The Effect of Feeding Irradiated Ergosterol to Cows on the Vitamin D Content of Milk

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Abstract
Two Holstein cows in the same stage of lactation, kept under winter feeding conditions, and consuming a good dairy ration, were fed various amounts of irradiated ergosterol dissolved in corn oil, over three-week periods. The vitamin D content of representative samples of butterfat collected during each period was determined biologically, by both the curative line-test and prophylactic bone-ash procedures, and compared with the vitamin D content of butterfat from the same cows when an equal volume of corn oil was fed. The antirachitic potency of the butterfat increased as the number of rat units of vitamin D fed increased—from 0.17 Steenbock rat units per gram during the control period to 2.5 units per gram when 200,000 rat units of the antirachitic factor were fed. This relationship was confirmed by bone-ash values obtained in prophylactic trials. Evidence is presented showing that vitamin D in cod liver oil is more efficient for calcification in chicks than that contained in butterfat from cows fed irradiated ergosterol. The practicability of feeding cows irradiated ergosterol so as to produce milk rich in vitamin D is discussed.

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