Abstract
A study is reported in which serum LH levels and average corpus luteum (CL) weights were determined following a single injection of 17 beta-estradiol on either Day 4 or 11 of the estrous cycle in ewes. The first day of estrus was designated Day 0 of the cycle. The ewes were treated in groups of 4 with a single injection of 750 mcg of 17 beta-estradiol into each ewe. Mean CL weights 2 days after estradiol treatment were compared with mean weights of CL removed from the same ewes at laparotomy on Days 6 or 13 of a previous control cycle. Injection of estradiol into ewes on Day 4 of the cycle increased CL weight whereas injection of ewes with the same dose of estradiol on Day 11 reduced CL weight. Differences in luteal weights due to treatment were not however significant. Serum LH rose to peaks of 7.2-21 ng/ml at 16-20 hours after estradiol treatment on Day 4 compared with peak levels of 62-102 ng/ml observed in ewes at estrus. On Day 11 treatment of ewes with 750 mcg of estradiol failed to induce increased LH release but in a single ewe injected with 2 mg of estradiol serum LH rose to 16.2 ng/ml. The results suggest that the effect of injected estradiol on the CL of the ewe may be partly determined by the amount of estradiol-induced LH released.
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