Influence of grazing intensity on cesium-137 levels in milk

The influence of grazing intensity on radiocesium concentrations in cows’ milk was studied by the accepted rotational grazing system of the Department of Dairy Industry, Utah State University. Three comparable groups of Holstein cows were chosen. The first group was included in the main herd, the second group followed the main herd in the same rotation but always a plot behind, and the third group had no access to pasture. A difference (P < 0.1) based on per cent deviation was found in cesium-137 levels in the milk of the first and second groups. For further statistical analysis, the data for the first and second groups were classified into two periods, based on whether precipitation occurred during sample collection. No significant difference (P > 0.1) was evident during the rainy period, but a significant difference (P < 0.001) was observed for the dry interval. The correlation coefficient for the same periods was significant (P < 0.0001) and positive. For both groups a significant positive correlation (P < 0.0001) was also obtained for strontium-90 versus cesium-137 concentration in milk. The third group, consuming only hay and grain, excreted 9 to 10% of its total intake of cesium-137 into the milk.