Heat tolerance level in dairy herds: a review on coping strategies to heat stress and ways of measuring heat tolerance

Tolerance to heat stress is worth noting considering the constant increase in the ambient temperature and high productivity that elevates the likelihood of heat stress in the dairy herd. Besides exposure to hot temperatures, increase in performance of dairy cows is positively related to heat load which results in heat stress. This necessitates the need to incorporate heat tolerance in the breeding objectives. Measuring heat tolerance is still a challenge and might be complex to assess in the dairy herd. Through regressing phenotypic performance of temperature–humidity index (THI), heat tolerance can be assessed. However, the use of the same THI across region might not be effective due to the differences within and among breeds in either same or different herds. The reason being the differing cow’s (Bos taurus) adaptive and productive response to increasing THI value across different areas. There is vast information about the THI values from the tropics and the temperate regions, however, there is still a gap for THI values for semi and arid places under the pasture-based system. Understanding the coping strategies by the dairy cow to heat stress is important. Various studies have outlined much on the coping strategies but there is still a need to relate the homeostatic and acclimation responses to tolerance to heat stress. This review focusses on discussing the heat stress coping strategies in relation to heat stress tolerance and the ways of assessment in a dairy herd.