A review and quantitative assessment of cattle-related thermal indices

Many thermal indices have been developed to assess the levels of heat stress imposed on cattle during hot weather. In this paper, the 16 cattle-related thermal indices are critically reviewed. The primary emphasis is to evaluate each index's coherence to the typical heat transfer characteristics of a cow. Other perspectives including incorporated environmental parameters in the equation(s), experimental data, correlated physiological responses, heat-stress thresholds, scope of application, specific cattle breed involved, and experiment location(s) are also well categorised and discussed. The coherence evaluation indicates that the main effects of environmental parameters on heat stress have been properly reflected, while some interactions between the parameters have been treated differently. Given the variety of the equations used to define the 16 indices and the wide range of information used to develop each index, we conclude that each thermal index is distinct to an extent that it should be selected and employed carefully.