Copper: what’s not on the label?

Copper is an essential nutrient. Dogs need it for iron metabolism, connective tissue formation, pigmentation, antioxidant defence and several other biological functions. But for all its benefits, more is not necessarily better.

When copper is either absorbed in excess, or the liver is unable to process and excrete copper effectively, it can accumulate within liver cells. Over time, that accumulation may contribute to oxidative damage, inflammation, cell death and fibrosis. What makes this particularly troubling is that the process may be silent: by the time obvious signs of liver disease emerge, significant damage may already have occurred.

A 2021 study[1] saw an increased incidence of copper-associated hepatopathy in dogs over the preceding decade, which “appears to have coincided with a change in the type of copper used in premixes added to commercial dog foods”. It also states that the increase “may have been exacerbated by consumer-driven desire for pet foods formulated with a high content of animal-based ingredients (eg, evolutionary diets), including certain organ meats, that might introduce additional copper and by trends favouring foods containing vegetables with a high copper content (eg, sweet potatoes”. It called for reconsideration of dietary copper recommendations for dogs and current guidelines for copper content in commercial dog foods.

Given the apparent rise in diagnoses of copper hepatopathy over recent years, even beyond the breeds with known genetic susceptibilities, owners naturally want to know what they can do to prevent this.  Even in a home diet that provides flexibility, we still need to be mindful of excesses and deficiencies when feeding whole foods. In fact, it was while checking guidelines on copper for a canine shiitake recipe that I discovered how difficult copper exposure is to assess in manufactured food.

How is a responsible dog owner supposed to prevent excessive copper exposure when it is almost impossible to establish from a label how much copper a dog is eating?

This is an absolute labelling and nutritional minefield.

What does the label actually tell us?

Despite all concerns about copper, there is no requirement to display total copper content on the label of a complete dog food. The mandatory analytical declarations for compound pet food concern categories such as crude protein, crude fat, crude fibre and crude ash. Copper is not normally among them.

Additives

The label may be required to identify the additives: this declaration tells us about copper supplied through the declared additive. For example, you might have seen copper sulphate, copper chelate or another copper compound followed by a quantity in milligrams per kilogram. But that tells us nothing about the total copper content of the finished food. The copper occurring naturally in meat, liver and other organs, fish, cereals, legumes and numerous plant ingredients isn’t quantified separately.

Total intake

The copper figure stated likely doesn’t cover the total copper the dog is consuming. The ingredient list cannot fill the gap. It tells us which ingredients have been used, usually in descending order by weight, but not how much copper each ingredient contributes. Even recognising a copper-rich ingredient doesn’t help: we can’t calculate the finished food’s total copper concentration.

For an owner trying to decipher an ingredient list, the question “How much copper is my dog eating?” may therefore have no answer.

Absorption

In diet, the quantity of copper is not the only consideration: absorbability is also a factor. The cupric oxide originally used in manufacturing as a copper source has very low bioavailability. But manufacturers later started using more absorbable additives like copper sulphate and, more recently, organic copper complexes and chelates.

Enhanced absorption may sound beneficial, but it can increase the effective copper exposure if amounts aren’t adjusted to take account. Unfortunately, the recommended minimum hasn’t always been revised downwards when more bioavailable sources replaced cupric oxide and no nutritional upper limit was established[1]. The consequence: dogs would be absorbing more copper from the same amounts of additive[2].

This adds another layer to the problem. Even a label that declared total copper cannot indicate how biologically available that copper was, or how differences in absorption had been allowed for during formulation.

Maximum intake?

FEDIAF distinguishes between a nutritional maximum, marked N (a safe upper intake limit established by dietary safety studies), and a mandatory legal maximum, marked L (a regulatory limit imposed by animal feed legislation).

Copper is marked L, not N. The letter matters.

Code Type What It Represents Individual dog safety ceiling?
 N  Nutritional Maximum General population benchmark for healthy animals based on available research data

NO

(Does not account for individual genetics, bioavailability or lifetime cumulative load)
 L Legal Maximum Mandatory regulatory cap on added feed additives for market compliance

NO

(An administrative market cap, not a demonstrated biological safety limit for an individual animal)

When FEDIAF’s 2025 nutritional guidelines list a copper maximum of 2.8 mg per 100 g dry matter, equivalent to 28 mg per kilogram of dry matter, that is the maximum concentration legally permitted in complete food. It is not a demonstrated safe upper intake for an individual dog.

Dog-specific limit for intake

To estimate a dog’s actual daily copper intake from a commercial food, copper expressed as milligrams per 1,000 kilocalories would be especially useful because it relates the nutrient to the amount of energy supplied. Once that figure and the dog’s daily energy intake were known, the arithmetic would be straightforward, right? Maybe, with the help of a mathematician.

But even then, we encounter another problem. What would we compare the result with?

This is what makes the apparently simple instruction to “stay within nutritional guidelines” so difficult to interpret. The label does not ordinarily reveal total copper. The legal maximum is not an individual intake limit. And there is no agreed nutritional ceiling that owners can use as a preventive target.

Recent studies are beginning to investigate intake levels associated with liver copper accumulation, but there is still no generally accepted nutritional maximum that owners can use[3].

Asking the manufacturer

An owner could contact the manufacturer and ask for the total copper concentration of the finished food, preferably in milligrams per 1,000 kcal.

But further questions would still be necessary.

Does the figure include both naturally occurring and added copper or just the premix? Is this amount based on laboratory analysis of the finished product, or calculated theoretically from the formulation? Is this a typical average value or a maximum specification? What is the expected batch-to-batch variation? Can you provide the total copper concentration in milligrams per 1,000 kcal?

Even if a full and helpful response from the manufacturer allowed the owner to estimate exposure, there is still no generally accepted nutritional guideline against which to assess the answers.

An information problem, not a feeding guide

None of this means that copper should be minimised indiscriminately. Copper is essential and deficiency also has consequences. Nor does it mean that owners should attempt to formulate low-copper diets without appropriate knowledge or veterinary involvement.

That is not the point.

The point is that owners are encouraged to read labels, follow nutritional guidelines and make informed choices. But in the case of copper, the label will not typically reveal total content, the declared quantity will not reflect bioavailability, and the legal maximum is a concentration limit for the food, not a nutritional maximum for the dog.

A food can be complete, compliant and legally marketed while leaving its purchaser unable to answer a very basic question: How much copper is my dog actually consuming, and is that amount appropriate over a lifetime?

That is not a failure by the owner to understand the label. It is information the label was never required to provide.

I began with what I thought was a simple question about staying within the guidelines. Right now, as far as I can determine, an ordinary owner may have no practical way to know.

 

References:

[1] Center SA, Richter KP, Twedt DC, Wakshlag JJ, Watson PJ, Webster CRL. Is it time to reconsider current guidelines for copper content in commercial dog foods? J Am Vet Med Assoc. 2021 Feb 15;258(4):357-364. https://doi.org/10.2460/javma.258.4.357 PMID: 33539212.

[2] Laura A Amundson, Brent N Kirn, Erik J Swensson, Allison A Millican, George C Fahey, Copper metabolism and its implications for canine nutrition, Translational Animal Science, Volume 8, 2024, txad147, https://doi.org/10.1093/tas/txad147

[3] Center, Sharon & VanVranken, Philip & Randolph, John & Sapa, Cali & Dowdy, Ben & Hull, McKenzie & Miller, Andrew & Wakshlag, Joseph & Glahn, Raymond & Wiesinger, Jason. (2025). Lower risk for liver copper accumulation in dogs fed copper-restricted diets versus those fed copper-replete diets. Journal of the American Veterinary Medical Association. 264. 1-10. DOI: 10.2460/javma.25.05.0295

 

Important Considerations:

  • Always consult your veterinarian before making any significant dietary changes, particularly where there are pre-existing health conditions or dietary restrictions.
  • If you are feeding commercial food, check the label for ingredients before giving more. Excessive intake of any foods can have adverse effects.
  • Ensure (where possible) that you use high-quality, organic products specifically formulated for pets (or better still, human grade ingredients) to avoid any potential adverse effects.
  • Introduce new foods gradually to avoid adverse effects such as gastrointestinal upset or diarrhoea.
  • I provide nutritional information purely as a helpful guide. Nutritional information on ingredients is obtained from the US Department of Agriculture’s FoodData Central site (https://fdc.nal.usda.gov/index.html) and any nutritional information provided in recipes is based on an online calculator: calories and other information will vary based on brands, ingredients and other factors.
  • Check nutrient levels and recommendations for your dog’s weight, age and activity. For example this nutritional guideline produced by FEDIAF.
  • I am not a professional canine nutritionist but supporting research is cited.
  • The recipes shared were created by me and tested in my kitchen – and tasted and approved by our doggy friends!