Synchronization of estrus with short- and long-term progestagen treatments and the use of GnRH prior to short-term progestagen treatment in ewes

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 (30mg) were inserted in the ewes for 7d in the FGA1 (short-term) and GnRH treatment groups, and for 12d in the FGA2 group (long-term). The ewes in the GnRH group received 10.5μg busereline acetate i.m. at the time of sponge insertion. Tiaprost tromethamol (PGF₂α; 0.294mg) and eCG (400IU) 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-PGF₂α regimen could be replaced with the 7-d-FGA-eCG-PGF₂α regime in sheep at the onset of the breeding season. However, the combination of GnRH with the latter regimen (7-d-GnRH-FGA-eCG-PGF₂α) increased the multiple birth rate and litter size in the ewes.