Dietary 5-Aminolevulinic Acid Alleviates Heat Stress-Induced Renal Injury in Laying Hens by Improving Mitochondrial Quality and Enhancing Antioxidant Activity

This study aimed to evaluate the effects of dietary 5-aminolevulinic acid (ALA) on laying hens to alleviate chronic heat stress-induced renal damage, resulting in improved egg productivity and eggshell quality. A total of 57 white-leghorn laying hens (46 weeks old) were randomly assigned to three groups and fed three experimental diets with different levels of ALA (0, 10, and 100 ppm) for 1 week. The birds in each group were then divided into two subgroups; one of the two subgroups was subjected to heat stress (33 °C for 3 weeks), whereas the other group was maintained at 24 °C. Heat exposure significantly decreased the laying rate and eggshell strength and caused renal damage, whereas ALA supplementation alleviated heat-induced poor productivity and renal damage. ALA increased the renal mitochondrial DNA copy number and downregulated the expression of the cGAS-STING pathway-related genes in the kidneys of heat-stressed hens. Furthermore, ALA upregulated the renal expression levels of <i>NRF2</i> and <i>HO-1</i>, whereas it downregulated those of <i>NF-κB</i> and tended to decrease the content of TBARS in the kidney (<i>p</i> = 0.07). Dietary ALA confers a renal protective effect by reducing heat-induced mitochondrial damage and enhancing antioxidant activity, which may contribute to improved productivity under chronic heat stress.