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Use of 6-Methyl-17-Acetoxyprogesterone and Pregnant Mare Serum to Induce and Synchronize Estrus in Ewes

Cornell University, Ithaca, New York

Abstract

Oral MAP and injected PMS were used in various combinations to test their effect on estrus synchronization and fertility of ewes during both the anestrous and estrous seasons. A total of 391 ewes was used in 5 trials which included 15 treatment groups.

During the anestrous period a combination of MAP and PMS was effective in synchronizing an average of 80% of the treated ewes in two trials. Fifty-one percent of ewes synchronized and bred lambed. MAP alone was ineffective in producing a synchronized estrus in anestrous ewes.

For fall-bred cycling ewes 60 mg. of MAP given orally for 20 days was more effective than 30 mg. daily for 16 days in both synchronizing ewes and maintaining their fertility. Normally cycling Dorset ewes were successfully synchronized in March with 60 mg. of MAP daily for 20 days.

Four combinations of MAP and PMS were tested on ewes at the beginning of the estrous season in late July and early August. All combinations tested were reasonably successful; however, maximum synchronization (100%) and apparent fertility (82%) were observed on a treatment including PMS before and after an 8-day MAP feeding period, although this was not statistically different from the other treatments.

Data on synchronization range, lambing range, lambing percent and fertility at the second post-treatment estrus are also presented.

¹ Department of Animal Husbandry.

² The financial assistance provided by the National Association of Artificial Breeders and the New York Artificial Breeders Cooperative is gratefully acknowledged. The technical assistance of G. L. Hunt has been invaluable.