Variations in the quality of butter, particularly in relation to the vitamin A, carotene and xanthophyll content as influenced by feeding artificially dried grass to stall-fed cattle

Abstract

THE natural diet of herbivora includes no vitamin A, but the carotene of green plants is transformed in vivo into the vitamin to an extent sufficient to provide for the needs of the animal. Milk from grazing cattle yields butter containing both vitamin A and carotene, the latter (with a small amount of xanthophyll) being responsible for the yellow colour. In the process of converting grass into hay for winter feeding, much of the carotene disappears, and in consequence winter butter is normally much paler than summer butter. A corresponding decrease in vitamin A content need not necessarily occur, since the lactating animal may utilise some of the vitamin A stored in the liver. It is important, therefore, that the vitamin A and carotene present in butter should be ascertained separately. Biological assay indicates the total growth-promoting effect, but this will be a summation of the contributions due to vitamin A and that fraction of the carotene which is transformed into the vitamin in the rat.