Effects of temperature and relative humidity on behavior and physiological indices in goats

High temperature and relative humidity (RH) affect the production and health of livestock. This study aimed to investigate the change rule of behavior and internal physiological status of goats under heat stress and determine the relationship between these factors. Eight 18-month-old female goats (non-pregnant or non-lactating) were randomly assigned to two environmental control chambers (labeled A and B; n = 4 per in each batch). Four temperatures (26 °C, 30 °C, 34 °C, and 38 °C) and four RH levels (35%, 5 0%, 65%, and 80%) were applied according to a 4×4 experimental design to establish a normal control (23°C, 50%) and the experimental treatments. The duration of each treatment was five days. The behaviors of the goats were monitored in the first two days, the physiological indices were measured, and serum was collected within 3-5 d. The respiratory rate and HSP70 mRNA expression significantly increased at 74.8 < temperature-humidity index (THI) < 76.51; T3 significantly decreased at 80.62 < THI < 82.92; and the behaviors related to metabolism also significantly decreased at 85.24 < THI < 88.74 (including heart rate and rumination). However, the behaviors related to vapor cooling (including respiratory rate, water intake and urination) showed an opposite trend at this stage. In addition, heat stress disrupted the balance of interleukin-2 (IL-2)/interleukin-4 (IL-4). These findings provide a reference for designing suitable environments for goat breeding. •We studied the key THI for goats under heat stress in environmental control chamber.•A THI of 74.80-76.51 is the comfortable environment threshold for goats.•A THI of 85.24 is the limit for goats to relieve heat stress by self-regulation.