Authors : C. Rose , W.B. Tucker , S.T. Willard , A. Williams , J. Fuquay , P.L. Ryan and C.S. Whisnant
Abstract: Ov-Synch is a successful ovulation synchronization protocol when used in lactating dairy cows, with pregnancy rates equaling those seen in animals bred at detected estrus and is now accepted as the industry standard protocol. However, when used in dairy heifers, current protocols do not achieve the same success as seen in dairy cows. Our objectives in this study were to: determine the most effective hormone treatment intervals for the administration of Gonadotropin Releasing Hormone (GnRH) and Prostaglandin F2 α (PG) to induce and synchronize ovulation of the dominant follicle in dairy heifers and) assess the influence of the different hormone treatment intervals on subsequent fertility in response to timed-AI. Heifers (n = 60) were synchronized on d 0 with a single GnRH injection (Cystorelin; 100 �g) and then divided into two groups. Heifers were treated with PG (Lutalyse; 25 mg) either on day 7 (n = 30) or day 12 (n = 30) followed by a second dose of GnRH (100 �g) 48 h later. All heifers were bred by AI 16 h after the last GnRH injection. Ultrasonography was performed daily on a sub-population of heifers (n = 9/group) to monitor follicular dynamics and blood was collected from an additional sub-population of heifers (n = 6/group) for serum LH analysis. Blood was collected from all heifers on days 3, 6, 12, 21 and 45 post-AI for serum Progesterone (P4) analysis. Peak concentrations of Luteinizing Hormone (LH) obtained 60 min after GnRH treatment did not different (p>0.05) between day 7 vs. day 12 heifers (15.3�1.9 and 13.5�2.2 ng mL 1, respectively). Total LH concentrations (0-16h post-second GnRH treatment) were 49.5�5.7 and 47.0�8.3 ng mL 1. Mean dominant preovulatory follicle size on day of second GnRH injection was 15.1�1.9 and 17.0�1.8 mm and did not differ (p>0.05) between 7 and 12 day heifers, respectively. Compared with day 12 heifers, day 7 heifers had higher pregnancy rates (10% vs. 27%, respectively) and a reduced incidence of behavioral estrus (87.5% vs 58.8%), respectively) within 18 days post-insemination. Of the day 12 heifers scanned, 44.4% (4/9) had persistent follicles. In addition, serum concentrations of P4 21 days post-AI were higher (p<0.05; 4.8 vs. 0.7 ng mL 1) for day 12 than for day 7 non-pregnant heifers. These data suggest that extending the interval between the initial GnRH and PG injections (12 vs. 7 days) failed to reduce the variability in response of dairy heifers to synchronization of ovulation.
C. Rose , W.B. Tucker , S.T. Willard , A. Williams , J. Fuquay , P.L. Ryan and C.S. Whisnant , 2008. Evaluation of Hormone Treatments in a Modified Ovulation Synchronization Protocol in Dairy Heifers. Journal of Animal and Veterinary Advances, 7: 154-159.