Dr. J.L. Goelz
Sheep are extremely sensitive to copper toxicity, more so than any other form of livestock. The source of the toxic levels of copper are usually feed or minerals that are formulated for cattle or swine that get fed to sheep by accident or out of ignorance. Copper Sulfate foot baths are highly toxic if sheep are allowed to drink the solution or gain access to the bag of concentrate. We had one situation where sheep were turned into an abandoned feed lot which contained copper wire. Sheep licked the wire and toxicity occurred. Unless premixes or mineral mixes are specifically formulated for sheep they will have toxic levels of copper and should not under any circumstances be fed to sheep. A safe level of copper in sheep feed is between 7-11 ppm of diet dry matter. The mineral molybdenum interacts with copper and prevents its absorption from the gut. Thus, if feed have high levels of molybdenum (3ppm) less copper will be absorbed and copper levels up to 20 ppm can be fed. Conversely, if feed have low levels of molybdenum more of the copper that is present will be available for absorption. The copper to molybdenum ratios should be 6:1 in sheep rations. Ratios of greater than 10:1 will result in acute toxicity.
Clinical signs of toxicity include weakness, anorexia, trembling, fast breathing, red urine, yellow discoloration to the gums and white areas of the eyes, and unexpected death. The organs of toxicity are the liver, kidney and red blood cells. Your local veterinarian and Diagnostic Laboratory can assist you in confirming a copper toxicity diagnosis. Copper Toxicity occurs as a herd problem and several animals will be affected. Generally, once a sheep shows clinical signs, the toxicity is fatal and treatment is usually unrewarding. The stress of handling often will precipitate the clinical signs and the toxicity. D-penicillamine, a chelating agent has been reported to be effective at 50 mg/kg per head per day for 6 days. Ammonium tetrathiomolybdate injected under the skin at a dose of 3.4 mg/kg every other day for three treatments has also been effective. The cost and availability of both of these products may prohibit their use. Supplementation of 2-16 ppm of molybdenum in the ration has been useful in controlling outbreaks. Again, prevention is the key with copper toxicity.