ALTERATION OF THE ESTRUAL CYCLE IN SHEEP BY USE OF PROGESTERONE AND ITS EFFECT UPON SUBSEQUENT OVULATION AND FERTILITY1

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Abstract
Two groups of sheep were studied, each receiving a different dosage of progesterone. One group of 18 ewes was given 14 daily subcut. injns. of 5 mg. of progesterone (in oil); 6 animals were started on the 4th day after the beginning of natural estrus, 6 on the 8th day and 6 on the 12th day. A 2d group of 12 ewes with 4 animals in each stage of the estrual cycle was treated in the same manner, with 10 mg. daily. Both dosages suppressed estrus during treatment. Laparotomies showed that ovulation was inhibited in 15 of the 18 ewes on the 5 mg. dosage, the other 3 having ovulated "quietly." At autopsy 2 of the 15 ewes showed a cystic condition of the ovaries which had developed during the interval between laparotomy and autopsy and another had a quiet ovulation during the same period. The remaining 12 ewes in this group all showed a post-treatment estrus and ovulation within 2-4 days after the last injn. The ovulation rate of these ewes was significantly depressed (1.4 as compared with 1.9 for the control ovulations) and only 44% of the recovered ova were fertilized. Ovulation was inhibited during treatment in all ewes on the 10 mg. dosage and estrus of normal duration occurred in every ewe on this dosage beginning from 3 to 3.5 days after the last injection. Each of these ewes had ovulated and showed normal-appearing corpora lutea at the time of autopsy. The avg. ovulation rate, 1.7 per ewe, was not significantly different from that of the immediately previous control estrus, 1.8, and 67% of the recovered ova were fertilized.