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The present study examined the effects of dietary vitamin A (VA) on antioxidant functions, immune functions and production performance in farmed sika deer. Forty healthy male sika deer (initial body weight (BW): 47.07 ± 4.75 kg; 8 months of age) were randomly assigned to four treatments on the basis of BW. The dietary treatments included a basal diet (containing 330 U/kg VA) supplemented with 0 (control), 2500, 5000 or 10,000 U/kg retinol acetate (500,000 U/g, Rovimix A500, Roche, Basel, Switzerland). The results showed that deer fed a diet supplemented with 5000 U/kg VA had higher (p <.05) average daily gains and gain:feed values than those from the control group. VA supplementation significantly increased (p <.05) glutathione peroxidase and superoxide dismutase activities and total antioxidant capacity and decreased (p <.05) the concentrations of reactive oxygen species in the serum. Additionally, serum immunoglobulin A, interleukin-2 and soluble CD8 were significantly increased (p <.05) when dietary VA supplementation was increased from 0 to 5000 U/kg. However, a high dose of VA supplementation (10,000 U/kg) caused decreased (p <.05) concentrations of serum tumour necrosis factor-α and interleukin-1. Deer that received feed supplemented with 5000 U/kg VA had higher (p <.05) dry antler yield than the control deer. The present results indicated that VA supplementation improved growth performance, antioxidant functions, immune functions and dry antler yield. Taken together, the suitable level of VA supplementation was found to be 5000 U/kg (total VA content 5330 mg/kg dry matter) for male sika deer during the first antler growth period. [ABSTRACT FROM AUTHOR]