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Fertility of Ewes Bred Naturally and Artificially after Estrous Cycle Synchronization with an Oral Progestational Agent¹

Cornell University, Ithaca, New York

Abstract

One-hundred-twenty western whiteface ewes were bred either naturally or artificially at either normal estrus or after synchronization of estrus with 6-methyl-17-acetoxyprogesterone given orally. The conception rates as indicated by lambing records were as follows: naturally bred at normal estrus, 50%; artificially bred at normal estrus, 49%; naturally bred at synchronized estrus, 61%; artificially bred at synchronized estrus, 16%. In all groups, except the naturally bred synchronized estrous group, 30-day non-returns indicated a higher conception rate than lambing data indicated, whereas in the naturally-bred-synchronized-estrous group several ewes were observed in estrus during the 30 days after breeding but lambed according to the first breeding. Of the 40 ewes fed the oral progestational agent, 37 were observed in estrus from 50 to 64 hours after the last feeding.

The apparent fertility of the rams used was quite variable, ranging from 26 to 74% conception, based on 30-day non-return data.

¹ 6-Methyl-17-Acetoxyprogesterone; Provera, kindly supplied by R. E. Gessert, The Upjohn Company, Kalamazoo, Michigan.