Early-life heat stress exposure impacts dairy calf feeding and thermoregulatory behaviour

Abstract:

Heat stress has well-known influences on dairy calf physiology, but less is understood about its influence on calf behaviour. This study evaluates milk replacer intake, standing activity, and lying behaviours of calves exposed to prenatal or postnatal heat stress or both.

Holstein calves were born to dams experiencing heat stress (HT; shade of a freestall barn) or cooling (CL; shade, fans, and soakers) during late gestation [~44 d before calving, prenatal; mean daily temperature-humidity index (THI) = 78]. They were then subsequently exposed to postnatal heat stress (shade and natural ventilation of an open-sided barn) or cooling (shade of the barn and forced ventilation by fans) from birth to weaning (56 d; mean daily THI = 77; n = 12 per prenatal °— postnatal treatment). Heat stress was confirmed by elevated respiration rates and rectal temperatures in both the prenatal dam and the postnatal calf. Calves were group-housed with automatic milk feeders to measure milk replacer (MR) intake. Calf behaviour was monitored using loggers and video.

Postnatal-HT calves consumed less MR per visit and tended to drink less per hour in the late morning compared with postnatal-CL calves. They also spent more time lying laterally and less time lying sternally in a tucked position overnight. Prenatal-HT calves spent more time standing across the day, especially at night, than prenatal-CL calves.

This study characterized behavioural responses of preweaning dairy calves exposed to chronic heat stress or active cooling during early-life developmental windows.