Abstract

The negative consequences of heat stress on the dairy industry are substantial. Elevated ambient temperatures lead to a cascade of detrimental effects, including declines in productivity and elevated morbidity and mortality at various life stages, including pre- and post-weaning, during the dry period, and during lactation. The impacts of elevated ambient temperatures leading to heat stress in lactating dairy cows have been well-established. These include changes in autonomic and behavioral thermoregulation, reductions in dry matter intake, impaired immunity and health, altered mammary gene expression, and reduced milk production. More recently, heat stress implications on non-lactating cattle, for example, the dry dairy cow, have begun to be documented. Heat-stressed dry cows have altered immune function, metabolism, mammary development, and milk production in the subsequent lactation, even after the heat stress insult has been removed. Further, there is substantial evidence of maladaptive responses arising from late-gestation intrauterine hyperthermia, affecting multiple tissues and organs, and persisting as lifelong deficiencies lowering dairy cattle survival and productive potential. As predicted, climate change trends will continue to affect dairy cattle. There is an urgent need to develop practical strategies to effectively identify dairy cattle at risk of heat stress and offer interventions tailored to their age and physiological status to prevent the onset of heat stress in these animals.