Chen Xiaoyang, Shu Hang, Sun Fuyu, Yao Junhu, Gu Xianhong
State Key Laboratory of Animal Nutrition, Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
College of Animal Science and Technology, Northwest A&F University, Xianyang 712100, China.
Animals (Basel). 2023 Aug 9;13(16):2562. doi: 10.3390/ani13162562.
Heat stress affects production and health in cows severely. Since it is difficult to define heat-tolerant animals, studies of response to heat stress are important for understanding dairy cows' health and production. However, information on the impact of heat stress on various indicators in heat-tolerant and heat-sensitive cows is sparse. This study aimed to investigate the effects of heat stress (HS) on blood, production, and physiological indicators in heat-tolerant and heat-sensitive cows. A total of 43 dairy cows were used from 9 May to 7 August 2021, under Temperature-Humidity Index (THI) measurements that ranged from 65.9 to 86.7. We identified cows that were tolerant or sensitive to HS based on the slope of the response of physiological and production traits against THI during the HS period by using a clustering method. After HS, serum glucose (Glu), cortisol (COR), 5-hydroxytryptamine (5-HT), and interleukin-6 (IL-6) levels of cows in the heat-tolerant group were lower than in the heat-sensitive group ( < 0.05). With THI as the predictor, the R for predicting respiration rate (RR) and body surface temperature (BT) in heat-tolerant cows was 0.15 and 0.16, respectively, whereas the R for predicting RR and BT in heat-sensitive cows was 0.19 and 0.18, respectively. There were low to moderate, positive correlations between RR, BT, and MY with THI, with Pearson correlation coefficients ranging from r = 0.11 to 0.4 in the heat-tolerant group, and from r = 0.24 to 0.43 in the heat-sensitive group. There was a low positive correlation between VT and THI, with a Spearman correlation coefficient of r = 0.07 in the heat-sensitive group. The heat-tolerant dairy cows had lower MY losses and had lower MY ( = 0.0007) in mixed models. Heat-tolerant cows with low-stress levels, through upregulating RR rapidly, increased their adaptability to thermal environments. They have better thermoregulation capability; the hypothalamic-pituitary-adrenal (HPA) axis regulated the thermoregulatory in animals by releasing a variety of neurotransmitters and hormones.
热应激对奶牛的生产和健康有严重影响。由于难以界定耐热动物，因此研究热应激反应对于了解奶牛的健康和生产状况很重要。然而，关于热应激对耐热和热敏奶牛各项指标影响的信息却很匮乏。本研究旨在调查热应激（HS）对耐热和热敏奶牛血液、生产及生理指标的影响。2021年5月9日至8月7日期间，在温度湿度指数（THI）范围为65.9至86.7的条件下，共使用了43头奶牛。我们通过聚类方法，根据热应激期间生理和生产性状对THI的反应斜率，确定了对热应激耐受或敏感的奶牛。热应激后，耐热组奶牛的血清葡萄糖（Glu）、皮质醇（COR）、5-羟色胺（5-HT）和白细胞介素-6（IL-6）水平低于热敏组（<0.05）。以THI作为预测因子，预测耐热奶牛呼吸频率（RR）和体表温度（BT）的R值分别为0.15和0.16，而预测热敏奶牛RR和BT的R值分别为0.19和0.18。RR、BT和产奶量（MY）与THI之间存在低到中等程度的正相关，耐热组的Pearson相关系数范围为r = 0.11至0.4，热敏组为r = 0.24至0.43。热敏组中，潮气量（VT）与THI之间存在低正相关，Spearman相关系数为r = 0.07。耐热奶牛的产奶量损失较低，在混合模型中产奶量也较低（= 0.0007）。低应激水平的耐热奶牛通过快速上调RR，增强了对热环境的适应性。它们具有更好的体温调节能力；下丘脑-垂体-肾上腺（HPA）轴通过释放多种神经递质和激素来调节动物的体温调节。
