Seasonal variation of carotene and vitamin A in butter-fat and in serum

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Abstract
Over a period of 2 yrs. the average vitamin A content of butter-fat of Ayrshire cows was for pasture-feeding, 31 I. U. and for stall-feeding, 15 I. U./g. of fat. The vitamin A activity of butter-fat due to carotene was 28% during pasture-feeding and 20% or less during stall-feeding. Carotene accounted for 34% of the vitamin A activity during May and June. Serum carotene and vitamin A values during pasture-feeding were 1.35 mg. and 150 I. U./100 ml. and during stall-feeding 0.23 mg. and 31 I. U./100 ml., respectively. Pasture-feeding for only a few hours a day maintains high levels of carotene and vitamin A in serum and butter-fat.

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