Seasonal Variations of Strontium90 and Calcium Levels in Jersey and Holstein Milk

Strontium90, calcium, and S.U. levels were studied in the milk of two breeds of dairy cows. Samples collected in the spring of 1961 showed a consistently-higher level of strontium90 and S.U. values than those collected during the summer. A possible explanation for this is that, in the spring, cows were on feed collected in 1960—when levels of fallout were higher than in 1961. There was a considerable difference between the two breeds in both spring and summer seasons with regard to calcium and S.U. values, but there was also a significant intrabreed variation. It was noted that both calcium and lactose levels are higher in Jersey than in Holstein milk. The possibility of a bound form of calcium is discussed.