H . Leibovich et al. Livestock Production Science 68 2001 79 –86
81
protein ad libitum and hay at 0.1 kg head day. infrared analyzer Milkoscan 134; N. Foss Electric,
Lambs were treated daily at 10:00 for 35 days with Hillerod, Denmark.
saline solution containing 0.1 mg kg body weight of oPL oPL group or oGH oGH group, or received
2.6. Radioimmunoassays saline only control group. Lambs were weighed at
the beginning of the injection period and once a Serum concentrations of oGH Peri et al., 1993,
week thereafter until the end of the injection period. IGF-I Breier et al., 1991 and oPL Kann, 1971
Group feed consumption was monitored daily. Blood were determined as described previously. Iodination
samples for hormone assays were collected from the of oGH and oPL was performed as described previ-
jugular vein on the morning time of day 34 of the ously Gertler et al., 1984. The inter- and intra-
injections, prior to the daily hormone administration, assay coefficients of variation were 12.4 and 8.7
to obtain serum, which was stored at 2 208C until
for IGF-I, 10.4 and 6.2 for oGH, and 8.8 and assayed.
6.4 for oPL, respectively. 2.7. Data analyses
2.4. Galactopoietic effects following administration of oPL and oGH
Lamb growth rates were calculated by fitting linear regressions to the body weight measurements
Forty-five multiparous ewes that lambed during 2 and then subjecting them to analysis of variance. The
weeks in October 1997 and 143 multiparous ewes model included the main fixed effects of experiment
that lambed during 2 weeks in October 1998 were 1, 2 and experimental group oPL, oGH and
used in two experiments to determine daily milk control. Lamb weight at the beginning of the
production, recorded weekly from lambing. In each experiment was used as a covariate. Results from
experiment, at about 8 weeks after lambing and each of the milk production experiments were ana-
when all ewes had passed their peak of lactation, lyzed separately. Data on milk production on each
they were assigned to three groups. Distribution of day of recording was analyzed by analysis of vari-
ewes into the different groups was according to their ance. The model included experimental group as the
weight and their daily milk production averaged main effect, and milk production on day 0, days from
across the last three daily milk records. The ewes lambing and ewe body weight at the beginning of the
were treated daily at 17:00 for 14 days with saline injection period were taken as covariates. Serum
solution containing 0.1 mg kg body weight of either hormone concentrations and milk composition were
oPL oPL group or oGH oGH group, or received subjected to analysis of variance to test for effects of
saline only control group. Milk production was treatment within day of sampling. Statistical analyses
monitored the day before the injections were begun were conducted using the Statistical Analysis Insti-
day 0 and then every 3 to 5 days, for up to 28 days. tute SAS computer package 1985. All data are
Body weight was recorded for all ewes before and at expressed as least squares means and standard errors.
the end of the hormonal injection periods. Group Differences of P
, 0.05 were considered significant. feed consumption was monitored daily in the first
experiment only. Blood samples were collected 10 to 11 days after initiation of hormone treatments at
3. Results
10:00 to obtain serum for assay for concentrations of IGF-I, oGH and oPL.
3.1. Comparison of oGH and oPL effects in growing lambs
2.5. Milk composition analysis Least-squares means and levels of significance for
Milk composition was evaluated on day 13 of the growth rates, and oGH, oPL and IGF-I serum
injection period in the second experiment only. concentrations are presented in Table 1. Experimen-
Concentrations of fat, protein, lactose and total solids tal group and initial weight of lambs had significant
in milk were measured using a semi-automated effects on growth rate. Both oGH and oPL had
82 H
. Leibovich et al. Livestock Production Science 68 2001 79 –86 Table 1
Growth performance, and oGH, oPL and IGF-I serum concentrations LS mean 6S.E.M. of control lambs and lambs treated daily for 35
1
days with 0.1 mg kg body weight of oPL or oGH Experimental treatment
Control oPL
oGH Experiment
1 No. of lambs
20 20
20 Initial body weight kg
23.5 60.6
23.2 60.6
24.1 60.6
a b
b
Growth rate kg d 0.48
60.01 0.53
60.01 0.53
60.01
2 a
a b
GH ng ml 7.5
61.0 8.1
61.0 12.2
61.2
2
PL ng ml N.D.
56.1 612.3
N.D.
2 a
a b
IGF-I ng ml 304
623 321
625 466
635 Experiment
2 No. of lambs
12 12
12 Initial average body weight kg
25.0 60.9
24.4 60.9
24.6 60.9
a b
b
Growth rate kg d 0.36
60.02 0.45
60.02 0.45
60.02
2 a
a b
GH ng ml 2.4
60.3 2.8
60.6 7.2
61.2
2
PL ng ml N.D.
58.5 615.6
N.D.
2 a
a b
IGF-I ng ml 310
615 308
620 365
616
1 a,b
Within rows, means with different superscripts are different P , 0.05.
2
Measured 34 days after the beginning of the injection periods. N.D., Not detectable.
profound and similar growth-stimulating effects of 3.2. Comparison of oGH and oPL effects in
approximately 10 and 25, in experiments 1 P ,
lactating ewes 0.01 and 2 P
, 0.005, respectively. The relative effects of the hormonal treatments on growth rates
At 6 weeks after lambing, ewes reached their peak were inversely related to the average growth rates of
lactation at an average of 2.4 and 2.1 kg d milk yield the control groups, which were 480 and 360 g d in
in experiments 1 and 2, respectively. The experiment experiments 1 and 2, respectively. Feed intake for
was started 8 weeks after lambing when the body control lambs averaged 1.51 and 1.41 kg DM d in
weight of ewes averaged 80 62.6 kg. Daily milk
experiments 1 and 2, respectively, and were numeri- production prior to and during the experimental
cally higher 6 for lambs treated with oGH or period is presented in Fig. 1. There were no pre-
oPL. Ovine GH, but not oPL, increased P , 0.05
treatment differences in milk yield among the treat- IGF-I concentrations Table 1. Concentrations of
ment groups for ewes in either experiment. For oGH in serum prior to treatment in all lambs
control ewes, milk production gradually decreased belonging to the control, oGH and oPL groups
during the injection periods in both experiments. In averaged 6.9 and 2.3 ng ml in experiments 1 and 2,
contrast, ewes injected with oGH experienced a respectively. Ovine GH serum concentrations re-
dramatic increase P , 0.001 in daily milk pro-
mained similar to the pre-treatment concentrations in duction within 5 to 6 days after the first day of
the control and the oPL groups, while treatment with injection. The maximum percentage increase in milk
oGH increased P , 0.05 oGH serum concentrations
production due to oGH was observed 10 days after at day 34 of the injection period to an average of
the first injection, being 45 to 55 above controls. 12.2 and 7.2 ng ml in experiments 1 and 2, respec-
At that point, the absolute daily yield was higher tively Table 1. Ovine PL was not detectable in
than that at peak lactation prior to the oGH in- serum from lambs prior to or during the treatment
jections. Injection with oPL also increased milk periods in lambs in control and oGH groups. In the
yields in both experiments, but the effect was oPL group, oPL concentrations at day 34 of the
moderate. The maximum percentage increase above injection period were 58
615 ng ml. control ewes was observed 11 days after the first
H . Leibovich et al. Livestock Production Science 68 2001 79 –86
83 Table 2
Milk yield and composition LS mean 6S.E.M. on the 13th day of
the injection period of ewes belonging to the control, oPL and
1
oGH groups Experimental group
Control oPL
oGH No. of ewes
15 15
15
a a
b
Milk yield l 1.91
60.1 2.14
60.1 2.97
60.1 Total solids
17.1 60.3
17.0 60.2
16.4 60.2
a b
b
Lactose 5.1
60.5 4.7
60.4 4.7
60.4
a a
b
Protein 5.6
60.1 5.6
60.1 5.1
60.1 Fat
5.6 60.2
5.7 60.2
5.5 60.2
1 a,b
Within rows, means with different superscripts are different P
, 0.05.
not detectable in control ewes or ewes treated with oGH, but averaged 73
611 ng ml in ewes treated with oPL. Feed intake for the oGH and oPL-treated
ewes averaged 3.6 and 3.8 kg DM d, respectively, numerically higher than the feed intake in control
ewes 3.1 kg DM d.
Fig. 1. Milk production in ewes treated daily for 14 days with 0.1
Results on milk composition are summarized in
mg kg body weight of oPL triangles, oGH open circles or saline squares. The values are given as LS means
6S.E.M. The
Table 2. The increase P , 0.05 in milk yield in the
numbers of ewes in each treatment were 15 in experiment 1 and
oPL and the oGH groups did not affect total solids or
47–48 in experiment 2.
fat concentration. However, percent protein was lower P
, 0.05 in the oGH group and percent injection P
, 0.01, being 25 and 20 in experi- lactose was lower P
, 0.05 in both the oPL and ments 1 and 2, respectively. Upon cessation of the
oGH groups. hormonal treatments, there was a decrease in milk
production within 10 to 14 days and daily milk yields for ewes in the treatment groups were not
4. Discussion
