AVIAN CAROTENOIDS 



of absorption, ^ ^' ^ ^ for it has recently been shown that the carotene in 

 lucerne is better utilized than carotene dissolved in arachis oil. ^ * 



The biological activities of the vitamin A precursors are very much 

 the same in hens as in rats. 5 3, 5 5- e o j^ claim that cryptoxanthin is 

 more active in chicks than in rats ^ ^' * ^ has not been substantiated ** 3, « 3 

 and the suggestion, made at the same time, that because of this crypto- 

 xanthin acts as a vitamin in its own right, must be rejected. Patel, 

 Mehl and Deuel ^ ^ have shown that it is converted into vitamin A (in 

 the intestinal wall) and used as such in the chick. There are no reports 

 of examinations of hens' faeces but Seybold and Egle ® * found that the 

 carotenoid distribution in goose droppings was very little different 

 from that in the food (nettle leaves). 



Usually between 15-25 per cent, of the total ingested caro- 

 tenoids ^ 1. « ^ are deposited in the body tissues, although it is claimed 

 that up to 40 per cent, are deposited when grass is the source ; ^ ^ only 

 2-5-7-0 per cent, of the alimentary carotenes are stored unchanged, 

 presumably owing to the major portion being converted into vitamin A. 



As is the case with mammals, carotene may be better absorbed by 

 adult hens from an oily medium ^ ^ but chicks appear to utilize carotene 

 in grass better than in oil. ^ '* It is, therefore, important to note that 

 carotene per se is of paramount importance in chick rearing and this is 

 emphasized by recent work which indicated that in young chickens, at 

 least, preformed vitamin A in the form of cod liver oil is not utilized. ^ 

 On the other hand, bob-white quails utilized vitamin A better than 

 carotene, fed either as lucerne meal or as p-carotene in cotton-seed oil. * ' 

 High doses of vitamin A reduce the carotenoid levels of the plasma 

 and liver of chickens 2'* and turkeys.'^ A similar phenomenon has 

 been noted with shank pigmentation **»' ^ although, in this case, 

 it is not certain whether the " pigment-depressing " factor is vitamin A 

 or not. This fall is in both cases probably due to the fact that in the 

 presence of large amounts of unsaturated lipids (as occur in cod liver 

 oil) the body stores of xanthophylls as well as of vitamin E are used up, 

 for Goldhaber, Zacharias and Kinsey'^ found that supplements of 

 crude xanthophyll extracts fed to chicks on a vitamin E deficient diet 

 prevented the appearance of signs of vitamin E deficiency in about 

 50 per cent, of the birds. The explanation given is that the xantho- 

 phylls exert an antioxidant effect. Food protein levels are important 

 in carotene assimilation for Mann' found that on a low protein diet 

 (13 per cent.) chicks begin to utilize carotene 22 days after hatching, 

 whilst on a high protein diet (17 per cent.) utilization is delayed until 

 35 or 42 days after hatching. 



During the development of the embryo the carotene'* and the 



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