Influence of Gonadotropic Hormones on Estradiol-Induced Corpus Luteum Regression in the Ewe

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Abstract
The injection of estradiol into the ewe after the middle of the estrous cycle resulted in early regression of corpora lutea (CL) (Hawk and Bolt, 1970). In contrast, estradiol administered in the early part of the estrous cycle caused extended luteal maintenance (Piper and Foote, 1968). Bolt, Kelley and Hawk (1970) noted that the injection of estradiol on day 3 caused the release of endogenous LH, as indicated by an increase in plasma LH concentrations similar to the LH peak observed at estrus (Niswender et al., 1968). This study was done to determine whether the luteal regression resulting from an injection of estradiol on day 10 could be prevented by administration of (1) exogenous gonadotropic hormones on day 3, (2) estradiol on day 3 when it will cause endogenous gonadotropin release, or (3) gonadotropic hormones on day 10 at the time the estradiol was administered. Eighty-four parous Rambouillet ewes of about 8 years of age and weighing approximately 55 kg were checked for estrus twice daily using vasectomized rams. Copyright © 1971. American Society of Animal Science . Copyright 1971 by American Society of Animal Science.

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