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Zinc : copper ratio (Zn:Cu) in dog and cat diets

A short guide to the role of Zinc : copper ratio (Zn:Cu) in dog and cat nutrition.

Zinc : copper ratio (Zn:Cu)

Zinc and copper compete for the same absorption pathways in the gut, which is why it matters not only how much of each there is, but also what proportion they form. The optimal Zn:Cu ratio in a dog's and cat's diet is taken to be about 8–15:1 [1]. When this balance drifts apart, an excess of one element silently sabotages the other — and it does so regardless of whether the absolute amounts are within the norm.

Why the proportion, not just the amount

Zinc and copper antagonize each other in both directions. A chronic excess of zinc — most often from supplements given "for the coat" over months — leads to a secondary copper deficiency and iron-unresponsive anemia [2]. In the other direction: an excess of copper (e.g. from a large amount of beef liver) disrupts the absorption of zinc [1]. On top of this comes a third player — calcium: too much bone, eggshell or calcium preparations blocks zinc absorption, so sometimes the problem is not too little zinc in the bowl, but the poor construction of the whole recipe [1].

What it means in practice

  • Too high Zn:Cu (too little copper) — typical for diets based on poultry with poultry liver, which has over a dozen times less copper than beef liver. It manifests as fading and rusting of the coat and anemia. Solution: change the type of liver to beef or lamb before reaching for a supplement. More in the article Copper.
  • Too low Zn:Cu (too little zinc relative to copper) — keratinization on the nose, elbows and paw pads, a dull coat, slow healing. In Nordic breeds (Husky, Malamute, Samoyed) zinc absorption is genetically impaired and they may require doses 2–3× higher than the norm — this is a topic to manage with a veterinarian [3]. First, however, check for an excess of calcium. More in the article Zinc.
  • In the cat this antagonism can be misleading: on very high-protein diets zinc can be on the edge while copper is within the norm — and we wrongly attribute skin problems to zinc itself, when the disturbed proportion is to blame [1].

A practical rule: do not supplement zinc, copper or iron in one meal — they compete for absorption. And never evaluate zinc or copper in isolation, only as a pair.

Sources

  1. National Research Council (2006). Nutrient Requirements of Dogs and Cats. National Academies Press. https://nap.nationalacademies.org/catalog/10668/nutrient-requirements-of-dogs-and-cats
  2. Pereira AM, Maia MRG, Fonseca AJM, Cabrita ARJ (2021). Zinc in Dog Nutrition, Health and Disease: A Review. Animals 11(4):978. https://doi.org/10.3390/ani11040978
  3. White SD, Bourdeau P, Rosychuk RAW, et al. (2001). Zinc-responsive dermatosis in dogs. Veterinary Dermatology. https://pubmed.ncbi.nlm.nih.gov/11360336/
  4. FEDIAF. Nutritional Guidelines for Complete and Complementary Pet Food for Cats and Dogs. https://europeanpetfood.org/self-regulation/nutritional-guidelines/