Chapter 39 Copper
SOURCES
Coins appear to be the primary potential source of excessive oral copper exposure in either dogs or cats. Copper poisoning was documented in a cat following ingestion of 32 Canadian pennies.1 Canadian pennies minted up to 1997 are composed of 98.5% copper. American pennies (standard weight, 2.5 g) minted up to and including the year 1983 contain 95% copper. Nickels (standard weight, 5 g) contain 75% copper, and dimes (standard weight, 2.268 g), quarters (standard weight, 5.67 g), and half-dollars (standard weight, 11.34 g) contain approximately 91.7% copper. Susan B. Anthony dollars (standard weight, 8.1 g) contain 87.5% copper. Copper poisoning could also conceivably occur as a result of excess copper leaching from copper piping. This would be highly unusual and most likely would not cause an acute intoxication.
Acute copper poisoning was reported in Canada geese following ingestion of water containing excessive copper concentrations following application of copper sulfate to a small, man-made pond.2 Copper sulfate is a common ingredient in fungicides and algicides and is also used in footbaths or topical solutions for cattle and sheep to control hoof infections. Copper sulfate is also commonly incorporated into various feeds or drinking water (e.g., for swine, rabbits, cattle, and poultry) to prevent deficiency diseases or to act as a growth promotant and/or antimicrobial agent. Copper sulfate is also used in some topical wound dressings. Copper oxide-containing capsules intended for oral supplementation for cattle could conceivably be ingested by dogs and cats. The author is aware of a dog ingesting an unknown amount of copper-containing wire. Other miscellaneous sources of copper include jewelry, pipes, toy parts, kitchenware, and numerous household objects.
TOXIC DOSE AND TOXICOKINETICS
No reported toxic doses for copper in dogs and cats were found in the literature. Approximate normal dietary range of copper in cats and dogs appears to be in the 3 to 10 ppm and 7 to 10 ppm range, respectively, on a dry weight basis. Adequate dietary intake for cats has been reported to be between 0.08 and 0.80 mg Cu/kg body weight/day.3 The author is aware of a case where a 3.4-g quarter (original weight ∼5.7 g) was surgically removed from the stomach of a small-breed dog (weight unknown) exhibiting signs of intermittent vomiting, lethargy, and abdominal tenderness associated with elevations of liver enzymes. The serum copper concentration was normal.
Elemental copper is primarily absorbed by the small intestine. The majority of copper is absorbed by active transport, whereas passive diffusion is known to occur at higher concentrations of dietary copper. The bioavailability and eventual uptake of copper can vary with the form of copper (e.g., copper sulfate, copper oxide, copper carbonate). The intestinal mucosal cells regulate copper transfer into the portal circulation in part by the use of intracellular metallothionein. Before being secreted into the general circulation, the copper is mostly bound to albumin. The liver is the primary organ of copper metabolism. In the liver, copper stores are divided into four intercellular pools: the biliary pool, ceruloplasmin, metalloenzymes, and copper-metallothionein complexes. Any excess copper is stored by lysosomes. The normal liver metabolizes copper by excreting excess copper into the bile as a copper-molybdenum-sulfate complex. Small amounts of copper are also normally excreted into the urine.
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