The Embark Copper Result in Chihuahuas: What Our Data Show, and Why Breeders Should Test, Not Cull

Chihuahua breeders are spaying and neutering healthy dogs over one line on an Embark report. Some are pulling whole lines from their programs. Others are going online to call breeders unethical because their dogs carry the copper variant.

Our data do not support any of it.

We have been tracking the Embark copper result in Chihuahuas since October 2024. As of October 2026, we have verified results for 87 Chihuahuas from seven breeding programs. Every one of them has normal liver bloodwork. Not one has shown signs of copper disease. That includes every dog with two copies.

This post explains what the copper result is, where the research behind it comes from, what our Chihuahua data show, and why the breed needs breeders adding dogs to the study, not removing dogs from the gene pool and tearing each other down.

What the Embark copper result is

Embark added a test called Copper Toxicosis (Accumulating) to its health panel in 2024. It looks for one variant in a gene called ATP7B. In people, this gene is linked to Wilson disease. In dogs, it helps move copper out of the liver and into bile.

Every dog gets one of three results:

• Clear (0 copies). The dog does not carry the variant.
• One copy. The dog carries one copy. Embark flags this as "Notable."
• Two copies. The dog carries two copies. Embark also flags this as "Notable."

"Notable" is not a diagnosis. It does not mean the dog is sick. It does not mean the dog will get sick. It means the dog carries a variant that has been linked to copper buildup in some other breeds.

Embark itself says the variant has incomplete penetrance and adult onset. It also says risk in breeds other than Labradors and Dobermans is unclear. That includes Chihuahuas.

We do not use the word "affected" for two-copy dogs. "Affected" is a clinical word. No clinical effect of this variant has been shown in our breed.

Where the research comes from

The link between this variant and copper buildup comes from Labrador Retrievers. It was later found in Dobermanns. No one has studied it in Chihuahuas, apart from this study.

The Labrador study has real limits:

• All 294 dogs were Labradors from one veterinary hospital in the Netherlands.
• It measured copper staining on liver biopsy, not illness.
• It did not give a rate of how many carriers get sick.
• The variant explained about 8% of the difference in liver copper between dogs. Another gene, ATP7A, changed its effect.
• Diet was not recorded.

Since then, the variant has turned up in many breeds that have no known copper disease. In Cavalier King Charles Spaniels, it was found in healthy control dogs with no copper in their livers. Those researchers concluded it does not cause disease on its own in that breed. Other researchers have advised against selecting against it until each breed's risk is known.

Bedlington Terriers have a well-known copper disease. That disease comes from a different gene, COMMD1. It is not what Embark is testing for here.

The short version: the copper result was built on one breed. Moving Labrador risk onto Chihuahuas is not supported by the evidence.

What our Chihuahua data show

As of October 2026, we have verified Embark copper results for 87 Chihuahuas from seven breeding programs. This is year 2 of a planned 8-year study.

• Clear (0 copies): 45 dogs (51.7%)
• One copy: 38 dogs (43.7%)
• Two copies: 4 dogs (4.6%)
• Total: 87 dogs

Nearly half the dogs, 42 of 87 (48.3%), carry at least one copy. The variant makes up 26.4% of all copies of the gene in the cohort.

Health status:

• Every dog has normal liver bloodwork.
• No dog has shown signs of copper disease.
• That includes all four dogs with two copies.

Programs differ a lot. The two largest programs in the study carry the variant at very different rates: 46.9% in one and 21.0% in the other. That gap is too large to be chance (p = 0.006). It is what you expect in a breed made of closed, line-bred programs, where a few popular sires shape a whole line. It also means no single kennel's numbers speak for the breed.

The overall numbers fit what geneticists call Hardy-Weinberg equilibrium. In plain words, the variant has been passed along freely, with no selection for or against it. That makes sense: breeders had no way to see it until Embark started reporting it in 2024.

Why "Notable" is not a diagnosis

Two facts keep anyone from tying this result to a sick dog right now.

1. The dogs are young. Copper-related liver disease shows up in adult dogs. Embark only started testing for this in 2024, so the dogs with results are young. The study has 6 of its 8 planned years still to run. A clean result today does not rule out a problem later. A "Notable" result today does not predict one either.

2. Copper has two causes. A dog can build up liver copper from genes, or from diet. Starting in 1997, dog food guidelines moved from copper oxide to forms of copper the body absorbs much more easily. Liver copper levels in dogs have climbed in the decades since. Breeds with no known copper gene now show copper-related liver disease.

The two causes look alike in bloodwork. Telling them apart takes a liver biopsy with copper measurement. So even if a Chihuahua with this variant did develop liver trouble, the variant could not be blamed without that workup.

That is why this study tracks diet, follows liver panels over time, and will fully investigate any dog that develops liver disease. That is how the question gets answered. A single DNA result cannot answer it.

What eliminating these dogs would cost

In our cohort, 48.3% of Chihuahuas carry at least one copy. Remove every one of them, and you remove nearly half the breeding dogs in one generation.

The Chihuahua gene pool is already small. Toy breeds trace back to a narrow founding base. Pulling half the dogs out at once does not just remove a variant. It removes whole bloodlines, along with everything else they carry: structure, temperament, longevity, and resistance to diseases we have not even identified yet. Loss of diversity on that scale is documented in other breeds. It does not come back.

And it would be done for a benefit no one has shown exists.

Spaying and neutering are permanent. A dog pulled from a program can be brought back. A spayed or neutered dog cannot. Every healthy Chihuahua sterilized over this result is a permanent loss to the breed, based on a test that was never studied in the breed.

We have said this from the start, and our data still support it: no breeding restrictions based on the copper result are recommended at this stage. If the data ever show that this variant causes liver disease in Chihuahuas, we will report it and change that advice. Until then, a dog's future should rest on that dog's actual health, not on a "Notable" flag.

Stop attacking other breeders over this result

A breeder whose dogs carry this variant has done nothing wrong. Nearly half the dogs we have tested carry it. If your dogs have not been tested, there is a good chance some of them carry it too.

The breeder who tested, got a "Notable" result, and shared it is the breeder doing the right thing. Testing and disclosure are what responsible breeding looks like.

When breeders get shamed online for sharing a result, the lesson everyone else learns is simple: don't test, or don't tell. That is the worst outcome for the breed. It leaves us with fewer results, hidden results, and no way to ever answer the question.

Public posts calling breeders unethical over this result are not protecting Chihuahuas. They are spreading a claim the evidence does not support, and they are scaring off the people whose data we need most.

If you have concerns about a dog's health, look at that dog's actual health records. If you have concerns about the copper result, help us study it.

Add your dog to the study

The only way to find out what this variant means in Chihuahuas is to follow a lot of tested dogs for a lot of years. Our goal is 200 or more verified dogs. Every dog counts:

• Clear dogs. We need them. A frequency study is only as good as its full count.
• One-copy dogs. Their health history over time tells us whether carriers stay healthy, as they do in every breed studied so far.
• Two-copy dogs. These are the most important dogs we can follow. A two-copy dog with normal liver values is just as valuable to the study as one with a problem.

What to send:

1. The full Embark PDF report, every page. The test must be from 2024 or later and include the copper result.
2. A current liver panel from a routine vet visit. Most standard chemistry panels already include it.
3. A follow-up liver panel every 1 to 2 years. Your dog's yearly wellness bloodwork works.

Email both PDFs to healthresearchataa@gmail.com with the subject line:

ATP7B Study - Embark Report + Liver Panel Submission

One dog per email. Include the call name, age, country, and registry.

Owner names, addresses, and contact details are never published. Dogs are reported by study ID.

Full details are on the study page: The Chihuahua ATP7B Variant Study.

Read the study

• Study page and how to take part: The Chihuahua ATP7B Variant Study
• Full interim report: Stringer T. CAH Testing in Chihuahuas. Interim analysis, year 2 of 8. Updated November 7, 2026.

Sources

1. Fieten H, et al. The Menkes and Wilson disease genes counteract in copper toxicosis in Labrador retrievers: a new canine model for copper-metabolism disorders. Dis Model Mech. 2016.
2. Wu X, et al. Association of the canine ATP7A and ATP7B with hepatic copper accumulation in Dobermann dogs. J Vet Intern Med. 2019.
3. Online Mendelian Inheritance in Animals. OMIA 001071-9615: Wilson disease in the dog.
4. Haywood S, et al. Copper toxicosis in Bedlington terriers is associated with multiple independent genetic variants. Vet Rec. 2023;193:e2832. doi:10.1002/vetr.2832
5. Nivy R, et al. Copper-associated chronic hepatitis in Cavalier King Charles spaniels. Vet Rec. 2024;194:e3561. doi:10.1002/vetr.3561
6. Embark Veterinary. Copper Toxicosis (Accumulating).
7. Center SA, et al. Is it time to reconsider current guidelines for copper content in commercial dog foods? J Am Vet Med Assoc. 2021;258(4):357-364.
8. Strickland JM, et al. Hepatic copper concentrations in 546 dogs (1982-2015). J Vet Intern Med. 2018.