Editors Note: This is a continuation of a three part series of Southern Livestock Standard, related to mineral supplementation and their importance in beef cattle production. Mineral prices have increased dramatically over the last year and this series is designed to help our readers get the most from their mineral program. Information for this series was provided by Johnny Rossi, University of Georgia Extension Service.
In this issue we will look at the microminerals.
There are 10 microminerals required by beef cattle. Seven of the 10 microminerals have established requirements and include iron, manganese, copper, zinc, selenium, cobalt and iodine. The microminerals chromium, molybdenum and nickel do not have an established requirement and are not normally added to mineral mixes fed to beef cattle. Only three of the microminerals (copper, zinc and selenium) are likely to be deficient in grazing beef cattle diets. Micromineral requirements and maximum tolerable levels for beef cattle are shown in Table 2.
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. Most forages in the Southeast have adequate levels of cobalt. However, it is usually added in the mineral mix at approximately 10 ppm to ensure no deficiencies. 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.
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.
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 rarely deficient in cow herds in the Southeast. 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.
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 make the mineral have a dark red color. Iron sulfate is available to the animal and should be used if iron supplementation is needed.
Manganese is required for normal reproduction and fetal and udder development. Manganese deficiency is rare and unlikely to be a problem in grazing cattle in Georgia. 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.
Selenium can be deficient in some areas of Georgia. 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 calfhood diseases like scours. Increased rates of retained placentas and poor reproductive performance are often observed in cows with selenium deficiencies.
Selenium is generally added to mineral mixtures in the form of sodium selenite. Selenium is very toxic and should be used in a premixed form only. The FDA allows selenium to be used at a level not to exceed 0.3 ppm of the dry matter in the total diet of beef cattle. In areas where deficiencies occur, use the maximum legal level. The FDA allows up to 120 ppm to be included in a salt-mineral mixture for free-choice feeding. Selenium deficiency should not be a problem if adequate amounts of selenium are consumed in the mineral supplement. However, the concentration of selenium in the supplement, and the labeled intake must not result in a total intake of more than 3 mg/d. Thus, a mineral labeled for intake of 4 ounces per head per day cannot exceed 26 ppm selenium.
Zinc is marginal to deficient in most Georgia forages. Zinc is a component of many enzymes and important for immunity, male reproduction, and skin and hoof health. Cattle have a limited ability to store zinc and thus zinc 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 is decreased once the ratio of iron to zinc exceeds 2:1. Some feedlots feed supplemental zinc methionine to improve hoof health and thus improve daily gains and feed efficiency.
Vitamins are closely linked to mineral metabolism and absorption. Vitamin A helps skin and mucous membranes stay healthy. Vitamin A requirements usually are met by grazing fresh, green, growing grass. Oxidation deteriorates vitamin A during storage, so diets based on stored feeds should be supplemented with Vitamin A. Supplement diets with vitamin A any time the major portion is stored feeds.
Vitamin A can be added to a mineral mix in a stabilized form to prevent oxidation. The minimum amount should be approximately 120,000 International Units (IU) of vitamin A per pound of mineral. Vitamin A can also be added to the grain mixture to provide 15,000 to 30,000 IU per head per day, depending on individual requirements. An alternative method is to inject 1.5 million IU subcutaneously if a source of dietary vitamin A is not available for 60 to 90 days, although unnecessary injections are discouraged in consideration of National Beef Quality Assurance guidelines.
Vitamin D aids the absorption of calcium and phosphorus from the intestine and their deposition in the bone matrix. Signs of vitamin D deficiency are similar to a calcium or phosphorus deficiency. Most cattle exposed to direct sunlight synthesize enough vitamin D, but cattle in a covered confinement feedlot may need supplemental vitamin D.
Vitamin E is usually present in the diet in sufficient quantities for all classes of cattle; however, a selenium deficiency could lead to an apparent deficiency of vitamin E. Vitamin E can be helpful for short term periods of stress that may occur when calves are co-mingled and transported at weaning.
Other essential vitamins are usually present in adequate quantities in the diet or are synthesized by bacteria in the rumen.
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