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

Dairy Cattle Research Branch, Animal Husbandry Research Division, Agricultural Research Center, Beltsville, Maryland

ABSTRACT

Fifteen first-service dairy cattle were bilaterally ovariectomized five, six, or seven days post-breeding. Eight of these cattle were given daily subcutaneous injections of progesterone at 25 mg per hundredweight and estrone at 6.25 µg per hundredweight; six cattle had normal pregnancies when killed 50–62 days post-breeding; uteri of the other two contained degenerating embryos. Seven animals were given progesterone alone; five had normal pregnancies at 27–89 days post-breeding. Of 20 clinically normal repeat-breeder cattle, three (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 five others contained degenerate embryonic membranes at 35 days. Fertility was not improved by ovariectomy and injection of hormones that maintained early pregnancies in a high percentage of first-service cattle.