Comparison of two dose rates and two management systems for synchronization of estrus in cattle

Two dose rates and 2 management systems for the synchronization of estrus in cattle, using prostaglandin F 2 alpha (PGF2 alpha), were compared within 3 dairy and 3 beef herds. There was no statistical difference in responses between herds or breeds. There was no statistical difference between the estrous response produced by the 12.5-mg dose rate (53.6%) and that produced by the 25-mg dose rate (56.7%, P = 0.5). The 10-day, 1-injection management system produced a 21.7% better estrous response than that produced by the 2-injection system (64.5% vs 42.8%, respectively; P = 0.0001). Most (79.5%) of the difference in estrous response between management systems was accounted for by cows not responding to the 2nd injection of the 2-injection system. The interval from injection to estrus after 1 PGF2 alpha injection was shorter than after 2 PGF2 alpha injections (63.6 +/- 25.2 vs 70.3 +/- 23.8 hours, respectively). The percentage of all cows in the artificial insemination program that were in estrus 56 to 80 hours after injection was 27.4%.