Physiological changes and behavioral responses in heat-stressed goats under humid tropical environment

Kacang (K) and Kacang Etawah (KE) cross goats are the major goat breeds that are important for farming livelihood and income and recognized for their tolerance to hot and humid tropical climates. As global warming progresses, the daily maximum temperature (T_max) is predicted to be continuously increased, which will challenge goat production in the future. The objective of this study was to evaluate the physiological and behavioral responses of the goats to the elevated T_max. Six K and six KE female goats were housed in a normal environment (average T_max: 33°C; temperature humidity index (THI): 76 to 86) for 6 weeks and then in a hot environment (average T_max: 38°C; THI: 76 to 92) for 7 weeks. During hot conditions, rectal, rectal surface, and skin temperature, respiration rate, hemoglobin, and cholesterol increased (p < 0.05), whereas glucose blood levels decreased (p < 0.01). Dry matter (DM) intake was lowered (p < 0.01), and DM digestibility was elevated (p < 0.01), whereas drinking water and body water retention were lowered but varied (p < 0.05) during hot weeks. Lying time increased during the hot weeks in both breeds (p < 0.01), whereas lying and ruminating as well as total ruminating time was longer (p < 0.05) in KE goats compared to K goats, which explain the greater (p < 0.05) DM digestibility in KE goats. The effect of the elevated T_max might be less severe since it also depends on the duration of the T_max and the variation of daily THI.