Methods for detecting heat stress in hutch-housed dairy calves in a continental climate

Heat stress indicators can be classified as animal-based or environmental with optimal indicators depending on the climate of interest . It is unknown whether previously established heat stress thresholds and THI equations translate well for calves in a continental climate or in individual housing situations. The objective of the present study was to establish associations between, and thresholds for, environmental and animal-based indicators of heat stress in Holstein dairy calves individually hutch-raised across a continental climate summer. A secondary objective was to determine the optimal THI equation for use in dairy calves in a continental climate. These objectives were accomplished through assessing correlations between dairy calf animal-based (i.e., RR, RT, and ST) and environmental indicators (i.e., dry bulb and black globe temperature, air speed, RH, and multiple THI equations), equating goodness of fit, and establishing environmental breakpoints at which physiological variables. In this study we hypothesized that animal-based indicators, particularly Skin Temperature, would be strongly correlated to dry bulb Temperature and Temperature Humidity Index, and that environmental breakpoints would be higher than those previously established for subtropical, group-housed Holstein dairy calves due to the greater temporal variation in ambient environment.