Roles of hCG in Advancing Follicular Growth to Ovulation after Concurrent Injections of PGF2α and GnRH in Postpubertal Holstein Heifers Bearing a CL

الملخص EN

A study was conducted to test the hypothesis that injecting Gonadotropin-releasing hormone (GnRH) concurrently with Prostaglandin F2 alpha (PGF2α) followed by an injection of human Chorionic Gonadotropin (hCG), would advance follicular growth to ovulation in Holstein heifers bearing a corpus luteum (CL).

After manual examination of the CL, group 1 (PGF; n=12) received an injection of PGF2α (25 mg, im).

Group 2 (PGF + GnRH; n=13) received an injection of GnRH (100 μg, im) immediately after an injection of PGF2α.

Group 3 (PGF + GnRH + hCG; n=12) received concurrent injections of PGF2α and GnRH followed with hCG (1500 IU, im) two days later.

Follicular size and day of ovulation were monitored by daily ultrasonographic examination from days 1 to 10.

Blood was collected on days-7, 0 (PGF2α administration), 2, and 7.

Progesterone was not different (P>.05) on days-7, 0, and 2 between the experimental groups.

However, it was higher (P<.005) in the PGF + GnRH + hCG group on day 7 compared to PGF + GnRH heifers, but not significantly higher than the PGF.

Additionally, heifers in the PGF + GnRH + hCG group ovulated earlier (P<.05) than heifers in the PGF + GnRH and the PGF group.

This data indicates that hCG advances follicular growth to ovulation in spite of high levels of progesterone when injected 48 h after concurrent treatments of GnRH and PGF2α on heifers bearing a CL.