The effect of prolonged breast-feeding on radiocesium retention in young rat.

Reason for the higher retention of 137Cs in the suckling than in the weanling rat was investigated. Rat pups, which were given 137Cs pre viously, were divided into two groups at 21 days of age, i.e., at the normal weaning age. One group weaned to the usual solid diet at this age, whereas the other group was kept under breast-feeding for one to two weeks longer beyond this normal weaning time. The latter group showed higher retention of 137Cs than the former. The dietary difference should be at least one of the most important factors associated with the long biological half-life of this nuclide in the suckling rats. However, the elevated body retention in the rats of prolonged breast-feeding was still less than that in the suckling rats of early days after birth. There fore, the high retention of 137Cs in the normal suckling rats may not be fully explained by the breast-feeding alone.