Preliminary studies on the use of an oral progestogen to induce oestrus and ovulation in seasonally anoestrous Thoroughbred mares

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Abstract
Daily oral administration of 30 mg allyl trenbolone (Regumate) for 10-15 days to 61 barren, maiden and lactating thoroughbred mares which were exhibiting either deep anestrus, shallow anestrus, prolonged spring estrus or lactation anestrus, resulted in 54 mares (88%) showing estrous behavior within 8 days, and 51 mares (84%) ovulating within 18 days, after the last dose of compound. Response rate was lowest in mares in deep anestrus. Of the 38 Regumate-treated mares which were covered during the induced estrus, 21 (55%) conceived. The practical value of this form of progesterone withdrawal therapy as a method for hastening the onset of the breeding season in thoroughbred mares is discussed.