Abstract
Simple Summary Chronic heat stress remains the most detrimental factor for broiler productivity in hot and desert regions. The manipulation of the lighting program is a useful and inexpensive tool to alleviate the negative effects of heat stress on broiler performance. The present study aimed to investigate the beneficial effects of an intermittent lighting (I.L.) program consisting of repeated periods of 1 h light to 3 h dark during a day on broiler performance under chronic heat-stress conditions. The results indicate that applying the I.L. program to heat-stressed broilers relieved the stress indicators and improved the immune response, physiological status, and growth performance of broilers. Therefore, the application of the I.L. program could be used as a beneficial strategy to recover broiler performance during heat-stress conditions. The effects of heat stress on broiler performance and immunological response were explored using lighting-program manipulation as a potential tool. The study included 200 Cobb500 broiler chicks that were one day old at the time of recruitment. The birds were divided into four-compartment groups with similar environments (five cages per compartment, ten chicks per cage). Starting from the fourth day of age, birds of two compartments received a continuous lighting program (23L:1D a day; C.L. groups) while birds of the other two compartments received an intermittent lighting program (1L:3D 6 times per day; I.L. groups). Within each lighting program during 22-42 d of age, one group was subjected either to a thermoneutral temperature at 24 degrees C or heat stress at 35 degrees C. The results reveal that stress biomarkers, especially the plasma concentrations of corticosterone (CORT), tumor necrosis factor-alpha (TNF-alpha), and malondialdehyde (MDA) were relieved by 46%, 27%, and 51%, respectively, in the I.L. treatment groups compared to the C.L. program in broiler chicks subjected to heat stress. The liver function was also improved by 24% and 32% in AST and ALT levels, respectively, in the I.L. program compared to the C.L. program in stressed birds. Furthermore, the I.L. program positively influenced the immune response of the heat-stressed broilers. Eventually, the I.L. program increased the heat-stressed broilers' body weight gain and feed conversion ratio. It can be concluded that applying the I.L. program to broiler chickens can effectively improve their physiological balance and growth performance under heat-stress conditions.