Dietary Grapeseed Oil Nano-Emulsion Improves Blood Health, Organ Histology, Antioxidant Status, Immune Ability, and Reduces Inflammation in Young Fattening Rabbits Exposed to Thermal Stress

Abstract Heat stress (HS) represents a major environmental impact on rabbits’ health, welfare, and production. Grapeseed oil (GSO) has improved health and growth. However, the mechanism by which it mitigates the negative effects of HS in growing rabbits is still under debate. This study explored the protective role of dietary grapeseed oil nano-emulsion (GON) against blood changes, immune dysfunction, organ histological damage, oxidative stress, and inflammation triggered by HS in growing rabbits. A total of 120 growing rabbits (5 weeks of age and average weight 657.32 g) were divided into 4 groups. The rabbits were administered with different doses of GON: 0 (HS, basal diet), 0.5 (GON0.5), 1 (GON1.0), and 1.5 (GON1.5) mL/kg of diet for 8 weeks under natural heat stress conditions. The results indicated that the GON1.0 and GON1.5 groups exhibited higher body weight values and gains than the other groups (P<0.05), showing a linear relationship with GON dietary levels. A quadratic relationship was observed between FCR and GON, with the optimal dose being 0.7 mL/ kg of diet. The GON1.5 group had higher red blood cell values than the other groups (P<0.05), while all GON groups had significantly reduced leukocyte counts compared to the HS group (P<0.001) in a quadratic manner. GON1.5 and GON1.0 significantly enhanced protein fractions in linear regression analysis. Additionally, ALT, AST, lipid profile, uric acid, LDH, GGT, and total and direct bilirubin were significantly decreased in all rabbits fed with GON (P<0.05) in a quadratic manner. Enriching diets with GON (1 or 1.5 mL) significantly improved antioxidant status (SOD and GPx) and immunity (IgG and IgM) in a quadratic manner. It also resulted in a quadratic decrease in oxidative stress (MDA and PC) and inflammation (IL-6, lysosome activity, and IFN-γ) levels compared to the HS group (P<0.001). There was a quadratic increase in IL-10 and nitric oxide with increasing the GON, and the optimal doses were 0.86 and 0.9 mL/kg of diet. The GON administration maintained organ architecture (liver, spleen, and intestines) and reduced the immune expression of iNOS in liver tissues induced by HS. Collectively, GON (1 mL/kg diet) is an effective feed additive for improving the health and growth of stressed rabbits by supporting antioxidant and immunity functions while reducing oxidative stress and inflammation pathways induced by HS.