352. Variations in the carotene and vitamin A contents of certain New Zealand butterfats

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Abstract
1. Chemical estimations of carotene and vitamin A in New Zealand butters from two of the principal butter-making districts of the North Island during the seasons 1935–6 show that the total vitamin A potency was fairly high.2. There were seasonal variations apparently due to nutritional rather than physiological causes. The minimum values (33–37 i.u./g. butterfat) for total vitamin A were found in late summer (February) at the time when the pasture normally tends to dry up, while the peak values (42–53 i.u./g. butterfat) occurred in late winter and spring (July-October). The variations in vitamin A potency with season were in the opposite direction to the variations recorded in the literature for Europe and America. The difference is no doubt due to the practice of stall-feeding in these countries in contrast with the all-the-year-round grazing commonly practised on dairy farms in New Zealand. The spring flush of grass is also later in the season in Europe than in New Zealand.3. The more deeply-coloured Jersey butterfat was only slightly richer in total vitamin A potency than Friesian butterfat.4. Contents of carotene and vitamin A in the fat of colostrum were very high, but reached normal values within 4 or 5 days after parturition.