Cattle Review: July–August

A review paper on heat stress was published by Lemal et al (2023) (10.3168/jds.2022-22727). Heat stress implies unfavourable effects on primary and functional traits in dairy cattle and, in consequence, on the profitability of the whole production system. The increasing number of days with extreme hot temperatures suggests that it is imperative to detect the heat stress status of animals based on adequate measures. However, confirming the heat stress status of an individual is still challenging, and, in consequence, the identification of novel heat stress biomarkers, including molecular bio-markers, remains a relevant issue. Currently, it is known that heat stress seems to have unfavourable effects on immune system mechanisms, but this information is of limited use in the context of heat stress phenotyping. In addition, there is a lack of knowledge addressing the molecular mechanisms linking the relevant genes to the observed phenotype. In this review, the authors explored the potential molecular mechanisms explaining how heat stress affects the immune system and, therefore, increases the occurrence of immune-related diseases in cattle. In this regard, two relatively opposite hypotheses are considered: the immunosuppressive action of cortisol, and the proinflammatory effect of heat stress. In both hypotheses, the modulation of the immune response during heat stress is highlighted. Moreover, it is possible to link candidate genes to these potential mechanisms. In this context, immune markers are valuable indicators for the detection of heat stress in dairy cattle, broadening the portfolio of potential bio-markers for heat stress.