Effect of dietary supplementation of macadamia oil on the growth, immune function, physio‐biochemical components and thyroid activity of growing rabbits

The current research aimed to assess the effects of dietary macadamia oil (MO) on carcass traits, growth performance, physio‐biochemical components, immune function, thyroid hormones and inflammation markers of growing rabbits. A total of 96 growing rabbits were randomly distributed into four treatments, with 24 rabbits in each group. The rabbits were fed a basal diet (control group) or a diet supplemented with MO at 0.5 (MO0.5), 1 (MO1.0) and 2 (MO2.0) mL/kg of diet for eight weeks. The daily body weight gain and feed conversion ratio showed a quadratic improvement with increasing levels of MO, and the optimal dose was 1.25 mL/kg of diet. Increasing levels of MO also had a quadratic effect on hepatic and renal functions. Dose‐response curves revealed that the optimal doses of MO were 1.50, 1.75 and 1.25 mL/kg of diet for total bilirubin, gamma‐glutamyl transferase, and creatinine respectively. A quadratic relationship was observed between the increased levels of MO and tumour necrosis factor‐α ( p = 0.038), interleukin‐6 ( p = 0.014) and immunoglobulins ( p = 0.016 and IgM p = 0.026). Additionally, a linear relationship was observed between the increment in MO levels and both nitric oxide ( p = 0.040) and interleukin‐4 ( p = 0.001). The activities of superoxide dismutase and glutathione peroxidase showed a linear increase with increasing dietary MO content, while xanthine oxidase showed a linear decrease. Total antioxidant capacity showed quadratic improvement ( p = 0.035) with the dietary treatment, with the optimal dose observed at 1.25 mL/kg of diet. The inclusion of MO in the diet had a linear effect on the activity of thyroxine ( p = 0.001). Therefore, supplementation of MO at a dose of 1 or 1.5 mL/kg of diet in growing rabbits' diets can improve growth and carcass traits, sustain thyroid function by supporting immunity, and reduce oxidative/inflammation pathways.