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Luteal Phase Insufficiency in the Ewe as a Consequence of Premature Induction of Ovulation by Intrafollicular Injection of Gonadotropins¹

University of Wyoming², Laramie 82071

Abstract

The largest ovarian follicle of ewes was injected on d 15 of die estrous cycle (2 to 3 d before the anticipated preovulatory surge of gonadotropins) with saline or either luteinizing hormone (LH) or follicle-stimulating hormone (FSH) in saline (5 µg). Ovulation was assumed based on the presence of an ovulation stigma at d 5 post-treatment. Control animals expressed estrus 2 to 3 d after treatment with saline, and during the estrous period ovulated from the treated follicle. Gonadotropin-treated animals ovulated from injected follicles prematurely and did not exhibit estrus. The stated observations with respect to time of ovulation were established by visual and hormonal criteria: (1) control follicles appeared to have ruptured within a day or two prior to relaparotomy (corpora hemorrhagica), whereas gonadotropin-treated follicles were in a more advanced stage of luteal development (corpora lutea); and (2) concentrations of systemic sera progesterone rose (P<.05) in LH- and FSH-treated ewes 2 d before such an increase in control animals. Luteal function was assessed by comparing sera concentrations of progesterone throughout the induced and spontaneous (vehicle controls) luteal phases. Premature stimulation of ovulation with either gonadotropin was followed by suppressed luteal function (maximum sera levels of progesterone in gonadotropin-treated animals and controls were slightly greater than 1 ng/ml and nearly 2.5 ng/ml, respectively; P<.01). No differences in the level of luteal function due to treatment with LH or FSH were observed. The duration of the luteal phases of gonadotropin-treated animals were similar to controls (approximately 17 d). Premature induction of follicular rupture in the ewe is followed by an insufficient luteal phase.

¹ Published with the approval of the Director of the Univ. of Wyoming Agr. Exp. Station as Journal Article No. JA 1220.

² Dept. of Anim. Sci.