Oklahoma State University (OSU) Extension Bulletin E-861
"Vitamin and Mineral Nutrition of Grazing Cattle"
opening paragraph:
Typical Mineral Composition of Common Oklahoma Forages
As a general rule, Oklahoma forages do not have severe mineral deficiencies or high levels of mineral antagonists compared to forages in many other states. When excessive amounts of antagonistic minerals are consumed, the availability of other minerals is reduced or completely blocked. Specific antagonists are discussed more extensively in the next section.
Several general principles are evident relative to supplementing minerals to grazing beef cattle in Oklahoma.
1. Almost all forage requires salt supplementation as a source of sodium.
2. Summer native range and prairie hay require phosphorus supplementation.
3. Most grasses common to Oklahoma are marginal to deficient in copper and zinc.
4. It is apparent that good quality legume-based forages require very little if any mineral supplementation with the exception of zinc and salt, depending on the amount of this type of hay provided in the total diet.
5. In addition, fescue forage is usually marginal to deficient in selenium, while Bermudagrass forage is marginal.
Remember that these values represent averages and that variation from location to location can be quite extreme. As discussed in the next section, each of these marginal to deficient minerals has been shown to impact immune function, reproduction, or both. Therefore, it is recommended that producers make certain that beef cows receive supplemental sources of these elements at least 60 days prior to calving through breeding and 30 to 60 days prior to weaning. Similarly, weaned calves and purchased stocker cattle should receive adequate copper, zinc, and selenium through a concentrate feed supplement or free-choice mineral.
Much more detail can be found on this topic in this very detailed paper from the OSU Extension office... If you prefer not to click on links, you can search online for the full article with this search:
Oklahoma State University (OSU) Extension Bulletin E-861
"Vitamin and Mineral Nutrition of Grazing Cattle"
thanks!
Drew