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Revisiting copper toxicity

Should you deworm with copper oxide wire particles?

In recent years, copper oxide wire particles (COWP) have been recommended as an anthelmintic for sheep and goats. Similarly, researchers are re-evaluating copper sulfate as a deworming agent [1]. The mention of copper (in any form) as a dewormer should automatically send up a red flag to most sheep producers, as most producers are aware of sheep's ultra-sensitivity to copper.

Copper has anthelmintic activity and has been historically used as a deworming agent in sheep; however, its use was discontinued because of toxicity issues. This is the situation with many "natural dewormers." They have anthelmintic properties, but in effective doses to kill the parasites, they risk toxicity to the animal.

Sheep are the species most prone to copper toxicity. Mature ewes of British breed origin appear to be the most vulnerable, and there is evidence to suggest that Finn and Texel sheep have a tendency to accumulate more copper in their livers than other breeds.

Sheep absorb copper from their diet in proportion to the amount of copper offered, not according to their dietary needs. Excess copper is stored in the liver. The storage level in the liver can take months or even years to reach a toxic level (> 1,000 ppm DM) [4,5]. Even then, it needs a stress to release the copper into the bloodstream. Copper toxicity results in liver disease, jaundice, and death.

The ratio of copper (Cu) to molybdenum (Mo) is the most important dietary factor affecting copper toxicity in sheep [5]. Ratios of 10:1 or less will prevent toxicity in most cases [5]. This is because molybdenum forms an insoluble complex with copper which prevents copper from being absorbed. Sulfur further complicates the Cu:Mo relationship by binding with Mo.

Copper absorption is more important than its concentration in the feed. Copper absorption in sheep is relatively poor, ranging from 1.4 to 12.8 percent [7]; however, young animals may absorb up to 90 percent of dietary copper. The availability of copper is reduced by the presence of molybdenum, sulfur, and iron. Fresh grasses are poor sources of copper in comparison to cured hay [7]. Acid soils increase copper and lower molybdenum in forages [7]. Liming can increase molybdenum in the forage and alter the Cu:Mo ratio.


Copper (Cu) requirements

Copper is important for immune function in livestock. In 1975, copper requirements for sheep were set at 5 ppm (mg/kg)[2]. The requirements were increased to 7 to 11 ppm in 1985 [3].

More recent recommendations use an equation to determine copper requirements for sheep. The equation includes various factors, including an absorption coefficent, which varies by the class and weight of sheep. The maximum tolerable copper concentration is considered to be 15 ppm for sheep, assuming normal levels of molybdenum (1-2 ppm DM) and sulfur (0.15-0.25 percent) in the diet [4].

Cattle require about 10 ppm of copper in their diet and can tolerate Cu levels ten times higher than sheep. Non-ruminants can tolerate even higher levels. This is why fertilizing pastures with pig or poultry manure can lead to copper toxicity in sheep. It is also why poultry litter should generally not be fed to sheep.

According to research, meat and dairy goats require and can tolerate much higher levels of copper than sheep [7]. In 1991, copper requirements for goats were established at 8 to 10 ppm [6]. Factoring in more recent data, the National Research Council (NRC) has recommended increasing the copper requirement of lactating goats to 15 ppm [7], mature goats and bucks to 20 ppm [7], and growing goats to 25 ppm [7].  While goats, especially meat goats, may have a higher tolerence than other ruminants, scientists have not identified a toxic level for goats [7].

The research on COWPs

Widespread resistance to anthelmintics has led scientists to pursue various non-chemical alternatives for controlling internal parasitism in small ruminants. One such alternative is copper oxide wire particles (COWP). While their mechanism of action is not fully understood, COWP have been proven to reduce barber pole worm infection in sheep and goats, especially young stock [8].

Copper boluses (Copasure©) are available for use for copper deficiency in cattle. These boluses can be repackaged into much smaller dosages (usually 0.5 to 2 g) for use in sheep and goats. The boluses can be administered with a pill or balling gun.

As compared to copper sulfate, copper oxide wire particles are poorly absorbed, thereby reducing the risk of copper toxicity [8]. Researchers have experimented with different doses of COWP and frequency of treatment to determine not only effectiveness of treatment(s), but also the effect on copper concentrations in the liver and the risk of copper toxicity. In the research trials, COWP have been used in sheep and goats, without creating unsafe levels of copper in the liver and without risk of copper toxicity.

Most of the research has been done with hair sheep and meat goats. Results have varied. COWP appear to be more effective in young animals than mature ones. A summary of research trials can be found in the fact sheet, Tools for managing internal parasites in small ruminants: copper wire particles by ATTRA/NCAT (National Sustainable Agriculture Information Service) and the American Consortium for Small Ruminant Parasite Control.

Guidelines for using COWPs

Copper oxide wire particles (COWP) are not the "magical bullet" to control internal parasitism in small ruminants. However, they may offer a viable alternative to sheep and goat producers who are experiencing complete anthelmintic failure or who seek non-pharmaceutical approaches to worm control.

It is important to note that COWPs are only effective against Haemonchus contortus (the barber pole worm) [8]. The barber pole worm is a blood sucking parasite that resides in the abomasum. It is the primary worm species affecting sheep and goats in warm, moist climates that experience summer rainfall. Other control methods are necessary to control coccidia and other gastro-intestinal nematodes. Other methods to control the barber pole worm may be more effective in mature animals.

There are several precautions to follow when using copper oxide wire particles. COWP should not be the only method of parasite control employed on a sheep or goat farm [8]. COWP should be part of an integrated parasite management program that includes many of the following practices: pasture rest and rotation, nutritional supplementation, genetic selection (between and within breeds), tanniferous forages, browsing, taller forages, mixed species grazing, zero-grazing, harvesting hay, minimum grazing heights, and selective deworming using the FAMACHA© eye anemia system. Fecal egg counts can be used to monitor pasture contamination and to test for drug resistance (and effectiveness).

Copper oxide wire particles should not be administered sub-therapeutically to sheep and goats. The FAMACHA© system should be used as a guide to determine which animals should receive a COWP bolus. It is generally recommended that sheep scoring 4 or 5 on the FAMACHA© eye anemia scale be treated for barber pole worm infection, whereas those scoring 1, 2, or 3 not be treated. It may be necessary to treat lambs, goats, and other at-risk animals that have FAMACHA© scores of 3, 4, and 5. Any animal showing symptoms of "bottle jaw" should be dewormed.

Sheep farms that have other risk factors for copper toxicity should probably not use COWP as a deworming agent. Though goats can experience copper toxicity, the risk is significantly less. Though there are breed differences, it is not known if hair sheep breeds have a higher tolerence for copper in their diets as compared to conventional wooled breeds.

Risk factors for copper toxicity
    Species: sheep
    Breed: some breeds more susceptible (e.g. Texel, Finn)
    Age: young animals absorb more dietary Cu
    Low Mo in soil, forages, or feeds
    Use of feed or minerals formulated for other species
    Fertilizing pastures with pig or poultry manure
    Feeding poultry litter
    Certain feedstuffs (e.g. DDGS) have high levels of Cu or Cu agonists.
    Lack of zinc in the diet (zinc reduces Cu liver stores)
    Acidic soils (increases Cu and lowers Mo )
    Copper water pipes

References and further reading
[1]  Simpson, M.M. 2011. "Use of Copper Sulfate to Control Haemonchus Contortus Infestation in Hampshire Ewes. University of Kentucky Master's Theses. Paper 135.
[2]  NRC. 1975. Nutrient Requirements of Sheep. Washington DC: National Academies Press.
[3]  NRC. 1985. Nutrient Requirements of Sheep. 6th rev. ed. Washington DC: National Academies Press.
[6]  Kessler, J. 1991. Mineral Nutrition of Goats. Goat Nutrition. 46:104-119.
[7]  Nutrient Requirements of Small Ruminants. 2007. Washington DC: National Academies Press.
[8]  Hale, M., J. Burke, J. Miller and T. Terrill. 2007. Tools for managing internal parasites in small ruminants: copper oxide wire particles. ATTRA/NCAT and ACSRPC.

This article was written in 2012 by Susan Schoenian.

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