The relation of the colour and vitamin A content of butter to the nature of the ration fed

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Abstract
When 10-25% of the concentrated foodstuffs in the ration of shorthorn cows is replaced by artificially dried grass no appreciable advantage in depth of yellow color of the butter fat is noted; but 50% of dried grass produces a distinct improvement. The inclusion of 40 lbs. of A.I.V. fodder (modified ensilage) daily in the winter rations raised the yellow color of the butter fat from both shorthorn and Ayrshire cows. There is a marked difference in the yellow color and carotenoid content of the butter obtained from shorthorn and Ayrshire cows even on the same diet. The "ceiling value," above which the yellow color will not rise even on a carotene-rich diet, is much higher for the shorthorn cow than for the Ayrshire; yet the true vit. A content is approximately the same in the butters from the 2 breeds. Samples of goat''s butter, though almost devoid of color, were very similar to cow''s butter in their true vit. A content. The carotene content was less than 5% of that of butter from cows at grass. Thus the color of goats'' butter cannot be used as an indication of its growth-promoting activity in comparison with cows'' butter, most of this activity being due to colorless preformed vit. A and not to carotene.