Seasonal Variations in the Vitamin a Content of Victorian Butterfat

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Abstract
The total vitamin A potency of butterfat (derived from cheese or butter) was detd. on samples from 3 Victorian districts and from King Island in Bass Strait in 1945 and 1947-48. Carotene was detd. colorimetrically and the Carr-Price test was used for vitamin A. The glycerol dichlorhydrin reagent was too insensitive. Sufficient samples were obtained from west Gippsland and Western District (Victoria) to show the seasonal fluctuation over a whole yr. There is a min. value for total vitamin A potency in the late summer or early autumn when the pastures have dried off and a maximum in the late winter or early spring following the appearance of new growth. Values obtained in 1945 were higher than those in the 1947-48 series. It is suggested that this is a concentration effect in that in 1945 normal quantities of carotene were ingested by the cows and secreted in a much smalle volume of milk than in the same period in 1947. It is apparent that there can be wide variations between values obtained each year at the same time. Comparison of samples of Feb. (1949) butterfats from the areas studied, with one from Orbost in e. Gippsland where pastures remain green and plentiful in late summer, underlined the importance of carotene in the feed and suggested that seasonal fluctuations in this area would be very much smaller than in the rest of Victoria. Comparison with figures in the literature shows that Victorian butterfats compare favorably with those in other parts of the world so far as vitamin A potency is concerned, the normal values probably being of the order of 18,000 I.U./lb. Minimum values of the order of 11,000 I.U./lb. are likely in late summer.