Nicotinamide Riboside Alleviates Heat Stress‐Induced Intestinal Dysfunction by Enhancing Antioxidant Capacity, Restoring Immune Homeostasis, and Modulating Gut Microbiota in a Boar Model

Heat stress (HS) induces adverse intestinal effects, including morphological damage, immune dysfunction, and microbial dysbiosis. Nicotinamide riboside (NR) supplementation has shown promise in protecting against intestinal injury. This study aimed to investigate the efficacy of NR in alleviating HS-induced intestinal damage in a porcine model. Eighteen boars were randomized into three groups (n = 6): control (CON, thermoneutral), heat stress (HS), and HS with NR supplementation (HS-NR). After an initial feeding phase, the HS and HS-NR groups were exposed to an HS environment (35 ± 1°C) for 2 weeks, while the CON group remained thermoneutral. Intestinal injury was assessed via histomorphology, biochemical parameters, transcriptomics, and microbiome sequencing. We found that NR supplementation significantly restored intestinal morphology and attenuated colonic oxidative stress compared to the HS group. Moreover, NR ameliorated HS-induced immune dysfunction and corrected gut microbial dysbiosis. These results suggest the therapeutic potential of NR as a nutritional intervention to mitigate HS-induced intestinal damage.