Synchronization of Estrus in Dairy Heifers with Prostaglandin F2α with or without Estradiol Benzoate

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Abstract
Efficiency of prostaglandin(PG)F2.alpha. with and without estradiol benzoate for synchronizing estrus in dairy heifers was examined in 2 field trials involving 33 herds and 909 heifers. Heifers were observed for estrus twice daily for 4 days, palpated rectally for reproductive status, and injected with 25 mg PGF2.alpha. 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 .mu.g of estradiol benzoate. Heifers were observed for estrus through 96 h. Of the heifers treated with PG, 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 PG 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 vs. 84.3%) or conceiving (54.7 vs. 57.5%). A greater proportion of heifers bred at 80 h conceived when previously treated with estrogen (52.9 vs. 39.0%). Conception rates after breeding at 72 h were low and not improved by estrogen treatment (29.7 vs. 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 wt 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.
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