Too Much Copper in Dog Foods?

I briefly mentioned this paper (Is it time to reconsider current guidelines for copper content in commercial dog foods?) in a blog post a couple of months ago, but I would like to draw more attention to the paper.

November 7th Update

Here is a link to a recent FDA listening session where one of the authors Dr. Sharon Center discusses the issue.

All of the authors are DACVIM Diplomates of the American College of Veterinary Internal Medicine, except Dr. Wakshlag who is a Diplomate of the American College of Veterinary Nutrition, and Dr. Watson who is a member of the European College of Veterinary Internal Medicine.

Dr. David Twedt, and Dr. Sharon Center are both widely recognized for their research on liver and gastrointestinal disease in both dogs and cats.

These researchers and others have noticed an increasing trend in copper-related liver disease over the past 15-20 years. They believe that this may have occurred as a result of a change in the type of copper used in many dog foods.

The researcher’s collective clinical opinion is that the increase began in 1997 after the development of new guidelines. Which required the use of copper sulfates or chelates in premixes which are far more bioavailable than the previously utilized copper oxide.

They do acknowledge that this could be a result of increased awareness. However, two studies that looked at tissue samples before and after the change lead them to believe that it is not a significant factor. (Strickland 2018,  Gange 2013)

In one study published in 2018 they looked at the hepatic copper concentrations of 546 dogs from the year 1982 to 2015.

In the Non predisposed breeds the median was 177.1 micrograms/g in the 1982–1988 period to a median of 278.0 microgram/g in the 2009–2015 period or a 57 percent increase.

In the Predisposed breeds the median cooper increased from 291.4 micrograms/g in the 1982–1988 period to 604.0 microframs/g in the 2009–2015 period or a 107 percent increase.

Predisposed breed are Labrador Retrievers, Doberman Pinschers, West Highland White Terriers and Dalmatians.

There was also a marked increase in the proportion of dogs exceeding 300 micrograms/g, 400 micrograms/g, and 1000 micrograms/g

They further argue that research comparing feral dogs with dogs fed foods compliant with AAFCO and NRC. The feral dogs have much lower Liver copper levels.

The authors reference two papers that demonstrate that the long term feeding of copper restricted diets is safe for healthy dogs. Ie Diets with less than the AAFCO minimum for copper in complete and balanced foods.

“long-term feeding of copper-restricted diets (copper intake ranging from 0.04 to 0.07 mg/kg/d [0.018 to 0.032 mg/lb/d]) is safe in healthy dogs, and dogs with unexplained fluctuations in serum hepatic enzyme activities, and dogs with various hepatic disorders, including congenital portosystemic shunts, acquired hepatic insufficiency, and copper-associated hepatopathy. In some instances, these diets have been fed to healthy dogs out of convenience because another dog in the household required a dietary adjustment, and to our knowledge, no dogs have developed clinical evidence of copper insufficiency (eg, anemia, neutropenia, neurologic signs, or changes in coat color or texture) while being fed these copper-restricted diets.”(Hoffmann 2013, Fieten 2014)

“Fifth, the current AAFCO recommendation for minimum daily copper intake for maintenance adult canine diets of 1.83 mg/1,000 kcal is equivalent to a copper intake of approximately 0.067 mg/kg/d for a medium- or large-sized dog (the precise conversion is done on the basis of metabolic body weight). This represents approximately 1.7 to 1.8 times the copper intake associated with copper-restricted diets (0.9 to 1.1 mg/1,000 kcal, ranging from approximately 0.04 to 0.07 mg/kg/d), which again, the authors have found to be safe for long-term feeding of healthy dogs and dogs with various hepatic diseases.”(Carter 2021)

Furthermore, the authors are of the belief that copper deficiency did not appear to be a problem before the 1997 update. They do consider; however that deficiency was possible but was not recognized. The researchers, however, are ultimately not convinced by this argument.

Most copper-restricted diets are also protein restricted. The authors believe that there is a need for copper-restricted maintenance diets without the accompanying protein restriction.  

One thing about NRC guidelines is that they only contain a recommended amount. They do not contain a minimum or maximum amount.

There previously was a upper limit prior to the 2006 NRC update, but that information was gleaned from swine.

AAFCO’s minimum amount of copper is above the NRC recommended amount of copper.

The researchers, while many others have considered, believe that both the minimum required amount of copper is too high and that a safe upper limit needs to be created for diets labeled complete and balanced.

Currently, the RA amounts per the 2006 NRC are 6mg Per Kg Dry Matter, assuming an energy density of 4000 kcals per KG, 1.5mg Per 1000 kcals. The recommended amount per the NRC for bodyweight is .2mg per kg bw^.75

AAFCO’s guidelines for adult maintenance are 1.83 mg/1000 kcal or 7.3 mg on a dry matter basis assuming energy density of 4000 kcal per kg.

FEDIAF recommend nutrient levels are 1.8 mg per 1000 kcals with an adult based MER of 110/ kcal per kg^.75 and 2.08 mg per 1000 kcals with an adult based MER of 95/ kcal per kg^.75.

This results in wildly varying amounts of Copper in pet foods, whether it is Kibble, Canned Food, Raw, Cooked, or Freeze-Dried Dog food.

It does need to be noted that many commercial pet foods are formulated for all life stages including growth. This means when formulating the food they are going off the minimum copper amount for growth and reproduction (12.4 mg/kg) not the lower adult maintenance minimum (7.3mg/kg)

It is also possible in your Home prepared raw or cooked diet depending on the ingredients used, but is much less likely as several studies indicate that a large percentage of homemade raw or cooked diets are actually deficient in copper.

However when looking more closely at the ratio diets, it is very possible that you are providing around 2.24 times the minimum based on 1000 kcal or 2.69 times on a dry matter basis if beef or lamb liver are primarily used.

“Five articles, published in the period of 2012 to 2018, report the analyzed levels of total copper in complete dry dog foods (5-9, Note 3). For 183 dry foods, the mean concentration and range were 18.0 mg/kg and 7.6-47.0 mg/kg dietary dry matter.” (Beynen, 2020)

Now Very few manufactures list the copper content on their bag or on their website As you can see from the table below. In order to find out how much copper is in the food you would have to contact the manufacturer.

NameAmt Copper
Annamaet Encore15.39mg/kg
Acana Light and Fit14.8 mg/kg
Natures Logic Distinction Beef10.6 mg/kg
Fromms Adult Gold13.12 mg/kg
Purina Pro PlanNot Listed
HillsNot Listed
Blue BuffaloNot Listed
KirklandNot Listed
Taste of the WildNot Listed
EarthbornNot Listed
NameAmt Copper
My Perfect Pet Boomers Chicken and Beef7.7 mg/kg
Northwest Naturals Lamb11 mg/kg
Vital Essentials Beef14 mg/ kg
Stella and Chewy’s Surf and Turf66.56 mg/kg
Steve’s Real Food7.6 mg/kg
Raised Right Beef13.29 mg/1000 kcal
All ProvideNot Listed
AnswersNot Listed
CaliRawNot Listed
Bones and CoNot Listed
Small BatchNot Listed
Raw BistroNot Listed
Raw Dog Food

Note on Raised Right the number listed is per 1000 kcal. Which per AAFCO IS 1.83 mg/1000kcal

All of these both kibble and raw are several times above what the observers in the previous study had found was safe for long term feeding of healthy dogs.  Which in the instance of the 30lb dog would between .65 and .53.

This is also good news for DIY feeders as copper is one of the nutrients deficient in home made foods.

It’s also important to add in the fact that in many areas if you your dog is drinking tap water they may also be getting Copper from the water.  This is highly variable based on where you live. If your house or apartment has copper plumbing this could also be contributing more copper to the diet.

This is one of the reasons why it is recommended to not use hot water from the faucet for baby formula. As the hot water dissolves copper more more easily.

This all goes to show that more research needs to be conducted to further refine the nutrient guidelines whether it means increasing the level required or decreasing the level required. More research needs to be conducted to determine what is the optimal level of various nutrients. More research needs to be conducted looking at the bioavailability, and how that impacts what the nutrient levels should be.

As of this writing there are currently no plans to update the NRC guidelines in the near future. The last time they were updated was 2006 and that took 3 years.

AAFCO is far more likely to update their guidelines.  If/when AAFCO decides to update the guideline it will likely still take several years to actually get implemented.  If AAFCO does institute a max level of copper it will likely result in many foods having to be reformulated.

As I’m sure you’ve notice we preach rotating between different food treats, chews and food toppers. This is another good reason to rotate between different foods so that they get carry levels of nutrients.

Copper Rich Ingredients commonly used in dog food and treats

  • Liver
    • Beef, Lamb, and Duck are significantly higher than Chicken, Turkey, and Pork
  • Shellfish such as Oysters or Shrimp
  • Heart
  • Chickpeas/Garbanzo Beans
  • Hempseed, Flaxseed
  • Peanut Flour
  • Peanut Butter
  • Quinoa
  • Kidney
  • Sardines
  • Salmon
  • Beans
  • Lentils
  • Sweet Potato
  • Rice
  • Potatos

Other ingredients such as Kelp, Spirulina, Kale, Wheat Grass, Basil, Spearmint, etc are often included at such small amounts that they are unlikely to add significant amounts of copper to your dog or cats diet.

This also assumes that the USDA database is actually accurate, which given enviormental changes, changes in farming practices, both livestock and agriculture, there ie reason to believe that many numbers within the USDA database are no longer fully accurate.

That doesn’t mean we should avoid these ingredients. Many of them also provide a wide range of other important nutrients such as Taurine, Thiamine, Iodine, Manganese, Vitamin A, Choline, and Phytonutrients, etc.

But it does demonstrate the importance of rotation so that your dog can receive a wide range of nutrients.

It’s possible that this has more to do with the specific types or copper added into the food instead of simply the total amount of copper in the diet.

What we can do in the meantime while the NRC and AAFCO guidelines don’t get updated.

Milk thistle, is commonly recommended by many veterinarians as supplements when treating dogs with liver disease as they can help support the liver. Studies have shown that milk thistle helps protect the liver cells and even repair the liver. Silybin the active compound in Milk Thistle is actually used in Denamarin which is often prescribed to dogs with liver disease.

One study showed that administering 50mg /kg of Silibinin 5 and 24 hours after a single dose of Amanita Phalloides (Death Cap), was able to prevent the death of all of the silibinin treated dogs. The silibinin treated dogs also had necrosis in the liver. Four of the 12 dogs died with signs of liver failure within 54 hours. While the others recovered by the ninth day.

While there are no research studies that I know of to support it’s use specifically in copper-associated liver disease, benefits have been shown in some studies of other types of liver damage, such as from chemotherapy drugs and liver toxins.

There are specific treatments that are used in dogs with copper storage disease such as supplemental Zinc which helps limit the absorption of copper allowing it to be excreated. This should only be done under the supervision of a veternarian.

Milk thistle also appear to be safe, and unlikely to cause harm.

That being the case why are we waiting for it to become an issue instead of trying to prevent it from becoming an issue. We are far too reactive instead of proactive. Especially when there are things we can do to potentially mitigate the risk.

That is why when it comes to things like this, it’s important to always consider the costs vs the benefits.

Supplements are almost always unproven to actually lower the risks of various issues. Many of us give joint supplements. We don’t really know if it will actually prevent joint issues in the future, but we give then anyway as the potential gain is ultimately worth the cost.

In this case the cost every couple of months to help detox and support the liver is relatively low, the potential benefit at the end of the day is that it may possibly lower the risk of them developing liver or kidney disease in the future.

Note if you are going to give Milk Thistle or a product containing Milk Thistle, it’s important to note if you are giving concentrated milk thistle or whether it is the whole herb. As the dosage is very different.

As with any supplement its important to always discuss them with your veterinarian prior to use.

Conclusion

We as pet parents ultimately need to be lobbying our politicians to fund more research into updating the guidelines instead of relying on industry funded studies. We need them to fund research to determine what level of nutrients is the optimal amount for our dog’s and cats. Not what the minimum is to survive. At the end of the day we want our dogs to thrive not just survive. More research needs to be done to determine what the safe upper limit should be of various nutrients. It is more likely than not that there are more nutrients besides Copper that should have maximum allowances. This is one reason that AAFCO should get out of at least the nutrient profile business and leave it up to people that are actually qualified to help shape the guidelines not people who are simply regulators.

This is also a reason why we need to advocate for the government to fund more research for our companion animals, as well as updating the NRC which was last updated in 2006.

In the meantime however we can give them supplements to hopefully prevent it from becoming an issue later down the road.

One note about Complete and Balanced dog foods. A food can ultimately get away with being above or below the guidelines as long as it is similar to a lead product or it passes an AAFCO approved Feeding Trial. An AAFCO approved feeding trial is only 26 weeks and only requires 8 dogs of which 6 must complete the trial. There are very few tests. More about the feeding trials can be found here.

So even if AAFCO puts a max amount of copper there are ways that companies can get away with including levels of copper beyond the maximum amount as there are already foods that are above the max levels for other nutrients.

Works cited

Beynen, Anton. (2020). Beynen AC, 2020. Copper in dog food. 165-178.

Center, S. A., Richter, K. P., Twedt, D. C., Wakshlag, J. J., Watson, P. J., & Webster, C. R. (2021). Is it time to reconsider current guidelines for copper content in commercial dog foods? Journal of the American Veterinary Medical Association 2021 258:4, 357-364, 357-364.

Bradley A, Webb CB, Twedt D. Hepatic copper and zinc concentrations in feral dogs versus dogs fed a commercial diet (abstr). J Vet Intern Med 2013;27:715–716.

Fieten H, Biourge VC, Watson AL, et al. Nutritional management of inherited copper-associated hepatitis in the Labrador Retriever. Vet J 2014;199:429–433.

Fieten H, Hooijer-Nouwens BD, Biourge VC, et al. Association of dietary copper and zinc levels with hepatic copper and zinc concentration in Labrador Retrievers. J Vet Intern Med 2012;26:1274–1280.

Gagné JW, Wakshlag JJ, Center SA, et al. Evaluation of calcium, phosphorus, and selected trace mineral status in commercially available dry foods formulated for dogs. J Am Vet Med Assoc 2013;243:658–666.

Hoffmann G, Jones PG, Biourge V, et al. Dietary management of hepatic copper accumulation in Labrador Retrievers. J Vet Intern Med 2009;23:957–963.

Johnston AN, Center SA, McDonough SP, et al. Hepatic copper concentrations in Labrador Retrievers with and without chronic hepatitis: 72 cases (1980–2010). J Am Vet Med Assoc 2013;242:372–380.

Strickland JM, Buchweitz JP, Smedley RC, et al. Hepatic copper concentrations in 546 dogs (1982–2015). J Vet Intern Med 2018;32:1943–1950.

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