Basic study on the improvement of animal production in the tropics, especially on the reproductive problems under heat stress conditions

热应激抑制动物的繁殖性能，从而降低热带地区的生产力。本研究从下丘脑-垂体-性腺轴的神经内分泌功能出发，分析了热应激条件下水牛性腺功能低下的机制，并从体温调节反应的角度比较了水牛和黄牛的耐热性，以期为水牛的高效利用提供依据。主要研究结果如下：1.热应激对卵巢切除山羊的垂体促性腺激素分泌无明显抑制作用，但类固醇能维持卵巢内的类固醇环境。电生理学方法记录的下丘脑GnRH脉冲发生器活动也没有显示出明显的热应激影响，尽管使用的动物数量很少。根据这些结果，推测热应激条件下的性腺功能低下与神经内分泌…的减少无关。下丘脑、脑下垂体功能增强。当每小时注射促性腺激素释放激素(GnRH)维持发情动物的搏动性促黄体生成素分泌时，在热应激条件下，卵巢反应(由血浆雌二醇浓度的增加和排卵决定)显著受到抑制。根据这些结果，卵巢的低反应性被认为是热应激条件下性腺功能减退的可能原因。超声传输时间流量计测量的卵巢血流量不受热应激的影响，因此排除了卵巢血供减少的可能性。在对水牛和黄牛耐热性的比较研究中发现，与黄牛相比，水牛的散热更多地依赖于体表的敏感热损失，而不是通过出汗和呼吸蒸发产生的无感热损失。在水牛中，在炎热的条件下，血液容量会迅速增加，这会导致流向皮肤的血液增加，并导致体表热量散失增加。较少

Heat stress suppresses the reproductive performance of animals and thereby reduces productivity in the tropics. In the present study, 1) the mechanisms of hypogonadism under heat stress conditions were analyzed in relation to neuroendocrine functions of the hypothalamo-pituitary-gonadal axis, and 2) heat tolerance of buffaloes was compared with cattle in terms of thermo-regulatory responses aiming at the efficient use of buffaloes in future. The results obtained were summarized as follows :1. Pituitary gonadotropin secretions were not suppressed by heat stress in ovariectomized goats in which ovarian steroidal milieu were maintained at constant levels by steroid implants. Hypothalamic GnRH pulse generator activity, as recorded by a electrophysiological method, also showed no apparent influence of heat stress, although a number of animals used was small. From these results, it was assumed that hypogonadism under heat stress conditions is not attributed to the decrease of neuroendocrine … More functions of hypothalamus and pituitary.2. Ovarian responses, as determined by the increase of plasma estradiol concentration and ovulation, were significantly suppressed under heat stress conditions, when the pulsatile LH secretion was maintained by hourly injection of GnRH in anestrous animals. From these results, a poor responsiveness of the ovary was considered as a possible cause of hypogonadism under heat stress conditions.3. Ovarian blood flow, as measured by the ultrasound transit-time flow meter, was not influenced by heat stress and therefore a possibility of the reduced blood supply to the ovary was ruled out.4. In the comparative study of heat tolerance of buffaloes and cattle, it was shown that heat dissipation in buffaloes was much depended on sensitive heat loss from body surface rather than insensible heat loss by evaporation through sweating and respiration compared with cattle.5. In buffaloes, a rapid increase of blood volume occurred under hot conditions, and this resulted in an increase of blood flow to the skin and contributed to an increased heat dissipation from body surface. Less