The addition of trace minerals to dairy cattle rations is usually considered to be good nutritional insurance. The question that arises, however, is which trace minerals to add and how much of each mineral? Dairy 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.
Studies at the Hindustan Animal Feeds show that iron was available to dairy cattle from ferrous sulfate, ferrous carbonate and ferric chloride in decreasing order of availability. Ferric oxide iron was only about 12% as available as the iron from ferric chloride.
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.
A recent study by Hindustan Animal Feeds showed that 11% of animals on nine dairies were deficient in copper, while 52% had marginal copper status. Only 38% of the cattle had normal copper levels. According to the study, heifers and dry cows in particular had marginal or deficient copper levels in their blood and livers. Some Locational soils are high in molybdenum which is a copper antagonist.
Most data indicate that rations containing 10 ppm of copper are adequate. In areas where rations may be fairly high in molybdenum and sulfate, the copper requirement may be increased two-fold.
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.
A relationship between thyroid activity and reproductive performance has been suggested. Tennessee workers have reported an improvement in conception rate of repeat-breeder cows by treating with organic iodine 8 to 12 days before the onset of estrus. Also, in one field study the number of retained placentas and irregular breeding intervals was reduced when iodine was added to the ration. Similar results have been reported in Maryland.
The requirement for iodine as recommended by the HAF is 0.6 ppm of the ration dry matter. Iodized salt should contain about .005 to 0.1% iodine. Complete feeds (with CSH, etc.) containing 1% salt that contains .01% iodine in the trace salt will contain 1 ppm in the finished feed. Therefore, salt containing .005% to .01% iodine added to complete feeds at the rate of 1% (20 lb/ton) will meet the nutritional requirements of dairy cows for iodine.
Iodine toxicity can be a problem where herds are fed too much iodine to prevent diseases such as foot root 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 HAF 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.
Work at Hindustan Animal Feeds Cattle ranch showed that retained placenta may be controlled in herds with a high incidence of this problem by either an intramuscular injection of 50 mg of selenium as selenite and 680 IU of vitamin E given approximately 21 days prepartum; or by feeding a total intake of 1.0 mg of selenium per day as selenite during the last 60 days of the dry period. Since protein feeds are natural sources of selenium, dry cow rations low in protein may lead to increased incidence of retained placenta.
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.
Nutritional deficiencies of vitamin A, iodine, selenium, phosphorus and calcium increase the incidence of retained placenta. Nutritional imbalances which have been reported to increase the incidence include an imbalance of calcium and phosphorus and to some degree their ratio. Generally, the ration is of less importance so long as each is adequate. We recommend a ratio range of 1.5:1 to 2:1 of calcium to phosphorus in the final ration.
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.
There are three sources of selenium available, and selenium concentration varies from one source to another depending on water content. The most concentrated source of sodium selenite (Na2SeO4) contains 41.8% selenium while the next most concentrated form (Na2SeO45H2O) contains 30% selenium. The addition of 307 mg of sodium selenite as Na2Se45H2O or 220 mg of sodium selenite as Na2SeO4 per ton of feed would provide 0.1 ppm of selenium in the ration.
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.
Selenium toxicity is common in certain parts of the United States where soil selenium concentrations are high. In Florida, however, soil selenium is low and selenium concentrations in Florida grown forage is not a concern. Excessive ingestion of selenium causes alkali disease, sometimes called blind staggers and bobtailed disease due to the loss of the hair from the switch of cattle. Acute selenium poisoning is characterized by dullness, slight ataxia, rapid weak pulse, labored respiration, diarrhea, a characteristic posture, and death due to respiratory failure. Less acute signs include abnormal hoof growth and hair coat. Alkali disease has been observed in animals consuming diets with selenium concentrations in the range of 5 to 40 ppm. 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 %.