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Reproductive Performance of Ewes in an Early-Weaning, Controlled-Breeding Program^{1, 2}

Oregon State University, Corvallis^,6

Abstract

A total of 48 crossbred ewes was used to study reproductive performance in a four consecutive lamb crop program which included early weaning (2 months) and subsequent breeding control treatments. Hormonal treatments included the use of fluorogestone acetate impregnated pessaries which were intravaginally placed and equine gonadotropin injections. Removal of the impregnated pessaries resulted in estrous activity within 2 to 3 days in the majority of both cyclic and anestrous ewes. In regard to total reproductive performance (breeding and lambing), a procedure involving utilization of the impregnated pessaries during two spaced periods was the most consistently effective procedure tested. An exception to this was in one study where treatment was initiated during anestrus in which an injection of equine gonadotropin given at the time of pessary withdrawal was the most effective treatment.

¹ Technical Paper No. 2718, Oregon Agricultural Experiment Station.

² Acknowledgement is made to Dr. G. E. Short, G. D. Searle and Company, Chicago, Illinois, for making available hormonal materials and partial finncial support for this study and to K. E. Rowe for advice in statistical analyses.

³ Present address: Department of Animal Science, University of Nebraska, Lincoln.

⁴ Present Address: Animal Science Department, California State Polytechnic College, Pomona.

⁵ Present Address: The Ford Foundation, P.O. Box 2379, Beirut, Lebanon.

⁶ Department of Animal Science.