Roth Z, Meidan R, Braw-Tal R, Wolfenson D
Department of Animal Science, Faculty of Agriculture, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot 76100, Israel.
J Reprod Fertil. 2000 Sep;120(1):83-90.
The aim of this study was to characterize the immediate effects of heat stress on plasma FSH and inhibin concentrations, and its involvement in follicular dynamics during a complete oestrous cycle, and to examine a possible delayed effect of heat stress on follicular development. Holstein dairy cows were oestrous synchronized and randomly assigned to either cooled (n = 7) or heat-stressed (n = 6) treatment groups. During a complete oestrous cycle, control cows, which were cooled, maintained normothermia, whereas heat-stressed cows, which were exposed to direct solar radiation, developed hyperthermia. At the end of this oestrous cycle (treated cycle), both groups were cooled and maintained normothermia for the first 10 days of the subsequent oestrous cycle. Throughout this period, follicular development was examined by ultrasonography, and plasma samples were collected. During the second follicular wave of the treated oestrous cycle, a significantly larger cohort of medium sized follicles (6-9 mm) was found in heat-stressed cows than in cooled cows (P < 0.05). The enhanced growth of follicles in this wave in heat-stressed cows was associated with a higher plasma FSH increase which lasted 4 more days (days 8-13 of the oestrous cycle; P < 0.05), and coincided with a decrease in the plasma concentration of immunoreactive inhibin (days 5-18 of the oestrous cycle; P < 0.05). During the follicular phase (days 17-20 of the treated cycle), heat-stressed cows showed an increase in the number of large follicles (>/= 10 mm), and the preovulatory plasma FSH surge was significantly higher in heat-stressed cows than in cooled cows (P < 0.01). The effect of heat stress was also observed during the first follicular wave of the subsequent cycle: the postovulatory plasma FSH concentration was higher (P < 0.01), but fewer medium follicles developed, and the first follicular wave decreased at a slower rate in previously heat-stressed cows than in cooled cows (0.40 and 0.71 follicles per day, respectively). This study shows both immediate and delayed effects of heat stress on follicular dynamics, which were associated with high FSH and low inhibin concentrations in plasma. These alterations may have physiological significance that could be associated with low fertility of cattle during the summer and autumn.
本研究的目的是描述热应激对血浆促卵泡素（FSH）和抑制素浓度的即时影响，及其在整个发情周期中对卵泡动态变化的影响，并研究热应激对卵泡发育可能产生的延迟效应。对荷斯坦奶牛进行发情同步处理，并随机分为凉爽组（n = 7）和热应激组（n = 6）。在整个发情周期中，处于凉爽环境的对照奶牛体温保持正常，而暴露在直射阳光下的热应激奶牛则出现体温过高。在这个发情周期（处理周期）结束时，两组奶牛都处于凉爽环境，并在随后发情周期的前10天保持体温正常。在此期间，通过超声检查卵泡发育情况，并采集血样。在处理周期的第二个卵泡波期间，发现热应激奶牛中直径6 - 9毫米的中等大小卵泡群显著大于凉爽奶牛（P < 0.05）。热应激奶牛这一波卵泡生长增强与血浆FSH升高幅度更大有关，且这种升高持续了4天多（发情周期的第8 - 13天；P < 0.05），同时与免疫反应性抑制素血浆浓度降低（发情周期的第5 - 18天；P < 0.05）相一致。在卵泡期（处理周期的第17 - 20天），热应激奶牛的大卵泡（≥10毫米）数量增加，且热应激奶牛排卵前血浆FSH峰值显著高于凉爽奶牛（P < 0.01）。在随后周期的第一个卵泡波期间也观察到了热应激的影响：排卵后血浆FSH浓度更高（P < 0.01），但发育的中等卵泡较少，且之前热应激奶牛的第一个卵泡波下降速度比凉爽奶牛慢（分别为每天0.40个和0.71个卵泡）。本研究显示了热应激对卵泡动态变化的即时和延迟效应，这与血浆中高FSH和低抑制素浓度有关。这些改变可能具有生理意义，可能与夏秋季节奶牛繁殖力低有关。
