Vitamin a Metabolism in Recessive White Canaries

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Abstract In recent years, a possible defect in vitamin A metabolism in recessive white canaries ( Serinus canaria ,) has been repeatedly discussed. It has widely been accepted that a reduced absorption of carotenoids from the small intestine results in an insufficient synthesis of vitamin A. Moreover, the uptake of vitamin A from the lower intestine has also been discussed. The aim of the present study was to investigate the utilization of ß-carotene and vitamin A by recessive white canaries (in comparison to coloured ones) as well as to quantify the accretion of vitamin A in the liver and vitamin A levels in plasma and fat tissues of canaries fed different doses of ß-carotene (≍ 6000iu vitamin A kg −1 diet) vs vitamin A (6000 or 18 000iu kg −1 diet). The results were as follows: i) coloured canaries supplied exclusively with ß-carotene maintained normal vitamin A levels in the liver. These data indicated that conversion rates of ß-carotene to vitamin A (as established for poultry) wer

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