Recovery of Carotene and Vitamin A from Butter when Cows were Fed Unlimited Quantities of Green Rye

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Abstract
To simulate pasturage conditions, three cows, two Ayrshires and one Holstein, were fed all the fresh green rye they would consume for 16 days. During the last 3 days the carotene ingested daily, and the carotene and vitamin A output in the milk were computed. Dialy intake of carotene averaged 3.507 gm. equivalent to nearly 6,000,000 international units of vitamin A. The butter produced had an average carotene content per pound of 4700 international units, and 8490 units as vitamin A, making a total vitamin A value of 13,190 international units. Of the carotene ingested daily only an average of 0.086% was recovered daily as carotene in the butter and only an average of 0.154% as vitamin A, or a total of 0.24% in terms of international units. The percentage of the total vitamin A value in the butter due to carotene was quite uniform for the three cows, averaging 35.5%. The data seem to indicate that when excessive amounts of carotene are fed, the ratio of carotene to vitamin A in the butter becomes rather constant at about 1 to 2, at least with Holsteins and Ayrshires (high vitamin A and low carotene breeds).
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