Abstract :
The objective of the present study was to determine the efficacy of the synchronization
of estrus using short- and long-term progestagen treatments in ewes at the onset of the
breeding season, and to evaluate the effect of the exogenous GnRH administration immediately
prior to short-term progestagen treatment on the reproductive performance. A total of
240 Tahirova cross-bred ewes, aged 18–24 months, and 40 rams, aged 2–4 years-old, were
used in the trial. Ewes were divided equally into 3 groups (n = 80 per group). Intravaginal
progestagen sponges containing FGA (30 mg) were inserted in the ewes for 7 d in the FGA1
(short-term) and GnRH treatment groups, and for 12 d in the FGA2 group (long-term). The
ewes in the GnRH group received 10.5 g busereline acetate i.m. at the time of sponge insertion.
Tiaprost tromethamol (PGF2 ; 0.294 mg) and eCG (400 IU) were injected i.m. on the
6th day of progestagen treatment in the GnRH and FGA1 groups, and on the 11th day in the
FGA2 group following sponge insertion. All ewes were hand-mated once at the detection
of estrus. The estrous response, fertility rate, multiple birth rate and litter size recorded
was 88.7, 87.3, 51.6% and 1.6 in the FGA1 group, 92.5, 71.6, 50.9% and 1.5 in the FGA2 group,
and 96.2, 89.6, 71.0% and 1.8 in the GnRH group, respectively. No significant difference in
estrous response between the groups was recorded, but the fertility rate in the FGA1 and
GnRH groups was significantly (P < 0.05) higher than in the FGA2 group. The occurrence
of multiple births and litter sizes were significantly (P<0.05) higher in the GnRH group,
compared to both the FGA1 and FGA2 groups, with the number of single lambs being significantly
(P < 0.05) higher in the FGA1 (48.4%) and FGA2 (49.0%) groups than in the GnRH
(29.0%) group. However, the differences recorded between any of the groups in terms of
the number of twin and triplet lambs were insignificant. In conclusion, it can be said that
estrous synchronization using the 12-d-FGA-eCG-PGF2 regimen could be replaced with
the 7-d-FGA-eCG-PGF2 regime in sheep at the onset of the breeding season. However, the
combination of GnRH with the latter regimen (7-d-GnRH-FGA-eCG-PGF2 ) increased the
multiple birth rate and litter size in the ewes.
