Effects of Pregnancy and Hysterectomy on the Ovaries of Pony Mares

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Abstract
The primary corpus luteum was marked with ink on day 3 after the end of estrus in pony mares which were either hysterectomized on day 3 or bred during the previous estrus. Mares were bred or hysterectomized early, middle or late in the breeding season and were necropsied 70, 140 or 210 days after the end of estrus. The weight of the primary corpus luteum was less (P<.05) on day 140 in hysterectomized mares than in pregnant mares. The primary corpus luteum regressed between days 140 and 210 in pregnant mares and between days 70 and 140 in hysterectomized mares. Secondary corpora lutea did not form in hysterectomized mares by day 70, based on both necropsy and palpation data. However, 12 of 17 pregnant mares ovulated by day 70. The changes that occurred in the size of the largest follicle, number of follicles > 20 mm and number of follicles 10 to 20 mm over days 10 to 68 were similar in hysterectomized and pregnant mares. Regression analyses indicated that in pregnant mares development of large follicles increased markedly during early pregnancy, as indicated by diameter of largest follicle and number of follicles > 10 mm and > 20 mm. At approximately the time when secondary corpora lutea began to form (day 34 to 70), the number of large follicles began to decrease. By day 210 the ovaries were devoid of follicles > 20 mm. The number of small follicles (< 10 mm) was not different for the 3 days of necropsy (days 70, 140 and 210). Copyright © 1974. American Society of Animal Science . Copyright 1974 by American Society of Animal Science.

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