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

热应激会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性腺功能减退的机制；从热调节反应的角度比较了水牛与牛的耐热性，以期今后水牛的高效利用。所得结果总结如下：1。在切除卵巢的山羊中，垂体促性腺激素分泌不受热应激的抑制，其中卵巢类固醇环境通过类固醇植入维持在恒定水平。通过电生理方法记录的下丘脑GnRH脉冲发生器活动也显示没有明显的热应激影响，尽管使用的动物数量很少。从这些结果可以推测，热应激条件下性腺功能减退不是由于神经内分泌的减少，而是由于下丘脑和垂体的更多功能。发情动物在热应激条件下，通过每小时注射GnRH维持脉动性LH分泌，卵巢反应（由血浆雌二醇浓度和排卵增加决定）明显受到抑制。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，由超声透射时间流量计测量，不受热应激的影响，因此排除卵巢血供减少的可能性。水牛和牛的耐热性对比研究表明，与牛相比，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的不感热损失。在炎热的条件下，水牛的血容量迅速增加，这导致流向皮肤的血流量增加，并有助于增加体表的散热。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