Vitamin a Metabolism in Recessive White Canaries
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 β-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 β-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 β-carotene maintained normal vitamin A levels in the liver. These data indicated that conversion rates of β-carotene to vitamin A (as established for poultry) were appropriate;
ii) recessive white canaries were totally unable to utilize β-carotene (based on vitamin A levels in blood, liver and fat);
iii) in comparison to coloured canaries, their efficiency in utilizing retinol was significantly lower. They needed three times the vitamin A intake of coloured canaries to achieve the same vitamin A levels in the liver;
iv) plasma vitamin A levels in coloured canaries did not reflect the vitamin A supply, but this blood level could be used to determine vitamin A status in recessive white birds.
Recommendations of vitamin A supplements for recessive white canaries should be given based on these data.