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Ovarian Activity and Hormonal Patterns in Gilts Fed Allyl Trenbolone^1,2,

University of Missouri³, Columbia 65211

Abstract

A study was conducted to establish the profile of reproductive hormones and the degree of ovarian activity in gilts fed either 2.5 or 15.0 mg of allyl trenbolone (AT) daily. Progesterone levels following regression of corpora lutea remained low (< 1 ng/ml) during progestin treatment. In gilts given 2.5 mg AT, plasma estradiol (E₂) levels fluctuated between 7 and 13 pg/ml during treatment and began to decrease by day 2 after withdrawal of AT. Gilts given 15 mg of AT had lower (P<.01) plasma concentrations of E₂ (2.5 pg/ml) during treatment; concentrations began to increase the day after withdrawal of AT, reaching a maximum of 13.1 pg/ml in 3.5 to 4.0 days. Luteinizing hormone (LH) levels were low (<1.5 ng/ml) during AT treatment. Daily feeding of AT prevented estrus in all gilts. A preovulatory surge of LH (4 ng/ml) was observed on the first day of the first post-treatment estrus. Gilts given 2.5 mg of AT daily had more (P<.01) follicles of ovulatory size during treatment and a higher frequency of cystic follicles after withdrawal than gilts given 15 mg of AT daily. Estrus was effectively synchronized in gilts given 15 mg of AT daily, whereas the feeding of 2.5 mg AT daily resulted in an increased incidence of anestrus.

¹ Contribution from the Missouri Agr. Exp. Sta. Journal Ser. No. 8718. Approved by the Director.

² The authors gratefully acknowledge the cooperation of Roussel-UCLAF, Paris, France, and Dr. S. K. Webel in providing financial and product support for the study, and thank T. C. Cantley for laboratory assistance and Betty Nichols for secretarial assistance in the preparation of the manuscript.

³ Dept. of Anim. Sci.