Fitzgerald J A, Stellflug J N
ARS, U.S. Sheep Exp. Sta., Dubois, ID 83423.
J Anim Sci. 1991 Jan;69(1):264-75. doi: 10.2527/1991.691264x.
Three studies were conducted to determine the effects of exogenous melatonin (M) on changes in scrotal circumference (SC), fertility and reproductive hormone concentrations of rams. Rams were initially housed in barns with controlled photoperiod and given 16 wk of long (16L:8D) or short (8L:16D) days. In Studies I and II, implants of M were given for 40 to 80 d beginning at maximal SC. Results showed that implanted rams had greater (P less than .05) blood M concentrations than nonimplanted controls. However, M did not prevent testicular regression. In Study III, M was given to rams after testicular regression had occurred. Rams were implanted with M weekly for 6 or 4 wk, followed by a withdrawal period of 4 wk (6:4, 4:4 respectively). Results showed that M (6:4) stimulated (P less than .05) testicular growth compared with nonimplanted controls. Treatment of rams with M for 8 mo did not affect LHRH-induced LH release (P greater than .05), but it reduced basal and LHRH-induced testosterone release (P less than .05). Reproductive performance of rams in Studies I and III was compared with that of nonimplanted rams. Fertility of M-treated rams in the spring from Studies I and III (86% to 91%) was similar to that in autumn (93%). Fertility of rams from Studies I and III exceeded (P less than .05) that of nonimplanted rams in April (59% to 62%). Net lamb production from ewes mated in the spring was greater if rams were treated with M and(or) photoperiod.
开展了三项研究以确定外源性褪黑素（M）对公羊阴囊周长（SC）变化、繁殖力及生殖激素浓度的影响。公羊最初饲养在光照周期可控的畜舍中，给予16周的长日照（16小时光照：8小时黑暗）或短日照（8小时光照：16小时黑暗）。在研究I和II中，从阴囊周长达到最大值开始，给予M植入物40至80天。结果显示，植入M的公羊血液中M浓度高于未植入的对照组（P < 0.05）。然而，M未能阻止睾丸退化。在研究III中，在睾丸退化发生后给公羊施用M。公羊每周植入M，持续6周或4周，随后有4周的停药期（分别为6:4、4:4）。结果显示，与未植入的对照组相比，M（6:4）刺激（P < 0.05）了睾丸生长。用M处理公羊8个月不影响促性腺激素释放激素（LHRH）诱导的促黄体生成素（LH）释放（P > 0.05），但降低了基础和LHRH诱导的睾酮释放（P < 0.05）。将研究I和III中公羊的繁殖性能与未植入公羊的繁殖性能进行比较。研究I和III中经M处理的公羊在春季的繁殖力（86%至91%）与秋季相似（93%）。研究I和III中公羊在4月份的繁殖力超过（P < 0.05）未植入公羊（59%至62%）。如果公羊接受M和（或）光照周期处理，春季配种母羊的净产羔数会更高。
