Copper: the nutrient nobody can agree an upper limit for

Short answer: copper is essential, it accumulates in the liver, and there is currently no scientifically grounded maximum for dogs. NRC 2006 left the safe upper limit unset. An AAFCO expert panel reviewed the literature in 2022, concluded the data were insufficient, and declined to set one. The EU limit that does exist was derived on environmental grounds — copper accumulating in soil from animal waste — not from canine liver disease.

Why copper is the hard one

Most nutrients are forgiving in one direction. Copper is not. Too little causes anaemia, coat depigmentation and connective-tissue defects. Too much accumulates in the liver, and unlike a water-soluble vitamin there is no convenient route out — the excess is excreted in bile, slowly, and if intake outruns that the liver stores the difference.

Some breeds carry a genetic predisposition to copper storage hepatopathy — Bedlington Terriers most famously, with Labradors, Dobermanns and West Highland Whites also over-represented. For those dogs the margin is narrower still.

So this is a nutrient where you would very much like a number for the ceiling. There is not a good one.

What the standards actually say

Wondering how this applies to your own pet? Build their bowl — two minutes, and it gives the exact grams for their weight.

NRC 2006 left the dog copper safe upper limit blank, because no adequate dose-response toxicity work existed to set it from.

AAFCO convened an expert panel and reported in 2022. Having reviewed the literature, the majority concluded there were insufficient empirical data to establish a safe upper limit or maximum tolerable level in normal dogs — and that setting a maximum would be, in their own framing, an arbitrary decision not based on science, with no assurance the chosen value would protect against liver disease. AAFCO therefore did not set a maximum. It upheld its existing guidance.

The panel did try to bound it. The no-observed-adverse-effect level in dogs appears to sit somewhere between roughly 112–124 mg/kg dry matter and 448–496 mg/kg — a fourfold spread, resting largely on a single study from 1972. That is the honest state of the evidence.

The European Union does impose a maximum of 25 mg/kg dry matter. It is the number most often quoted as though it were a canine safety threshold. It is not: it was set on ecological grounds — copper passing through the animal into waste, and accumulating in soil and water. It may well be a sensible number for dogs. Nobody established it as one.

A correction we made to our own internal document. An earlier Growlrr regulatory note stated that AAFCO had adopted the EU's 25 mg/kg limit. Checking the primary source before publishing this, that is wrong — AAFCO declined to set any maximum. The EU has the limit; AAFCO does not. We have corrected the internal document and are noting it here, because a site that asks you to check its numbers should show what happens when a check fails.

What this means if you are cooking at home

Two practical things.

Liver is the variable that matters. Organ meat is extraordinarily copper-dense — far more so than muscle. A little is genuinely useful; a habit of feeding liver several times a week is an uncontrolled copper intake layered on top of whatever else you are giving. This is the single most common way a home-cooked bowl ends up copper-heavy, and it is easy to fix by treating liver as occasional rather than staple.

Copper does not act alone. Zinc and copper compete for absorption, and the relationship runs both ways: high zinc suppresses copper uptake, and copper status falls as the ratio narrows in the other direction. This matters because the underlying requirement studies largely set each mineral in isolation — the zinc requirement was not established under controlled copper intake, and vice versa. Adding a zinc supplement for a dull coat, on its own, is not a neutral act.

How we treat it

Copper is the binding constraint in our formulation — the nutrient that sets the ceiling on the whole block rather than one line item among many. We hold it well inside the range the AAFCO panel identified, and we do not read the absence of a published maximum as permission to be relaxed about it.

We supply it as copper proteinate, an organically bound form, which is generally better absorbed than the copper sulphate the reference studies used. We take no credit for that in the arithmetic: we meet the figure as written and treat the better absorption as margin rather than as licence to supply less. Where a standard is uncertain, the conservative reading is the only defensible one.

The full account of where NRC 2006 is thin, and what we do about each gap, is in our regulatory position.

Build your pet's bowl →

References

AAFCO Copper in Dog Foods Expert Panel report (2022). Association of American Feed Control Officials, Pet Food Committee.
National Research Council (NRC). Nutrient Requirements of Dogs and Cats. Washington, DC: National Academies Press; 2006 — dog copper SUL not established.
European Union maximum for copper in complete pet food: 25 mg/kg dry matter, derived on environmental accumulation grounds.