Mineral and vitamin supplements are added to livestock diets to correct deficiencies in the primary feed sources. Forages and grains are often deficient in specific minerals depending on soil composition and plant species. Supplements are provided as loose minerals in feeders, compressed salt blocks, or mixed into prepared rations. The specific mineral requirements and deficiency risks vary by species, geographic region, and production stage.
Calcium and phosphorus are required in a ratio of approximately 2:1 for most livestock. Forages are typically adequate in calcium but may be low in phosphorus. Grains are higher in phosphorus but low in calcium, so the ratio must be balanced. Magnesium deficiency causes grass tetany in cattle grazing lush spring pastures high in potassium. Salt (sodium chloride) is provided free-choice year-round, as both sodium and chloride are rarely present in adequate amounts in feedstuffs.
Selenium is deficient in soils across large regions of North America, including the Pacific Northwest, Great Lakes, and Northeast. Selenium deficiency causes white muscle disease in calves and lambs and contributes to retained placenta in cows. Copper deficiency causes poor coat color, diarrhea, and impaired immune function in cattle. However, copper is toxic to sheep at relatively low levels, requiring species-specific supplementation strategies. Zinc is important for hoof health, wound healing, and skin condition. Iodine deficiency causes goiter in newborn animals and is common in goitrogenic areas.
Loose mineral mixes are preferred over blocks for most species because animals can consume the required amount without working against the hardness of the block. Salt blocks are effective for delivering salt and supplemental trace minerals. Medicated supplements incorporate ionophores, dewormers, or growth promotants. Free-choice minerals should be protected from rain and direct sun in a covered feeder that is cleaned regularly.