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parturition weeks 2 to 20 of pregnancy. Birth weight was determined by weighing lambs individually at parturition. All ewes gave birth after week 20 of pregnancy, but the day of
parturition varied within the 21st week of pregnancy. Weeks of pregnancy were calculated from the predicted day of ovulation 3 days after the last prostaglandin injection.
2.2. Blood sampling and processing
Blood samples in aliquot of 10 ml were drawn with plain vacutainer or sterile syringes from the jugular vein from around 900 to 1000 h weekly. The sampling time was executed consistently
prior to feeding. The day of weekly bleeding was chosen based on the 7-day interval from the predicted day of ovulation assigned as day 3 after the last prostaglandin injection. The blood
samples were allowed to clot in a cool ice box and transported to the laboratory for further separation of serum by centrifugation. The serum
samples were then kept frozen −20°C for later progesterone analyses.
2.3. Progesterone analyses
Serum progesterone concentration was measured in duplicate by the solid-phase technique radioimmunoassay Diagnostic Products Corporation, Los Angeles, CA, with slight
modification for ovine progesterone concentration ranges Manalu et al., 1996
. The radioactivity of progesterone-bound tubes were counted in an automatic gamma counter. The concentrations
of standard progesterone samples were used to construct a standard curve ranging from 0.1 to 20 ngml. A sample volume of 100
μl serum was used in the assay for samples with serum progesterone concentrations ranging from 0.1 to 20 ngml. For samples with progesterone
concentrations lower than 0.1 ngml, the sample volume was increased to 200 μl to bring the
progesterone concentrations in range with the standards used. All serum progesterone concentrations were within the range of the standard progesterone used to construct the standard
curve. Inter- and intra-assay variation coefficients were 9.0 and 4.0, respectively.
2.4. Statistical analyses
Progesterone concentrations were the mean during two phases of pregnancy: the embryonic weeks 0 to 7, and fetal weeks 8 to 20 phases of pregnancy. The main effects of litter size and
phases of pregnancy with their respective interaction on maternal serum progesterone concentration were tested by an ANOVA, using animal×phase as an error term, in a
randomized design with factorial arrangement unequal n. Variations in the mean serum progesterone during the total gestation period and lamb birth weight were tested by an ANOVA
in a randomized design. The mean maternal serum progesterone concentrations during the whole pregnancy in the respective litter size were correlated with lamb birth weight by using regression
and correlation analysis
Snedecor and Cochran, 1982 .
3. Results
There was no effect of fetal number on serum progesterone concentration during the embryonic phase weeks 0 to 7 of pregnancy. Mean maternal serum progesterone concentration during
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weeks 0 to 7 of pregnancy in the ewes carrying 1, 2, or 3 fetuses was 5.3±0.3, 6.2±0.7, and 6.6±0.5 ngml, respectively. During weeks 8 to 20 of gestation, ewes carrying multiple fetuses
had a higher progesterone concentration P0.01 than those carrying a single fetus. There was no significant difference in serum progesterone concentration between ewes carrying twin and
triplet fetuses. The mean maternal serum progesterone concentration during weeks 8 to 20 of pregnancy in the ewes carrying 1, 2, or 3 fetuses was 16.9±1.4, 25.3±1.5 and 26.8±2.5 ngml,
respectively. Ewes carrying multiple fetuses had a higher mean serum progesterone concentration increased to 42.1 and 50.3 for twins and triplets, respectively, when compared
to those carrying a single fetus P0.05. There was, however, no difference in the mean serum progesterone concentration during pregnancy between ewes carrying 2 and 3 fetuses. The mean
maternal serum progesterone concentration during the whole period of pregnancy in the ewes carrying 1, 2, or 3 fetuses was 13.2±1.0, 18.7±1.0, and 19.8±1.7 ngml, respectively
Table 1 .
Table 1. Mean ±SE maternal serum progesterone ngml during weeks 0 to 7 W
–7
, weeks 8 to 20 W
8 –20
, and during the whole pregnancy period W
–20
, and mean lamb birth weight
a
As normally observed in prolific sheep, the increased litter size increased the total lamb birth weight curvilinearly, with a resultant decrease in average lamb birth weight P0.01. Total lamb
birth weights in the ewes carrying 1, 2, or 3 fetuses were 1.9±0.1, 3.2±0.2, and 4.2±0.4 kg, respectively. Total lamb birth weight in the ewes carrying triplets increased by 114 and 28
when compared to those carrying a single or twin fetuses, respectively. The ewes carrying twin fetuses had a total lamb birth weight increase by 67 when compared to those carrying a single
fetus. The mean lamb birth weight in the ewes carrying triplet fetuses decreased by 28 and 17 when compared to those in carrying a single or twin fetuses, respectively. In the ewes carrying
twin fetuses the average lamb birth weight decreased by 17 when compared to those carrying a single fetus P0.05
Table 1 .
Ewes carrying a single fetus, had higher mean maternal serum progesterone concentrations during weeks 0 to 7, 8 to 20, and during the entire pregnancy, and higher lamb birth weight at
parturition P0.05 r
2
=0.57, 0.75, and 0.76, respectively. The distribution of total lamb birth weight at various maternal serum progesterone concentrations in the ewes carrying a single fetus
are setout in Fig. 1
. In the ewes carrying twins, ewes with higher mean maternal serum
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progesterone concentration during weeks 8 to 20, and during the entire gestation had a higher lamb birth weight at parturition P0.05 r
2
=0.48 and 0.42, respectively. There was a negative correlation between the mean maternal serum progesterone concentration during weeks 0 to 7
with the total lamb birth weight at parturition in this litter size. Distribution of total lamb birth weight at various maternal serum progesterone concentrations in ewes carrying twin fetuses is
presented in
Fig. 2 . In the ewes carrying three fetuses, ewes with higher mean maternal serum
progesterone concentration during weeks 0 to 7, 8 to 20, and during the entire pregnancy had a higher lamb birth weight at parturition P0.05 r
2
=0.54, 0.52, and 0.46, respectively. Distribution of total lamb birth weight at various maternal serum progesterone concentrations in
the ewes carrying triplet fetuses are setout in Fig. 3
.
Full-size image 3K
Fig. 1. Total lamb birth weight at parturition within various ranges of serum progesterone concentrations during the entire gestation period in Javanese thin-tail sheep carrying a single
fetus.
Full-size image 3K
Fig. 2. Total lamb birth weight at parturition within various ranges of serum progesterone concentrations during the entire gestation period in Javanese thin-tail sheep carrying twin
fetuses.
Full-size image 3K
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Fig. 3. Total lamb birth weight at parturition within various ranges of serum progesterone concentrations during the entire gestation period in Javanese thin-tail sheep carrying triplet
fetuses.
4. Discussion
