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Synchronization of Estrus in Dairy Heifers with Prostaglandin F₂ with or without Estradiol Benzoate¹

West Virginia University, Morgantown 26506

ABSTRACT

Efficiency of prostaglandin F₂ with and without estradiol benzoate for synchronizing estrus in dairy heifers was examined in two field trials involving 3 3 herds and 909 heifers. Heifers were observed for estrus twice daily for 4 days, palpated rectally for reproductive status, and injected with 25 mg prostaglandin F₂ if they were not pregnant and had a palpable corpus luteum. Forty to forty-eight hours later, 194 of the treated heifers were injected with 400 µg of estradiol benzoate. Heifers were observed for estrus through 96 h. Of the heifers treated with prostaglandin, 179 were assigned to be bred 12 h after observation of estrus. One hundred and ten were assigned to be bred at 80 h after prostaglandin treatment in trial 1 and 112 at 72 h after treatment in trial 2. Treatment with estradiol benzoate did not affect the percentage of animals showing estrus (86.7 versus 84.3%) or conceiving (54.7 versus 57.5%). A greater proportion of heifers bred at 80 h conceived when previously treated with estrogen (52.9 versus 39.0%). Conception rates after breeding at 72 h were low and not improved by estrogen treatment (29.7 versus 38.7%). Of the heifers presented for synchronization, 9.4% were pregnant to an unknown breeding, 2.2% had anomalies of the reproductive tract, and 12.1% were immature. Puberal status of heifers varied widely among herds and was more dependent on body weight than height at withers or frame size. Heifers as young as 12 mo were puberal in some herds, and heifers as old as 22 mo were prepuberal in other herds.

¹ Published with the approval of the Director of the West Virginia Agricultural and Forestry Experiment Station as Scientific Paper No. 1763. Supported by Hatch Project 224 (NE72). Division of Animal and Veterinary Sciences.

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