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Luteinizing Hormone Release and Ovulation in Anestrous Ewes¹

West Virginia University, Morgantown 26506 and U. S. Department of Agriculture, Beltsville 20705

Abstract

An experiment was designed to test for differences in response of dry and lactating ewes to treatments expected to cause gonadotropin release during the anestrous season. A total of 40 lactating ewes averaging 33 days postpartum and 40 dry ewes, were each assigned at random to two treatment groups in either March, April, May or June, 1971. Each ewe on treatment 1 (control) received an intravaginal sponge containing 20 mg flurogestone acetate (Cronolone) for 4 days. Ewes on treatment 2 each received a sponge for 4 days plus implants (20 mg) of putrescine 24 hr. prior to and at sponge removal and an injection of 25 µg estradiol-17ß 24 hr. after sponge removal. Jugular venous blood samples were taken at the time of sponge insertion, and at 72, 96, 108, 120, 132, 138, 144, 150 and 156 hr. thereafter (or at –24, 0, 12, 24, 36, 42, 48, 54 and 60 hr. relative to the time of sponge removal). Luteinizing hormone (LH) remained at baseline levels (near 1 ng/ml) in all ewes until 24 hr. after sponge removal. In control ewes, LH remained near baseline levels thereafter, increasing (P< 0.05) to 2 ng/ml at 42 and 48 hr. after sponge removal in the dry ewes only. In ewes on treatment 2, LH increased to 21.1, 6.8 and 3.6 ng/ml at 36, 42 and 48 hr., respectively, in the dry ewes and to 6.9, 10.6 and 5.9 ng/ml at the same hours in lactating ewes and then returned to baseline levels. Levels of LH varied with treatment, month and lactational status of the ewe as well as with time (P< 0.01). Ewes receiving treatment 1 did not show estrus, and ovulation occurred in only five of the 20 dry ewes. In treatment 2, 17 of 20 lactating ewes were in estrus but only two ovulated, while 13 of 15 dry ewes showed estrus and 12 of 19 ovulated. It is concluded that LH release occurred later and was of lesser magnitude in lactating than in dry anestrous ewes.

¹ Published with the approval of the Director of the West Virginia Agricultural Experiment Station as Paper No. 1269. Supported by Hatch Funds. Cronolone sponges provided by G. D. Searle and Co.

² Department of Animal and Veterinary Sciences, W.V.U.

³ Agricultural Research Center, U.S.D.A.