Editor's Note: The following information is an excerpt from an eXtension.org article written by Bill Weiss, professor and extension dairy specialist with The Ohio State University. It is the fourth of a six-part series on emerging nutrition topics.

Proper mineral nutrition of dairy cows is essential for high milk yields, efficient reproduction, and good health. Meeting the 2001 NRC requirements for dairy cows in most situations will result in adequate status for most minerals. However, for some minerals and some situations, NRC requirements are inadequate and additional supplementation will be necessary.

Experiments conducted after the NRC was published have shown that the NRC requirement for manganese (approximately 15 ppm) is inadequate to prevent a deficiency and the actual requirement is probably 30 to 50 ppm. Other newer data suggest that the NRC requirement for cobalt (approximately 0.11 ppm) may not result in optimal vitamin B-12 status, and cows may need at least twice as much cobalt (approximately 0.25 ppm). However for all other minerals, no evidence is available suggesting that the NRC requirements are not adequate in most situations.

The NRC requirements assume a typical cow, fed a typical diet, and housed and managed under typical conditions. Two situations which are not ‘typical’, but occur very frequently, are excessive intakes of sulfur and potassium.

When diets (including contributions from water) are high in sulfur, substantial modification of copper and selenium supplementation may be needed. If diets are high in potassium, magnesium supplementation should be increased above the standard safety levels.