Proper mineral nutrition and supplementation is essential to animal health and high levels of milk production. A lack of attention to the mineral content of the total ration frequently leads to increased disease and reproductive problems. Likewise, too great an emphasis on mineral supplements frequently leads to using a variety of costly supplements with no apparent justification.
Calcium and Phosphorus
Over 70% of the total minerals in the body are calcium and phosphorus. About 99% of the calcium and 80% of the phosphorus of the body are present in bones and teeth. Bone, therefore, not only serves as an organ of structure, but also as a reservoir of both calcium and phosphorus.
Calcium and phosphorus are closely related elements and are laid down in bone in a ratio of 2.2 parts calcium to 1 part phosphorus. This means that a deficiency or an overabundance of either mineral could interfere with the proper utilization of the other. An imbalance of either mineral can cause them to bind with each other and become unavailable to the animal. Studies have also shown that phytate phosphorus, the major form of organic phosphorus occurring in plants, is generally available to the ruminant unless the concentration of calcium in the diet is very high. Utilization of other minerals such as magnesium may also depend on adequate calcium and phosphorus nutrition.
The importance of calcium and phosphorus in dairy rations has been recognized for several years. For a period of time, more minerals were frequently added to the ration than needed. With the adverse publicity about phosphorus getting into lakes and streams, dairymen are now more concerned about having an adequate but minimum amount of phosphorus in the ration. Fecal excretion of phosphorus does depend on the amount of phosphorus in the diet, and it has been shown that for every g/d decrease in phosphorus intake fecal excretion decreases by 0.55 g/d, while for each g/d increase, fecal phosphorus increases by 0.8 g/d.
No longer can we consider only the concentrate and ignore such important feeds as silage, hay and outside mineral mixtures. Availability of the minerals in a forage depend on forage type. As an example, studies have shown that absorption of calcium from corn silage-alfalfa hay diets was higher than when alfalfa was fed alone. Although alfalfa is higher in calcium than corn silage, calcium in alfalfa appears to resist digestion. True absorption of calcium was shown to be lower from alfalfa hay and higher from corn silage than the values currently used by the NRC. True absorption of phosphorus from these forages was also found to be higher than the values used currently.
Vitamin D is associated with calcium absorption and utilization. Since in the presence of vitamin D, calcium is absorbed more efficiently, phosphorus is also used more effectively.
While the bone stores of phosphorus are large, an inadequate supply of phosphorus in the ration will soon lead to borderline deficiencies. Such deficiencies have been identified as reduced appetite, lowered disease resistance, a decline in reproductive efficiency, poor feed utilization and increased incidence of milk fever. Since the two elements are combined in bone, the mobilization of calcium as a result of parathyroid gland actions is accompanied by the incidental mobilization of phosphorus. Therefore, if calcium is not being actively mobilized from body stores, the ruminant depends on a daily intake of phosphorus. Studies have shown that low phosphorus diets for beef heifers have resulted in decreased bone density and mineral content.
Calcium and phosphorus are important in several body functions. Calcium functions in cell equilibrium, heart beat and muscle contraction, and blood coagulation. Phosphorus is present in all living cells of the body as part of many enzyme systems and is essential in the utilization, transfer and storage of energy and in protein metabolism. Phosphorus is also necessary for normal growth and function of rumen microorganisms, especially cellulose digesters. It is also a major blood buffer.
Magnesium
Magnesium functions in many important enzyme systems in the body, as a constituent of bone, and in muscle contractions. Magnesium in the bone probably has a structural function as well as a storage function.
Grass tetany is the common condition associated with a magnesium deficiency in ruminants. Several states (Kentucky, Tennessee, Virginia, Pennsylvania, Maryland, West Virginia, Georgia, Florida, and Alabama) have reported grass tetany in beef cows on wintering rations. The condition occurs more frequently in cattle grazing small-grain pastures in early spring and is usually related to low levels of blood magnesium. Supplemental feeding of magnesium to cows grazing such pastures has been very effective in preventing the tetany syndrome. Dairy cattle receiving grain in addition to such pastures have not been reported as having a problem.
High levels of nitrogen and potassium fertilization have been associated with a greater incidence of the tetany syndrome, and appear to make that magnesium which is present less available to animals. Apparently, increased production of ammonia in the rumen reduces magnesium absorption. This is why you do not need a beef mineral with added potassium during grass tetany season.
Some studies have reported that magnesium has a relaxing effect on animals. This is probably true to the extent that symptoms of a magnesium deficiency include hyper-irritability, increased nervousness, restlessness, muscle twitching, grinding of teeth and excessive salivation.
Potassium
The third most abundant mineral element in the cow's body is potassium. Potassium plays many important roles in the body, It is involved in several enzyme systems, influences muscle activity (notably cardiac muscle), and within the cells it functions (like sodium in the extracellular fluid) by influencing acid base balance and osmotic pressure, including water retention. Potassium is a major mineral component of milk, and is also excreted in sweat, which makes it an important consideration in hot climates such as the southern United States.
Most rations appear to meet minimum potassium requirements. Some ingredients, however, such as brewers' grain, are notably low in potassium. Dairies using large quantities of wet brewers' grain or other feeds low in potassium should consider supplementation. Most forages are quite high in potassium and do not need to be supplemented on beef minerals.
Potassium has been linked to milk fever. High levels of potassium in the diet of dry cows has been related to increased incidence of milk fever. It is recommended to limit the intake of these minerals during the dry period.
Non-specific deficiency symptoms, including slow growth, reduced consumption and efficiency, stiffness and emaciation, have been reported.
Sulfur
Sulfur is an important element in the synthesis of protein because two important amino acids, methionine and cysteine, contain sulfur. These two amino acids are prominent in protein structure and proteins are involved in practically all body processes. In ruminants, sulfur makes up about 0.15% of the body tissue and about 0.03% of milk.
Sulfur is an important anion for close-up dry cows in the prevention of milk fever. Maximum sulfur allowance during the dry period should be between 0.40 and 0.50% of the ration dry matter.
A number of indicators of sulfur deficiencies have been reported. These symptoms are reduced feed intake, slower gains, dullness, lower digestibility, and reduced milk production.
Sodium Chloride (Salt)
Supplemental salt is needed in all current dairy cattle rations fed in Florida. It is usually added as trace mineral (TM) salt or as a packaged, complete mineral in the ration rather than feeding free-choice. A concentrate should contain about 1% TM salt (up to 1.5% with high silage rations) and a complete feed 0.5 to 1.0%. Mixing salt with the other ration components takes advantage of its condiment qualities and assures adequate intake of salt. Dry cows and heifers should have free access to salt and other needed minerals when grain consumption is limited. Salt intake to heavy springers should be limited or blended with the ration to prevent udder edema. If udder edema is a problem, reduce the sodium and potassium content of the ration. Since pasture forages are high in potassium, prepartum cows may need pasture restricted.
Sodium functions in maintaining body fluid balance, osmotic pressure regulation, and acid-base glucose and for amino acid transport and is a controlling factor in nerve transmission. Chlorine is a factor in extracellular fluid. It functions in maintaining the acid-base balance, in osmotic regulation, and in the formation of hydrochloric acid that is important to digestion in the abomasum.
Salt deficiency causes an intense craving for salt, lack of appetite, poor growth, haggard appearance, lusterless eyes, a rough haircoat and lowered milk production. Recovery is rapid with the addition of salt to the diet.
TRACE MINERALS
Animals need trace minerals only in very small quantities. For this reason, salt is sometimes used as a carrier for all the trace minerals.
Trace minerals should not be added to dairy rations indiscriminately. Many rations will contain adequate levels without their addition. If a trace mineral problem is suspected, have your ration tested and make adjustments in the mineral mixture accordingly. Too much of a particular mineral could further antagonize the situation.
Iron
The role of iron in the body is mainly as part of the processes of cellular respiration, as a component of hemoglobin, myoglobin and cytochrome, and in certain enzymes. About 60 to 70% of the iron in the body is found in hemoglobin and 3 to 5% in myoglobin. Traces of copper are required for the utilization of iron in hemoglobin formation.
The need for iron in the diet of the adult dairy cow is estimated at about 100 mg/day. Minimum iron requirement for healthy dairy calves is about 30 mg per day. Calf requirements for dietary iron depends on the iron status of their dam and the calf's body stores. Calves with high iron stores appear to use those stores in preference to dietary iron, while those with lower stores have a higher requirement for dietary iron. Calves fed an exclusive whole milk diet (milk is low in iron) will develop iron deficiency anemia within 2 to 3 months. This practice is desirable in growing veal calves.
Iron deficiency in most dairy cattle rations has rarely been observed. Deficiency symptoms reported in calves include reduced weight gains, listlessness, inability to withstand circulatory strain, reduced appetite and anemia.
Iron deficiency seldom occurs in older dairy cattle unless as a result of severe loss of blood caused by parasitic infestations, injury or disease.
Manganese
Manganese is needed in the body for normal bone structure, for reproduction and for the normal functioning of the central nervous system. It is found stored primarily in the liver and kidneys. Its functions are believed to be in the activation of several enzymes.
Studies with dairy cattle indicate that 40 ppm of manganese in the ration would appear to meet the requirements with a margin of safety. Most dairy rations contain levels of manganese in excess of the suggested requirements. This is especially true where forages are available. Excessive amounts of manganese in the diet increase blood lipids and cholesterol and change the composition of fatty acids in the blood, liver and heart which could affect their normal function.
General symptoms of manganese deficiency include impaired growth, skeletal abnormalities, disturbed or depressed reproductive function, nervous disorders of newborn, and defects in lipid and carbohydrate metabolism.
Copper
Copper is essential to the activity of certain enzymes and, along with iron, is necessary for the synthesis of hemoglobin. It is also an important element for normal immune function. Low copper status may contribute to increased susceptibility to infections such as mastitis. Studies have shown that liver copper stores decrease dramatically in late pregnancy, and reach their lowest point five weeks prior to calving.
A variety of copper deficiencies have been reported, including anemia, retarded growth rate, failure to fatten, loss of body weight, diarrhea, and depigmentation of hair. A characteristic of copper deficiency is a swelling of the ends of the leg bones above the pasterns.
In some state such as ours, Kentucky, soils are high in iron and molybdenum which is a copper antagonist.
Zinc
Zinc is closely associated with a number of enzymes in the body and is a component of the enzyme carboxypeptidase and the hormone insulin. It appears that zinc is required for normal mobilization of vitamin A from the liver. This is verified by the fact that skin lesions and corneal changes in zinc deficient animals are similar to those occurring in animals deprived of vitamin A. In calves, a zinc deficiency has resulted in leg and bone disorders, parakeratosis, impaired vision, and rough and thickened skin.
Zinc deficiencies reported are similar to many other nutrient deficiencies. This observation indicates that zinc is probably involved in the metabolism of one or more nutrients. A number of sources of zinc are available.
Supplemental zinc in organic form has often been beneficial in prevention of, and as a therapeutic aid to, hoof problems of dairy cattle and of foot rot. The role of zinc in maintaining skin tissues and the inflammatory response is probably responsible for this effect.
Cobalt
Cobalt is a component of vitamin B12 and therefore affects blood formation. A nutritional anemia in cattle and sheep living in cobalt-deficient soils has successfully been treated with cobalt. Microorganisms in the rumen of these animals utilize cobalt to synthesize B12.
Adding cobalt and copper to the diet of ruminants has been shown to increase rumen microbial activity and enhance digestion of some forages. A general recommendation for ruminants is 1 mg per day per 1000 lbs body weight. Converted to ppm, a total level of 0.1 to 0.15 ppm in ruminant rations should be adequate to prevent any possible cobalt deficiencies.
Cobalt carbonate has been reported to be a good source of cobalt. Other sources are cobalt sulfate and cobalt oxide.
Iodine
The primary physiological requirement for iodine is the synthesis of hormones by the thyroid gland that regulate energy metabolism. Since iodine functions as a part of the hormone thyroxine and thyroxine is produced by the thyroid gland, a deficiency of iodine causes an enlargement of the gland. Birth of goitrous calves which are sometimes weak or dead and may be hairless is a sign of borderline or definite dietary iodine deficiency even though the cows may appear normal. Milk iodine levels reflect the cow's iodine status. Goiter may develop in nursing calves as a result of an iodine deficiency in the cows' diet.
Iodine toxicity can be a problem where herds are fed too much iodine to prevent diseases such as footrot and lumpy jaw. Symptoms observed and reported are tearing eyes, nasal discharge, bulging eyes, nervousness, rough hair coat including loss of hair, sluggish movement, reduced appetite, tracheal congestion that causes coughing, and lowered milk production. Recovery from iodine toxicity is rapid after the excess iodine is eliminated from the diet.
Excessive levels of dietary iodine result in high blood iodine, excretion of large amounts of iodine in urine and feces, and increased secretion into milk. The Food and Drug Administration (FDA) is concerned with high levels of iodine consistently in milk.
Selenium
The importance of selenium in cattle feeding is continuously being evaluated and has been considered an essential element for cattle since 1957. The current recommendation listed by the NRC is 0.3 ppm. However, in 1993 the FDA lowered the maximum selenium allowance from 0.3 to 0.1 ppm, citing concerns over environmental impact of selenium excreted by animals.
The classic deficiency symptoms reported in the literature for livestock are white muscle disease in calves, stiff lamb disease, and muscle degeneration in pigs, and is related to reproductive problems in cattle such as retained placenta. Selenium plays a key role in the immune system, protecting white blood cells from the toxic by-products known as oxidants resulting from the destruction of pathogens. Both selenium and vitamin E are necessary to prevent white muscle disease and for normal immune response in cattle.
There are many factors which are related to retained placenta. Disease, stress, and nutrition are considered the primary factors related to a high incidence of this problem. In many herds where the incidence is high, the cause or causes need to be determined and eliminated. Diseases should be eliminated by developing a good herd health program with the cooperation of your veterinarian.
Other conditions associated with retained placenta include infections, difficult calving, and hormonal deficiencies. Also, retained placenta occurs more frequently during the colder months and less during the warmer months. As usual, high-producing cows seem to be more susceptible than low-producing cows.
The selenium level of the hair of cattle is a useful indicator of both selenium deficiency and selenium toxicity. Most studies have shown that cattle with hair values consistently below 0.25 ppm probably need supplementation and that over 5 ppm may lead to clinical signs of selenosis.
Trace minerals are required in minute amounts and therefore difficult to justify mixing by an individual for feeding to a given dairy herd. A few dairymen do, however, have complete and/or trace mineral mixtures formulated to their specifications. In doing so, one must remember that mineral mixtures will need to be updated from time to time to keep pace with major ration ingredient changes. This is especially true with the balance of calcium and phosphorus.
Generally, about 60 to 1000 lbs of a complete mineral is needed per ton of finished feed on a DM basis. The ratio of calcium to phosphorus needed in the mineral mixture varies considerably depending on the ingredients used in the feed.
Blood is sometimes used to determine the adequacy or deficiency of a mineral compound in the ration. The normal values of certain mineral elements reported in bovine blood are: calcium, 10 mg %; phosphorus, 4-6 mg %; and magnesium, 2-4 mg %.
The following weight equivalents (Table 5 ) and conversion notes are given for your consideration.
Chelated Minerals
The term chelate comes from the Greek meaning crab's claw. The term is applicable since the mineral is surrounded by a molecule which holds the mineral in a claw-like manner. Chelating and sequestering agents which occur as natural compounds in feedstuffs may increase or decrease mineral absorption and utilization. Commercially-produced chelated minerals may have greater bioavailability than nonchelated forms of the same mineral, especially in nonruminant animals such as the chick and pig, because they are more soluble at the site of absorption. In ruminant animals, chelated minerals have been of less concern due to the rumen microbes and their involvement in digestion.
Currently, several minerals are available in chelated form. Among these are magnesium, copper, cobalt, iron, manganese and zinc. Under certain conditions ruminants have responded to mineral chelates, but it is not clear from the studies reported whether this response is due to the form of the mineral or simply to increased mineral consumption. Zinc-methionine may have an advantage in treatment of footrot and its prevention in problem herds, as well as improved immune response in cattle. However, there is limited research to support these conclusions. Copper availability may be low for ruminants in areas where molybdenum and sulfur are high. Providing copper in a form that does not interact with these antagonists would be advantageous, but it is not clear that copper chelates meet this objective.
While chelated minerals may have a special role under certain conditions and in future dairy cattle feeding programs, information presently available does not consistently show advantages for their inclusion in the diet. Also, some nutritionists find it more economical to add more of a nonchelated mineral rather than use a more bioavailable chelated mineral.
