Effect of Dietary Calcium on Secretion of Strontium into Milk

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Abstract
Dairy cows were raised from 5 months to 2 1/2 years of age on either (a) a basal ration that supplied 54 g calcium/day or (b) the same basal ration but supplemented with inorganic, Sr90 free calcium so as to supply 121 g/calcium/day. Animals in both groups consumed essentially the same amount of Sr90 and produced the same amount of milk. The milk from animals on the basal ration contained 8. 4pc Sr90 1. as compared to 4. 4. in milk from animals on the supplemented ration. Therefore the Sr90 secretion into milk was approximately inversely proportional to calcium intake as was predicted from earlier experiments. This relationship was confirmed by a double tracer study using Sr85 and Ca47. The extent to which the same relationship would hold outside the range of calcium intakes and dietary conditions used in the present study is not known. About 50 % of the Sr90 and calcium in the milk originated from the diet and about 50 % from the body of the cow.