Effects of reversing the light-dark cycle on growth performance and intestinal health in heat-stressed broilers

Heat stress (HS) has severely restricted the growth and yield of livestock and poultry and has become a major obstacle to the development of animal husbandry. Reversal light-dark cycles (RLD) are a low-cost and highly effective method to regulate circadian rhythms. However, current studies have not demonstrated whether this method can improve the intestinal injury induced by HS in broilers. The RLD method was applied to HS broilers to observe the feeding behavior and condition of each group. The model was constructed for 21 days. Intestinal tissues were collected, and the experiment was carried out by HE staining, molecular biology, 16S rRNA sequencing, and other methods. This research found that HS not only hinders the growth and development of broilers but also leads to increased stress levels in the body and impairs intestinal function. After RLD treatment, the body weight of HS broilers increased significantly. In addition, it alleviates oxidative stress caused by HS, promotes the release of melatonin, and reduces the expression of cortisol (CORT) and HSP70. RLD also induced increased gene and protein expression of tight junction proteins and clock genes. Analysis of microbial diversity in the cecum showed that RLD could alter the structure of the cecal microbial community by increasing the abundance of Enterococcus faecalis, Lactobacillus, Bacteroidetes, and Ruminococcus. Furthermore, the activities of intestinal digestive enzymes and absorption enzymes were significantly improved. In conclusion, RLD improves the growth performance of broilers under HS conditions by reducing the stress response and protecting intestinal function.