Pigs are highly susceptible to heat stress and cannot sweat. Indoor systems without adequate ventilation become dangerously hot in UK summers, causing significant welfare problems.
Heat-stressed pigs experience profound physiological and behavioural distress. The inability to sweat means that pigs rely entirely on respiratory evaporative cooling, which is energetically costly and inadequate in extreme heat. Pigs crowding near water drinkers and away from feeding areas demonstrate the intensity of thermal discomfort. Gestating sows in heat stress abort or farrow prematurely, causing piglet mortality and sow distress. Broiler pig finishing buildings in hot summers can reach temperatures that cause acute heat stroke mortality without adequate ventilation. Unlike dairy cattle heat stress, pig heat stress receives less public attention despite comparable welfare significance.