Copper - Cu

Essential for the formation and activity of red blood cells, it acts as a cofactor in many biochemical reactions. Without copper, iron is not properly incorporated into hemoglobin — a dog or cat with a copper deficiency may be anemic even with a sufficient supply of iron [1]. Copper is also responsible for the pigmentation of the skin and coat (melanin production) and, through the enzyme lysyl oxidase, for the formation of collagen and elastin — that is, the health of connective tissue, joints, vessels and proper wound healing [2]. It is a nutrient that requires calculation, not estimation by eye: two diets with an identical percentage of liver can have a completely different copper result.

Where it's found: Mammalian liver — above all beef and lamb. Poultry liver contains over a dozen times less copper and on its own almost never suffices. About 5–7% beef or lamb liver usually covers the requirement [2].

Deficiency: Deficiencies rarely occur with a balanced diet containing meat and offal. Most common in diets based on poultry without beef or lamb liver, and as a result of absorption disorders caused by an excess of zinc, calcium or vitamin C. Symptoms: rusting and fading of the coat (especially in dark-coated dogs — black turns into a rusty shade), anemia that does not resolve after iron supplementation, and poorer wound healing [1].

Excess: In most healthy dogs and cats a small excess is efficiently removed by the liver and excreted in the bile. Copper does, however, accumulate in the liver, and chronic excess damages it silently, without early symptoms (copper-associated hepatopathy) [3].

Species difference and predisposed breeds

Some dog breeds have a genetic predisposition to accumulating copper in the liver. The classic example is the Bedlington Terrier with a mutation of the COMMD1 gene, which prevents proper copper excretion [4]. The Labrador Retriever, Doberman, West Highland White Terrier and Dalmatian are also predisposed [5]. In these breeds it makes sense to periodically monitor liver parameters (ALT, ALP, bilirubin), to keep to the lower limit of copper supply, and — in the case of liver disease — to follow a diet consulted with a veterinarian. Cats tolerate fluctuations in copper better than dogs and have no described breed predispositions to copper toxicosis; with reasonable amounts of liver, an excess is unlikely in them [1].

What to watch for

Zinc and copper compete for absorption — excessive zinc supplementation can cause a secondary copper deficiency and vice versa [1]. More in the article Zinc. With anemia, do not automatically assume an iron deficiency — also check copper (see Iron). If the calculator shows a copper deficiency, first change the type of liver to beef or lamb before reaching for a supplement; if you are already using beef liver, do not add a copper supplement without a clear need.

Sources

1. National Research Council (2006). Nutrient Requirements of Dogs and Cats, Chapter 7 — Minerals. National Academies Press. https://nap.nationalacademies.org/catalog/10668/nutrient-requirements-of-dogs-and-cats
2. Amundson LA, Kirn BN, Swensson EJ, Millican AA, Fahey GC (2024). Copper metabolism and its implications for canine nutrition. Translational Animal Science. https://pmc.ncbi.nlm.nih.gov/articles/PMC10787350/
3. Center SA, Richter KP, Twedt DC, et al. (2021). Is it time to reconsider current guidelines for copper content in commercial dog foods?. JAVMA 258(4):357. https://doi.org/10.2460/javma.258.4.357
4. van De Sluis B, Rothuizen J, Pearson PL, van Oost BA, Wijmenga C (2002). Identification of a new copper metabolism gene by positional cloning in a purebred dog population (COMMD1/MURR1). Human Molecular Genetics 11(2):165-173. https://pubmed.ncbi.nlm.nih.gov/11809725/
5. Dirksen K, Fieten H (2017). Canine Copper-Associated Hepatitis. Veterinary Clinics of North America: Small Animal Practice. https://pubmed.ncbi.nlm.nih.gov/28063745/