Minerals needed in large amounts in the diet are termed "macro minerals." These include calcium, phosphorus, potassium, magnesium, sodium and sulfur. Minerals needed in small amounts are called "micro" or "trace minerals." The micro or trace minerals of most concern are cobalt, copper, iron, iodine, manganese, selenium, and zinc. Methods of mineral supplementation vary. Minerals may be added to a diet individually, mixed in a protein supplement, fed as a separate mineral mix, or a combination of the following methods. Different mineral sources vary in "bioavailability." Bioavailability is defined as the proportion of the ingested element that is absorbed, transported to its site of action and converted to a physiologically active form (Spears et al., 1991) and thus should be more than simply absorption.
Salt: Salt can be included in a complete ration at a rate of 0.3% of the ration (DM Basis) when it is uniformly mixed and separation of ingredients is not a problem. Cattle feeders wishing to use feedlot manure as fertilizer should keep salt levels at 0.2-0.3% of the ration. These levels do not contribute to salt pollution.
Calcium and Phosphorus: A calcium to phosphorus ratio of less than 1:1 or more than 8:1 may reduce performance. The typical calcium to phosphorus ratio is 1.5 to 2.0:1 for beef cattle. However, high levels of calcium from legumes do not appear to depress gains in growing rations (bioavailability of 31-41%). Maximum calcium levels are sometimes included in computer software to prevent limestone being used simply as a "filler" in least-cost computer rations. Calcium carbonate levels in excess of 1% of the ration dry matter may depress performance.
Diets high in fat require additional calcium. A 0.2% calcium addition is recommended when 2-5% added fat occurs (Axe, 1991). Basically, a 1% increase in fat corresponds to a 0.1% increase in supplemental calcium.
Potassium: Cattle require .6 to .8% potassium in the diet. Finishing cattle on high concentrate or all-concentrate rations will probably require supplementation of this mineral. Excessively high levels of potassium interfere with magnesium absorption, resulting in increased incidence of phosphatic urinary calculi.
Sulphur: Sulphur supplementation should be considered when non-protein nitrogen is added to diets of beef cattle. This is also a consideration when high levels of corn silage are fed. A nitrogen to sulfur ratio of 10-15:1 ratio is suggested.
Cobalt: Cobalt requirements have not been set but approach 0.1 ppm on a dry matter basis. The first sign of a cobalt deficiency in cattle is depressed appetite. Because cobalt is a component of vitamin B-12, it's requirement might increase with higher levels of propionate production in the rumen (Strasia and Owens) which corresponds to high grain feeding.
Copper: High levels of sulfur, molybdenum, calcium and zinc can reduce copper absorption. A copper to molybdenum ratio no less than 4:1 should insure adequate copper availability (Petersen, 1987). Milo and barley-based diets contain sufficient concentrations of copper, but corn- or wheat-based diets require supplemental copper (Strasia and Owens).
Iodine: Normally, iodine must be supplemented to a feedlot diet. Cold stress increases the turnover rate of iodine and cause an even greater need for iodine (Strasia and Owens).
Iron: Many trace mineral packages contain iron oxide. This compound is added for its red color and not for its iron content since iron oxide is very low in bioavailability. Other iron sources are needed if there is a deficiency. Ferrous sulfate is high in bioavailability while ferrous carbonate is moderate in bioavailability.
Manganese: High levels of calcium or phosphorus will increase the need for manganese.
Selenium: Most selenium compounds are quite volatile. Have a good air control system and use a gas mask when handing and mixing concentrated selenium pre-mixes.
Zinc: Corn-, milo or barley-based diets are usually zinc deficient. Wheat ranges from being adequate to having levels four times the zinc requirement (Strasia and Owens). Bulls and steers may have more problems with a zinc deficiency than heifers and some strains of Holstein-Fresian cattle will have higher zinc requirements.
Mineral Requirements for Growing/Finishing Cattle
| Calcium, % Phosphorus, % Potassium, % Magnesium, % Sodium, % Sulfur, % Copper, ppm Iron, ppm Manganese, ppm Zinc, ppm Cobalt, ppm Selenium, ppm Iodine, ppm |
0.4-0.6 0.3-0.4 0.6-0.8 0.2-0.3 0.08-0.1 0.05-0.2 6-10 50-100 20-50 50-75 0.1-0.15 0.1-0.2 0.2-1.0 |
All values are 100% Dry Matter Basis.