Cornell scientists warn of excess copper in dog diets

Cornell University scientists warn that some commercial dog foods may contain too much copper, which can increase the risk of liver disease for all dogs but particularly in certain breeds.

Food and Drug Administration officials are considering evidence regarding whether the concentrations in dog food could be harmful.

Dr. Sharon A. Center is an emeritus professor of internal medicine at Cornell’s College of Veterinary Medicine, where she specializes in liver disease. She said chronic consumption of excess copper can lead to copper-associated hepatopathy, signs of which include abdominal swelling, decreased appetite, diarrhea, increased thirst and urination, jaundice, lethargy, and vomiting.

A veterinarian who is monitoring a pet’s liver enzymes can identify increased alanine aminotransferase as an early sign of the disease, she said, but confirmation requires a liver biopsy. Treatments with chelation can cost several thousand dollars, and affected dogs need to permanently switch to copper-restricted diets.

In a January 2022 announcement from the Cornell veterinary college, Dr. Center said that copper-associated hepatopathy is no longer just a disease of predisposed breeds, such as Labrador Retrievers or Doberman Pinschers, but a potential problem for any dog with a sustained excess of dietary copper.

She also is the lead author of a related commentary article in the Feb. 15, 2021, issue of JAVMA, along with collaborators from Cornell, Colorado State University, Tufts University, the University of Cambridge, and Veterinary Specialty Hospital of San Diego. That article describes rising hepatic copper concentrations in dogs during the past 20 years, associations between elevated concentrations and inflammatory disease, and a shift among pet food manufacturers away from mixing copper oxide into dog food in favor of more bioavailable forms such as copper sulfate.

Dr. Center said in an interview that she hopes to raise awareness among veterinarians, regulators, and pet food producers, and she is encouraging the FDA and the Association of American Feed Control Officials to consider setting upper limits on copper in canine diets rather than only minimum concentrations.

Dr. Joseph J. Wakshlag, a professor of clinical nutrition and of sports medicine and rehabilitation at Cornell, has collaborated with Dr. Center in examining the risks of copper in canine diets. He said the current copper minimums were set to guard against deficiency, and he noted that dog foods sold in the European Union recently became subject to copper limits.

Officials with the FDA Center for Veterinary Medicine said in response to questions that they have been reviewing scientific literature regarding the role and amount of copper in dog foods for the past year.

Anne Norris, spokesperson for the CVM, said the FDA has received some reports of dogs that developed liver disease with suspected links to excess dietary copper. Those complaints have been uncommon, and evidence suggests some dog breeds have genetic predispositions for diseases that affect their ability to metabolize copper.

“The FDA has been reviewing the relevant facts and current scientific literature to assess whether regulatory intervention is appropriate,” she said. “As part of its assessment, FDA scientists are looking at the level of copper in the food, the physiology of the particular animal the food is intended for, how much of the food the animal is likely to eat over the course of a lifetime, and other potential exposures that might add to the animal’s overall dose.

“We are aware of some papers on the topic of copper toxicosis in dogs and will continue to track this issue as the veterinary community advances its understanding.”

Norris said CVM and AAFCO officials have discussed establishing a maximum amount of copper in dog food. In the absence of such a limit, manufacturers remain subject to a regulatory principle that no more of an ingredient should be used than is necessary to provide the intended effect.

“For copper-containing ingredients, this would be no more than is needed to meet the animals’ nutritional requirements,” she said.

Dr. Valerie J. Parker is a professor of small animal internal medicine and nutrition at The Ohio State University. She is an internal medicine specialist and nutritionist and is not connected with the work by Dr. Center and Dr. Wakshlag. She thinks the February 2021 JAVMA commentary made a valid point that it’s worth considering how much copper is in pet foods, whether that amount is justified, and whether it should be lowered.

Dr. Parker said it’s unclear whether dog food generally contains too much copper, though, since the amount can vary by tenfold or sometimes even thirtyfold between two products. She said the low-copper diets available today tend to be general formulations for dogs with liver diseases, including liver failure or hepatic encephalopathy.

“The lowest-copper commercially available diets are not necessarily diets that you would want to feed a 2-year-old otherwise healthy dog because they are lower in protein,” Dr. Parker said.