Animal products are an significant link in the food chain by means of which radionuclides reach the human population, because the grazing animal is an effective collector of contamination via plants. There are many factors that influence the degree of exposure of farm animals to radionuclides, such as metabolic properties of the specific nuclide, and feeding and management practices. Exposure affects the wellbeing of animals which will generally acquire higher body burdens than will the human populations dependent upon them.
Animals can be a source of radioactivity when their meat and bones are used as food and through their products: for example, milk the and eggs. When 'fresh' radioactive materials enter the organism of the cow, iodine, molybdenum, strontium and barium can be found in the milk. Iodine is the critical substance and cows should be put on stored fodder if pastures have been subjected to radioactive fallout. One survey noted that hen's eggs accumulated a considerable amount of radioactive nuclides - up to 8% of the daily uptake of iodine-131. There was 20-50 times more radioactivity in the yolk than in the egg whites. It was noted that if eggs, laid during the early days of fallout, are immediately washed, much of the radioactivity is removed from the shell.