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Functional Capabilities of Experimentally Induced Corpora Lutea in Ewes¹

University of Wisconsin, Madison

Abstract

The functional life-span of experimentally formed corpora lutea (CL) in mature non-pregnant ewes was measured in terms of estrual cycle length and interval to next ovulation. Natural CL were removed from each of two ewes (group I) on day 5, 9, and 13 of the estrual cycle to determine interval to heat or ovulation. Two groups of four or five ewes per stage were ovulated by a single intravenous injection of unfractionated pituitary extract (UPE) 48 hours prior to laparotomy on day 5, 9, or 13. In group II both natural and induced glands were injected with India ink for later identification. Original CL were removed completely in group III and the induced glands were marked and left in situ.

Twenty-six pretreatment cycles averaged 17.0 days. Ewes in group I returned to estrus 2.0 to 3.5 days after CL removal. Subsequent cycles were 15.5 to 18.0 days in length. Experimental cycles in group II were of normal duration, i.e., 16.0 to 20.0 days, regardless of the stage when CL were added. When new CL were added and natural ones removed (group III), experimental cycle lengths were: at day 5, 16.5 to 18.5 days for three ewes and 7.0 days for one ewe; at day 9, 13.0 to 16.0 days for five ewes; and at day 13, 14.0 to 15.0 days for four ewes and one ewe had functional CL when slaughtered at 18.5 days. The corpora lutea added on days 5 and 9 became functional, but did not lengthen the cycle.

Ewes that failed to ovulate as a result of UPE treatment had cycles of 16.0 to 18.5 days duration.

The results suggest that ovine corpora lutea are maintained during the estrual cycle by a factor extrinsic to the gland and determined before the fourth day, but still present or effective at days 5 and 9. They also indicate that a single injection of UPE had no effect on the life span of natural CL.

¹ Published with the approval of the Director of the Agricultural Experiment Station. Paper No. 890 from the Division of Genetics and No. 355 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.

³ Present address: University of Cairo, Cairo, Egypt.

⁴ The authors wish to acknowledge aid in surgery given by R. A. Bellows, W. E. Collins, A. P. Labhsetwar, S. E. Mares, A. C. Menge, E. M. Rigor, F. Stormshak, and E. W. Wickersham.