Heat stress is an increasing threat to farmed poultry welfare as summer temperatures rise with climate change. Understanding thermal tolerance limits guides management and building design improvements.
Heat stress in poultry causes acute suffering and chronic welfare deficits. Acutely stressed birds pant continuously, increase water intake, adopt prostrate postures and become lethargic. Severe heat stress leads to respiratory alkalosis, cardiovascular failure and death. Chronic moderate heat stress reduces immune function, increases susceptibility to disease and disrupts normal social behaviour. High-density broiler sheds with poor ventilation are particularly vulnerable to heat emergencies during heatwaves, with limited capacity to respond rapidly enough to prevent mortality events. The welfare cost of chronic heat stress in the months before extreme events is less visible but affects millions of birds.