Most likely, forages are not able to meet the requirements of cattle for several essential minerals regardless of season. In Tennessee, phosphorus, copper, zinc, and selenium are deficient in most grazing situations. While forages are not completely devoid of these minerals their content is often low and varies from season to season and farm to farm. Think of mineral supplements as “bridging the gap” between what our forages can provide to what the animal requires.
Generally speaking, commercial cattle minerals will offer graduated levels of phosphorus, copper, and zinc due to their biological importance and varying concentrations in forage. Phosphorus is part of most, if not all, metabolic processes, making adequate daily phosphorus intake very important. An 1,100 lb beef cow in lactation needs 24 grams of phosphorus per day. Common TN forages provide 19 to 23 grams to grazing cows of that size, leaving the need for one to five grams of phosphorus from a supplemental source. Each percentage unit of phosphorus in a mineral supplement equates to one gram of supplemental phosphorus when consumed at about 3.5 ounces per day.
In situations where surplus sulfur exists in soil, water and forages, copper supplementation becomes more critical. Sulfur is a known antagonist to copper and copper requirement is likely increased in the presence of excess sulfur. Copper in an organic form may not be as susceptible to sulfur antagonism. Therefore, choosing a cattle mineral with increased copper content and a portion from an organic source may be necessary if copper deficiency or sulfur interference is suspected. Copper and zinc are required in a specific ratio to each other, thus when copper is increased it is advisable to increase zinc proportionally.
The level of selenium in a mineral supplement may vary, but is generally from 26 to 52 parts per million, depending on intended consumption level. The amount of supplemental selenium that can fed to livestock has a daily maximum set by the U.S. Food and Drug Administration and exceeding that limit is not an option. That being the case, selenium yeast is often included as source of selenium that is more bioavailable.
Though daily amounts are often only a minuscule part of the total diet, minerals can have a great influence on animal performance and an operation’s bottom line. Stockdale’s carries a complete line of mineral supplements to fit most any forage program.
Royce Townes, Ruminant Nutritionist Tennessee Farmer’s Cooperative