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Estrus, Ovulation and Fertility in Gilts Subsequent to the Oral Administration of 6-Methyl-17-Acetoxyprogesterone¹

Michigan State University, East Lansing

Abstract

Trials were conducted with 149 gilts, 41 control gilts and 108 gilts fed from 0.4 to 1.6 mg. of 6-methyl-17-acetoxyprogesterone per lb. body weight daily, by twice-a-day feeding, in an average of 3 to 7 lb. of ration daily per gilt. The duration of treatment was from 7 to 27 days. The gilts ranged from 190 to 310 lb. in body weight.

The amount of ration offered influenced the ability to control accurately the time of estrus and ovulation in a group of treated gilts fed together. A high degree of control of the time of estrus and ovulation was obtained when gilts were fed 0.5 mg. of 6-methyl-17-acetoxy-progesterone per lb. body weight daily, by twice-a-day feeding for 15 days, in a limited amount of daily ration (an average of 3 to 4 lb. daily per gilt). Eighty-nine percent of the gilts came into estrus 4 to 5 days after the end of progestational treatment. The conception rate in gilts bred at the controlled estrus was 77%. The estimated ovulation rate at the controlled estrus (14.5 per gilt) and the number of fetuses recovered 35 days following service at the controlled estrus (11.1 per gilt) were not significantly greater than in comparable age and weight control gilts (11.5 and 9.3, respectively).

¹ This study was supported, in part, by The Upjohn Company, Kalamazoo, Michigan. The authors wish to express appreciation to J. B. Stafford and E. C. Miller, Department of Animal Husbandry, for obtaining the gilts and to G. H. Conner, Department of Surgery and Medicine, for the preparation of vasectomized boars. Submitted with the approval of the Michigan Agricultural Experiment Station, June 6, 1960 as Journal Article 2637.

² Endocrine Research Unit—Departments of Animal Husbandry and of Physiology and Pharmacology.

³ Department of Animal Husbandry.