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Some Effects of Progesterone on Experimentally Induced Corpora Lutea in Ewes¹

University of Wisconsin, Madison

Abstract

Estrual cycle lengths have been studied in four different treatment groups of mature ewes. An intravenous injection of 2500 I.U. HCG on day 5 of the estrual cycle produced one or two new corpora lutea on day 7 in 11 ewes. Natural corpora lutea were removed on day 7, and the induced glands were marked with India ink at that time. Estrual cycles in this group averaged 13.6±0.52 days in length. Progesterone (10 mg. per day) was given subcutaneously to 11 ewes on days 4 through 7 in addition to the ovulating dose of HCG on day 5. The natural corpora were removed on day 5, and the new glands were marked on day 7. These ewes had estrual cycles 14.0± 0.56 days in length. Progesterone (10 mg. per day) was given subcutaneously to 11 ewes on days 4 through 7, the natural corpora were removed on day 5 and no new glands were induced. The estrual cycles of these control animals averaged 9.2±0.17 days in length. Natural corpora were removed on day 5 from six ewes at the same time the ovulating HCG treatment was given. The new glands (marked on day 7) thus were formed in the relative absence of progesterone. No behavioral estrus was observed at the time the new glands were formed. Estrual cycle lengths averaged 19.8± 1.08 days. It is suggested that the presence of progesterone at the time new corpora are induced during the estrual cycle acts to shorten the life span of such corpora lutea in ewes.

¹ Published with the approval of the Director of the Agricultural Experiment Station. Paper No. 920 from the Division of Genetics and No. 370 from the Department of Meat and Animal Science. This work was done under a cooperative agreement between the Wisconsin Agricultural Experiment Station and the Dairy Cattle Research Branch, U.S.D.A., and is supported in part by the Branch.

² Agent of the Dairy Cattle Research Branch, U.S.D.A.