Changes with age in the absorption of radiocaesium by sheep

The absorption of ionic 137Cs was determined in groups of lambs ranging in age from 11 to 59 weeks fed ewes' milk or fresh perennial ryegrass. Absorption was measured as either the apparent (Aa) or true absorption coefficient (At). Whereas Aa declined with age, At appeared not to change with age but was higher (1.00) when the 137Cs was incorporated in milk, than when administered in a way which simulates incorporation into solid feed (0.80-0.85). Previously observed differences in transfer coefficients for animals of different ages appear not to be due to changes in transfer across the gut.