Microminerals
There are several microminerals that beef cattle require; iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), selenium (Se), cobalt (Co), and iodine (I). Only three of the microminerals (Cu, Zn, and Se) are likely to be deficient in grazing beef cattle diets.
Iron
Iron is primarily required for the formation of hemoglobin. Deficiency symptoms include anemia, depressed immunity and decreased weight gains. Iron deficiency is rarely observed in grazing cattle. Iron oxide is often included in mineral mixtures, but is unavailable to the animal and serves only as a coloring agent to give the mineral a dark red color. Iron sulfate is available to the animal and should be used if iron supplementation is needed.
Manganese
Manganese is required for normal reproduction, and fetal and udder development. Manganese oxide is the most common form of manganese used in mineral mixes. Corn-based diets are low in manganese and supplementation is necessary when feeding these diets.
Copper
Copper is the most common micromineral deficiency in grazing cattle. Copper is an important component of many enzyme systems essential for normal growth and development. Deficiency signs include reduced fertility, depressed immunity and reduced pigmentation of hair (black hair changes to red). Dietary deficiencies can occur, but most deficiencies are caused by the consumption of antagonists, which reduces copper absorption. Copper should be supplemented as copper sulfate, tribasic copper chloride or an organic complexed form because copper oxide is very poorly absorbed.
Zinc
Zinc is a component of many enzymes and is important for immunity, male reproduction, and skin and hoof health. Cattle have a limited ability to store zinc and supplementation is always necessary. Zinc absorption is closely tied to copper absorption, and the zinc to copper ratio should be kept at approximately 3:1. In addition, high levels of iron can decrease zinc absorption. Absorption of zinc decreases once the ratio of iron to zinc exceeds 2:1.
Selenium
The soils (and therefore the feeds) in many regions are low in selenium, and a few areas have too much. Unlike most other essential trace nutrients, selenium supplementation offers a narrow range between deficiency and toxicity. Selenium deficiency causes white muscle disease (similar to muscular dystrophy) in newborn calves. Selenium deficiency can also cause calves to be weak at birth and increase their susceptibility to calf-hood diseases like scours. Increased rates of retained placentas and poor reproductive performance are often observed in cows with selenium deficiencies.
Cobalt
Cobalt functions as a component of vitamin B-12, which is synthesized in the rumen by bacteria.
The primary deficiency symptom is loss of appetite and poor growth. High-grain diets require more cobalt than forage based diets, and cobalt should always be included in the mineral mix when feeding grain-based diets.
Iodine
Iodine is an essential mineral for function of the thyroid hormones that regulate energy metabolism.
The first sign of iodine deficiency is goiter in newborn calves. Iodine is usually supplemented as ethylenediamine dihydroidide (EDDI). The maximum legal supplementation of EDDI is 50 mg per head per day. In some instances, EDDI has been included in diets to prevent foot rot; however, the amount of EDDI required to prevent foot rot is much higher than requirements and most likely will not prevent foot rot when included at the legal maximum.
Recap of Mineral Needs
Micromineral nutrition is vital to overall herd health and reproductive efficiency. Supplementation of minerals can occur through a variety of means, including free-choice loose mineral mixes, trace mineral blocks, and fortified energy and/or protein supplements. Controlling daily intake is a constant challenge, but management strategies can be used to ensure proper daily intake of minerals.
This article also appeared in Mid-America Farmer Grower, February 11, 2019.
