Reproductive management of dairy cattle based on synchronization of estrous cycles.
High-yielding dairy cows (199) were allotted to a control group or one of two groups for synchronization of estrus. Synchronization of estrus was accomplished by either insertion of a progesterone-releasing intravaginal device (progesterone coil) for 7 days with .5 mg of the prostaglandin analogue cloprostenol (Estrumate) administered 1 day before removal of the progesterone coil, or by administration of .5 mg of Estrumate followed 13 days later by a progesterone coil inserted for 9 days. Following each estrous synchronization regimen, cows were inseminated during a fixed 6-day period (insemination week). Into one-half of the cows of each treatment group, a second progesterone coil was inserted 12 days following the fixed-time insemination for 9 days. Cows that calved within 21 days were included in a cluster and were treated and inseminated simultaneously at regular 3-wk intervals. Thus, insemination of synchronized cows was during only 6 out of each 21 days. The estrous synchronization regimens were applied so that the first fixed-time insemination for any cow occurred between 59 and 79 days after calving. Control cows were inseminated following estrus, commencing 59 days after calving. Conception rates for cows of groups 1, 2, and 3 were 50, 56, and 51%. Pregnancy rates at 25 days following the fixed-time insemination were 53, 78, and 69%, and at 100 days after calving, 57, 75, and 65%. A system of reproductive management is proposed in which observations for estrous behavior and inseminations are only during 6 days out of each 3 wk.