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

## TL;DR

This study shows how different heat stress indices affect sow reproduction in a temperate climate, identifying the most effective index for predicting reproductive outcomes.

## Contribution

The study introduces THI6 as the best thermal index for assessing heat stress effects on sow reproduction in temperate climates.

## Key findings

- THI2 and THI6 were linked to more live-born piglets and fewer mummified fetuses at values below 74.
- THI1 was associated with an increased number of stillborn piglets.
- THI6 provided the best overall fit for evaluating heat stress effects on reproductive performance.

## Abstract

This study examined the effects of heat stress (HS) on sow reproduction using 11 different thermal indices in a temperate climate area. The number of live-born piglets, stillbirths, and mummified fetuses per litter were recorded in the farm management software. From January to December 2023, we recorded 13.7 live-born piglets per litter, 1.06 stillborn piglets per litter, and 0.45 mummified fetuses per sow. The mean temperature was 24.08 °C, humidity 63.70%, and air speed 3.2 m/s. The temperature–humidity index (THI) showed that THI2 and THI6 were linked to more live-born piglets and fewer mummified fetuses, with optimal results below a THI of 74. THI1 was associated with an increased number of stillborn piglets. THI6 was the best thermal comfort index for studying the effects of HS on reproductive performance in this study. Sow reproductive outcomes are influenced by specific thermal signals. THI2, THI6, and THI1 are suggested for assessing HS-related reproductive outcomes in sows in temperate climates. Integrating these indices with physiological biomarkers, such as cortisol levels or infrared thermography, could improve reproductive efficiency and animal welfare.

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.