THE EFFECT OF ESTRADIOL VALERATE ON FOLLICULAR DYNAMICS AND SUPEROVULATORY RESPONSE IN COWS WITH SYNCRO-MATE-B IMPLANTS

Two experiments were designed to evaluate the effect of estradiol valerate on follicular dynamics and superovulatory response in cows with Syncro-Mate-B (SMB) implants. In Experiment 1, 5 mg estradiol valerate (E2), injected at the same time as superstimulation treatments were initiated, resulted in fewer corpora lutea (CL), ova/embryos collected and fertilized ova (P < 0.05) than if E2 was administered with the SMB implant 7 days earlier. In Experiment 2, 31 beef cows and 26 Holstein cows were placed in one of four treatment groups. Group I (control) cows were superstimulated on Day 9 (estrus = Day 0). On Day 2, cows in Groups II, III, and IV received SMB and cows in Group III received E2. On Day 9, cows in Group IV received E2, and all cows were superstimulated with Folltropin. The number of CL did not differ (P > 0. 19) among groups. However, there were more follicles < 10 mm and fewer fertilized ova and transferable embryos (P < 0.02) in Group IV cows. Ovarian ultrasonography revealed that the diameter of the largest follicle in Group III cows declined from Day 2 to Day 7 and subsequently increased until Day 13. In contrast, Groups I, II and IV were characterized by apparently linear growth between Days 2 and 13. Differences (P < 0.05) were detected between Days 5 and 9. Mean diameter of the largest follicle was smaller for cows in Group III than for the remaining groups on Day 9. It was concluded that SMB did not adversely affect superovulatory response and that E2 administration resulted in atresia of the antral follicles in the cows with SMB implants.