Management of reproduction in dairy heifers based on the synchronization of estrous cycles.
Israeli-Holstein breed dairy heifers (n=571), 13 to 15 mo old, were utilized in two experiments. In Experiment 1, the reproductive performance of synchronized heifers was compared with that of untreated controls. The heifers in both groups were inseminated following the detection of estrus. In Experiment 2, all heifers were synchronized and inseminated following the detection of estrus. Half of the animals in this experiment also received one or two fixed-time inseminations 72 and 96 h after the last synchronization treatment. Synchronization of estrous cycles was performed by two prostaglandin F2alpha (PG) injections given 12 d apart. In the control group of Experiment 1, observation of estrous behavior and insemination of heifers detected in estrus were carried out daily throughout the experiment. In the synchronized groups of Experiments 1 and in 2, the management of reproduction consisted of estrus detection followed by the insemination of heifers in estrus carried out only during 6 d of every 3 wk. Five days following the second PG injection, 86% of the heifers were detected in estrus, 71% of them at 49 to 96 h after treatment. In Experiment 1, age at first insemination, age at conception, and conception rate were, respectively, 425 d, 446 d and 54% in the control group vs 432 d (P<0.02), 449 d and 62% in the PG-treated group. In Experiment 2, the respective figures were 436 d, 462 d and 59% in the group inseminated following the detection of estrus vs 427 d (P<0.002), 464 d and 51% (P<0.05) in the group in which heifers were inseminated at estrus and also received one or two fixed-time inseminations.
Kaim
M
M
Institute of Animal Science, A.R.O., The Volcani Center, Bet Dagan 50250, Israel.
Rosenberg
M
M
Folman
Y
Y