Effects of thermal stress on calf welfare.

Cold and heat stress present welfare challenges for dairy calves. The consequences of thermal stress on biological functioning have been well documented, and many housing and management strategies have been evaluated to mitigate those detrimental impacts. In cold weather, mitigation strategies have largely focused on nutritional interventions or limiting heat loss with resources such as bedding or jackets. In hot weather, heat abatement strategies such as supplemental shade, increased environmental air exchange through passive ventilation, and forced air movement through mechanical ventilation have been evaluated. Recently in Wisconsin's continental climate, our group evaluated how 2 aspects of calf welfare-the needs for thermal comfort and social contact (i.e., pair or group housing vs. individual housing)-may align or conflict in winter and summer, respectively. In both seasons, calves pair-housed in outdoor hutches preferred social proximity. When 2 calves shared a hutch, the heat load was greater than for a single calf, which may be beneficial for thermal comfort in winter. In summer, the potential detriments from the additional heat load of 2 calves was mitigated with passive hutch ventilation, which calves preferred. Nonetheless, knowledge gaps remain regarding the impacts of thermal stress on calves' affective states, and much remains unknown about their preferences and motivations for specific thermal stress mitigation resources. Future research to address these gaps could improve our understanding of calf welfare and inform best practices for calf management.