Powell M R, Kaps M, Lamberson W R, Keisler D H
Department of Animal Sciences, University of Missouri, Columbia 65211, USA.
J Anim Sci. 1996 Oct;74(10):2292-302. doi: 10.2527/1996.74102292x.
Ten experiments utilizing 1,659 ewes were conducted to determine the potential of melengestrol acetate (MGA)-based treatments in inducing and synchronizing estrous activity in ewes during the nonbreeding season. In May or June, ewes were given .25 mg of MGA.ewe-1.d-1 or control diet and(or) a subsequent i.m. injection of zeranol, estradiol-17 beta, or oil vehicle. Fertile rams were introduced, and estrous and(or) lambing responses were determined. In Exp. 1, more (P < .01) ewes given MGA for 14 d followed by 5 mg of zeranol (i.m.) were in estrus than controls. Melengestrol acetate and zeranol independently induced estrus in Exp. 2, with MGA-treated ewes exhibiting the greatest lambing response (P < .05). The optimum duration of feeding MGA was 8 d vs 11 or 14 d (Exp. 3). In Exp. 4, as the dose of zeranol increased, synchrony of estrus increased but lambing response decreased. A dose of 1.25 mg of zeranol represented a compromise in estrous and lambing response and was determined to be optimally effective when given 54 h after the last feeding of MGA (Exp. 5). Shortcomings in lambing responses were treated in Exp. 6 by supplementing ewes with MGA after breeding, which proved unsuccessful, and in Exp. 7 by substituting estradiol-17 beta for zeranol, which proved effective when given 54 h after the last feeding of MGA (Exp. 8). In Exp. 9, use of MGA + estradiol increased (P < .05) the estrous and subsequent lambing response of 30-d postpartum ewes temporarily weaned of their lambs. In contrast, lambing response of 90-d postpartum ewes treated with MGA + estradiol was not increased by temporary removal of lambs (Exp. 10). These data collectively support the hypothesis that treatment of ewes with MGA + estradiol is an effective and practical approach for inducing and synchronizing a fertile estrus in ewes during the non-breeding season.
进行了十项实验，共使用1659只母羊，以确定基于醋酸美仑孕酮（MGA）的处理方法在非繁殖季节诱导和同步母羊发情活动的潜力。在五月或六月，给母羊投喂0.25毫克/只·天的MGA或对照日粮，和（或）随后进行肌肉注射玉米赤霉醇、β-雌二醇或油剂。引入可育公羊，并确定发情和（或）产羔反应。在实验1中，接受MGA处理14天然后肌肉注射5毫克玉米赤霉醇的母羊发情的数量比对照组多（P < 0.01）。在实验2中，醋酸美仑孕酮和玉米赤霉醇分别诱导发情，接受MGA处理的母羊产羔反应最大（P < 0.05）。投喂MGA的最佳持续时间为8天，而非11天或14天（实验3）。在实验4中，随着玉米赤霉醇剂量增加，发情同步性提高，但产羔反应降低。1.25毫克玉米赤霉醇的剂量在发情和产羔反应之间达到了平衡，并确定在最后一次投喂MGA后54小时给予时效果最佳（实验5）。在实验6中，通过在配种后给母羊补充MGA来处理产羔反应的不足之处，但未成功；在实验7中，用β-雌二醇替代玉米赤霉醇，结果证明在最后一次投喂MGA后54小时给予时有效（实验8）。在实验9中，使用MGA + 雌二醇增加了（P < 0.05）产后30天暂时断奶的母羊的发情和随后的产羔反应。相比之下，对产后90天的母羊用MGA + 雌二醇进行处理，通过暂时断奶并未增加其产羔反应（实验10）。这些数据共同支持了这样一个假设，即对母羊用MGA + 雌二醇进行处理是在非繁殖季节诱导和同步母羊可育发情的一种有效且实用的方法。
