Embryo Survival in First-Service and Repeat-Breeder Cattle after Ovariectomy and Hormone Therapy

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Abstract
Fifteen first-service dairy cattle were bilaterally ovariectomized 5, 6 or 7 days post-breeding and given daily subcutaneous injections of progesterone at 25 mg per cwt and estrone at 6.25 mcg per cwt, or progesterone alone. Eleven cattle had normal pregnancies when killed 27-89 days post breeding. Of 20 clinically-normal repeat-breeder cattle, 3 (15%) were pregnant at 53-99 days after a control service. Seventeen were rebred, ovariectomized and given exogenous hormones. Three (18%) were pregnant at 38-62 days; uteri of 5 others contained degenerate embryonic membranes at 35 days. Fertility was not improved by ovariectomy and hormone replacement therapy.