Methods to induce earlier onset of cyclicity in transitional mares

Abstract

The purpose of this study was to investigate methods to induce earlier onset of cyclicity in transitional mares. Two experiments were conducted evaluating the effect of follicular aspiration to advance the onset of cyclicity, more succinctly define criteria for selection of mares for follicular aspiration and to compare aspiration to deslorelin treatment for initiating cyclicity in transitional mares. In Experiment 1, anestrous mares were assigned to control (n=6) or follicular aspiration (n=11). The control mares were monitored twice weekly, until ovulation was detected. The aspiration mares were similarly monitored until a follicle >35 mm was identified, then transvaginal ultrasound guided follicular aspiration was performed. After aspiration, the mares were monitored for luteal tissue formation. In Experiment 2, anestrous mares were assigned to control (n=14), follicular aspiration (n=10), or deslorelin (n=12). The control mares were treated as in Experiment 1. The aspiration mares were monitored in the same manner as Experiment 1 but were treated only if uterine edema was present. The deslorelin treated mares were monitored similarly to the aspiration mares, but instead of aspiration the mares were administered deslorelin. In both experiments, plasma was obtained at each examination from all mares to verify a rise in progesterone. In Experiment 1, the time from January 1 to the first rise in serum progesterone was 23.8 days earlier for aspiration treated mares than for control mares (80.5±7.3 and 104.3±8.8 days, mean±SE, for aspiration and control groups, respectively; P=0.024). In Experiment 2, there was no significant difference in time from January 1 to the first rise in serum progesterone between groups (100.4±5.8, 113.0±3.0 and 110±6.7 days, for the aspiration, control and deslorelin groups, respectively, P=0.328). However, if mares that did not receive a repeat aspiration treatment due to lack of uterine edema are excluded, there was a significant difference between the aspiration and control groups (93.9±6.7 and 113.0±3.0 days, for the aspiration and control groups, respectively, P=0.045). Results of this study indicate that follicular aspiration of a follicle > 35 mm during late transition may be a means to advance the onset of cyclicity in mares.