Pennies made after 1982 contain high levels of zinc. If ingested by pets, these toxic levels of zinc can cause damage to red blood cells and/or gastrointestinal damage. Damage to the kidneys, lungs and pancreas may also occur.
Toxic consumption: There is no established threshold for toxicity. All incidents of exposure should be reported immediately.
Richardson, J.A. (2002). Zinc Toxicosis from penny ingestions in dogs. Veterinary Medicine(February):96-9.