Walkden-Brown S W, Restall B J, Norton B W, Scaramuzzi R J
Department of Agriculture, University of Queensland, Australia.
J Reprod Fertil. 1994 Mar;100(2):521-31. doi: 10.1530/jrf.0.1000521.
The effects of season, diet and exposure to oestrous females on LH and testosterone secretion were examined in mature cashmere bucks to determine whether there is a seasonal cycle of LH and testosterone secretion, and whether this can be modulated by long-term differential nutrition and exposure to oestrous females. Three-year-old bucks were individually housed under natural photoperiod at 29 degrees S 153 degrees E and fed diets of high (crude protein 17.6%, metabolizable energy 8.3 MJ kg-1) or low (crude protein 6.9%, metabolizable energy 6.6% MJ kg-1) quality for 16 months ad libitum (n = 6 per treatment). Blood samples were collected to determine pulsatile LH and testosterone secretion immediately before experimental feeding, one month later, and every second month thereafter. Samples were collected for an 8 h period on successive days with the bucks isolated on the first day and each exposed to a single oestrous doe for the duration of the second day. In the absence of oestrous females, bucks exhibited a circannual pattern of secretion for both hormones with pulse frequency and mean concentrations highest in late summer and autumn and lowest in late winter and spring. Testosterone pulse amplitude followed a similar pattern, but LH pulse amplitude was highest in spring and lowest in autumn, indicating a seasonal shift in the relationship between the two hormones. Exposure to oestrous does increased LH and testosterone secretion depending on both season and diet. Responses were evident during summer, autumn and early winter, with bucks on a high quality diet exhibiting an earlier and more prolonged period of responsiveness than did bucks on a low quality diet, peaking in February compared with June. The magnitude of the LH and testosterone response was also significantly greater in bucks on a high quality diet. Weight loss during autumn appeared to reduce responsiveness in both treatments. These results demonstrate that there is a seasonal cycle in LH and testosterone secretion in mature cashmere bucks, and that nutrition and oestrous females are powerful modulators of the secretion of these hormones in a seasonally dependent way.
研究了季节、饮食和接触发情母羊对成年绒山羊公羊促黄体生成素（LH）和睾酮分泌的影响，以确定LH和睾酮分泌是否存在季节性周期，以及这是否可通过长期不同的营养状况和接触发情母羊来调节。将三岁的公羊单独饲养在南纬29度、东经153度的自然光照周期下，随意喂食高质量（粗蛋白17.6%，代谢能8.3兆焦/千克）或低质量（粗蛋白6.9%，代谢能6.6兆焦/千克）的日粮16个月（每种处理6只）。在实验性喂食前、一个月后以及此后每隔两个月采集血样，以测定LH和睾酮的脉冲式分泌。连续几天在8小时内采集样本，第一天将公羊隔离，第二天每只公羊与一只发情母鹿接触。在没有发情母羊的情况下，公羊两种激素的分泌均呈现出每年一次的模式，脉冲频率和平均浓度在夏末和秋季最高，在冬末和春季最低。睾酮脉冲幅度遵循类似模式，但LH脉冲幅度在春季最高，秋季最低，表明两种激素之间的关系存在季节性变化。接触发情母羊会增加LH和睾酮的分泌，这取决于季节和饮食。在夏季、秋季和初冬期间有明显反应，高质量日粮的公羊比低质量日粮的公羊表现出更早且持续时间更长的反应期，高质量日粮的公羊在2月达到峰值，而低质量日粮的公羊在6月达到峰值。高质量日粮的公羊中LH和睾酮反应的幅度也显著更大。秋季体重减轻似乎会降低两种处理方式下的反应性。这些结果表明，成年绒山羊公羊的LH和睾酮分泌存在季节性周期，并且营养状况和发情母羊是以季节依赖性方式对这些激素分泌进行有力调节的因素。
