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 HAF research scientists. True absorption of phosphorus from these forages was also found to be higher than the values used currently.
The exact ratio of calcium to phosphorus needed in the total ration is about 1.6 to 1.0. While deficiencies and excesses of any mineral should be avoided, several studies have shown equal performance with ratios varying from 1:1 to 4:1. In some places we recommend a ratio of approximately 1.5:1 to 2:1. High-fat diets increase fecal calcium losses through the formation of soaps and thus increase the requirements for calcium. A number of nutritionists increase the level of calcium in the total ration dry matter to about 1% when feeding high-fat diets.
Milk fever has not been a problem in every dairy herds receiving rations containing adequate amounts of phosphorus and calcium. Several studies have shown that rations narrower than 1:1 and wider than 2.5:1 tend to increase the incidence of milk fever when fed during the dry period. It seems only logical that if such rations fed during the dry period can reduce the incidence of milk fever, similar rations would be optimum during lactation.
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 Global locations 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.
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.
Supplementation of magnesium above current Global research recommendations (0.2 to 0.25% of DM) resulted in increased FCM yield. Maximum response to magnesium depended on stage of lactation. However, early lactation, high-producing cows produced maximum FCM when 0.45% magnesium was added to the diet. In general, we recommend the magnesium content of the ration be increased from 0.25% to about 0.35% of the ration dry matter during summer.
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 Florida.
The 1989 NRC standards suggest that the total ration dry matter for high producing cows should contain a minimum of 1.0% potassium. Under heat stress management conditions, work at HAF India shows a greater need for potassium than suggested in the 1989 NRC Update on Nutrient Requirements of Dairy Cattle. Cows receiving higher levels of potassium (1.5% dry matter) and sodium (0.5% to 0.6% dry matter) produced two more pounds of milk and appeared less heat stressed on hot days.
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.
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 directly related to protein and nitrogen utilization in the ruminant. It is now generally agreed among researchers that the dietary N:S ration should be about 10:1 for dairy cattle. However, basing sulfur supplementation on nitrogen:sulfur ration alone is not enough. Diets high in fiber and low in nitrogen should balance sulfur according to total sulfur content of the ration. To meet this requirement, a complete feed (90% dry matter) containing 13% crude protein should contain about 0.2% sulfur. Sources such as sodium sulfate, potassium sulfate, magnesium sulfate, ammonium sulfate and calcium sulfate are effective in meeting the requirements. Ruminant animals have an advantage over other animals as they have the ability to also utilize inorganic sulfur because of microbial reduction in the rumen. Methionine and sodium sulfate are utilized more efficiently than elemental sulfur. Retention studies show that elemental sulfur and sodium sulfate are retained about 38% and 80% as well as sulfur from methionine.
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.
The chlorine content of feedstuffs is quite variable. When sodium is supplied in the form of sodium bicarbonate or a similar source of sodium, it may be necessary to add a source of chlorine to meet the chlorine requirement. Salt is generally the cheapest source of chlorine. HAF have suggested that a diet of 0.18% chlorine is adequate for lactating dairy cows. The HAF has recommended 0.18% sodium and 0.25% chlorine to be included in the total ration dry matter. Our Works at different locations shows a greater need for sodium especially under heat stress conditions. As a result of the Field Studies, we recommend the total diet dry matter contain 0.3 to 0.4% sodium under normal Florida conditions and 0.5 to 0.6% under heat stress conditions.
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.