Résumé
The administration of various high levels of vitamin A over different time course periods showed no classical signs of toxicity in growing broiler chicks. Feeding different levels of vitamin A [200.000 and 400.000 IU/kg diet] was associated with an elevation of plasma level of the vitamin. However single doses of the vitamin [8.000 and 16.000 IU/bird/day] orally or intramuscularly were less effective in raising the plasma level of the vitamin. Liver content of vitamin A was higher than control through out the entire experimental period, even in the period where the vitamin was withdrawn from the ration. Regardless of the dose and route of administration of vitamin A, plasma B-carotene levels were markedly reduced in response to giving high levels of the vitamin. The pattern of plasma B-carotene level in control healthy chicks showed a marked reduction at the age of 26 days followed by a progressive rise afterward. Feeding vitamin A-supplemented diet to growing chicks for a prolonged period was associated with reductions in plasma cholesterol levels compared with control