Dietary L-Arginine and Zinc Oxide Nanoparticles Improve Growth Performance, Oxidative Status, Immunity, and Intestinal Integrity Indicators in Heat-Stressed Weaned Rabbits

This study evaluated the effects of adding zinc oxide nanoparticles (ZnNP), L-arginine (L-Arg), or a combination of both to the diets of growing rabbits to mitigate the physiological and productive consequences of heat stress. Two hundred and eighty 35-day-old New Zealand White rabbits were randomly assigned to four experimental treatments, with 70 rabbits per treatment and seven replicates (10 rabbits/replicate). The control group (Ctr) received the base diet without additives, while the diets of the other groups were fortified with arginine (L-Arg; 3 g/kg), zinc oxide nanoparticles (ZnNP; 40 mg/kg), or a combination of both (Arg-Zn). The results showed that the combined Arg-Zn significantly improved weight gain rate, feed conversion rate, carcass weight, and nutrient digestibility compared to the control group (p < 0.05). At the physiological level, we observed increased serum levels of total antioxidant capacity (T-AOC), glutathione peroxidase (GPx), superoxide dismutase (SOD), immunoglobulin G (IgG), immunoglobulin A (IgA), and triiodothyronine (T3), along with decreased levels of malondialdehyde (MDA), alanine aminotransferase (ALT), and aspartate aminotransferase (AST, p < 0.05) in Arg-Zn-fed rabbits. However, adding the Arg-Zn mixture contributed to a reduction in pathogenic bacteria counts and increased the volatile fatty acid (VFA) levels. At the molecular level, the gene expression of the inflammatory cytokines IL-6 and tumor necrosis factor alpha (TNF-α) decreased; however, the gene expression of claudins-1 (CLDN-1), cationic amino acid transporter-1 (CAT-1), mucin-2 (MUC-2), sodium-glucose co-transporter-1 (SGLT-1), and interferon gamma (IFNγ) increased (p < 0.05) in Arg-Zn-fed rabbits. These results suggest that dietary supplementation with ZnNP and L-Arg may serve as an effective nutritional strategy for improving growth performance, antioxidant status, immune function, and intestinal integrity in rabbits exposed to high ambient temperatures.