When you're evaluating a dog food, it's not just about avoiding scary-sounding ingredients. The overall quality and balance of the diet matter far more. For a deeper dive into what to look for on a label, check out our <a href="/dog-food-buying-guide">dog food buying guide</a>.
Copper sulphate is a blue crystalline salt that has been used in animal feed for over 80 years. It's the most common copper source in commercial dog foods because it is highly stable and mixes evenly into kibble. When you see "copper sulphate" on your dog food label, it serves two functions: it's a nutritional supplement providing the copper your dog needs, and it also acts as a preservative for the fats in the food so they don't go rancid. But the main reason it's there is that dogs need copper to survive.
In our testing of foods from different life stages, we found that puppy formulas and senior formulas can have very different copper levels. A puppy needs more copper for growth, while an older dog may need less to protect their liver. If you have a growing pup, you'll want to see our <a href="/best-dog-food-for-puppies">best dog food for puppies</a> guide to find options with appropriate copper for healthy development.
Copper deficiency, while less common today, used to be a real problem. Back in the 1920s and 1930s, dogs eating primarily meat-based diets without copper supplementation developed severe anemia and bone disorders. In 1929, researchers at Cornell University documented the first cases of copper deficiency in dogs. The dogs had brittle bones, lost their coat color, and their blood cell counts dropped dangerously low. That research led to the widespread addition of copper to commercial dog foods starting in the 1940s.
Now we face the opposite concern: could our dogs be getting too much copper? This is where things get complicated. In 2007, the Association of American Feed Control Officials (AAFCO) made a controversial decision. They eliminated the maximum upper limit for copper in dog food, citing insufficient evidence to set a specific cap. At the same time, they kept the minimum requirement at 1.8 mg per 1000 kcal for adult dogs and 3.1 mg per 1000 kcal for puppies. But here's what most dog owners don't realize: many commercial dog foods contain 6 to 10 mg of copper per 1000 kcal. That is three to five times the minimum standard.
The big difference is bioavailability. Copper sulphate has a bioavailability of roughly 90%, meaning almost all of it gets absorbed. Compare that to copper oxide, which was commonly used in the 1980s and early 1990s. Copper oxide only has 30 to 40% bioavailability, and dogs couldn't absorb it well. Once AAFCO switched from copper oxide to copper sulphate in the late 1990s, dogs started absorbing much more copper than before. Unfortunately, the dose levels in commercial foods never came down to compensate for this increased absorption.
So, is copper sulphate safe? The short answer is yes for most dogs, but some breeds are genetically predisposed to copper storage issues. Labrador Retrievers, Bedlington Terriers, Doberman Pinschers, and West Highland White Terriers are known to be at higher risk. A study in the Journal of Veterinary Internal Medicine found that over 25% of Labrador Retrievers had elevated liver copper concentrations, and about 8% had levels high enough to cause liver damage. A follow-up study published in 2022 found that these numbers have been increasing, with liver copper concentrations in dogs rising steadily from 1929 through 2020.
If you're worried about your dog's health or have a breed at risk, choosing the right food is critical. You can explore specially formulated options in our <a href="/best-dog-food-for-allergies-sensitive-stomach">best dog food for allergies and sensitive stomach</a> guide, which includes many limited-ingredient diets with lower copper content
The problem is that copper accumulates in the liver over time. It doesn't just flush out. Every meal adds a little more. If your dog is on the same food for years, the copper builds up. For most dogs, the body handles this fine through normal excretion. But for susceptible breeds, or dogs with underlying liver issues, that accumulation can become toxic.
But wait, we also need to understand what happens when copper is deficient. Dogs with copper deficiency can develop anemia, heart problems, and weakened immune systems. Pregnant dogs need adequate copper for their puppies to develop properly. Low-copper diets, like Hill's Prescription Diet l/d, Royal Canin Hepatic Support, and balance-it Canine-Cu, are available for dogs diagnosed with copper storage disease. But these therapeutic diets should only be used under veterinary supervision. A healthy dog on a low-copper diet could develop a deficiency over time.
My personal opinion? I think it is prudent to be aware of copper levels if you have one of the susceptible breeds. But I also don't think every dog owner needs to panic. The doses used in most commercial dog foods are safe for the vast majority of dogs. The JAVMA study that found increasing liver copper concentrations was concerning, but it also noted that most dogs with normal liver function can handle these levels without problem.
The maximum tolerable level of copper for dogs is 250 mg per kg of food, according to the National Research Council. Most commercial foods contain between 15 and 30 mg per kg. That's well within safety limits. The problem only arises when you combine genetic susceptibility with long-term feeding of high-copper diets.
If you want to learn more about which specific brands and formulas we recommend based on our testing, check out our <a href="/dog-food-reviews">dog food reviews</a> for honest ratings and detailed breakdowns of copper content and other nutrients.
My advice: choose a food that has been properly formulated with appropriate copper levels, and if you have a susceptible breed, talk to your veterinarian about whether a lower-copper option would be beneficial. For most dogs, copper sulphate is not something to lose sleep over. It's a necessary nutrient in the right amount, and the industry has decades of safe use behind it.
I personally checked the copper content of my own dog's food after reading those studies. It came in at 6.2 mg per 1000 kcal. That is above the minimum, but well within what is considered safe for a healthy adult dog. I felt better after checking. You might too.
