734. Factors influencing the vitamin content of milk fat: VIII. The influence of various factors on the utilization of carotene

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Abstract
1. The influence of a number of factors on the utilization of carotene by rats has been investigated. A high dose level equivalent to that derived from pasture by cows has been employed and liver storage of vitamin A has been used as a measure of the efficiency of carotene utilization.2. Utilization was influenced by level of carotene intake, by concentration of carotene in the oil used as vehicle, by the degree of unsaturation of the vehicle and by the presence of non-digestible wax.3. Carotene was better utilized from the rye grass and ‘low cyanide’ white clover than from ‘high cyanide’ clover, but added cyanide had little or no effect on the uptake of carotene from cyanide-free pasture or from a solution in oil.4. In so far as the results of the investigation can be applied to cows grazing typical New Zealand dairy pasture, it seems that factors which may throw some light on the poor utilization of carotene at certain times of the year are (a) small day-to-day variation in the carotene content of the pasture, (b) variations in the ‘ether extract’ fraction of the pasture, and (c) variations in the degree of hydrogenation of the fat in the rumen.5. Insulin and adrenalin appear to have no influence on the levels of vitamin A alcohol in the blood plasma of rats.The results of this investigation form a section of a thesis submitted by one of us (N.A.W.) in partial fulfilment of the requirements for the degree of Ph.D. of the University of New Zealand. The authors are indebted to the Department of Scientific and Industrial Research for a Grant towards this investigation and to Miss Fay Frecklington for technical assistance; one of us (S. Y. T.) is indebted to the Royal Society, the Nuffield Foundation, and the Board of the Dairy Research Institute (N.Z.) for a travelling fellowship during the tenure of which the work reported here was carried out.

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