Heat stress is one of the environmental factors that most severely affects milk industry, as it has impact on production, immune responses and reproductive performance. The present study was conducted with high-performance Holando-Argentino cows. Our objective was to study TNF-α and its receptors pattern expression in cows from a region characterized by extreme climatic seasonality. Animals were evaluated in three periods: spring (n = 15), summer (n = 14) and autumn (n = 11). Meteorological records from a local station were used to estimate the temperature and humidity index (THI) by means of an equation previously defined. A THI higher than 68 is indicative of stressing conditions. During the summer period, the animals were exposed to 8.5 ± 1.09 h of heat stress, or THI > 68. In spring, stress hours were reduced to 1.4 ± 0.5 every day, while during the autumn, there were no recorded heat stress events. Expression of TNF-α, and its receptors was determined by qPCR. During the summer, TNF-α and its receptors expression diminished drastically compared to the rest of the year, when stressful conditions were infrequent. We conclude that animals that are not physiologically prepared to resist high temperatures might have a less efficient immune response, reinforcing the need to develop new strategies to improve animal welfare.

热应激是影响牛奶行业最严重的环境因素之一，因为它会影响生产、免疫反应和繁殖性能。本研究是用高性能荷兰-阿根廷奶牛进行的。我们的目标是研究来自以极端气候季节性为特征的地区的奶牛的 TNF-α 及其受体模式表达。在三个时期对动物进行评估：春季 (n = 15)、夏季 (n = 14) 和秋季 (n = 11)。来自当地气象站的气象记录用于通过先前定义的方程来估计温度和湿度指数 (THI)。高于 68 的 THI 表示压力状况。在夏季，动物暴露于 8.5 ± 1.09 小时的热应激，或 THI > 68。在春季，应激时间减少到每天 1.4 ± 0.5，而在秋季，没有记录到热应激事件。TNF-α 及其受体的表达通过 qPCR 确定。在夏季，当压力条件不常见时，与一年中其他时间相比，TNF-α 及其受体的表达急剧下降。我们得出的结论是，在生理上没有准备好抵抗高温的动物可能具有较低效率的免疫反应，这加强了开发新策略以改善动物福利的必要性。