Copper deficiency and toxicity in ruminants (Proceedings)

Copper deficiency occurs when the diet contains an abnormally low amount of copper (primary copper deficiency) or when copper absorption or metabolism is adversely affected (secondary copper deficiency).

Copper deficiency occurs when the diet contains an abnormally low amount of copper (primary copper deficiency) or when copper absorption or metabolism is adversely affected (secondary copper deficiency). If inadequate amounts of copper are available to tissues in the form of essential metalloenzymes, the signs of copper deficiency (hypocuprosis) may occur. Clinical signs in ruminants include diarrhea, decreased weight gain, unthrifty appearance, anemia, changes in coat color (achromotrichia) or wool quality, anemia, spontaneous fractures, lameness (epiphysitis) and demyelinization (enzootic ataxia of sheep and goats, or swayback). One of these syndromes usually predominates in a given herd.

The minimum recommended dietary copper concentration (dry matter basis) is 4 to 10 ppm (mg/kg) for cattle, 5 ppm for sheep, and 7 ppm for merino sheep. Young animals and fetuses are more susceptible to copper deficiency than mature animals, and cattle are more susceptible than sheep. Secondary copper deficiency is associated with high dietary levels of molybdenum, sulfates, zinc, iron, or other compounds. Secondary copper deficiency often presents with clinical signs of diarrhea and weight loss or unthriftiness. It has been called teart, peat scours, renguerra, pine, and salt lick disease.4 Salt sickness in Florida appears to be the result of combined copper and cobalt deficiencies. The cause of copper deficiency in clinical cases is often multifactorial and can be difficult to quantify. In addition, unknown factors cause clinical expression of copper deficiency in ruminants to be manifested as a variety of syndromes.

Clinical syndromes and differential diagnosis

Profuse watery diarrhea with poor weight gains and/or weight loss is a common syndrome seen in ruminants with copper deficiency. When it occurs on boggy pastures that contain high concentrations of molybdenum, it has been referred to as teart. Decreased weight gains or weight loss as a herd problem can have many other causes, including parasitism, trace mineral deficiencies (selenium, cobalt), protein calorie malnutrition, and Johne's disease. A syndrome characterized by epiphyseal enlargement, stiffness, and unthriftiness is seen in young ruminants and is the result of copper deficiency and is sometimes called pine. Copper deficiency can cause spontaneous fractures in ruminants. Enzootic neonatal ataxia (swayback) of lambs and kids is characterized by progressive incoordination and recumbency that begins with the hind limbs and progresses to the front limbs. It has also been reported in deer and pigs. Inadequate keratinization of wool and achromotrichia is the result of imperfect oxidation of free thiol groups during hair growth and keratinization. Subsequently, the wool fibers do not crimp normally, and they appear to be "stringy" or "kinky". A copper containing enzyme, tyrosinase (polyphenyloxidase), is needed to convert ltyrosine to melanin. With copper deficiency, this conversion is slow and hair is lighter in color than normal (achromotrichia). Loss of wool crimp and pigmentation changes in sheep or cattle, respectively, occur late in the course of copper deficiency. In addition to the above clinical syndromes that may occur alone or jointly, copper deficiency may be associated with anemia6 (altered iron metabolism) or infertility. Infertility is probably multifactorial and may not respond to an increase in copper intake alone. Copper deficiency also seems to result in decreased immune function in ruminants.

Pathogenesis

A frank dietary deficiency of copper results in hypocuprosis and eventual clinical signs. Also, a variety of conditions can decrease copper absorption from the gastrointestinal tract (large intestine in sheep and small intestine in cattle). The interactions between dietary copper, molybdenum, and sulfates (or sulfur) are important. Excess dietary molybdenum can lead to the formation of sparingly soluble cupric molybdates in the rumen that are not absorbed from the intestine. The addition of excess sulfur or sulfates in the diet and/or water can result in the formation of insoluble copper thiomolybdates in the rumen. The interactions between these three elements are complex. The infertility seen with secondary copper deficiency may be due to excess circulating oxythiomolybdates which interfere with the release of luteinizing hormone. It is important to note that at low sulfur concentrations in the diet excess molybdenum has a minimum effect on decreasing copper absorption. Even when no dietary molybdenum or sulfates are present, only about 5% of ingested copper is normally absorbed. Excessive calcium in the diet, particularly in the form of limestone, decreases copper absorption. Excessive iron, 30 mg/kg of body weight or 1200 ppm in the diet of calves, reduces copper absorption. Overgrazing, with the subsequent ingestion of excess soil also decreases copper absorption. In addition, excess cadmium (3 to 7 ppm) or excess zinc (100 to 400 ppm) reduces hepatic copper concentration, probably through the combined effects of decreased absorption and competition with copper for hepatic metallothionein. It had been suggested that excess dietary selenium might interfere with copper absorption and/or utilization, recently, this has been shown not to occur. Copper is an essential component of a number of mammalian enzymes. Some of the medically important copper-containing enzymes are (1) the cytosol form of superoxide dismutase (copper and zinc), (2) cytochrome oxidase (c and aa3), (3) lysyl oxidase, (4) ascorbic acid oxidase, and (5) ceruloplasmin.16 In addition, normal copper nutrition appears essential for iron absorption and transportation of iron to the liver and reticuloendothelial system and is thus necessary for normal hemoglobin formation. The precise pathophysiology of most of the copper deficiency syndromes is not known. However, the central role of copper in preventing cellular oxidative damage and its role in iron and sulfur metabolism are probably important.

Epidemiology

Copper deficiency can occur when diets are inadequate in copper or contain excess amounts of interfering substances, particularly sulfates and molybdenum. This occurs in many parts of North America. Forages and water can be sources of molybdenum, sulfur, and sulfate. To avoid primary copper deficiency, pasture (dry matter) should contain over 5 ppm of copper, with 3 to 5 ppm considered marginal, and less than 3 ppm deficient. Soil copper concentrations are generally slightly lower than that of the harvested forage. Molybdenum adversely affects plant uptake of copper. Forage molybdenum concentrations greater than the copper concentrations often lead to secondary copper deficiency, even when forage copper is adequate. Since copper content in grasses and legumes can be different, forage samples must be randomly selected to reflect dietary intake. Forage copper concentrations as high as 12 to 27 ppm have been associated with copper deficiency when molybdenum levels are high. The critical ratio of copper to molybdenum in feeds is 2:1, with 5:1 recommended for sheep and 5:1 to 10:1 for grazing cattle.

Clinical pathology and diagnosis

The primary site of copper reserves is the liver. Normal liver copper concentrations in cattle are approximately 60 to 120 ug/g (ppm) and in sheep 80 to 200 ug/g on a dry weight basis (dry matter basis; DMB). Hepatic copper concentrations as high as 250 ug/g DMB are not unusual in supplemented ruminants (even over 350 ug/g DMB in sheep). Blood copper concentrations can be maintained near normal until hepatic copper concentration falls to less than 35 ppm DMB, at which time the serum copper concentration invariably begins to decrease. When using blood samples for copper determination, serum or plasma is normally preferred. Plasma copper concentration is usually about 5% greater than an identical serum copper concentration. Normal serum copper is 0.7 to 1.2 ppm (ug/ml). Serum or plasma copper concentrations of 0.4 ppm or less are considered as evidence of frank deficiency. Values of 0.4 to 0.7 ppm are marginal and are difficult to interpret. Approximately 50% to 90% of the copper in serum or plasma is present in ceruloplasmin. The remainder is bound to albumin or amino acids. The correlation between serum copper and serum ceruloplasmin was found to be weak (0.50); thus ceruloplasmin is not commonly used to aid in diagnosing copper deficiency. Hepatic copper concentration is the preferred diagnostic sample and is easily secured at necropsy. Hepatic copper values less than 35 ppm DMB are considered deficient. However, surgical biopsy is necessary for live patients, and, since laboratories generally require 1 g or more of tissue, a biopsy instrument with an internal diameter of 3 to 5 mm is necessary. Liver biopsy can place the patient at increased risk for black disease or bacillary hemoglobinuria, the risk of which can be decreased by prior vaccination and post-biopsy administration of penicillin. The tissues of young animals (neonates) contain variable amounts of copper compared to adults of the same species. In sheep, serum and liver copper concentrations are the same for lambs (1 week of age) and adults. The plasma copper levels in lambs are low at birth, but rise to adult values by 1 to 7 days of age. Plasma copper levels in the bovine neonate are lower than in mature cattle. In the bovine neonate hepatic copper concentration changes little from birth to maturity; however, copper distribution in the liver is quite variable in the neonate. Because of these differences, interpretation of neonatal serum copper concentrations is difficult. Milk is a poor source of copper, containing only 0.2 to 0.6 ppm in normal ewes and 0.01 to 0.02 ppm in severely copper deficient ewes or cows. Milk copper in cattle is 0.05 to 0.2 ppm. To make matters worse, molybdenum is concentrated in milk. Response trials using injectable copper are also a valid means of diagnosis. However, adequate numbers of control animals are necessary for evaluation. Also, accurate measurement of clinical disease, production parameters such as feed efficiency or other such objective criteria are necessary for interpretation.

Treatment and control

Treatment of copper-deficient animals is usually possible, and the prognosis is guarded to good, depending on the severity of the lesions. When excess molybdenum, sulfate, and other factors leading to secondary deficiency are present, they can be overcome to some extent by increasing dietary copper or by injecting copper. Injectable copper glycinate (30% copper by weight) is given to adult cattle at the rate of 400 mg (120 mg copper) subcutaneously. Calves are given 100 to 200 mg of copper glycinate (30 to 60 mg of copper), depending upon their age. One injection may be effective as a treatment/supplement for up to 4 to 6 months in cases of primary copper deficiency. However, in cases of excess molybdenum, sulfates, and/or sulfur, repeat injections may be necessary. Injections of copper glycinate frequently result in large swellings, granulomas, or abscesses and may be cosmetic considerations for some cattle. The reactions can be minimized by using sterile technique and using the subcutaneous tissue of the brisket as the injection site. Copper can be supplemented to cattle in salt-mineral mixes in situations in which adequate consumption (1 to 2 ounces [28 to 56 g]/cow/day) of the salt-mineral mix occurs. These mixes are usually 0.2 to 0.6% copper. Feed grade copper sulfate (CuSO4-5 H2O) is 25% copper on an as fed basis (40% copper on dry matter basis). Feed grade copper oxide is usually 50% copper as fed (80% copper on a 100% dry matter basis). To make a 0.4% copper salt mixture, add 7.2 g of CuSO4 or 3.6 g of CuO to each 454 g (1 pound) of salt. For large batches add 32 pounds of CuSO4 or 16 pounds of CuO per ton of salt. Salt mixtures for sheep should usually contain only 0.0625% to 0.13% copper (0.25% to 0.5% copper sulfate). Copper supplements can be added to a total mixed ration easily in the form of trace mineral-vitamin premixes or premix-containing pellets. Copper sulfate can be added to molasses or other sweet feed at 0.363 g/head/day for mature cattle and correspondingly less for calves. This would supply approximately 91 mg of copper to a 450kg (1000pound) cow per day or 10 ppm of the total diet (20 pounds [9.1 kg] of dry matter). The copper in CuSO4 is more available than that in CuO. In some countries copper EDTA (copper disodium edetate) solutions are used as injectable copper supplements. The dosage of copper is usually the same as that recommended for copper glycinate solutions. However, acute deaths can occur following its use in cattle. Another method of copper supplementation involves the oral administration of copper oxide needles (fine rods, 1 to 10 mm long) placed in gelatin capsules which dissolve in the reticulo-rumen and liberate the CuO wires. These wires reside in the reticulum and abomasum and slowly release copper for absorption. These boluses are currently available in the U.S. (Copasure) and contain either 25 g or 12.5 g per bolus. The usual recommended dosage is 25 g per animal 500 pounds or greater. One 12.5 g bolus is recommended for calves and the usual dose is 2 to 4 g for ewes and does, which is an extra label recommendation for sheep and goats. The copper oxide needles are thought to provide copper supplementation for 4 to 12 months. Sheep are particularly susceptible to copper toxicity, and appropriate care is necessary when supplementing them. Sheep can easily be intoxicated when consuming cattle supplements or feeds. Continued monitoring of hepatic copper concentration from slaughtered animals is an important tool in evaluating copper supplementation methods in cattle and sheep. Lambs can be given 35 mg of copper sulfate per head twice weekly to prevent swayback in endemic areas. The usual recommendation by the National Research Council is 10 ppm (10 mg/kg) of the total diet on a dry matter basis (DMB) for cattle. However, diets of 20 ppm are commonly fed to lactating dairy cattle. The most important goal of copper supplementation is to provide adequate dietary amounts without over supplementing or risking toxicity.

Toxicity

Previous NRC publications stated 100 ppm of the diet is the maximum tolerable level for cattle; however, the experience of many clinical cases and some research26 would indicate that 40-50 ppm of the diet in cattle is the threshold for toxicity. New NRC documents reflect these thoughts. Copper toxicity in cattle usually manifests as peracute hepatic necrosis in individual animals within a herd. Therefore, the cattle are normal one day and dead or dying the next day. Cases occur sporadically often following some form of stress. The clinical signs typical of Cu toxicity in sheep (Heinz body formation leading to intravascular hemolysis with hemoglobinuria and icterus) can occur in cattle; however, this clinical manifestation is much less common in cattle. Acute copper toxicity characterized by hepatic necrosis can also occur after copper injections. Sheep should not be fed more that 10 ppm Cu and for some diets this may be too much. Signs of toxicity include intravascular hemolysis with hemoglobinuria (Heinz body anemia prior to hemolysis) and occasionally acute hepatic necrosis. Goats are intermediate to cattle and sheep and it is better to be conservative and supplement goats in a similar manner to sheep.

Copper deficiency is uncommon in sheep and goats. They are more efficient at absorbing Cu from the diet than other ruminants such as cattle or bison. Each ruminant species seem to have subtle variations in the ability to absorb adequate (or excess) Cu from dietary sources. There also exist some wide variations among animals of the same species, breed, or herd. Intestinal parasites have a marked affect on Cu metabolism in small ruminants. Therefore, before making a diagnosis of Cu deficiency (primary or secondary) in these species you should be certain they are relatively free of parasites for a period of time before sampling to determine Cu status. "Valbazen can cure some Cu deficiency problems".

Reference values for CU in sheep and goats

Methods of supplementing Cu to sheep and goats is parallel to those used for cattle or other species: grain mixes with added Cu, TMR's, salt mineral mixes, and boluses. However, if these species are supplemented a strict protocol for monitoring liver Cu concentrations should be initiated at the same time the supplements are started. Liver Cu concentrations for the group should be examined at 3-6 months after supplementation is started and periodically thereafter.

The margin of safety for sheep is very small and the margin for goats is not much greater. Remember, in the case of cattle on low sulfate and molybdenum rations the Cu needs are about 10 ppm of the diet and toxicity can occur with 40-50 ppm Cu in as little as 6 months. The interference (SO4, Mo) is the unknown in the equation. The same is the case for sheep and goats with 5-7 ppm Cu needed and 15-25 ppm as potentially toxic. Concurrent Se deficiency can increase the toxicity of Cu in ruminants. A large number of materials contain large of amounts of Cu and can cause toxicity when fed to small ruminants (even in very small amounts). These include things such as subterranean clover, grain for horses, pig feed, dog food, cat food, cattle feeds and cattle salt-mineral mixes, and mineral supplements for horses.

Copper toxicity in small ruminants usually manifests itself as a hemolytic crisis with hemolytic anemia, icterus, and hemoglobinuria. Acute hepatic necrosis is an uncommon manifestation (versus cattle). Diagnosis is based on clinical signs, liver Cu and kidney Cu concentrations, and appropriate pathology. Treatment of clinical cases is very difficult because hemolytic crises can recur several times in individual animals. Supportive care, fluid therapy (hemoglobinuria can severely damage renal function), and blood transfusions may all be necessary in individual animals. Specific therapy includes sulfate and molybdate compounds to help "tie-up" excess Cu and speed Cu excretion. One such protocol recommends the oral administration of 200 mg sodium molybdate and 3 grams of sodium sulfate per head per day for 3 weeks (Humphries, et al, 1986). Another report suggests doses of 500 mg ammonium molybdate and 1 gram of sodium sulfate daily for 4 weeks (Bulgin, 1993). Ammonium molybdate is relatively expensive and not clear for use as a feed additive. Sodium molybdate is less expensive and it is cleared for use in feeds.

References available on request