Semester

Summer

Date of Graduation

2013

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

Marlon Knights.

Abstract

Using 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 efficacy of P.G. 600RTM, a mixture of gonadotropins with FSH-like and LH-like activity, to increase fertility in anestrous ewes and, in particular, following pre-treatment with progesterone delivered via controlled internal drug releasing (CIDR) devices. The objective of this study was to evaluate the effects of P.G. 600RTM on reproductive success in progesterone-treated non-lactating anestrous ewes. Ewes, which had been separated from rams for at least one month prior to the beginning of the experiment, received CIDR inserts five days prior to introduction of rams. In the first experiment, ewes were assigned randomly to receive either a 3 mL injection of P.G. 600RTM [i.m., 240 IU equine chorionic gonadotropin (eCG) and 120 IU human chorionic gonadotropin (hCG)] at CIDR insert removal or no further treatment. In the second experiment, ewes were assigned randomly to receive either a 3 mL injection of P.G. 600RTM one day prior to insert removal or no further treatment. In experiment 1, incidence of estrus was significantly greater for treated ewes than control ewes, while prolificacy (number of lambs born per ewe lambing) tended to be higher in treated ewes. In experiment 2, treated ewes had significantly higher conception rates and pregnancy rates to first service and tended to have higher overall pregnancy rates than control ewes. A greater percentage of ewes lambed in the treated group than in the control group; however, prolificacy was not different between the groups. In addition, overall lambing rates in ewes treated with P.G. 600RTM were significantly higher than those of the control group. An injection of 3 mL of P.G. 600RTM (240 IU eCG and 120 IU hCG) one day prior to CIDR removal significantly increased reproductive success in progesteronetreated non-lactating anestrous ewes. Further, the gonadotropin injection was determined to be economically beneficial.

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