The use of dietary calcium intake of dairy ruminants to predict the transfer coefficient of radiostrontium to milk

Transfer coefficients (the equilibrium ratio between radionuclide activity concentration in milk or meat and the daily intake of radionuclide) are widely used to predict the contamination of animal products following the release of radionuclides into the environment. For a transfer coefficient to be generally applicable, its value must be constant for a range of circumstances. However, this is not the case for radiostrontium, the behaviour of which is strongly influenced by that of the homeostatically controlled nutrient, calcium. In this study, a relationship is derived between radiostrontium transfer coefficients and dietary calcium intake which takes into account the observed ratio for strontium:calcium transfer to milk. This relationship is tested against a range of observed data collated from the literature (n = 30) and found to account for 93% of the variability in transfer coefficient values. Model calculations show that a reduction in F-m of at least 40%-60% would be expected if dairy cattle, fed rations typical for well-managed herds, were supplemented with 100-200 g per day. Larger reductions would be predicted when dietary calcium intake is low.