Toxic levels in the diet affect teeth and bone structure and the use of other nutrients. The entire Great Lakes area and most of the northern section of the United States are subject to an iodine deficiency. Iodine is essential for production of thyroxine, a hormone that regulates metabolic rate. A deficiency causes enlargement of the thyroid gland, a condition called goiter. High nitrates in the rations are thought to interfere with the uptake of iodine by the thyroid gland.
Iodized salt is recommended with high-nitrate feeds and for pregnant cows.
Trace mineralized salt should be an adequate source of iodine except with high-nitrate rations. Iron functions in certain enzyme systems and as a part of the hemoglobin in red blood cells. A deficiency of iron is not likely to occur with adult cattle, under reasonable parasite control, in most areas of the United States. A deficiency of manganese in beef cattle under natural conditions has been reported in only a few areas. This deficiency is found in Washington and other northwestern areas.