1452
Effects of various doses of gonadotropin stimulation on reproductive performance of seasonally anestrous ewes
The use of exogenous gonadotropins as part of an estrous induction protocol can have beneficial effects on fertility in ewes bred out-of-season. Few studies have evaluated the ability of a mixture of eCG (FSH-like) and hCG (LH-like) (P.G. 600, Intervet, Millsboro, DE ) to increase fertility in ewes bred out-of-season, specifically following the pre-treatment with progesterone delivered via CIDR devices. Previously, our lab found that administering 3 mL of the gonadotropin mixture 1 d prior to CIDR removal increased conception rate, pregnancy to first service, lambing rate and the overall percentage of ewes that lambed. The objective of this study was to evaluate the dose effects of a gonadotropin mixture on reproductive performance of seasonally anestrous ewes. Crossbred ewes (n = 200) from 3 farms in WV and PA received CIDR inserts (between the months of May and July) 5 d prior to introduction of rams. At insert removal, all ewes were assigned randomly to receive a 5 mL injection (i.m., 400 IU eCG, 200 IU hCG) of P.G. 600, a 3 mL injection (i.m., 240 IU eCG, 120 IU hCG) of P.G. 600, or receive no further treatment. The reproductive performance parameters that were measured include pregnancy rate, prolificacy, pregnancy retention, and lambing rate. Analysis of variance was conducted using the GLM procedures of SAS, and least squares means were computed. None of measured reproductive performance parameters was significantly affected by the different doses of gonadotropin stimulation (P > 0.05). It is possible that no effect of the gonadotropin stimulation may be due to the high reproductive performance observed in the control ewes. In conclusion, administration of various doses of a gonadotropin mixture at progesterone withdrawal had no effect on reproductive performance of ewes bred outside their normal breeding season.
Keywords: Gonadotropin stimulation, Anestrus, Ewe