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Effects of Hysterectomy and Corpus Luteum Induction on Pituitary-Ovarian Relationships in the Ewe¹

University of Wisconsin, Madison

Abstract

The effects of hysterectomy have been studied at different stages of the estrous cycle in ewes with both spontaneous and induced (HCG) corpora lutea. Hysterectomy maintained both kinds of corpora lutea beyond the normal life span. Accessory corpora lutea were formed in experiments where ewes with induced corpora lutea were autopsied 24 to 26 days after hysterectomy, but were not found in experiments where autopsy was 2 or 5 days after hysterectomy. In the latter case induced corpora lutea were significantly smaller than natural glands, and larger follicles with some luteinization were present. LH activity averaged lower following hysterectomy in ewes with spontaneous corpora lutea but higher in ewes with corpora induced by HCG. The corpora lutea were the same age in each case, but ewes of the latter group were 3 days farther along in their original estrous cycle. Luteal tissue weights in ewes slaughtered on day 26 following hysterectomy on day 6 or day 14 of the estrous cycle were intermediate between day-6 and day-14 values. Progesterone content increased from day 6 to day 14 and remained high in hysterectomized ewes slaughtered on day 26; however, the amount of progesterone synthesized in vitro by luteal tissue and follicular activity was not affected. Although LH activity appeared to increase from day 6 to day 14 of the cycle, ewes hysterectomized on day 14 had lower LH activity than those hysterectomized on day 6 when both were slaughtered on day 26.

¹ Published with the approval of the Director of the Agricultural Experiment Station. Paper No. 1036 from the Genetics Laboratory and No. 421 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. It was supported in part by the Branch and also by funds from a Ford Foundation grant.