Abstract: [Objective] To explore the effects of heat stress on immune and reproductive function of lactating cows. [Method] From 2021 to 2022,40 lactating cows were tested in a dairy farm in Xingyi City,Guizhou Province. [Result] The temperature in cowshed is the highest in summer （June-August）.Compared with other seasons,the blood sugar and urea nitrogen levels, immunoglobulin G（IgG）and immunoglobulin A（IgA）contents,interleukin 1β（IL-1β）and interleukin-6（IL-6） in serum of lactating cows in this season are significantly decreased（P<0.05）. The average weight loss of lactating cows increased significantly（P<0.05）,and the average feed intake decreased significantly（P< 0.05）. The estrus interval of lactating cows is longer than other time periods. [Conclusion] Under the condition of heat stress,the immune performance of lactating cows is significantly reduced,and the reproductive function is also negatively affected. It is suggested that dariy farms should pay more attention to lactating cows in the actual breeding process,especially in the high temperature weather in summer,and scientific and reasonable feeding management methods should be adopted to ensure the healthy production of dairy cows.

Key words: heat stress, lactating cow, serum biochemical indexes, immune function, reproductive function