Clinical experience with deslorelin (Ovuplant (TM)) in a Kentucky Thoroughbred broodmare practice (1999)

Palpation records of 155 Thoroughbred broodmares maintained on one of seven farms (3-80 mares per farm) that were administered deslorelin on one or mo re estrous cycles (204 treated cycles) during the 1999 breeding season were retrospectively examined. Some deslorelin-treated mares were also treated with hCG (2500 units intravenously), or had no ovulation-inducing drugs adm inistered, during different estrous cycles of the same season. Most mares w ere treated with an ovulation-inducing drug after returning to their reside nt farm following breeding and were subsequently examined by transrectal ul trasonography daily until ovulation was confirmed, and again 13-14 and 15-1 6 days after ovulation for determination of pregnancy status. Per-cycle pregnancy rate for all 155 mares bred was 53%, and for all deslor elin breedings was 57%. Per-cycle pregnancy rates for mares ovulating 0-1 d ays, 1-2 days, and 2-3 days after treatment with deslorelin did not differ (P > 0.05). Forty-six mares received more than one treatment during the bre eding season, yielding 115 breedings (estrous cycles) for comparison of pre gnancy rates among treatments. Per-cycle pregnancy rates for these mares di d not differ among treatments (P > 0.10). No differences due to treatment were detected in mean interval to ovulation (P > 0.10). Mean interovulatory interval was longer for deslorelin-treated mares than for untreated or hCG treated mares (P < 0.01). Eighty percent ( 80%) of deslorelin-treated mares had interovulatory intervals of 18-25 days , and 19% had interovulatory intervals > 25 days. Ninety-seven percent (97% ) of untreated or hCG-treated mares had interovulatory intervals of 18-25 d ays, and none had interovulatory intervals > 25 days. More deslorelin-treat ed mares had extended (> 25 days) interovulatory intervals than hCG- or non treated-mares (P < 0.05). In this group of Thoroughbred mares, it appeared that season (month) and management (farm) factors had only minor effects on the incidence of extended interovulatory intervals following use of deslor elin.