Heat stress in pregnant sows: Thermal responses and subsequent performance of sows and their offspring.

Seasonal infertility is a significant problem in the swine industry, and may be influenced by photoperiod and heat stress. Heat stress during gestation in particular affects pregnancy, resulting in long-term developmental damage to the offspring. This review summarizes what is known about how heat stress on the pregnant sow affects lactation and her offspring. Sows responded to heat stress during gestation with increased rectal temperature, respiration rate, and skin temperature, and tended to reduce their activity-which may have changed their body composition, increasing the adipose-to-muscle ratio. Heat stress during gestation caused temporary insulin resistance during lactation, but this metabolic state did not seem to affect health, lactation, or rebreeding performance of the sow. Heat-stressed sows also presented with a shorter gestation period and reduced litter birth weight, although weaning weights are not affected when these sows are moved to thermoneutral conditions for lactation. The offspring of gestational heat-stressed sows, however, possessed unique phenotypes, including elevated body temperature, greater fat deposition, and impaired gonad development. Thus, gestational heat stress may significantly impact a herd through its effects on sows and their offspring. Further work is necessary to determine the magnitude of the effects across fa cilities and breeds.