http://www.sheepandgoat.com/articles/revisitingcopper.html Revisiting copper toxicity in sheep Should you deworm your sheep (or goats) with copper oxide wire particles (COWP)? Susan Schoenian Sheep and Goat Specialist Western Maryland Research & Education Center University of Maryland Extension Date created or last revised: 17-May-2008 Recent press announcements have advocated the use of copper oxide wire particles (COWP) as a deworming agent in sheep and goats. Similarly, at the 2008 annual meeting of the Southern Section of the American Society of Animal Science, a graduate student presented the results of a study in which mature ewes were selectively dewormed with copper sulfate. The mention of copper (in any form) as a deworming agent should automatically send up a red flag to most sheep producers as most producers understand sheep's 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 liver than other breeds. Sheep absorb copper from their diet in proportion to the amount of copper offered, not according to their body’s need. 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). 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. Ratios of 10:1 or less will prevent toxicity in most cases. 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; 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. Acid soils increase copper and lower molybdenum in forages. Liming can increase molybdenum in the forage and disturb the Cu:Mo ratio. Copper oxide wire particles (COWP) 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.