Research on adaptation for hot environment by dairy cow

在热环境下，比较了荷斯坦与日本黑（F1）和荷斯坦牛(H)杂交牛在几个生理参数上的适应性。试验选用8月龄H和F_1犊牛2头。小牛被暴露在高温（30℃）在气候室两天。测定总可消化营养物质（TDN）摄入量和直肠温度（RT），记录肺声像图和心电图。颈静脉取血，测定红细胞体积（PCV）、血红蛋白浓度（Hb）、红细胞计数（RBC）、白细胞计数（WBC）。其余血样分离至血浆，测定血浆中总蛋白（TP）、葡萄糖（Glc）、游离脂肪酸（FFA）、甲基组氨酸（MeHis）的浓度。热应激降低了TDN的摄入量，尤其是H犊牛。高温胁迫使H的温度升高到40 ~ 41℃，而F的温度保持在39℃以上。热应激增加了两只犊牛的呼吸速率（RR）。30℃处理第1 ~第2天，F_1的RR升高，hm降低。热应激增加了FI的心率（HR），而降低了Holstein，从这些结果可以推测，尽管TDN和HR的降低表明热量产生减少，但Holstein必须承受RT的升高。而F_1可以通过促进由喘气增加估计的热损失来避免RT的升高。热应激对两种犊牛的PCV、Hb、RBC、WBC、TP和FFA的影响几乎未被发现。但荷斯坦犊牛TP高于F_1。实验期间血浆血糖水平维持在正常范围内。热应激使两种犊牛血浆MeHis升高。与F_1相比，热应激增加了荷斯坦的等离子体MeHis。特别是H-1的MeHis和TDN摄入量发生了很大的变化。已知能量不足动物的血浆MeHis由于肌原纤维蛋白降解而升高，血液中肌原纤维释放的MeHis增加。因此，我们推测，本研究中热应激引起的MeHis增加部分是由于TDN摄入量减少引起的。本研究结果表明，F_1的耐热性优于荷斯坦，其耐热性特征表现为有效热损失。少

Under hot environment, adaptability of crossbred cattle between Holstein and Japanese black (F1) and Holstein cattle (H), was compared, on several physiological parameters. Experiments were carried out using two H and F_1, calves aged 8 months. The calves were exposed to high temperature (30 ℃) for two days in the climatic chamber. Total digestible nutrients (TDN) intake and rectal temperature (RT) were measured and pneumotachogram and electrocardiogram were recorded. Blood samples were taken via jugular vein Blood samples were used for measurement of packed cell volume (PCV), hemoglobin concentration (Hb), red blood cell count (RBC), and white blood cell count (WBC). The other blood samples was separated to plasma for measurement of plasma concentration of total protein (TP), glucose (Glc), free fatty acid (FFA), and Nmethylhistidine (MeHis). TDN intake was decreased by heat stress, especially in H calves. RT in H was elevated to 40-41 ℃by heat stress, while that in F, was kept on abo … More ut 39 ℃. Respiratory rate (RR) in both calves was increased by heat stress. However, from first day to second day of 30 ℃, RR in F_1 was increased but that m H decreased. Heart rate(HR) in FI was increased by heat stress, while Holstein was decreased From these results, it is presumed that Holstein obliged to suffer the elevation of RT in spite of the decrease in heat production suggested from the decrease in TDN and HR. While F_1 could avoid the elevation of RT by the promotion of heat loss estimated from the increase in panting. The influence of heat stress on PCV, Hb, RBC, WBC, TP, and FFA in the both calves were almost not recognized. However, TP in Holstein calf were higher than that in F_1. Plasma Glc levwls were maintained within normal range through experimental periods. Plasma MeHis in the both calves was increased by heat stress. Plasma MeHis of Holstein was more increased by heat stress than that of F_1. Especially, MeHis as well as TDN intake in H-1 was greately changed. It is known that plasma MeHis of animal under energy deficient is increased due to myofibrillar protein degradation and MeHis released from myofibril increase in blood. It was presumed, therefore, that the increase in MeHis by heat stress in this study were partially caused due to decreased TDN intake. The results of this study suggest that F_1 is superior in heat tolerance to Holstein, and the characteristics of the heat tolerance in F1 are represented as the effctiv heat loss. Less