Heat stress occurs when an animal's heat load is greater than its capacity to lose heat. Cows feel hot sooner than we do. High air temperature, humidity, solar radiation and low air movement contribute to increased risk.
When cows are too hot, they change their behaviour to try to cool down, this often has an impact on production as they spend less time eating and ruminating. Heat-stress can also increase their risk of lameness and incidence of disease, and affect reproduction as well as impacts welfare.