Use of progestagen–gonadotrophin treatments in estrus synchronization of sheep

Abstract

The main objective of this study was to investigate the effectiveness of certain progestagen–gonadotrophin treatments on synchronization of estrus in sheep. In Experiment I, 30 Chios ewes were treated at the beginning of the breeding season with medroxyprogesterone acetate (MAP) intravaginal sponges for 12 days and a single i.m. treatment of either FSH (Group 1,10 IU, n=8; Group 2, 5 IU, n=8; Group 3, 2.5 IU, n=8) or eCG (Group 4, 400 IU, n=6) at the time of sponge removal. Ten days after sponge removal laparotomy was performed to record ovarian response. Clinical estrus was observed in more (though not at a significant level) FSH treated than eCG treated sheep (62.5% versus 33.3%). Administration of 400 IU eCG resulted in the highest mean number of CL per ewe ovulating (2.8±0.2), with administration of 10 IU FSH producing the next best results (2.1±0.3). Statistically significant differences in the mean number of CL per ewe ovulating were found only between ewes in Group 3 (1.7±0.4) and Group 4 (2.8±0.2) ( P<0.05). In Experiment II, 53 Chios and 30 Berrichon ewes were treated during the mid-breeding season with MAP intravaginal sponges for 12 days and a single i.m. treatment of either 10 IU FSH (27 Chios and 16 Berrichon ewes) or 400 IU eCG (26 Chios and 14 Berrichon ewes), at the time of sponge removal. Ewes that were in estrus on Days 2–4 and 19–23 after sponge removal were mated to fertile rams. No significant differences were recorded between treatment or breed groups in the proportions of ewes observed in estrus after treatment. In the Berrichon breed, FSH administration resulted in higher lambing rates (93.8% versus 57.1%, P<0.05) and higher mean number of lambs born per ewe exposed to rams (1.4±0.2 versus 0.8±0.2, P<0.05) than that of eCG. After treatment with eCG, the mean number of lambs born per ewe exposed to rams was higher in the Chios than the Berrichon breed (1.4±0.2 versus 0.8±0.2, P<0.05). After treatment with FSH, the lambing rate was higher in the Berrichon than the Chios breed (93.8% versus 63.0%, P<0.05). In conclusion, a single FSH treatment (5 or 10 IU) at the end of progestagen treatment appears to be more effective than eCG for the induction of synchronized estrus in sheep at the beginning of the breeding season, with no cases of abnormal ovarian response observed. During the mid-breeding season FSH (10 IU) appears to be equally as effective as eCG (400 IU) in respect of lambing rate and mean number of lambs born per ewe.