Ž .
gas chromatography, as were the faecal samples. The ratios of even chain synthetic Ž
. and odd-chain alkanes naturally occurring in the plant cuticular wax in the faeces and
herbage were used to derive estimates for intake, proportion of grass and clover in the diet and in-vivo digestibility. Intake was calculated using C32 and C33 alkanes, and in
vivo digestibility using C35 and C36. Diet composition was estimated using a least-
Ž .
squares optimisation procedure EatWhat, Dove and Moore, 1995 . Diet composition, intake and digestibility estimates are mean values for the 10-day period over which the
faecal samples were collected. A further sub-sample of the ryegrass and browntop herbage was analysed for total nitrogen concentration.
Liveweight gain was measured over the 2-week period that encompassed the faecal sampling period, in order to relate these estimates to animal performance. At the start of
Ž .
the intake measurement period lambs on browntop Agrostis capillaris L. and white
Ž .
Ž .
clover BWC were heavier than those on perennial ryegrass Lolium perenne L. and Ž
. Ž . Ž
. white clover Trifolium repens L.
RWC 37.6 kg vs. 34.2 kg, P s 0.002 , but SD
Ž .
lambs did not differ significantly from TD 36.8 kg vs. 35.0 kg, P s 0.19 . At the end of the measurement period, the difference in liveweight between BWC and RWC had
Ž .
diminished 39.8 kg vs. 38.2 kg, P s 0.07 . Daily intake was analysed on the basis of per animal, per unit of liveweight, and per unit of metabolic liveweight. Statistically
similar comparisons were obtained in each case, and results are presented only for intake per animal.
2.4. Statistical analysis For animal-related variables, group means for each treatment were compared by
Ž .
Ž .
analysis of variance ANOVA , using a split-plot model 7 df in which grass species Ž
. formed the main-plot and drench regime the split-plot. Grass species effect 1 df was
Ž .
Ž .
tested against replicate x grass species effect 2 df
and the drench 1 df
and Ž
. Ž
. drench = species effect 1 df was tested against residual error 2 df . Main-plot means
for pasture variables and larval density, and the trigger-drenched group mean faecal egg Ž
. Ž
. count after log
transformation were compared by one-way ANOVA 3 df with grass
10
Ž .
species 1 df tested against residual error.
3. Results
3.1. LiÕeweight gain and herbage intake Ž
. Ž
. Liveweight gain was higher P s 0.06 on RWC than on BWC Table 1 , but did not
differ between suppressive or trigger-drenched lambs. Daily feed intake was higher Ž
. Ž
. P s 0.003 for lambs grazing RWC than for those grazing BWC Table 1 . The effect
of anthelmintic regime on intake was not significant, however there was a tendency for lambs receiving the suppressive drench to eat more than trigger-drenched lambs when
Ž on RWC but a reverse trend on BWC grass species = anthelmintic drench interaction,
. P s 0.11 .
G.P. Cosgro
Õ e,
J.H. Niezen
r Applied
Animal Beha
Õ iour
Science 66
2000 71
– 85
76
Table 1 Effect of grass species and anthelmintic drenching regime on the liveweight gain, daily herbage intake, proportion of clover in the diet and in vivo digestibility of the
diet of grazing lambs Item
Anthelminitic status Grass species
Statistical significance
a b
Ryegrass Browntop
S.E.D. S.E.D.
P value Species
Drench Species= Drench
y1 y1
Ž .
Liveweight gain g hd day
Suppressive 271
186 46.6
72.7 0.06
0.60 0.35
Trigger 290
126
y1 y1
Ž .
Intake kg DM hd day
Suppressive 1.65
1.10 0.074
0.086 0.003
0.86 0.11
Trigger 1.49
1.24 Clover proportion
Suppressive 0.53
0.24 0.012
0.237 0.18
0.20 0.02
Trigger 0.49
0.31 Ž .
Digestibility Suppressive
68 60
2.64 7.10
0.48 0.42
0.14 Trigger
65 67
a
S.E.D.sstandard error of difference between means for anthelmintic status within grass species.
b
S.E.D.sstandard error of difference between means for grass species within level of anthelmintic status, and for interaction.
Fig. 1. Mean sward surface height of ryegrass–white clover and browntop–white clover treatments, compared with the target height, during summer and autumn, and for the duration of the intake measurement period
Ž .
indicated by arrows .
3.2. Proportion of cloÕer in diet Ž
. The proportion of clover in the diet Table 1 was higher for trigger-drenched than for
Ž suppressive-drenched lambs grazing on BWC
grass species = anthelmintic drench .
interaction, P s 0.02 . In contrast, trigger-drenched and suppressive-drenched lambs had a similar proportion of clover in their diet on RWC. For both trigger-drenched and
suppressive-drenched lambs, the proportion of clover in the diet was higher on RWC than on BWC. In vivo digestibility was not significantly affected by grass species or
anthelmintic treatment, although the lowest recorded value was for the suppressive-
Ž .
drenched lambs grazing on BWC Table 1 .
Table 2 Ž
. Herbage mass, total lamb liveweight and herbage allowance for ryegrass-white clover RWC and browntop-
Ž .
white clover BWC swards Pasture treatment
Statistical significance
a
RWC BWC
S.E.M. P value
y1
Ž .
Herbage mass kg DM ha April
905 1555
162.7 0.11
May 960
1560 88.5
0.05
y1
Ž .
Total lamb liveweight kg LW ha April
386 530
5.76 0.003
May 466
479 11.8
0.50
y1
Ž .
Herbage allowance kg DM kg LW April
2.35 2.94
0.31 0.31
May 2.07
3.26 0.23
0.06
a
S.E.M.sstandard error of means.
3.3. Pasture characterisation Ž
Sward height was slightly less than the target height of 5 cm during the period April .
Ž .
22–May 1 when intake measurements were made Fig. 1 . Total herbage mass was Ž
. stable through April and May Table 2 , but was lower for RWC than BWC during April
Ž .
Ž .
P s 0.11 and May
P s 0.05 . The mean botanical composition of the swards,
Ž . Ž .
Fig. 2. Species composition of ryegrass–white and browntop–white clover treatments before a and after b the intake measurement period. For each component, composition is calculated as a proportion of the live
dry-matter.
Table 3 Ž
. Nematode larval density on pasture swards and faecal egg counts of trigger-dosed lambs natural means
Ž .
Ž .
grazing swards of ryegrass-white clover RWC and browntop-white clover BWC
a
Pasture treatment Statistical significance
b
RWC BWC
S.E.M. P value
y1
Ž .
Larval density number L3 larvae kg DM April
2260 9870
7897 0.51
May 3800
1110 1184
0.12
y1
Ž .
Faecal egg count eggs g fresh faeces March
3110 4000
3498 0.35
May 840
1190 777
0.23 June
300 260
321 0.65
a
Analysis of variance performed on Log transformed data.
10 b
S.E.M.sstandard error of means.
Ž determined from the pluck samples taken in late March before the intake measurement
. Ž
. period and in early May at the end of the intake measurement period are shown in
Ž Fig. 2. Both swards contained a high proportion of dead matter 74 and 34 for RWC,
and BWC, respectively, before intake measurement, and 17 and 19 for RWC and .
BWC, respectively, after intake measurement . To more accurately describe the compo- sition available for grazing, sown grass, white clover, unsown grass and other unsown
species are expressed as proportions of the live fraction. On this basis, the proportion of white clover was 30 for RWC and 20 for BWC before intake measurement, and
Ž .
14 for both RWC and BWC after intake measurement Fig. 2 . The nitrogen concentration of ryegrass and browntop was 52 and 53 g kg DM
y1
, Ž
. respectively data not shown . No corresponding analysis was conducted for white
clover because insufficient dried herbage remained after analysis for alkane concentra- tion.
3.4. LarÕal L3 density on pasture and faecal egg counts Estimates of larval density showed no consistent pattern with time, and did not differ
Ž .
significantly between grass species for the estimates made in April and May Table 3 . Ž
. The faecal egg count for TD lambs declined from March Table 3 . The slightly higher
count for BWC compared with RWC lambs in March and May was not significant.
4. Discussion
