Long-term and Multigenerational Effects of Heat Stress in Pregnant Sows

Heat stress causes seasonal infertility in sows that is characterized by reduced farrowing rates and litter size. In addition, heat stress may cause long-term developmental changes to offspring during gestation that impact their subsequent performance. Sows respond to heat stress during gestation with increased rectal temperature, respiration rate, and skin temperature. An additional coping mechanism is reduced activity that may change body composition (leading to fatter, less-muscled sows). Heat-stressed sows have shorter gestation length and reduced litter birth weight but weaning weights were not changed when sows were heat-stressed during gestation and then moved to thermoneutral for lactation. Heat stress during gestation causes insulin resistance during lactation, but this metabolic state does not seem to affect health, lactation or rebreeding performance. Boars and gilts from sows that are gestational heat stress have a variety of potentially detrimental phenotypes related to body temperature regulation, immune function, carcass composition, and reproduction. Further work is necessary to determine the magnitude of the effects across a variety of facilities and genotypes.