Pigs are particularly susceptible to heat stress. Unlike many other species, pigs have very few functional sweat glands and cannot pant effectively. Their primary natural heat dissipation mechanism — wallowing in mud or water — is unavailable in most commercial systems. Climate change is making heat stress an increasingly significant welfare threat in pig production across Europe and beyond.
Physiology of Heat Stress in Pigs
Pigs begin to experience heat stress above approximately 18-22°C (dependent on humidity and pig size). The upper critical temperature for finishing pigs is around 25°C; below this threshold, metabolic heat production can be dissipated; above it, active cooling is required. Sows are particularly vulnerable due to the metabolic heat generated during lactation.
Welfare Impacts
Reduced feed intake and growth rate
Increased aggression as pigs compete for cooler areas
Elevated cortisol indicating chronic stress
Increased respiratory rate (panting) — a welfare indicator of heat load
Impaired reproductive performance: reduced libido in boars, farrowing difficulties in sows, poor weaning weights in piglets
In severe cases: prostration, coma, and death
Cooling Strategies
Ventilation: Adequate airflow at pig level is the most important cooling mechanism in housed systems. High-pressure fogging systems combined with good ventilation significantly reduce effective temperature.
Drip/snout coolers: Drip systems over pigs' necks and snouts allow evaporative cooling — highly effective and well-received by pigs.
Wallowing provision: Outdoor pigs should have access to mud wallows or water sprinklers; wallowing is the most natural and effective cooling mechanism available to pigs.
Shade: Essential for outdoor pig systems; sufficient shade area to accommodate all pigs simultaneously
Feeding management: Restrict feeding to cooler parts of the day; increase feed ration after temperature drops
Water provision: Ensure adequate clean water supply — heat-stressed pigs dramatically increase water intake