A study from Cornell University has highlighted a concerning trend: processed foods fed to dogs are causing liver damage due to excessive copper content. This issue, however, has not received the same level of attention as other dog food scares, such as melamine or vitamin D toxicity, or the grain vs grain-free debate.
Copper is an essential trace mineral for dogs, as they cannot produce it and must obtain it through their diet. It plays a crucial role in activating enzymes for metabolic functions, building red blood cells, and maintaining healthy connective tissue, skin, and coats. Historical studies show a significant increase in copper levels in dogs’ livers over time, with an average of 10 micrograms (mcg) per gram in 1929, 200 mcg per gram in 1982, and 453 mcg per gram in 1995.
A more recent comparison between feral dogs and lab dogs raised on commercial dog food revealed that the lab dogs had three times more copper in their livers, averaging 472 mcg per gram compared to 152 mcg in feral dogs. This suggests that the commercial dog food they consumed is a primary source of the increased copper levels.
Researchers have found that the rise in copper levels is not linked to breed-specific diseases but rather to the amount of copper in the diet. High amounts of copper were identified in commercial dog foods, with 58% of liver biopsies showing inflammatory liver disease and copper concentration over 400 mcg per gram. This indicates that more than half of the dogs may be affected by excess copper.
Excess copper in dogs leads to copper toxicity, which accumulates in the liver, causing inflammation and damage, potentially leading to liver failure and death. Most dog owners are unaware of this issue because dogs do not show symptoms until the damage is advanced. The only early sign is a change in ALT levels, which are enzymes contained within liver cells.
Signs of liver damage in dogs due to copper toxicity include abdominal swelling, diarrhea, loss of appetite, jaundice, increased thirst, and vomiting.
The Association Of American Feed Control Officials (AAFCO) sets nutrient guidelines for pet food manufacturers, which should address the levels in dog food to prevent such health issues.
AAFCO’s nutritional requirements are primarily minimum standards to ensure pets receive the essential nutrients needed to avoid disease. There are no specified optimal levels, with occasional maximum levels for certain nutrients.
How Much Copper Is Toxic To Dogs? The minimum copper requirement for adult dogs is 7.3 mg/kg, and for puppies, it’s 12.4 mg/kg. However, dog food manufacturers can add as much copper as they wish, as long as they meet these minimums. In 2007, AAFCO removed the safe upper limit for copper, which was previously set at 250 mg/kg in dry diets.
Increased Copper In Dog Food: The question arises as to why pet food manufacturers are adding more copper to their products. Most pet foods undergo multiple heating processes, extrusion, and then sit on shelves for extended periods, leading to significant nutrient loss. Cooking can destroy about 40% of copper and other nutrients.
To compensate for these losses, pet food manufacturers add a standard premix, which consists of lab-made vitamins and minerals, often sourced from China, to replace nutrients lost during processing and meet AAFCO standards. With few maximum limits, manufacturers can add substantial amounts, making the food appear more nutritious.
AAFCO Changed The Type Of Copper In Dog Food: About 15 years ago, most premixes contained an inorganic form of copper with low bioavailability, copper oxide. AAFCO recommended a more bioavailable form like copper sulfate. Since then, many premium foods have used even more bioavailable organic forms, such as copper chelate, leading to increased copper content in dog foods and consequently in dogs’ livers.
This change by AAFCO was surprising given that: Dogs require minimal copper for health; there were no reports of copper deficiencies; copper levels in dogs’ livers were rising; no peer-reviewed studies examined copper requirements; and there was no AAFCO re-evaluation of the minimum copper requirement.
Copper-Rich Ingredients In Dog Food: Some ingredients rich in copper found in commercial dog foods include liver, fish and seafood, chickpeas, sweet potatoes, sunflower seeds, and kale. Many grain-free foods use chickpeas and sweet potatoes as a starch source, along with a mineral premix.
How Much Copper Should There Be? Pet foods are not required to disclose copper amounts in the Guaranteed Analysis on the label. If you seek a low-copper dog food, you must contact the manufacturer for details. Aim for copper levels close to the minimum requirement of 7 mg/kg.
For adults, the copper requirement is 3 mg/kg. For puppies, it is 12.4 mg/kg. If your dog food maker cannot tell you the amount of copper in the food, do not buy that brand. Look for a company that can provide information about the copper levels in their food. Do not risk your dog eating toxic levels of copper as it can seriously harm him.
References: Center Sa, et al. Is It Time To Reconsider Current Guidelines For Copper Content In Commercial Dog Foods? Journal Of The American Veterinary Medical Association. 2021; 258:357-364.
Strickland JM, Buchweitz JP et al. Hepatic copper concentrations in 546 dogs (1982-2015). J Vet Intern Med. 2018 Nov;32(6):1943-1950.
