Roles of hCG in advancing follicular growth to ovulation after concurrent injections of PGF 2 and GnRH in postpubertal holstein heifers bearing a CL

Ricky Johnson, Alcorn State University
William A. Bennett, University of Mississippi Medical Center
Evelin J. Cuadra, Alcorn State University
Victor Njiti, Alcorn State University
Yoonsung Jung, Alcorn State University
Melissa Mason, Alcorn State University


A study was conducted to test the hypothesis that injecting Gonadotropin-releasing hormone (GnRH) concurrently with Prostaglandin F2 alpha (PGF2) 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 PGF2 (25mg, im). Group 2 (PGF + GnRH; n=13) received an injection of GnRH (100g, im) immediately after an injection of PGF2. Group 3 (PGF + GnRH + hCG; n=12) received concurrent injections of PGF2 and GnRH followed with hCG (1500IU, 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 (PGF2 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 PGF2 on heifers bearing a CL. Copyright © 2010 Ricky Johnson et al.