ABSTRACT
The animals most exposed to trace element deficiencies are the domestic animals, and in particular the ruminants. There is no disagreement concerning the essentiality of chromium, manganese, iron, copper, cobalt, zinc, selenium, molybdenum, and iodine, though chromium is of minor interest in animal nutrition. An enormous amount of literature has accumulated on trace elements and on the problems they create in connection with deficiency diseases and poisonings in animals. Deficiency conditions in ruminants would make livestock farming completely impossible in certain districts were they not corrected. The iron content of sow's milk is much too low to satisfy requirements, and when pigs are confined indoors and not allowed to root about in the soil, a deficiency condition is likely to develop. Interaction between various essential and toxic elements thus plays an essential role in trace element nutrition.
