Use of a gamma- or hard beta-emitting radioisotope to assess milk intake in suckling mouse pups.

A radioisotopic method to assess milk intake during suckling in mice is described. The method is based on the transfer of a gamma- or hard beta-emitting radioisotope from the lactating mother to the litter. The radioactivity of individual pups is determined at intervals by whole-body counting. The transfer of 22Na, 32P as orthophosphate, 51Cr as chromate, and 125I as iodide was examined; 125I showed particularly suitable characteristics. The procedure proved to be simple, accurate and reproducible for the comparison of mild consumption between pups within a litter and between litters. The procedure was suitable for studies using a foster mother.