Effects of Vitamin A on the Antioxidant Systems of the Growing Chicken

  • Surai, P.F. (Department of Biochemistry and Nutrition, Scottish Agricultural College) ;
  • Kuklenko, T.V. (Department of Physiology, Biochemistry and Nutrition, Poultry Research Institute)
  • Received : 2000.01.18
  • Accepted : 2000.03.08
  • Published : 2000.09.01


The present study was conducted to evaluate effects of the increased dietary vitamin A supplementation on the vitamin A, vitamin E and ascorbic acid concentrations in the plasma and liver and activities of some enzymes in the liver of the growing chicken. One hundred and twenty female chickens at 4 weeks of age were divided in 6 equal groups in accordance with their body weight. They were housed in cages and fed on standard wheat-barley-based broiler diet balanced in the major nutrients. Vitamin A was supplemented in the form of retinyl acetate. Control diet was supplemented with 10 IU/g and experimental feeds were supplemented with 50, 100, 500, 1000 and 2000 IU/g. At days 42 and 56 of the development 8 chickens from each group were killed, plasma and liver were collected for vitamin and enzyme analyses. The increased vitamin A supplementation was associated with its increased accumulation in the liver and with a reduction of ${\alpha}-tocopherol$ concentrations in the plasma and liver. The blood plasma was more resistant to vitamin A concentration changes and the retinol level was elevated only when the vitamin A dose exceeded 100 IU/g feed. Ascorbic acid concentration in the liver was elevated when moderately high vitamin A supplementation was used but significantly decreased at the highest vitamin A dose. Similar changes were observed with glycogen concentration in the liver. Activities of hexokinase, glucose-6-phosphatase and lactate dehydrogenase in the chicken liver were also dependent on vitamin A supplementation, decreasing with highest vitamin A doses. Therefore the observations showed that the vitamin A excess compromises antioxidant system of the growing chickens suggesting that prooxidant activity may be responsible for at least part of the toxicity of vitamin A.

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