Synchronization of Estrus and Ovulation by Subcutaneous Injection with Fenprostalene in Grazing Heifers

Abstract

In an attempt to synchronize estrus and ovulation, a total of 39 Holstein heifers, 13-to 19-month-old, in a pasture were injected subcutaneously with PGF₂-alpha analogue (Fenprostalene, A-75). In Experiment I, 21 heifers in the luteal phase were administered with 2 ml of A-75 (1 mg of Fenprostalene). Nineteen heifers that showed estrus 2-5 days after injection of A-75 were inseminated, and 13 heifers became pregnant. In Experiment II, 11 heifers which were in the luteal phase 10 days after the initiation of the experiment I were injected with 2 ml of A-75. Five heifers showing estrus by 54 hr after injection of A-75 were inseminated, and all became pregnant. The remaining 6 heifers were administered with GnRH-A at 55 hr after treatment with A-75 and inseminated 24 hr after the GnRH-A injection, since they did not show estrus by 54 hr after the A-75 injection. Two heifers became pregnant as a result of this treatment. Consequently, 38 heifers (97.4%) out of 39 (31 in Experiment I & II, 8 in natural estrus) were inseminated, and 27 heifers (69.2%) became pregnant within 13 days after the initiation of the experiment I.