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Synchronization of Estrus in Beef Cattle with PGF₂ and Estradiol Benzoate¹

West Virginia University, Morgantown 26506 and The Upjohn Company, Kalamazoo, NI 49001

Abstract

Five trials were conducted to compare the efficacy of one or two intramuscular injections of PGF₂ , with or without subsequent treatment with estradiol benzoate, for synchronization of estrus in beef cows and heifers with palpable corpora lutea. Intramuscular injection of 400 µg estradiol benzoate 48 hr after PGF₂ increased the precision of synchronization of estrus in both lactating beef cows and heifers (P<.05). Onset of estrus within a target period 56 to 86 hr after PGF₂ was increased by 23 and 15 percentage points, in the cows and heifers respectively, by the estrogen treatment. Response was not altered when estradiol benzoate was given 40 vs 48 hr after PGF₂ . Conception and pregnancy rates were not altered by estradiol benzoate. A second injection of PGF₂ 12 days after the first gave no advantage in synchronization of estrus in animals with palpable corpora lutea at the time of the first injection.

¹ Published with the approval of the Director of the West Virginia Agricultural Experiment Station as Scientific Paper no. 1453, from the Division of Animal and Veterinary Science. Supported by Hatch Project 224 (nE-72).