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.热应激（Heat Stress, HS）严重制约了畜禽的生长与生产性能，已成为畜牧业发展的重大阻碍。可逆光暗周期（Reversal Light-Dark Cycles, RLD）是一种低成本且高效的昼夜节律调控手段，然而当前研究尚未证实该方法能否改善热应激诱导的肉鸡肠道损伤。本研究将RLD干预应用于热应激肉鸡模型，观测各组肉鸡的采食行为与生理状态。实验周期为21天，期间采集肠道组织，并通过苏木精-伊红（HE）染色、分子生物学、16S rRNA测序等技术开展相关实验。研究结果显示，热应激不仅会阻碍肉鸡的生长发育，还会升高机体应激水平并损伤肠道功能。经RLD干预后，热应激肉鸡的体重显著提升。此外，RLD可缓解热应激引发的氧化应激，促进褪黑素的释放，并降低皮质醇（CORT）与热休克蛋白70（HSP70）的表达量。RLD还可上调紧密连接蛋白与时钟基因的基因及蛋白表达水平。对盲肠微生物多样性的分析表明，RLD可通过提升粪肠球菌、乳杆菌、拟杆菌门以及瘤胃球菌属的丰度，改变盲肠菌群的群落结构。此外，肠道消化酶与吸收酶的活性也得到显著提升。综上，RLD可通过降低应激反应、保护肠道功能，改善热应激环境下肉鸡的生长性能。