Control of Ovulation as a Practical Reproductive Management Tool in Cattle

Abstract

Infertility in cattle is often caused by poor estrus detection which results in insemination timing error. Estrus detection failure is also a major cause of missing heat and delayed start of re-breeding after carving. Synchronization of estrus by using gestagen or prostaglandin (PG) F2α has been extensively used for improving estrus detection efficiency. However, variation in intervals from treatment to estrus was too large for the existing estrus synchronization methods to be of practical value, for a timed artificial insemination after treatment with gestagen or PGF2α results in disappointing conception rates. Recently, a program for synchronization of estrus using GnRH and PGF2α has been developed. GnRH is administered at first irrespective of estrus cycle to induce ovulation of dominant follicle and a follicular wave, and then PGF2α is given 7 days later for luteal regression, followed by second GnRH injection 30 to 48 hours after the PGF2α. Cattle can be inseminated artificially at a fixed time, 16 to 24 hours after the second GnRH, since ovulation is usually synchronized 24 to 32 hours after the second GnRH. Satisfactory pregnancy rates after synchronization of ovulation and timed AI have been reported in north America as well as in Japan. The greatest advantage of the ovulation synchronization and timed AI program is that virtually 100% of the animals can be inseminated within a certain period with a satisfactory pregnancy rate. Moreover, the program does not require estrus detection. Further studies on the synchronization programs and on factors influencing conception rate after timed AI would significantly improve reproductive management of cattle.