本试验旨在研究热应激对肉牛血清内分泌激素含量、抗氧化酶活性及生理生化指标的影响。选择9头8月龄体重(210±20) kg的健康锦江黄牛,分别测定非热应激期和热应激期牛舍环境温度和相对湿度,并测定试验牛血清中内分泌激素含量、抗氧化酶活性及生理生化指标。结果表明:1)热应激期试验牛的呼吸频率和腹泻率均显著高于非热应激期(P＜0.05);在热应激期第1阶段,试验牛的直肠温度显著升高(P＜0.05),而后逐渐恢复正常; 2)与非热应激期相比,热应激期肉牛血清中三碘甲状腺原氨酸(T₃)含量显著降低(P<0.05),甲状腺素(T₄)含量差异不显著(P>0.05);皮质醇(COR)含量在第20天显著升高(P<0.05),而后逐渐恢复正常;葡萄糖(GLU)含量在第60天降低了41.55%(P<0.05);超氧化物歧化酶(SOD)和碱性磷酸酶(ALP)的活性在第40天明显下降(P<0.05);丙二醛(MDA)含量和乳酸脱氢酶(LDH)活性显著升高(P<0.05)。这表明夏季高温高湿环境诱发了锦江黄牛的热应激反应,热应激牛表现为直肠温度升高,内分泌系统紊乱,抗氧化能力降低。但随着热应激时间的延长,试验牛直肠温度、血清内分泌激素含量逐渐恢复正常。

This study was conducted to investigate the effects of heat stress on endocrine hormone content, antioxidant enzyme activity and physiological and serum biochemical indices of beef cattle. Nine eight-month-old Jinjiang cattle with an initial body weight of (210±20) kg were fed in normal and heat stress periods. During the trials, temperature and relative humidity of cattle house were determined. The serum samples of beef cattle were collected, and then endocrine hormone content, antioxidant enzyme activity and physiological and serum biochemical indices of beef cattle were determined. The results showed as follows: 1)breathing frequency and diarrhea rate of beef cattle in heat stress period were significantly higher than those in normal period (P＜0.05); in heat stress period the rectal temperature of beef cattle was significantly increased on 20th day (P＜0.05), and then gradually recovered to normal. 2)Compared with normal period, triiodothyronine (T₃) content in serum was lower significantly (P＜0.05), but thyroxine (T₄) content was not changed (P＞0.05); cortisol (COR) content was significantly increased on 20th day (P＜0.05), and then gradually recovered to normal; the glucose (GLU) content in serum was decreased by 41.55% on 60th day (P＜0.05); the activities of superoxide dismutase (SOD) and alkaline phosphatase (ALP) in serum were significantly lower on 40th day (P＜0.05), but the content of malondialdehyde (MDA) and the activity of lactate dehydrogenase (LDH) were significantly increased (P＜0.05). These results indicate that high temperature and high humidity induce heat stress of beef cattle, and heat stress can enhance the rectal temperature and increase the content of cortisol, and decrease the contents of T₃ and glucose. However, the rectal temperature and endocrine hormone content of beef cattle would gradually recover to normal with the extension of heat stress time.