Heat stress is a significant welfare problem for pigs in intensive indoor systems, with pigs' limited sweating capacity making them particularly vulnerable to high temperatures.
Heat stress causes significant acute suffering in pigs. When temperatures exceed comfortable thresholds, pigs display obvious distress — respiratory rate increases dramatically, animals spread on cool surfaces and are reluctant to move, and feed intake falls. Severe heat stress causes hyperthermia, cardiovascular compromise, and death in extreme cases. The inability of pigs to sweat combined with their body shape makes them exceptionally vulnerable to high temperatures. Indoor housing systems without adequate cooling infrastructure expose pigs to heat stress conditions that wild or extensively managed pigs would manage through behavioural thermoregulation including wallowing. The provision of water-based cooling systems, adequate ventilation, and shade in outdoor systems is a welfare necessity during warm weather.