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Control of Estrus and Ovulation in Gilts by Orally Effective Progestational Compounds

Michigan State University,¹ East Lansing

Abstract

Estrous activity was not inhibited in 3 of 11 gilts receiving from 0.9 to 2.0 mg. of 17-alpha-acetoxyprogesterone per lb. body weight per day by oral administration. The control of estrus and ovulation has been obtained in mature gilts by twice-a-day feeding of 6-methyl-17-acetoxyprogesterone. Twice-a-day feeding of 0.8 to 1.6 mg. of 6-methyl-17-acetoxyprogesterone per lb. body weight per day resulted in complete inhibition of estrus and follicular growth during the treatment period. Estrus occurred, on the average, 4.4 days from the end of treatment, and the start of estrus was synchronized within a 36-hour period. Autopsy following the controlled estrus demonstrated that ovulation had occurred.

Immature gilts receiving 1.6 mg. of 6-methyl-17-acetoxyprogesterone for 10 days followed by the subcutaneous injection of 1000 I.U. of equine gonadotropin came into estrus within a 12-hour period 4 days following the gonadotropin injection. Autopsy 24 to 36 hours after the start of the induced estrus indicated that the follicular development and subsequent ovulation were normal.

Orally active progestational compounds, administered as feed additives to the normal ration, could offer a means of controlling the time of breeding in swine applicable at the practical level.

¹ Endocrine Research Unit—Department of Animal Husbandry and of Physiology and Pharmacology. The author acknowledges the valuable assistance of J. E. Ahrenhold, Department of Physiology and Pharmacology, the generous cooperation of J. A. Hoefer and G. B. Stafford of the Department of Animal Husbandry in obtaining gilts used in this study, and the contributions of L. J. Bratzler and R. J. Deans of the Meats Laboratory, Department of Animal Husbandry for arranging the specific autopsy times required in this study. This study was supported, in part, and the progestational compounds and hormones supplied, by The Upjohn Company, Kalamazoo, Michigan. Submitted for publication with the approval of the Michigan Agriculture Experiment Station, August 25, 1959, as Journal Article No. 2488.