Heat Stress Assessment Using Multiple Thermal-Comfort Indices and Its Impact on the Reproductive Performance of Sows and Their Offspring in a Temperate Climate

This study aimed to evaluate and compare the effects of HS on sow reproductive performance using 11 different thermal indices calculated from environmental data in a temperate climate. Reproductive records, including live-born piglets, stillbirths, and mummified fetuses per litter, were obtained using farm management software. The overall means for live-born piglets, stillbirths, and mummified fetuses per litter from January to December 2023 were 13.7, 1.06, and 0.45, respectively, whereas the temperature, relative humidity, and air velocity were 24.08 °C, 63.70%, and 3.2 m/s, respectively. Temperature–humidity index (THI): THI2 and THI6 were significantly associated with the number of live-born piglets (p < 0.001) and mummified fetuses (p < 0.05) per litter, with optimal reproductive outcomes observed at values below 74. THI1 was significantly associated with the number of stillborn piglets (p < 0.05). Based on the Akaike information criterion (AIC) values, THI6 provided the best overall fit for evaluating the effects of HS on reproductive performance. Reproductive outcomes in sows respond to trait-specific thermal signals. THI2, THI6, and THI1 are recommended for assessing HS-related reproductive outcomes in sows raised under temperate climatic conditions.