Pigs are much more sensitive to heat than other animals because they lack the ability to sweat. Therefore, high temperatures can lead to heat stress which causes poor performance. Heat stress affects both breeding herds and grower-finisher pigs.
Pigs raised in heat stress conditions will have more fat deposits than those reared in cooler environments, due to alteration in nutrient utilization to more fat growth than protein growth when less feed is consumed (Baumgard et al., 2015).
Intestinal integrity, function and metabolism can be compromised due to prolonged heat stress. This may partially be attributed to the reduced nutrient intake or as a consequence of potential changes in digesta flow rates and motility as a result of this reduced feed intake (Pearce et al., 2013).
Heat stress can contribute to leaky gut – therefore increased permeability to bacteria and an inflammatory response in the pig (Baumgard et al., 2015).
Heat stress impacts on semen quality in boars by reducing the motility and increasing the % of abnormal sperm within 2 weeks from initiation of heat stress (Cameron et al., 1980).
Feed intakes are compromised during heat stress in an attempt to decrease metabolic heat production (Baumgard et al., 2015).
Piglets born to heat stressed sows have increased core body temperature making them more susceptible to heat stress after birth (Baumgard et al., 2015).
The metabolism of these piglets is also modified – less muscle and more fat tissue deposits during the growing stage (Johnson et al., 2015).
In breeding herd, heat stress can cause seasonal infertility, and in sows an increased wean-to-estrus interval and failure to express estrus (Bloemhof et al., 2013).
Due to reduction in feed intakes by sows, milk production is depressed, which leads to lower piglet body weight gains (Black et al., 1993).
During heat stress, the mammary gland of the sow may not receive adequate amounts of glucose, resulting in reduced mammary lactose and subsequent milk production other than due to less feed intakes in sows (Baumgard et al., 2015).
Heat stress experienced by sows 14-21 days before insemination can have large negative impact on farrowing rates, and between 7-12 days before insemination on total pigs born per litter (Bloemhof et al., 2013).
Heat stress can also contribute to stillbirths and decreased born alive piglets (Bloemhof et al., 2013).