Abstract: The heat stress of pig herds seriously affected pig production, reduced production performance, increased costs and threatened animal health. Accurately evaluating the heat stress level of pig herds were great significance for alleviating heat stress and improving pig breeding benefits. This paper comprehensively summarized and analyzed the hazards of heat stress in pig herds, the evaluation indicators of heat stress, and the environmental heat stress evaluation system based on multiple literatures. It expounded the impact and causes of heat stress on the physiological functions, behavior, immune function and production performance of pig herds; introduced the evaluation indicators of heat stress such as behavioral, physiological and blood indicators of pigs; and summarized the evaluation methods of widely used environmental heat stress evaluation models, such as the Temperature-Humidity Index (THI), Effective Environmental Temperature (EET), etc. The advantages, limitations and improvement directions of different thermal environment evaluation systems were discussed in detail, and it was pointed out that Bjerg's effective environmental temperature evaluation model could more comprehensively evaluate the heat stress level in pig houses and was more suitable for the rapid evaluation of environmental conditions in pig farms. This paper aimed to provide a reference for optimizing the pig house environment and promoting the sustainable development of the pig industry, and at the same time pointed out that in the future, more factors should be comprehensively considered to optimize the existing evaluation system and develop more accurate and convenient evaluation models.

Key words: pig; rehmannia polysaccharides; sows; fattening pigs; reproductive performance; growth performance; plant extracts; feed additive