Minerals are inorganic elements needed for growth and maintenance of bone, osmotic balance, muscle and nerve function, body enzymes, hormones and body cells.
Mineral absorption efficiency varies by mineral and mineral source.
Feeding large amounts of some minerals can reduce the absorption of other minerals.
Macrominerals are needed in higher amounts (grams). They include: calcium, phosphorus, sodium, chlorine, potassium, magnesium, and sulfur.
Decreasing Dietary Cation-Anion Difference (DCAD) in the pre-fresh diet can reduce the incidence of milk fever. Increasing DCAD in the lactating cow diet can reduce metabolic acidosis.
Trace minerals are needed in smaller amounts (milligrams or micrograms). They include: iodine, iron, copper, cobalt, manganese, zinc, selenium, and molybdenum.
Minerals are inorganic elements needed for growth and maintenance of bone, osmotic balance, muscle and nerve function, body enzymes, hormones and body cells. The amounts of different minerals recommended for cows are dependent in part on production, body size, and environment, as well as other dietary factors. Usually, absorbed mineral needs are calculated by adding up the amount needed for each particular body function including, maintenance, milk production, growth, and pregnancy. With the exception of milk fever, it is rare to see a major mineral deficiency but small mineral shortages and/or imbalances can cause health and reproductive problems. Often, these problems aren’t immediately apparent but show over the long term. As production increases, mineral deficiencies become more apparent.
Overfeeding minerals can be expensive and can result in health problems. “Maximum tolerable level” is the maximum amount of a particular mineral that can be fed over a period of time without negatively affecting animal performance. Mineral toxicity problems can occur on commercial dairies, especially when multiple mineral supplements are fed and the entire mineral supply is not accounted for when developing or assessing the ration.
Mineral Absorption and Usage
As with other nutrients, not all of a fed mineral is actually absorbed and used by the cow
In general, mineral absorption is lower than absorption of other nutrients.
Some minerals are absorbed and used more efficiently than others. For instance, about 90% of potassium in grains and forages will be absorbed, but only 20-30% of the magnesium in these feeds is available to the cow.
The availability of minerals varies with source. For example, inorganic mineral supplements in the sulfate form are generally more available than those in the form of oxides. Organic sources of minerals are the most available. With organic mineral sources, such as Zinpro®, minerals are combined with an amino acid (Zinpro® = zinc + methionine) making the mineral easier for the cow to absorb.
Some minerals will decrease the absorption of other minerals. For example, high potassium levels in the diet decrease magnesium utilization.
With many minerals, as their amount in the diet increases, the percentage absorbed decreases. This has been recognized with calcium, zinc, and iron.
Age of the animal can also affect mineral absorption. Generally, older animals have a decreased ability to absorb minerals.
Feeding too much of one mineral can cause a reduction in the utilization of another mineral. The following is a list of known mineral interactions.
Mineral Concentrations in Feedstuffs
The mineral content of both concentrates and forages varies. With forages, fertilization, soil, and plant species primarily dictate mineral content. With concentrates, processing methods can affect mineral content. It is recommended that wet chemistry methods be used for mineral analysis rather than NIRS (near infrared spectroscopy).
Macromineral concentrations are usually reported as a percentage of the feed or ration. Micromineral concentrations are reported in either parts per million (ppm or mg/kg) or milligrams per pound (mg/lb). (1 ppm = mg/lb x 2.2)
Macromineralsare minerals that are needed in higher amounts (grams) by the cow and found in higher concentrations in the body.
They include the following:
Calcium is primarily needed for bones, teeth, nerves, muscles, blood clotting, and body enzymes. Milk contains a large amount of calcium. 98% of the cow’s body calcium is found in the bone. Blood calcium levels are critically important to the cow’s health. Therefore, this level is tightly controlled by the cow’s endocrine system, specifically the parathyroid gland. When the parathyroid gland recognizes that blood calcium is low, calcium reserves are mobilized from the bone and intestinal calcium absorption is increased from the diet. Unfortunately, rapid significant drops in blood calcium cannot always be counteracted by these mechanisms. The result is milk fever.
According to the 2001 NRC, a Holstein dairy cow (1500 pounds (650 kg) body weight, 65 months of age, producing 99 lbs (45 kg) of milk) requires 76.5 grams of absorbable calcium per day or 180 grams of calcium per day. At 59.2 pounds of dry matter intake, the calcium requirement as a percentage of the diet dry matter is 0.67%. Generally, it has been recommended that the calcium:phosphorus ratio be maintained between 1:1 and 2:1. But, according to the NRC (2001), the effects of variations in the calcium-to-phosphorus ratio have been overemphasized. Studies have shown that ratios between 1:1 and 7:1 result in nearly equal performance, provided the animal’s phosphorus requirement is met. Severe calcium, Vitamin D, or phosphorus deficiency results in rickets in young animals or osteoporosis and osteomalacia in older animals. High calcium reduces the absorption of other minerals, especially zinc and phosphorus. Exceeding 1% dietary calcium has been associated with intake depression although diets containing up to 1.8% calcium have reportedly been fed without problems. Because calcium is a cation, feeding extra calcium may alleviate rumen acidosis to a minor extent.
One U.S. survey found that commercial dairy rations averaged 0.48% phosphorus despite the fact that published requirements at that time were much lower. Popular opinion has been that the more phosphorus fed, the better cows will breed back. But, now, because of environmental concerns, efforts are being made to reduce phosphorus excretion while still providing enough dietary phosphorus for optimum performance.
As with all nutrients, cows really require a certain number of grams of phosphorus, depending on the amounts needed for various body functions. But, nutritionists often determine the amount of dry matter that the cow is expected to eat and express the phosphorus requirement as a percentage of the diet. The National Research Council (NRC, 2001) requirements for Holstein cows producing 55, 77, or 99 lbs of milk (25, 35, and 45 kg) are 44.2, 56.5, 68.8 grams of absorbable phosphorus or 65, 83, and 97 grams of total phosphorus per day. With daily dry matter intakes at 44.7, 51.9, and 59.2 pounds, respectively, that would be equal to 0.32, 0.35, and 0.36% phosphorus in the ration. If intakes were 95% of those estimated above, ration phosphorus requirements would be 0.34, 0.37, and 0.38%.
Phosphorus is used for making bone, milk, and muscle. It is involved in many body functions, including energy transfer. Signs of phosphorus deficiency include a reduction in intake, stiff joints, lameness, lost milk, and poor reproduction. There is no evidence that feeding phosphorus beyond requirements improves reproduction. One research summary of phosphorus studies conducted from 1971 to 1998 concluded that reproduction was not improved by supplementing phosphorus above 0.32% of the diet. The early studies that reported poor reproduction fed less than 0.20% phosphorus in the diet. Dietary phosphorus concentrations this low can reduce rumen microbial growth and ration digestibility, having an indirect negative effect on reproduction. A Wisconsin trial with 48 Holstein cows showed no significant differences in reproduction or milk production when cows were fed 0.35 or 0.45% dietary phosphorus for an entire lactation. A German study used rations with 0.33 or 0.39% phosphorus for two lactations plus the dry period and found no differences in milk production (16,500 lbs or 7,500 kg) or reproduction.
One reason that people have balanced for higher levels of phosphorus over the years has been to provide a margin of safety. When a farm has only one ration for the milking herd, nutritionists have wanted to make sure that fresh cows with lower intakes receive enough phosphorus. But, by doing so they have exceeded the phosphorus needs of cows in later stages of lactation. By making high-groups and fresh-cow groups on farms, phosphorus can be more accurately fed. This reduces the total amount of phosphorus fed to the herd each day and reduces phosphorus waste. Feeds vary in their phosphorus content. Greater reliance on feed and forage analyses will help to fine-tune phosphorus feeding.
Blood phosphorus levels often fall below the normal 4-6 mg/dl just before or after calving. This is a hormonal effect, not a nutritional problem. When parathyroid hormone is released to combat low blood calcium, it increases the amount of phosphorus lost in urine and saliva. Cortisol may also depress blood phosphorus levels. Treating hypocalcemia (milk fever) usually results in an increase in blood phosphorus levels. Since low blood phosphorus usually occurs as a secondary problem to milk fever, raising dietary phosphorus levels before and after calving usually has little benefit. More severe phosphorus deficiency (2-4 mg/dl) over a period of time can result in rickets in growing animals or in osteomalacia. A sign of severe phosphorus deficiency is pica, chewing on wood or bone. The maximum tolerable level of dietary phosphorus is estimated at 1.0% of the diet dry matter (NRC, 2001).
Sodium is needed for osmotic pressure regulation, acid-base balance, body fluid balance, and nutrient transport. Sodium is needed for heart function. Sodium is also an important component of the rumen buffering activity of saliva. The cow efficiently uses sodium but little is stored in available body reserves. Therefore, when the diet is deficient in sodium, the negative effect is quickly seen. Signs of sodium deficiency can be seen in 1-2 weeks and include, drinking urine from other cows, licking and chewing on objects, intake decline, and milk production decline.
Generally, grains and forages don’t provide much sodium. Sodium is supplemented, primarily in the form of salt (NaCl). Sodium in the form of salt is completely available to the cow. Its availability from sodium bicarbonate is also high. Cows will consume salt free choice. Normally, required amounts of sodium are added to rations and then salt (in blocks or granular form) is offered free choice. The NRC (2001) recommends 0.22% sodium in the diet as the requirement of a Holstein cow producing 99 lbs (45 kg) of milk and consuming 59.2 pounds (26.9 kg) of dry matter per day. With high levels of sodium consumption, water intake will increase. Maximum tolerable dietary salt concentration is 4% or about 1.6% sodium (DM Basis) for milking cows (NRC, 2001).
Chlorine is important for its role in body metabolism, transport of nutrients, and acid-base balance. Chlorine is also an important part of stomach acids. Chlorine is generally fed to cows in the form of salts, such as NaCl (salt) and KCl (potassium chloride). These salts are quickly made soluble and the chloride ion is absorbed from the cow’s digestive tract. Chloride is a major anion that accepts electrons in the body. Chloride from NaCl (salt) is absorbed with 100% efficiency. Chloride from KCl is absorbed with 95% efficiency. Generally, if the cow’s sodium requirement is met with salt, the chloride requirements will also be met. If some of the sodium requirement is met using something like sodium bicarbonate, another chloride source, such as KCl, will be needed to meet the chloride needs of the cow.
If a cow is deficient in chloride, her body will reduce chloride excretion in the urine and manure in order to conserve chloride as much as possible. Cows given diets low in chloride will readily consume free-choice salt if it is offered. Signs of chloride deficiency include, loss of weight, reduced dry matter intake, and eye defects. Lack of chloride will increase the pH of the blood. The NRC (2001) chloride requirement for a Holstein cow producing 99 lbs (45 kg) of milk and consuming 59.2 pounds (26.9 kg) of dry matter per day is 0.28% of the diet dry matter.
High levels of dietary chloride will hurt the cow more in warm weather than in cold weather. High dietary chloride will increase metabolic acidosis. This is because potassium and sodium losses via sweat and increases in rumen acidosis already make metabolic acidosis more prevalent during warm weather. Chloride is not lost through sweat and cows will eat more salt to replenish sodium. As a result chloride: sodium ratios become unbalanced. This is one reason why sodium and potassium bicarbonate feeding is recommended during heat stress. No maximum tolerable level of chloride has been determined but the maximum tolerable level of salt in the diet is 4% (DM Basis) for milking cows (NRC, 2001).
Potassium is needed for many body functions including, regulation of osmotic pressure, nerve impulses, muscle contraction, transport of oxygen and carbon dioxide, acid-base balance, and body reactions involving enzymes. The cow does not store potassium well, so a daily supply is vital. The NRC (2001) estimates that 90% of the potassium in grains, forages, and minerals is absorbed. Potassium levels in forages grown on heavily manured fields may be quite high. Potassium is usually supplemented as potassium chloride, potassium carbonate, potassium sulfate, or potassium bicarbonate.
Cows deficient in potassium will have reduced water and feed intake, body weight loss, and reduced milk production. Potassium deficient cows may chew on wood or bone and their haircoat may lose its shine. The NRC (2001) potassium requirement for a Holstein cow producing 99 lbs (45 kg) of milk and consuming 59.2 pounds (26.9 kg) of dry matter per day is 1.06% of the diet dry matter, but heat stress may increase this requirement. The maximum tolerable level of potassium is 3% (DM Basis) (NRC, 2001). Potassium fed beyond requirements may decrease magnesium absorption and its excretion by the cow may be detrimental to the environment.
Magnesium is essential for bone growth and maintenance, the nervous system, and body enzymes. Magnesium is also important for fiber digestion in the rumen. Although much of the body’s magnesium is stored in the bone, bone magnesium is not easily available for the cow to use when the dietary magnesium supply is low. So, adequate dietary magnesium is essential for the cow. Blood magnesium levels are used to assess the magnesium status of cows.
Magnesium is normally supplemented in the diet, usually with magnesium oxide. Forages and grains supply a significant amount of the dietary magnesium. Magnesium absorption is generally low. With magnesium oxide, its particle size can have a large effect on bioavailability. The NRC (2001) estimated the efficiency of absorption of inorganic magnesium, such as magnesium oxide, at 50%. Magnesium in grains and forages is generally 20-30% available.
Magnesium (or grass) tetany is a magnesium deficiency commonly seen when cows are primarily fed grass pasture which is growing rapidly under cool spring or fall conditions. Cool weather and potassium fertilization will reduce the amount of magnesium found in growing plants. When rumen pH is above 6.5, magnesium absorption is reduced. The high potassium content, high rumen ammonia from soluble protein, and low starch levels often found with pasture-based diets all tend to increase rumen pH. High dietary nitrogen or potassium can directly reduce magnesium absorption. Feeding ionophores, such as Rumensin® or Bovatec®, can increase magnesium absorption but ionophores are not approved for all cows in all countries. The signs of magnesium tetany (deficiency) include, nervousness, restlessness, twitching of muscles, grinding of the teeth, and profuse salivation. Magnesium tetany also occurs around calving time.
The NRC (2001) magnesium requirement for a Holstein cow producing 99 lbs (45 kg) of milk and consuming 59.2 pounds (26.9 kg) of dry matter per day is 0.20% of the diet dry matter. Major exceptions are in situations where high dietary potassium and/or high non-protein nitrogen levels decrease magnesium absorption. In the latter case, higher levels of dietary magnesium (0.3-0.35%) are recommended.
Excessive magnesium consumption (above 0.5% of the ration DM) can result in cows getting black diarrhea. The maximum tolerable level of magnesium was 0.4% in the 1989 NRC. However, this has changed in the 2001 NRC, which states that the cow can excrete large amounts of magnesium in the urine so magnesium toxicity is not a problem.
Sulfur is acomponent of amino acids, specifically methionine, cysteine, homocysteine, and taurine, and B vitamins, specifically biotin and thiamin. The rumen microbes need sulfur in order for them to manufacture amino acids and protein from non-protein nitrogen and to manufacture biotin and thiamin.
Requirements for sulfur have been developed primarily based on the needs of the rumen microbes. It is generally recommended that the ratio of nitrogen:sulfur be between 10:1 and 12:1 in the diet. According to the 2001 NRC, milking cows should have 0.20% sulfur in their diets. Dietary sources of sulfur include: protein, methionine, cysteine, methionine hydroxy analog, sodium sulfate, potassium sulfate, magnesium sulfate, ammonium sulfate, and calcium sulfate. Most of the sulfate consumed by the cow is changed into sulfide by the rumen microbes. It is then either incorporated into microbial protein or it is absorbed and oxidized to sulfate in the liver. ulfur in the form of sulfate or sulfide is utilized better than elemental sulfur.
High levels of dietary sulfur can inhibit the absorption of other minerals, particularly copper and selenium. The signs of sulfur toxicity include blindness, muscle problems, and coma. The cow’s breath will smell of hydrogen sulfide (like rotten eggs). A high level of dietary sulfur (0.50%) has been found to cause polioencephalomalacia (PEM), which is related to thiamin deficiency. The first signs of PEM include dullness, blindness, muscle tremors, and a backwards bending of the head. More extreme symptoms include circling, head pressing, convulsions, and death. The maximum tolerable level of dietary sulfur according to the 2001 NRC, is 0.40%. Drinking water may contain sulfur at levels that can be harmful. Reduced feed and water intake has been observed in cases where water sulfur content was 1100 ppm (.11%).
Dietary Cation-Anion Difference (DCAD)
Decreasing DCAD for Pre-fresh Cows
Fresh cows need a lot of calcium to make colostrum and milk. Hormones normally work to mobilize calcium from the cow’s bones and to increase the efficiency of dietary calcium absorption at calving time. The hormones keep blood calcium at normal levels (9-10 mg/dl). nfortunately, these hormones are inhibited when diets high in potassium or sodium are fed. This situation frequently occurs when feeding diets high in grass grown on heavily manured fields or alfalfa. Forages grown under drought conditions frequently have high potassium contents. Potassium and sodium are cations like calcium.Cations alkalinize the blood making its pH higher. High potassium will also decrease the availability of dietary magnesium. Low blood magnesium will prevent the cow’s system from recognizing low blood calcium levels, further decreasing hormone production, calcium mobilization, and calcium absorption.
One way to make the cow’s blood acidic is by adding anionic products to the diet during the last three weeks before calving. This method should be used when low potassium forages are not available. In the past, sulfates such as ammonium sulfate, calcium sulfate (gypsum), and magnesium sulfate were used as anionic sources. Now, chlorides such as calcium chloride, magnesium chloride, and ammonium chloride are recommended over sulfates because they have been shown to be more effective. There are also commercial anionic products, for example, Bio-Chlor® and Soy-Chlor®.
To effectively use anionic products, first analyze forages for calcium, magnesium, sodium, potassium, chloride, sulfur, and phosphorus. Adjust the diet so that the dietary cation-anion difference (DCAD) is –5 to –10 mEq/100 g (-23 to –45 mEq/lb). DCAD is calculated as [(Potassium (K) + Sodium (Na) – (Chloride (Cl) + Sulfur (S))]. Most diets will need 0.6 to 0.8% chloride to significantly decrease DCAD. When using anionic products, maintain diet calcium at 1-1.5%. Dietary magnesium should be at 0.40%, phosphorus at 0.35%, and sulfur at 0.45%.
The goal when lowering DCAD is to make the cow’s blood more acidic. Urine pH can be used to monitor blood pH. Average urine pH during the last week before calving should be between 6.0 and 6.5 for Holsteins and for Jerseys, 5.8 to 6.2. If the average urine pH falls below 5.5, the cow’s blood is too acidic and dry matter intake will be decreased. It is best to measure urine pH about 4 to 6 hours after feeding. Increase or decrease dietary chloride according to the urine pH.
Increasing DCAD for Lactating Cows
Recent research has shown that we need to be concerned not only with rumen acidosis but also with metabolic acidosis. We know that the rumen microbes suffer under acidic conditions. The cells of the cow’s body also have trouble when they encounter too much acid. Acids change enzyme activities and affect the structure of molecules. The cow’s regulation of blood pH is almost as important as her need for oxygen. Although cows do not have many sweat glands, they will sweat a certain amount during hot weather and lose electrolytes. Heat-stressed cows lose a lot of potassium and they can become potassium deficient. The loss of potassium increases blood acidity. Researchers have found that they can increase blood pH by increasing the dietary cation-anion difference (DCAD). Raising DCAD increases the ability of the cow’s blood to buffer acids and this raises blood pH (decreasing acidity).
Researchers have found positive milk production responses when they have raised DCAD to 35-45 meq/100 g DM. The author has been able to achieve 30-35 meq/100 g DM on commercial dairies in northeastern U.S. and has seen positive results. With the current mineral sources available, it is difficult and costly to achieve 35-45 meq/100 g DM. A study conducted on a commercial dairy in Florida only raised DCAD from 19 to 25, yet successfully raised milk production by 3 pounds (89.5 vs. 86.5 poundsor40.7 vs. 39.3 kg). Generally, it will require 1.6-1.8% dietary potassium, 0.75-1 pound (0.34-0.45 kg) of added buffer (sodium bicarbonate or sodium sesquicarbonate), and 0.40% dietary sodium to significantly increase DCAD. Chloride levels also need to be controlled (<0.40%). Therefore, potassium carbonate will probably need to be used rather than potassium chloride (a more popular source of potassium in the feed industry).
Trace Minerals (or Microminerals)
Trace Minerals (or Microminerals) are minerals that are needed in smaller amounts (milligrams or micrograms) by the cow and found at lower concentrations in the body.
They include the following:
Trace minerals facilitate enzymatic reactions in the body. Often, the status of a particular trace mineral in the body is measured by the activity of the enzyme associated with it rather than measuring the amount of the actual mineral in the blood. For example, the activity of glutathione peroxidase indicates an animal’s selenium status. Typically, the amounts of trace minerals in feeds and forages are not routinely measured in the lab and “book values” are relied upon when balancing rations. Because of this, trace mineral problems may not be readily apparent, especially in the case of mineral interactions.
Vitamin B12 contains cobalt. The rumen microbes can produce vitamin B12 as long as they are supplied with an adequate amount of cobalt. Vitamin B12 is needed in the liver for the cow to make glucose from the volatile fatty acid, propionate, produced in the rumen. In order to assess cobalt status in an animal liver vitamin B12 content is assessed. Levels less than 0.1 microgram/gram wet weight indicate a problem (NRC, 2001). Sources of supplemental cobalt include cobalt chloride, cobalt nitrate, cobaltous carbonate, and cobaltous sulfate. The NRC (2001) cobalt requirement for dairy cows is 0.11 ppm (mg/kg) and the maximum tolerable concentration is 10 ppm (mg/kg). There is inconsistent research evidence showing improvements in fiber digestion when higher levels of cobalt are fed (0.25 to 0.35 ppm (mg/kg)). Some have speculated that cobalt may increase associations between the rumen microbes and forage particles. Signs of cobalt deficiency include poor intake, weight loss, anemia, weakness, rough hair coat, and poor resistance to infection.
A number of enzymes in the body contain copper. These enzymes are needed for electron transport, for bone and tissue development, for hemoglobin (for oxygen transport), and for immune function. Since copper is needed for hair pigment, loss of hair color (or hair turning brownish-red or gray), especially around the eyes, is a key sign of copper deficiency. Sulfur, molybdenum, iron, zinc, and calcium can all reduce copper absorption if they are fed at high levels. When evaluating rations for copper, it is important to not only analyze feeds and forages for copper but also for molybdenum, sulfur, and iron. At least a 6:1 copper:molybdenum ratio is recommended. Selenium may improve copper absorption.
The NRC (2001) requires 0.5 mg/day absorbed copper for cows less than 100 days pregnant, 1.5 mg/day for 100-225 days pregnant, and 2.0 mg/day for more than 225 days pregnant. The NRC (2001) copper requirement for a Holstein cow producing 99 lbs (45 kg) of milk and consuming 59.2 pounds (26.9 kg) of dry matter per day is 11 ppm (mg/kg). It is noted that higher levels may be needed when high dietary molybdenum, sulfur, or iron reduce copper absorption. Copper retention is high (50-60%) in young calves but once the rumen develops, copper absorption is greatly reduced (1-5%) (NRC, 2001). Copper is generally supplemented in oxide, sulfate, and carbonate forms, although copper oxide is poorly utilized.
Copper toxicity is more common than many other mineral toxicities. Liver copper can increase well in advance of any outward signs of toxicity including jaundice and hemoglobin problems. The NRC (2001) maximum tolerable level of copper is 40 ppm (mg/kg) except if the diet contains a large amount of molybdenum. Different species and breeds use copper with different efficiencies. For example, when Jersey and Holstein cows were fed the same diet, the livers of the Jerseys was higher in copper. Jersey cows may be more likely to experience copper toxicity. Sheep are highly susceptible to copper toxicity.
Iodine is needed to make the thyroid hormones involved in regulating basal metabolism rate and the use of energy in the body. The NRC (2001) iodine requirement for a Holstein cow producing 99 lbs (45 kg) of milk and consuming 59.2 pounds (26.9 kg) of dry matter per day is 0.44 ppm (mg/kg). Compounds found in soybean, cottonseed meal, canola meal, cabbage, and turnips can reduce iodine retention or usage. For this reason the 1989 NRC recommended 0.6 ppm (mg/kg) as the iodine requirement. Iodized salt is often used to meet iodine requirements. The Great Lakes region and Pacific Northwest of the U.S. are known to be low in iodine. An enlarged thyroid gland (goiter) is usually the first sign of iodine deficiency. Iodine toxicity can occur at 5 ppm (mg/kg) dietary DM. Signs of iodine toxicity include runny eyes and nose, excess saliva production, and coughing.
Iron is a component of hemoglobin, part of the blood necessary for oxygen and carbon dioxide transport in the body. Enzymes used for electron transport in the body also require iron. Anemia, a paleness and weakness associated with low hemoglobin, is a sign of iron deficiency. Poor immune function is also associated with iron deficiency. Feeds and forages typically contain enough iron for the cow. Calves fed only milk may require iron supplementation. The NRC (2001) requirement for a young calf is about 150 ppm (mg/kg). The NRC (2001) iron requirement for a Holstein cow producing 99 lbs (45 kg) of milk and consuming 59.2 pounds (26.9 kg) of dry matter per day is 17 ppm (mg/kg). Normally, dietary iron concentration will run between 100-250 ppm for lactating cows. High concentrations of iron (>1000 ppm (mg/kg)) can reduce the absorption of other trace minerals such as, copper, zinc, and manganese, resulting in deficiencies. The NRC (1980) recommended 1000 ppm (mg/kg) as the maximum tolerable concentration for dietary iron. But, some research studies have shown problems with the absorption of other trace minerals at lower levels (250-500 ppm). Excessive iron may also increase oxidative stress (damaging body cells), increasing the need for anti-oxidants such as selenium and vitamin E.
Manganese is needed for enzymes that produce bone and cartilage. It is needed for reducing the oxidative stress that damages body cells. Manganese is also necessary for normal reproduction. Manganese deficiencies have resulted in increased number of silent heats, lowered conception rates, and deformities in calves at birth. The NRC (1989) suggested 40 ppm (mg/kg) manganese for all dairy cows but an absolute requirement was not given. Large amounts of calcium, potassium, or phosphorus in the diet can decrease the availability of dietary manganese. High iron levels have reduced manganese retention in calves. The NRC (1980) recommended 1000 ppm (mg/kg) as the maximum tolerable concentration for dietary manganese. Manganese toxicity is rarely seen but is evidenced by poor growth rates and poor feed intake.
Molybdenum is needed for good animal health and is a part of enzymes in milk and body tissues. But, it has been difficult to show molybdenum deficiencies in cows so supplemental molybdenum has not been recommended. High levels of molybdenum can reduce the absorption of copper and sometimes phosphorus. So, molybdenum toxicity is usually copper deficiency. The maximum tolerable concentration of molybdenum is 10 ppm (mg/kg) (NRC, 1980). With excessive molybdenum consumption, levels of xanthine oxidase in milk will increase.
Selenium is a part of the enzyme, glutathione peroxidase, which functions to reduce oxidative stress and cellular damage. Selenium is also found in other enzymes and proteins in the body. Adequate selenium is important for proper functioning of the immune and reproductive systems and for proper growth. A sign of selenium deficiency is white muscle disease (nutritional muscular dystrophy). This causes weakness in the legs and joints and muscle tremors. Death results from heart failure. Selenium passes through the placenta to the calf. If the dam receives inadequate selenium, deficiency symptoms may be seen in the calf.
Supplementing selenium to animals in geographic regions with low soil selenium has reduced the incidence of retained placentas, metritis, cystic ovaries, mastitis, and udder edema. In the U.S., regions east of the Mississippi River and west of the Rockie Mountains are low in selenium. Sodium selenite and sodium selenate are used as supplemental selenium sources.
According to the U.S. FDA, no more than 0.3 ppm (mg/kg) supplemental selenium can be fed to cows. The NRC (1989) requirement for selenium is 0.3 ppm (mg/kg) in the diet. But, the experiments relied upon to make this recommendation actually supplemented 0.3 ppm (mg/kg) selenium and the total dietary level of selenium ranged from 0.35-0.4 ppm (mg/kg) (NRC, 2001). The amount of selenium required is partly dependent on dietary vitamin E. Low levels of vitamin E increase the amount of selenium needed. High calcium or sulfur in the diet may decrease selenium absorption.
According to the 1989 NRC, the maximum tolerable level of selenium in the diet is 2 ppm (mg/kg). Alkali disease and blind staggers are associated with selenium toxicity. Signs of selenium toxicity include, hair loss, lameness, and weight loss.
Zinc is a part of many different enzymes that perform a variety of functions in the body. Nutrient metabolism, reproduction, immune function, and hoof integrity are all dependent upon zinc. Zinc can interfere in the absorption of copper and copper can interfere with the absorption of zinc. Signs of zinc deficiency include reduced intake, reduced growth, poor hoof integrity, swollen hocks, and skin perakeratosis. The NRC (2001) zinc requirement for a Holstein cow producing 99 lbs (45 kg) of milk and consuming 59.2 pounds (26.9 kg) of dry matter per day is 52 ppm (mg/kg). The maximum tolerable concentration of zinc is between 300 and 1000 ppm (mg/kg) (NRC, 2001). At this level, zinc interferes with copper absorption. As a result, toxicity symptoms are related to copper deficiency.
Alves de Oliveira, L., C. Jean-Blain, S. Komisarczuk-Bony, A. Durix, and C. Durier. 1997. Microbial thiamin metabolism in the rumen simulating fermenter (RUSITEC): the effect of acidogenic conditions, a high sulfur level and added thiamin. Brit. J. Nutr. 78:599.
Beede, D.K. and J.A. Davidson. 1999. Phosphorus: Nutritional management for Y2K and beyond. In: Proceedings of the Tri-State Dairy Nutrition Conference, Fort Wayne, Indiana, April 20-21, 1999, p. 51.
Beede, D.K., D.S. Lough, D. Morse, W.K. Sanchez, and C. Wang. 1988. Macromineral requirements and allowances for lactating dairy cattle. In: Proceedings of the 1988 Cornell Nutrition Conference for Feed Manufacturers, East Syracuse, NY, p. 109.
Beede, D.K., W.K. Sanchez, and C. Wang. 1992. Macrominerals. In: Large Dairy Herd Management. Edited by H.H. Van Horn and C.J. Wilcox. P. 272.
Berger, L.L. 1995. Trace minerals…..major nutrients. Hoard’s Dairyman. August 25, 1995, p. 546.
Chase, L.E. 1998. Phosphorus in dairy cattle nutrition. In: Proceedings of the 1998 Cornell Nutrition Conference for Feed Manufacturers, Rochester, NY, p. 212.
Chase, L.E. and C.J. Sniffen. Minerals in dairy cattle nutrition. Cornell University Animal Science Mimeo.
Gooneratne, S.R., A.A. Olkowski, R.G. Klemmer, G.A. Kessler, and D.A. Christensen. 1989. High sulfur related to thiamin deficiency in cattle: A field study. Can Vet J. 30:139.
Harris, Jr., B. Mineral needs of dairy cattle. University of Florida, Florida Cooperative Extension Service.
Kandylis, K. 1984. Toxicology of sulfur in ruminants: Review. J. Dairy Sci. 67:2179.
National Research Council. 1989. Nutrient requirements of dairy cattle. 6th rev. ed. Natl. Academy Press, Washington, DC.
National Research Council. 2001. Nutrient Requirements for Dairy Cattle. 7th rev. ed. Natl. Acad. Sci., Washington, DC.
Satter, L.D. and Z. Wu. 1999. Phosphorus nutrition of dairy cattle – What’s new? In: Proceedings of the 1999 Cornell Nutrition Conference for Feed Manufacturers, Rochester, NY, p. 72.
Smith, R.M. Trace minerals for dairy cattle of the Northeastern United States. Blue Seal Feeds Publication.
Wu, Z. and L.D. Satter. 1998. Milk production and reproductive performance of dairy cows fed low or normal phosphorus diets. J. Dairy Sci. 81(Suppl. 1):326.
Phosphorus Nutrition and Excretion by Dairy Animals
B. Harris, Jr., Ph.D. et al., University of Florida
Dietary Cation-Anion Balancing of Rations in the Prepartum or Late Dry Period
B. Harris, Jr., Ph.D. and D.K. Beede, Ph.D., University of Florida
Mineral Needs of Dairy Cattle
C.R. Staples, Ph.D., University of Florida
Mineral and Vitamin Nutrition of Dairy Cattle
Rick Grant, Ph.D., University of Nebraska - Lincoln
Phosphorus Nutrition and Excretion by Dairy Animals
B. Harris, Jr., D. Morse, H.H. Head, and H.H. VanHorn, University of Florida
Salt for Dairy Cattle
The absorption of copper and zinc by cattle consuming diets containing the antagonists molybdenum, sulfur, and iron
J.A. Paterson et al., Montana State University
In: Feeding the Dairy Herd, North Central Regional Extension Publication, J.G. Linn et al.
Magnesium Bioavailability Update
George Miller, Premier Chemicals