Behavior during the estrous cycle of mares can affect their performance and therefore inhibition of cyclical ovarian activity is indicated. We hypothesized that implants containing the GnRH analog deslorelin downregulate GnRH receptors and inhibit ovulation in mares. The estrous cycles of Shetland mares were synchronized with 2 injections of a PGF_2α analog. One day after the second injection (day 0), mares received 9.4 (group D1, n = 6) and 4.7 mg deslorelin (D2, n = 5) as slow-release implants or 1.25 mg short-acting deslorelin as a control (C, n = 5). Ultrasonography of the reproductive tract and ovaries and observation of estrous behavior and collection of blood samples for analysis of progesterone and LH concentrations were performed every second day until day 10 and thereafter at 5-d intervals. Stimulation tests with the GnRH-agonist buserelin were performed on days 10 and 45. Until day 50, there were less spontaneous ovulations in group D1 (P < 0.01) and estrous behavior was reduced in groups D1 and D2 compared with group C (P < 0.05). The time until first ovulation (D1 62.0 ± 8.6, D2 44.2 ± 14.1, C 22.2 ± 3.1 d, P < 0.05) and the number of days with estrous behavior (P < 0.05) differed among groups. On day 10 after treatment, a GnRH stimulation test revealed interactions between group and time (P < 0.001) in plasma LH concentration that were no longer detectable on day 45 after treatment. In conclusion, long-acting deslorelin implants result in a transient downregulation of pituitary GnRH receptors that is associated with inhibition of ovulation and estrous behavior in Shetland mares.

母马在发情周期期间的行为会影响它们的表现，因此需要抑制周期性卵巢活动。我们假设含有 GnRH 类似物 deslorelin 的植入物下调 GnRH 受体并抑制母马的排卵。设得兰群岛母马的发情周期与 PGF _{2α 的}2 次注射同步模拟。第二次注射后一天（第 0 天），母马接受 9.4（组 D1，n = 6）和 4.7 mg deslorelin（D2，n = 5）作为缓释植入物或 1.25 mg 短效 deslorelin 作为对照（C , n = 5)。每隔一天进行一次生殖道和卵巢的超声检查，观察发情行为并收集血样以分析孕酮和 LH 浓度，直到第 10 天，然后每隔 5 天进行一次。刺激试验用的GnRH激动剂布舍瑞林进行直到50天天10和45执行的，有在组D1（以下自发排卵P <0.01）和发情行为在组D1和D2降低与C组（比较P < 0.05）。距第一次排卵的时间 (D1 62.0 ± 8.6, D2 44.2 ± 14.1, C 22.2 ± 3.1 d,P < 0.05）和发情行为天数（P < 0.05）在各组之间存在差异。在治疗后第 10 天，GnRH 刺激试验显示血浆 LH 浓度在组和时间之间的相互作用（P < 0.001），在治疗后第 45 天不再检测到。总之，长效 deslorelin 植入物导致垂体 GnRH 受体的短暂下调，这与抑制设得兰群岛母马的排卵和发情行为有关。