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

Abstract

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 Fm 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.

Generic relationship between calcium intake and radiostrontium transfer to the milk of dairy ruminants

“…The relationship was validated using published data for the transfer of radiostrontium to the milk of dairy cattle [4]. Although we suggested that it should be possible to use the relationship for other ruminant species, by identifying an appropriate value for the calcium content of the milk, there were insufficient data available at the time to allow this hypothesis to be tested.…”

“…However, the use of a single transfer coefficient is not valid for radiostrontium since its behaviour is strongly influenced by that of the homeostatically controlled, essential element, calcium [3,4]. The calcium requirement of an animal varies due to factors such as milk yield and stage of pregnancy [4]. In response to these changing requirements, the calcium intake of dairy animals will change throughout the year.…”

“…(1) with measured values of F m Sr for a species other than cattle. As it has previously been shown that OR milk-diet is similar for most species of animals [3], we have assumed the same value of 0.11 we previously used to estimate F m Sr for cattle [4]. The majority of the goats (57 of the 69) were of the Saanan breed; therefore, a value for the calcium content in milk of 1.26 g kg -1 has been assumed, based on published data for this breed [11].…”

“…Typically, in countries such as the UK [5], the calcium intake by dairy goats will be in the range 15-30 g d -1 whilst that of cows will be 70-150 g d -1 . Recently, we derived a relationship between the radiostrontium transfer coefficient to milk (F m Sr) and the dietary calcium intake of dairy animals [4]: (1) where OR milk-diet is the observed ratio of the comparative transfers of strontium and calcium from the diet to the milk [3], [Ca] milk (g kg -1 ) is the concentration of calcium in the milk, and I Ca the daily intake of Ca (g d -1 ). On the basis of published evidence [3,6], it was assumed that OR milk-diet is a constant when the calcium intake is adequate, and a value of 0.11 was advised for use in the calculation of F m Sr [4].…”

“…In many cases the requirement for equilibrium is a limitation to the use of transfer coefficients, although in the case of milk, equilibrium is usually rapidly achieved. However, the use of a single transfer coefficient is not valid for radiostrontium since its behaviour is strongly influenced by that of the homeostatically controlled, essential element, calcium [3,4]. The calcium requirement of an animal varies due to factors such as milk yield and stage of pregnancy [4].…”