Variations in the carotene and vitamin A values of the milk fat (butter) of cattle of typical English breeds

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Abstract
The carotene and vit. A in the butter of each of 4 pairs of cows were detd. spectrophotometrically each month from calving to the end of lactation. The cows represented typical English breeds, and were stall-fed during the winter and pasture-fed in Spring and Summer under typical English conditions. Individual variations among cows of the same breed are large but except for abnormally high values of colostrum, the carotene and vitamin A values of the butters are much more dependent on diet than on stage of lactation. Comparison of the summations of carotene plus vit. A values places the breeds in order of vitamin A[long dash]activity of the butters, Guernsey > Friesian > Ayrshire > Shorthorn. The differences between butters of the last 3 breeds are scarcely significant.