Pigs are highly susceptible to heat stress due to their limited capacity to thermoregulate — they have few sweat glands and rely primarily on panting and wallowing. In intensive production systems, summer heat represents a significant welfare challenge affecting health, reproduction, and productivity. Proactive heat stress management is both a welfare obligation and an economic necessity.
Physiology of Heat Stress
Pigs have an upper critical temperature of approximately 25–28°C (lower for heavy finishing pigs, higher for piglets). Above this threshold, heat dissipation mechanisms are overwhelmed, and core body temperature rises. Consequences include:
- Reduced feed intake (pigs eat less when hot to reduce metabolic heat production)
- Increased water consumption
- Increased respiratory rate (panting)
- Reduced growth rates and feed conversion efficiency
- Reproductive consequences: reduced libido and sperm quality in boars; delayed return to oestrus in sows; embryonic loss in early pregnancy
- Increased disease susceptibility from compromised immune function
Environmental Temperature Management
Ventilation: Forced ventilation systems with appropriately sized fans and inlets maintain air movement — aim for air velocities of 0.5–1.5 m/s in the pig zone during hot weather. High-pressure spray cooling (evaporative cooling) systems reduce air temperature substantially in hot climates.
Cooling systems: Drip coolers over sow necks during farrowing reduce hyperthermia. Wet-mat systems in aisles allow pigs to cool by conduction. Showers in finishing pens provide evaporative cooling. Wallowing pools in outdoor systems are highly effective — wallowing is a natural thermoregulatory behaviour.
Insulation: Adequate roof insulation reduces solar heat gain — poorly insulated metal-roofed buildings can reach extreme temperatures.
Feeding and Water Management
Feeding during cooler night hours maintains intake during hot periods. Reducing dietary energy density reduces metabolic heat production. Water availability is critical — pigs need 5–10L/day normally, 15–20L/day in heat stress. Multiple nipple drinkers with adequate flow rates (1L/minute minimum) prevent competition for water access.
Monitoring
Temperature and humidity monitoring inside pig buildings enables proactive management. Heat-humidity index (THI) calculations predict risk level. Early morning observation of pig behaviour (lying spread out rather than huddled, panting, reduced activity) provides welfare status indicators. Mortality monitoring for unexpected deaths during heat waves triggers immediate management response.