By placing adult stock animals together with their litters on purified diets at parturition, the effects of many dietary factors on lactation can be tested in 3 wks. On a purified diet, marked leucopenia and granulocytopenia occur in 3 wks.; daily supplements of brewers'' yeast or liver extract improve but do not entirely prevent the blood dyscrasia. Supplementation with low levels of "folic acid" (concentrate) has not produced beneficial effects on the blood dyscrasia or on lactation.