Effect of heat stress on the reproductive performance of sows: comparison of different thermal-comfort indices in a temperate climate

Abstract

Context Heat stress is a major environmental factor negatively affecting animal health and production efficiency of the sow, and causes significant economic losses to the global pig industry. Researchers have developed various thermal indices with different characteristics for assessing the level of heat stress in pigs, including the temperature–humidity index (THI), black globe–humidity index (BGHI), effective temperature (ET), equivalent temperature index of sows (ETIS), and enthalpy (H), among others. Aims The aim of this study was to evaluate the effect of heat stress on reproductive performance by using different thermal indices based on environmental variables in a temperate climate and to compare the goodness-of-fit among them. Methods In total, 2951 sow reproductive records were analysed for a Puebla farm in the northern hemisphere. Key results The overall means for pregnancy, farrowing, and abortion rates over the period from January to December 2020 were 83.1%, 80.67%, and 5.2%, whereas temperature, relative humidity, and air velocity were 24.3°C, 63.0%, and 3.7 m/s respectively. The highest rates of pregnancy and farrowing over the study period were observed in March, while the abortion rate was highest in December. However, the mean daily temperatures exceeded 25°C between March and June, being higher the upper limit of the thermoneutral zone for sows. Many thermal indices have been used to estimate the level of heat stress in pigs, such as the THI, BGHI, ET, and ETIS. We used 11 thermal indices to measure the degree of heat stress affecting fertility traits of animals. Pregnancy and farrowing rates were highest for THI2 and THI6 values, reflecting moderate stress at pregnancy and farrowing periods. Statistically significant differences were found between the THI2, THI4, THI6, and ET values and the pregnancy, farrowing, and abortion rates (P < 0.05). Conclusions Our results showed that the THI2 performs better for evaluating the level of heat stress in sows than do other thermal-comfort indices such as the THI4, THI6, and ET. Implications These results may be useful for accurate assessment of heat stress to mitigate its effects and avoid significant economic losses in sows in temperate climates.