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能力，从而降低热带地区的生产力。本研究从下丘脑-垂体-性腺轴神经内分泌功能的角度分析了热应激条件下水牛性腺功能减退的机制，并从温度调节反应的角度比较了水牛和黄牛的耐热性，以期为今后水牛的有效利用提供参考。主要研究结果如下：1.在卵巢切除山羊中，卵巢类固醇环境通过类固醇植入物维持在恒定水平，热应激不会抑制卵巢促性腺激素分泌。下丘脑GnRH脉冲发生器的活动，通过电生理学方法记录，也没有表现出明显的热应激的影响，虽然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减退不是由于神经内分泌的减少， 关于我们 下丘脑和垂体的功能。在热应激条件下，通过每小时注射GnRH维持LH的脉冲式分泌，可显著抑制卵巢的反应（通过血浆雌二醇浓度的增加和排卵来确定）。从这些结果来看，卵巢反应性差被认为是热应激条件下性腺功能减退的可能原因。卵巢血流量，如超声渡越时间流量计所测量的，不受热应激的影响，因此排除了卵巢血供减少的可能性.通过对水牛和黄牛耐热性的比较研究发现，水牛的散热主要依靠体表的显热损失，而不是通过出汗和呼吸等方式蒸发的非显热损失.在水牛中，在热的条件下发生的血容量的快速增加，这导致增加的血液流向皮肤，并有助于增加从体表散热。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