Effect of vitamin A and/or E on plasma enzymatic antioxidant systems and total antioxidant capacity of broiler chickens challenged with carbon tetrachloride

This study was conducted to investigate the effect of vitamin A and E supplementation on the antioxidant defences of broiler chickens against carbon tetrachloride (CCl4)-induced oxidative stress at 4 weeks of age. Superoxide dismutase (SOD) and glutathione peroxidase (GPX) activities as well as total antioxidant (TAO) level were analysed before and after CCl4 challenge. Day-old Lohman broiler chickens (n = 144) were randomly assigned to six factorially arranged dietary treatments consisting of vitamin A [1.35 (control) or +20 mg/kg] and vitamin E [20 (control), +40 or +60 mg/kg]. The background of vitamins A and E in the basal diet was 4500 IU (1.35 mg) and 30 IU (20 mg) respectively. At 4 weeks of age, eight chickens from each treatment were bled before interperitoneal injection with 1 ml of CCl4 (mixed with olive oil in a ratio of 1:1) and bled again 24 h post-injection. Vitamin E supplementation decreased (p < 0.05) the activity of both SOD and GPX and showed a tendency (p = 0.07) for TAO reduction. CCl4 attenuated SOD and GPX activities as well as TAO level. The decrease was profound (p < 0.05) in chickens fed the basal diet as well as those fed basal diet supplemented with 20 mg vitamin A. TAO levels behaved similarly when chickens were challenged with CCl4. After CCl4 injection, SOD activities of all experimental groups were equivalent. The presence of vitamin A decreased (p < 0.05) plasma GPX activity in chickens fed the basal diet supplemented with 40 mg/kg of vitamin E. Results of this experiment suggested that vitamin E supplementation elevated antioxidant enzyme activities while vitamin A supplementation attenuated this effect. Vitamin E supplementation improved the total reducing power by maintaining comparable levels of TAO upon CCl4 challenge. Further experiments need to be carried out to investigate the role of vitamin A in oxidative stress and to evaluate the lipid peroxidation products.