Influence of Heat Stress During Early, Mid and Late Pregnancy of Gilts

THE increased numbers of large-scale swine confinement units has resulted in more operations farrowing during all months of the year. Previous observations made at this station indicate that sows farrowing during the summer months have smaller litters and lighter weaning weights than those farrowing during the cooler months. The periods of gestation in which high ambient temperatures have the most adverse effects on embryo mortality have not been well established. Edwards et al. (1968) found that gilts exposed to heat stress 1 to 15 days postbreeding had fewer viable embryos at 30 days post-breeding than gilts exposed to the same stress 15 to 30 days postbreeding. Tompkins, Heidenreich and Stob (1967) also reported fewer viable embryos when gilts were stressed 1 to 5 days postbreeding. These data suggest that heat stress may interfere with early development and implantation of the embryo. Heitman, Hughes and Kelly (1951) concluded that exposure of sows approximately 85 days pregnant to high ambient temperatures would result in death of the sow before it would cause death and abortion of the litter.