Heat stress leads to a decrease in feed intake and severely affects the feed conversion rate, weight gain, and egg production performance of chickens, causing significant economic losses in the poultry industry. Heat stress reduces the laying rate of hens, decreases egg weight, increases breakage rates, lowers fertilization and hatching rates of breeding eggs, and can lead to a decline in chickens' resistance and immunity, and even large-scale deaths, with 5% of broiler deaths before market being related to heat stress. How to mitigate the adverse effects of heat stress and reduce or avoid unnecessary losses has become a concern for poultry producers.

     The Impact of High Temperature on Feed Intake and Production Performance:

     The optimal temperature range for laying hens is 13-26°C, where the metabolic energy required to maintain body temperature is at its lowest, feed conversion rate is highest, and production efficiency is best. When the environmental temperature exceeds 26°C, the difference between chicken body temperature and environmental temperature decreases, making it more difficult for body heat to dissipate, which triggers a stress response. Under heat stress, the excitement of the feeding center is partially inhibited, while the weakened activity of the digestive tract increases the fullness of the digestive tract, leading to increased water intake to expedite heat dissipation and reduce heat load, which further reduces feed intake. The reduction in feed intake is a protective response of animals to maintain thermal balance under high temperature conditions. In the temperature range of 21-30°C, for every 1°C increase in temperature, feed intake decreases by 1.6%; in the range of 32-38°C, for every 1°C increase, feed intake decreases by 4.6%.

     When feed intake decreases, the intake of energy and protein correspondingly decreases, while the increase in water intake lowers the concentration of digestive enzymes in the intestines, shortening the time that food stays in the digestive system, which affects the digestibility of nutrients to some extent, especially the digestibility of most amino acids, thereby affecting the production performance of chickens. Laying hens show a decrease in egg weight, thinner and more brittle eggshells, rough surfaces, and an increase in breakage rates; broilers experience reduced growth rates and feed utilization. The decrease in poultry production performance caused by increased temperature accounts for about 80% of the total decline, while the performance decline due to insufficient energy intake only accounts for 20%.