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Journal of Dairy Science Vol. 83 No. 3 471-476
© 2000 by American Dairy Science Association ®
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Estrus Synchronization of Lactating Dairy Cows with GnRH, Progesterone, and Prostaglandin F2alpha

Z. Z. Xu 1 and L. J. Burton 1

1 Livestock Improvement Corporation Ltd., Private Bag 3016, Hamilton, New Zealand

The reproductive performance of synchronized cows was compared with that of nonsynchronized cows. In trial 1, cyclic cows in five seasonal herds were randomly divided into two groups. Cows in one group (n = 515) were treated with a GnRH agonist and an intravaginal progesterone device, followed in 7 d by a PGF2alpha injection, and the device was removed 1 d after PGF2alpha. Cows in the other group (n = 512) did not receive any treatment and acted as control. In trial 2, the treatments were similar to those used in trial 1 except that the progesterone device was removed at the time of PGF2alpha injection (synchronized: n = 516; control: n = 512). The estrus synchronization rate was 92.8% in trial 1 and 92.2% in trial 2. Conception rate to first artificial insemination (AI) was lower for synchronized cows than for control cows in trial 1 (56.5 vs. 62.7%), but similar in trial 2 (64.6 vs. 63.3%). Across both trials, the pregnancy rate during the AI breeding period was greater for the synchronized cows (85.6%) than for the control cows (81.2%). The synchronization treatment reduced the interval from start of the breeding season to conception for cows conceiving by AI (8.9 vs. 14.8 d) or by AI or natural mating (14.1 vs. 21.6 d). The synchronization protocol used in trial 2 achieved better conception rate than that used in trial 1, but the precision of estrus was less in trial 2 than in trial 1.

Key Words: estrus synchronization • reproductive performance • dairy cow

Submitted on May 24, 1999
Accepted on October 21, 1999




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