Phosphorus would not be required, on average, for dry mature cows, except when low quality forages such as corn stover or prairie hay are the base feedstuffs, but cows nursing calves are marginal or deficient in phosphorous even with high quality forages. Phosphorous is often added by mixing di-calcium phosphate of other phosphorous source with salt. Trace Mineral Supplementation A general comparison of trace mineral requirements with trace mineral content of feeds suggests common forages typically contain adequate levels of cobalt and iron, although marginal deficiencies may occur. Copper, manganese and zinc are marginally deficient in many feedstuffs. Iodine is commonly deficient and localized selenium deficiencies have been reported in this region.
Most grains are poor sources of trace minerals.
Periodic testing of feedstuffs will point out potential deficiencies. For small herds, however, supplementation may be cheaper than testing. Potential Mineral Problems for Cow Herds in the Cornbelt Documented deficiency problems are common in the cornbelt for only a few minerals. In addition to phosphorous which was mentioned earlier, these include copper, magnesium, and selenium. Copper Many forages contain adequate levels of copper, however a deficiency can still develop.