Effect of seasonal thermal stress on oxidative status, immune response and stress hormones of lactating dairy cows

Abstract This study aimed to assess the impact of seasonal thermal stress on oxidative stress, immune response, and stress hormones of lactating dairy cows under subtropical regions with different levels of temperature-humidity index (THI). A total of 32 healthy lactating Holstein dairy cows experienced 4 seasons (8 cows/season), the physiological parameters were categorized into low THI (LTHI, THI = 42.97 ± 0.95) in Winter, moderate THI (MTHI, THI = 61.84 ± 0.42) in Spring and Autumn, and high THI period (HTHI, THI = 86.09 ± 0.23) in Summer. The blood samples were collected twice in each season to measure oxidative stress, inflammatory and hormonal parameters. Our results showed THI had a positive correlation with the rectal temperature (R2 = 0.821, P