The experiments of Thomas and MacLeod1 have shown that the incorporation of from 30,000 to 60,000 rat units per day of vitamin D as irradiated yeast in the diet of a dairy cow results in the production of a milk high in antirachitic properties. This effect of feeding irradiated yeast has also been reported by Steenbock and co-workers2 and by Wachdel.3 The results of Thomas and MacLeod not only show the effective antirachitic quality of such milk as measured by bioassays on rats, but also indicate that on the basis of rat units fed, irradiated yeast is approximately three times as effective in producing antirachitic properties in milk as viosterol (irradiated ergosterol). The studies of Hess, Lewis, MacLeod and Thomas4 have demonstrated that the substitution of milk produced by cows fed 60,000 vitamin D rat units per day as irradiated yeast for the ordinary cow's milk
WYMAN ET, BUTLER AM. ANTIRACHITIC VALUE OF MILK FROM COWS FED IRRADIATED YEAST. Am J Dis Child. 1932;43(6):1509–1518. doi:10.1001/archpedi.1932.01950070078007
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