 21-day

intervals until weaning. The ewes remaining on the

plots during the post-weaning period were weighed

using a similar protocol. The stocking rates were

calculated using ewe numbers only for both the pre-

and post-weaning periods.

Table 2 Grazing periods of the CaPKN treatment from 1991–96.

Pre-weaning period Post-weaning period

Start End Duration (days) Start End Duration (days)

1991 15 May 5 August 82 5 August 30 October 86

1992 1 May 5 August 97 5 August 30 October 86

1993 28 April 12 August 106 12 August 28 October 77

1994 26 April 10 August 106 10 August 1 November 82



Sheep performance in extensified upland grassland 107


Statistical analysis

Analyses of variation were carried out on all variables

measured as plot means using Genstat 5 release 3

(Lawes Agricultural Trust, 1987). The data for each year

were analysed separately, but, as new animals were

used every year on each treatment, it was also consid-

ered valid to include year in the analysis, and a further

analysis was undertaken. Significant differences

between treatments and years are recorded in the text.

Results

Sward surface height and changesin ewe numbers

Mean sward surface heights and the number of changes

in ewe numbers required to maintain the sward surface

height are presented as means over the years 1991–96

for each of the treatments in Table 3. Although the

protocol required all swards to be grazed to a sward

surface height of 4Æ0 ± 0Æ5 cm, differences between the

treatments in sward surface height were highly signi-

ficant during both the pre- and post-weaning periods

(P < 0Æ01 and P < 0Æ001 respectively). The main differ-

ence in sward surface height occurred in the spring

(Figure 1). The higher input treatments (CaPKN and

CaPK) had higher sward surface heights at the initiation

of grazing and this was probably as a result of a

combination of earlier growth and greater growth rates

of herbage. The difference in mean post-weaning sward

surface height was caused by the faster decline of sward

surface height in the lower input treatments. In the Ca

and Nil input treatments this occurred at an earlier date

with only the core group of ewes remaining on the

plots. The higher input treatments supported a larger

number of ewes in the post-weaning period, resulting

in a greater degree of accuracy in maintaining the

required sward surface heights. The number of changes

in ewe number (Table 3) reflected the ease of manage-

ment of the swards. All treatments required at least four

changes during the pre-weaning period. The CaPK and

Ca treatments required a significantly greater number

of changes than the Nil treatment (P < 0Æ05). However,

although fewer alterations in ewe number were

required during the post-weaning period, the high

input treatments required significantly more changes

(P < 0Æ001) with the trend CaPKN ¼ CaPK > Ca ¼ Nil.

Lamb live weights

Cumulative lamb liveweight gain (kg ha)1) during the

pre-weaning period for each of the years is presented in

Figure 2. In 1991 and 1992, there were five weighing

dates and in 1993–96 there were six weighing dates

from turnout to weaning. The final value represented

the total lamb liveweight gain to weaning for each

treatment. Highly significant differences occurred

between the treatments in each year and between the

years under study. In 1991, there were no significant

differences (P > 0Æ05) between the CaPK, Ca and Nil

treatments although the mean of these treatments

showed a 22% reduction (P < 0Æ01) compared with

the CaPKN treatment. Greater differences occurred

among the treatments during 1992–93, although there

was no significant difference between the CaPKN and

the CaPK treatments during this period. However, the

Ca and Nil treatments produced 19% and 37% less

(P < 0Æ01) than the mean of the CaPK and CPKN

treatments in 1992 and 28% and 31% less (P < 0Æ01)

than the mean of the same two treatments in 1993. The

differences between the treatments were even greater

in 1994, 1995 and 1996. Highly significant differences

(P < 0Æ001) occurred between the treatments in each of

the years with the trend CaPKN > CaPK > Ca > Nil.

Pre-weaning lamb liveweight gain, averaged over the

6 years, demonstrated the same trend with CaPK, Ca

and Nil treatments producing 17%, 31% and 45% less

(P < 0Æ001) lamb liveweight gain, respectively, than the

CaPKN treatment.

Individual lamb liveweight gains during the pre-

weaning period are presented in Table 4. No significant

Table 3 Sward surface height (cm) and number of stock changes, mean 1991–96.

Sward surface height (cm) Number of changes

Treatment Pre-weaning Post-weaning Grazing season Pre-weaning Post-weaning Total

CaPKN 4Æ49 3Æ95 4Æ30 4Æ39 1Æ72 6Æ11

CaPK 4Æ38 3Æ87 4Æ20 4Æ67 1Æ50 6Æ17

Ca 4Æ32 3Æ58 4Æ05 4Æ67 0Æ78 5Æ44

Nil 4Æ00 3Æ39 3Æ77 4Æ00 0Æ56 4Æ56

s.e. (46 d.f.) 0Æ055 0Æ051 0Æ047 0Æ159 0Æ174 0Æ276

Significance ** *** *** * *** ***

*P < 0Æ05; **P < 0Æ01; ***P < 0Æ001.



differences (P > 0Æ05) were detected between the treat-

ments in daily lamb liveweight gain of the core animals

in any single year or over the whole experimental

period. The individual lamb liveweight gains were low

in the first year of the experiment (1991). This reflected

the later start date of the pre-weaning period and

higher individual lamb weights at that time. Significant

differences were detected between years (P < 0Æ001)

and mean lamb liveweight gain increased by 27% over

this period. Although no significant treatment · year

interactions (P > 0Æ05) were found, there was a slight

decline in individual lamb performance in the CaPK, Ca

and Nil treatments (9%) during 1996, whereas the

CaPKN treatment recorded a further 6% increase. The

highest mean individual lamb liveweight gains occurred

in 1995 and that corresponded with the warmest,

sunniest and driest year.

Stocking rate and ewe live weights

Mean ewe stocking rates for the pre-weaning, post-

weaning and total grazing periods are presented in

Table 5. When meaned over the 6 years, highly signi-

ficant differences (P < 0Æ001) occurred between the

treatments in the pre-weaning, post-weaning and total

grazing periods. Only the Ca and Nil treatments, during

the post-weaning period, had similar ewe stocking

rates. Over the 6 years the CaPK, Ca and Nil treatments

supported 19%, 32% and 47% fewer ewes pre-weaning

and 26%, 43% and 51% fewer ewes post-weaning,

than the CaPKN treatment. The data for individual

years are presented in Figure 3. Although overall,

highly significant differences (P < 0Æ001) were detected

between CaPKN and CaPK treatments, no differences

in stocking rate were recorded between the two

Figure 1 Sward surface height (cm)

during the grazing period, mean of 1991–

96 for: (a) CaPKN (b) CaPK (c) Ca and

(d) Nil treatments. Vertical bars show

standard errors.



treatments during the pre-weaning period of 1993 and

the post-weaning periods of 1993 and 1994. Consider-

able year-to-year variation was encountered in post-

weaning stocking rate of the CaPKN treatments,

whereas the post-weaning stocking rates of the CaPK

treatment increased to high levels in 1993 and 1994

followed by a subsequent decline. The post-weaning

stocking rates of the lower input treatments (Ca and Nil)

Figure 2 Cumulative lamb liveweight gains (kg ha)1) during: (a) 1991 (b) 1992 (c) 1993 (d) 1994 (e) 1995 and (f) 1996 for CaPKN

(r), CaPK (j), Ca (h) and Nil (n) input treatments. Vertical bars show standard errors.



remained remarkably constant over the 6 years with no

significant difference (P > 0Æ05) between the two treat-

ments being detected. Although considerable yearly

variation in stocking rate also occurred during the pre-

weaning period, the Nil treatment alone demonstrated a

consistent and substantial decline in stocking rate over

the 6 years. By 1996, pre-weaning stocking rates were

81%, 94%, 73% and 47% of their initial values for

CaPKN, CaPK, Ca and Nil treatments respectively.

Ewe liveweight gains, from turnout to weaning for

1991–96, calculated for five separate grazing periods

(each of approximately 21 days), are presented in

Figure 4. Initially (period 1) there was a modest

liveweight gain of all ewes introduced onto the experi-

ment. However, during the next period (period 2),

highly significant (P < 0Æ001) differences in ewe live-

weight gain were detected between treatments. Ewes

grazing on the CaPKN and the CaPK swards lost 88Æ8and 37Æ4 g d)1, respectively, whereas ewes on the Ca

and Nil treatments gained 34Æ8 and 80Æ5 g d)1 respect-

ively. By grazing period three (7–9 weeks after turnout)

ewes on all treatments showed a loss in live weight,

losing on average 60Æ1 g d)1. The ewes recorded modest

liveweight gains during the latter part of the pre-

weaning period. Mean ewe liveweight gain increased

by 33 g d)1 during period 4 and 37 g d)1 during period

5 (immediately prior to weaning).

Individual ewe liveweight change data, over the post-

weaning period, are given in Table 6. Overall treatment

differences were significant (P < 0Æ05) with the Nil input

treatment producing the lowest ewe liveweight gain.

Highly significant differences occurred between years

(P < 0Æ001) and a significant treatment · year interaction

was detected (P < 0Æ05). No significant differences were

detected between the treatments over the period 1991–

94. However, significant differences (P < 0Æ01) were

detected between the treatments in 1995 with ewes on

the CaPKN treatment gaining 64Æ7 g day)1, whereas

ewes on the Nil treatment lost 10Æ4 g day)1 over the post-

weaning period. The lower input treatments also had

significantly (P < 0Æ05) lower ewe liveweight gains dur-

ing 1996 with the Nil treatment having less than half of

the liveweight gain of the CaPKN treatment.

Pre-weaning body condition scores of the core group

ewes showed no treatment effects (P > 0Æ05) in any of

the years under study. The condition score remained

within the range 2Æ50–2Æ75 during the pre-weaning

period in each of the years.

The ewe body condition scores at the end of the post-

weaning period are presented in Table 7. Highly signi-

ficant differences occurred between treatments

(P < 0Æ001) and between years (P < 0Æ001). During the

early years of the experiment (1991–94) there was little

difference between the treatments. However, in a

similar trend to the ewe liveweight gains, the lower

input treatments produced significantly lower ewe body

condition scores during 1995 and 1996 (P < 0Æ01). In

1995, the CaPKN treatment produced the highest ewe

body condition score with the Nil treatment producing

the lowest scores whereas in 1996 it was the CaPK

treatment that produced the highest score with the Ca

treatment producing the lowest scores.

Discussion

Modern agricultural policy in the UK is formulated to

effect a reduction in the intensity of farming over a

significant area of land. Reducing fertilizer inputs is

seen as a means of reducing pollution, curbing

unwanted surpluses and increasing bio-diversity while

reducing the stocking rate of sheep and cattle (Lowe,

1995). Many hill and upland areas rely, almost exclu-

sively, on forms of agriculture based on grassland and

livestock production with little alternative commercial

use available. The present experiment was initiated to

assess the effect of the cessation of applications of

fertilizer nutrients to previously well-fertilized upland

pastures. Our premise was such that, even though

fertilizer use may decline or be restricted, efficient

sward utilization would still continue. There is little

information on the comparable animal performance on

reduced fertilizer treatments over such a period of time.

A comparison with previous studies indicated that

similar pre-weaning lamb liveweight gains and ewe

stocking rates were obtained from the higher input

Table 4 Individual lamb liveweight gains (g d)1) from 1991–96.

Year

Treatment 1991 1992 1993 1994 1995 1996 Mean

CaPKN 131 171 165 174 189 206 174

CaPK 160 165 171 171 198 183 175

Ca 135 169 181 171 181 165 167

Nil 162 152 177 184 187 162 171

Mean 149 164 174 174 189 179

s.e. (6 d.f.) 16Æ1 9Æ1 10Æ2 9Æ0 6Æ3 11Æ2

s.e. = 5Æ8 and 7Æ1 for yearly means and overall treatment

means, respectively, error d.f. = 46.

Table 5 Mean stocking rate by ewes for pre-weaning, post-

weaning and total grazing periods (ewes ha)1) from 1991–96.

Year CaPKN CaPK Ca Nil

s.e.

(46 d.f.)

Signifi-

cance

Pre-weaning 29Æ7 24Æ2 20Æ3 15Æ9 0Æ69 ***

Post-weaning 23Æ9 17Æ6 13Æ7 11Æ8 0Æ88 ***

Total 27Æ1 21Æ2 17Æ3 13Æ9 0Æ75 ***

***P < 0Æ001.



treatments in the present study to those obtained from

perennial ryegrass receiving 200 kg N ha)1 and peren-

nial ryegrass/white clover reseeds 4–6 years old (Davies

et al., 1992).

Sward height is widely accepted as a measure of

sward state and the guidelines and principles of the

technique have been described by Parsons et al. (1986)

and Hodgson et al. (1986). The changes in grazing

pressure required to correspond to the changes in sward

state can be achieved by either closing an area for

conservation, as outlined by Maxwell and Treacher

(1987), or by adjusting animal numbers in ‘put and

take’ experiments. Both systems have been used suc-

cessfully in sheep systems and animal production

experiments (Maxwell, 1986; Davies et al., 1989). In

the present study, adjustments of ewe numbers allowed

sward surface height to be maintained within the

guidelines developed for sheep systems (Maxwell and

Treacher, 1987) in all the treatments. Significant

differences in sward surface height were detected

between the treatments. However, this was mainly

due to differences in sward surface height in early

spring and late autumn with the sward surface height,

on all treatments, being held close to 4Æ0 cm during

most of the grazing period. Clearly the higher input

treatments required higher stocking rates to maintain

sward surface height, during the pre-weaning period,

but required only slightly more adjustments than the

lower input treatments. However, the higher input

treatments required more changes in ewe numbers

during the post-weaning period and, thus, demanded a

greater intensity of management to maintain the target

Figure 3 Stocking rate (ewes ha)1) for:

(a) pre-weaning (b) post-weaning and

(c) total grazing periods from 1991 to 96

for CaPKN (u), CaPK (j), Ca ( ) and

Nil ( ) input treatments. Vertical bars

show standard errors.



sward surface height. This indicates that swards with

lower inputs of nutrients would require a lower level of

labour input than the higher input treatments. How-

ever, a 5-year study into the extensification of grassland

grazed by sheep in the Massif Central region of France

(Theriez et al., 1997) suggested that extensive systems

would require better long-term planning over several

years in resource management compared with higher

input systems. That study concluded that the technical

skill requirement was at least equal to that required for

intensive systems.

Prior to the experiment it was assumed that the

stocking rate for the Nil input treatment would be

approximately 12 ewes ha)1 over the grazing period,

and the number of core ewes (five) was determined on

the basis of plot size. This estimation of ewe stocking

rate seemed to be adequate during the early years of the

experiment. However, as the productivity of the Nil

input treatment declined, it became difficult to main-

tain the core group on this treatment during the post-

weaning period. This had the effect of progressively

reducing the length of the grazing season to such an

extent that by 1996 grazing ceased 21 days earlier than

that on the high input treatments. It was clear that the

plot size of the Nil input treatment was insufficient to

support the stock numbers necessary to estimate

adequately individual animal performance and pre-

cisely control the post-weaning sward height.

The mean individual live weights of both ewes and

lambs at weaning (42Æ4 kg and 25Æ0 kg respectively) for

1991–96 fell within the acceptable range for the breed

reported in earlier studies (Maxwell et al., 1997). This

indicated that the sward height (controlled at 4 cm)

provided adequate nutrients and energy for acceptable

lamb growth. As in previous studies (Maxwell et al.,

1994), the similarity of the pre-weaning condition

scores of the ewes also suggests that the sward height

provided an adequate diet for the ewes to act as an

Figure 4 Mean ewe liveweight gain

(g d)1) in the pre-weaning period in

1991–96, during five separate grazing

periods each of approximately 21 days

for CaPKN (u), CaPK (j), Ca ( ) and

Nil ( ) input treatments. Vertical bars

show standard errors.

Table 6 Ewe liveweight change (g d)1) during the post-

weaning period from 1991–96.

Year

Treatment 1991 1992 1993 1994 1995 1996 Mean

CaPKN 77Æ9 83Æ0 97Æ9 75Æ6 64Æ7 63Æ3 77Æ1

CaPK 97Æ3 113Æ2 91Æ5 63Æ5 56Æ6 97Æ6 86Æ7

Ca 82Æ6 92Æ3 104Æ3 80Æ5 69Æ5 72Æ4 70Æ6

Nil 58Æ1 99Æ6 113Æ7 69Æ5 )10Æ4 31Æ7 60Æ3

Mean 79Æ0 97Æ0 102Æ6 72Æ4 33Æ2 57Æ8

s.e. (6 d.f.) 13Æ12 19Æ27 14Æ72 16Æ57 8Æ09 12Æ74

s.e. = 10Æ12, 8Æ26 and 20Æ24 for yearly means, overall treatment

means and treatment · years, respectively, error d.f. = 46.

Table 7 Body condition scores of ewes at the end of the

grazing period in the autumn in 1991–96.

Year

Treatment 1991 1992 1993 1994 1995 1996 Mean

CaPKN 2Æ78 3Æ13 3Æ30 3Æ37 3Æ07 2Æ78 3Æ07

CaPK 2Æ92 3Æ17 3Æ20 3Æ23 2Æ98 2Æ90 3Æ07

Ca 2Æ77 3Æ00 3Æ35 3Æ12 2Æ79 2Æ48 2Æ92

Nil 2Æ70 3Æ05 3Æ17 3Æ12 2Æ53 2Æ67 2Æ86

Mean 2Æ79 3Æ09 3Æ25 3Æ18 2Æ84 2Æ71

s.e. (6 d.f.) 0Æ093 0Æ092 0Æ079 0Æ133 0Æ068 0Æ049

s.e. = 0Æ061 and 0Æ050 for yearly means and overall treatment

means, respectively, error d.f. = 46.



effective buffer against any production or nutritional

deficiencies (Meat and Livestock Commission, 1981).

Individual lamb liveweight gain is more sensitive to

differences in sward height during the post-weaning

period (Davies et al., 1992) when the buffering effect of

the ewe has been removed, but this was not assessed in

the present experiment.

Treatment differences in ewe performance during the

early part of the pre-weaning period were identified in

each of the years. The higher input swards produced a

ewe liveweight loss during this period whereas the

lower input swards recorded a modest gain. There is

much evidence to show that sward height and especi-

ally direction of change of sward height, together with

associated stocking density changes, influences the

growth rate of sheep (Alcock et al., 1986; Penning et al.,

1994; Armstrong et al., 1995) and cattle (McGilloway

et al., 1999). These studies provided evidence that the

grass pseudostem acted as a barrier to defoliation and

also that the proportion of youngest leaf in the diet

increased with sward height. There is also evidence

(Fischer et al., 1997) that higher stocking rates reduced

the rate of intake in sheep. As in these previous studies,

the falling sward height produced lower liveweight

gains, indeed a loss of live weight occurred in the ewes

grazing the higher input swards (CaPKN and CaPK)

during this period. However, the effect was transitory

and these treatment differences had disappeared by

approximately 3 weeks later.

Significant treatment effects were identified on ewe

performance during the post-weaning periods in 1995

and 1996. Ewes from the lower input treatments,

especially the Nil input treatment, showed a liveweight

loss in 1995 and only a modest liveweight gain in 1996.

This, coupled with the significantly lower body condi-

tion scores of these ewes, indicated that the Nil input

treatment could cause a reduction in reproductive

performance (Gunn et al., 1990). This effect could be

accounted for, in part, by the lower post-weaning sward

height of the low-input treatments. However, the

treatments were kept within the guidelines of

4 ± 0Æ5 cm falling to 3 cm in the autumn. The effect

seemed to increase with the increasing duration of the

experiment even though the swards were managed in

the same way each year. Work in Scotland (Water-

house, 1996), Wales (Rhind et al., 1998) and Uruguay

(Gonzalez et al., 1997) indicated that extensive systems

could lead to possibilities of poor animal welfare

through reduced animal care and restricted nutrition

of the animal during early and adult life. It was stressed

that preferential nutritional treatment should be given

to young ewes to ensure satisfactory lambing perform-

ance. It has been reported (Gunn et al., 1990) that the

recovery of ewe body condition score during the period

between weaning and mating will largely determine the

levels of reproductive performance. For the female

ruminant it seems to be the level of energy intake above

that required for maintenance that influences the

ability to grow and conceive (Sinclair and Agabriel,

1998). Although maternal fat reserves can effect foetal

growth during late pregnancy (McNeill et al., 1999), it is

also known that nutritional supply during the very

early stages of pregnancy can affect placental growth

and the subsequent pattern of nutritional partitioning

to the foetus (Robinson et al., 1999). Our results

indicate that swards receiving no fertilizer nutrients

may require different management during the post-

weaning period to ensure adequate recovery of ewe

body condition score prior to mating. The effects were

most strongly identified in 1995 when very low rainfall

was recorded during the grazing period and, thus, may

be exacerbated during periods of severe environmental

stress. Treweek et al. (1997) studied the effect of sheep

grazing at different times of the year and at different

intensities on ewe live weights. They showed that a

combination of tight winter and spring grazing, fol-

lowed by grazing at higher sward heights during the

subsequent summer, resulted in better maintenance of

ewe live weights during the latter part of the summer

and autumn. If stock are to be used for the maintenance

of semi-natural habitats, as suggested by Hearn (1995),

then the adoption of higher sward heights during the

post-weaning period, or even supplementary feeding,

may be necessary. Earlier work (Large and Spedding,

1976; Large and King, 1978) proposed the use of more

appropriate sheep breeds, such as Soay sheep, in low

input systems. Indeed Simm et al. (1996) suggested that

considerable scope for improvement existed by selec-

tion for adaptation to extensive conditions.

The most obvious effect of reducing inputs to upland

swards was the reduction in lamb liveweight gain and

ewe stocking rate. Lamb liveweight gains obtained

during the pre-weaning period from the CaPKN treat-

ments were similar to those from perennial ryegrass

reseeds receiving 200 kg N ha)1 previously recorded in

the uplands (Davies et al., 1989). The Nil input treat-

ment consistently produced a lower total lamb live-

weight gain and demonstrated a 45% reduction

compared with the CaPKN treatment over the 6 years.

The two other treatments were intermediate in their

total lamb liveweight gain with the CaPK and Ca

treatments recording a reduction in total lamb live-

weight gain of 16% and 31%, respectively, relative to

the CaPKN treatment. The CaPK treatment had the

effect of increasing the white clover (Trifolium repens L.)

content of the swards (Fothergill et al., 1995) compared

with all other treatments and during 1993, the CaPK

treatment produced similar lamb liveweight gains to the

CaPKN treatment. However, the white clover content

was unstable and the sudden decline of white clover



that occurred in 1995 was associated with the low

liveweight gain of the CaPK treatment relative to the

CaPKN treatment in that year. A full account of the

herbage characteristics and sward composition associ-

ated with these changes in animal output will be

presented in a later paper.

Even more striking was the reduction in ewe stocking

rate caused by the lowering of fertilizer inputs. The

relative ewe stocking rate of the treatments is presented

in Figure 5 which shows that the reduction in fertilizer

inputs had a substantial effect on ewe stocking rate. It is

also clear that the effect of withdrawing fertilizer inputs

on ewe stocking rate was progressive and that after

6 years the performance of the Nil input treatment was

still declining relative to the higher fertilizer input

treatments. By 1996, the Nil input treatment showed a

63% reduction in ewe stocking rate compared with the

CaPKN treatment.

The information from this experiment shows the

degree to which animal output was impaired by

reducing fertilizer inputs. The complete withdrawal of

fertilizer inputs into the sward had a dramatic effect,

reducing total lamb liveweight gain, ewe stocking rate

and length of grazing season but with little impact on

the individual lamb liveweight gain. However, in

common with other studies, the post-weaning perform-

ance and condition score of the ewes suggested that

problems with the reproductive performance of the

flock could occur and this indicates that special care

must be taken to manage ewes, from low input systems,

appropriately during the autumn and winter.

Acknowledgments

The authors would like to thank the Bronydd Mawr

Management Group for their help and encouragement

during the experiment and the Bronydd Mawr farm

staff for their invaluable assistance in the handling and

routine care of the animals. We would also like to thank

the anonymous referees of this journal for their helpful

and constructive comments. The research was funded

by the UK Ministry of Agriculture Fisheries and Food.

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