DNA Testing a Rescue Dog: What It Can and Can't Tell You
Shelter breed labels are educated guesses, and research shows they're often wrong. Here's what a DNA test can tell you about your rescue dog, how to read a very mixed result, and what DNA can't explain.
By PuppyGenes · How we research and write our guides
A DNA test is a far better guide to a rescue dog's breeds than the label on its shelter card, which is usually a best guess based on looks. Studies comparing shelter labels with DNA have found they often miss breeds or name ones the dog doesn't have. A test can show your rescue's estimated breed mix, its coat and size genetics and its genetic diversity. It can't explain your dog's history or predict exactly how it will behave.
The short version
- Shelter labels are educated guesses made from appearance.
- Research shows they're often wrong, especially for dogs with several breeds in their background.
- Most shelter dogs are mixes, and a mix of four or five breeds is almost impossible to read by eye.
- Unresolved ancestry is normal in very mixed dogs and doesn't mean a test failed.
- Breed tendencies are a starting point, not a forecast of how your dog will behave.
- Dogs adopted from abroad may have ancestry that doesn't closely match any modern breed.
Why shelter breed labels are often wrong
Several studies have compared the breeds shelters write down with what DNA shows:
- Adoption agencies: in a study of dogs adopted from 17 locations, agencies had named specific breeds for 16 dogs. DNA found an agency's named breed among a dog's main breeds in only 4 of the 16, and for 14 of them it didn't detect every breed the agency had listed.
- Two large shelters: a study of 919 shelter dogs in Phoenix and San Diego found only about 5% were purebred. At one shelter, staff matched at least one breed in about two-thirds of dogs, but agreement fell to about one in ten when they tried to name more than one breed.
- Pit bull-type labels: in a study of 120 dogs at four shelters, staff labelled 62 dogs as pit bull-type, while DNA identified 25. Staff also often disagreed with each other.
None of this is a criticism of shelter staff. Telling a mix of several breeds apart by eye is close to impossible, and the researchers behind the San Diego and Phoenix study suggested shelters focus on describing each dog's behaviour and physical traits instead.
What a DNA test can tell you about your rescue
The PuppyGenes report covers six sections:
- Breed ancestry: an estimated breed mix shown as percentages, including any ancestry that could not be resolved.
- Coat colour: predicted colour, pattern and markings where the sample supports them.
- Physical appearance: coat and body features such as coat length, curl, shedding, muzzle and tail, each with its own confidence.
- Temperament and size predictions: breed-informed tendencies and an estimated adult height and weight, which is handy for a young rescue.
- Genetic diversity: an inbreeding estimate compared with the lab's reference panel of dogs.
- Oral microbiome: a snapshot of the bacteria measured in the saliva sample. Context, not a diagnosis.
The report does not include genetic disease or health screening.
Reading a very mixed result
Rescue dogs often come back with three, four or more breeds, some in small amounts. A few things help when you read a result like that:
- Big shares tell you the most. A breed making up around half or a quarter of your dog's DNA likely came from a parent or grandparent.
- Small shares come from further back, often a great-grandparent or beyond, and they're the least certain part of any result. Our guide to breed percentages explains how shares map to a family tree.
- Unresolved ancestry is part of the answer. It's the share of your dog's DNA that couldn't be confidently assigned to a single breed, including small contributions too uncertain to report on their own.
- Looks may not match. A handful of genes control how a dog looks, so a rescue can resemble one breed and carry several others. Our guide to DNA results that don't match a dog's looks explains why.
Using results for training and care
Breed results are most useful as context. A dog with herding breeds in its mix may enjoy games that give that instinct an outlet, and a dog with scent hounds may love sniffing games. Our guide to what a dog's breed means for daily care covers how to use that context.
What breed results can't do is predict your individual dog. A 2022 study of more than 18,000 dogs found breed explains only about 9% of behavioural differences between individual dogs. A rescue's history, socialization and personality matter far more. If you're working through fear, reactivity or other behaviour problems, a qualified trainer or a veterinary behaviourist is the right next step, whatever the DNA says.
Rescue dogs from other countries
Some rescues in Canada come from other countries, including places where free-roaming "village dogs" are common. Village dogs are more genetically diverse than purebred dogs, and a 2015 study of village dogs in 38 countries found that while some populations descend almost entirely from European breeds, others, including those in Vietnam, India and Egypt, show little sign of European breed ancestry.
A dog with that kind of background may not closely match any modern breed. Its result can show more unresolved ancestry, or small amounts of several breeds, than a dog bred locally from breed lines.
Frequently asked questions
- Is my rescue dog's breed label right?
- It might be partly right, but research suggests it's often incomplete. In studies comparing shelter labels with DNA, staff frequently missed breeds or named ones the dog didn't have, especially when a dog had several breeds in its background. A DNA test gives you an estimate based on the dog's own genetics instead of its looks.
- What breed is my rescue dog?
- A DNA test is the best way to find out. It estimates your dog's breed mix as percentages, along with any ancestry that couldn't be resolved. Many rescues turn out to be mixes of several breeds, which is why they're so hard to identify by eye. Our guide to identifying your dog's breed compares the options.
- Can a DNA test help with my rescue's behaviour?
- It can add context, such as which breed instincts might be in the mix, but it can't predict your dog's personality. Breed explains only a small share of behaviour differences between individual dogs. For behaviour problems, work with a qualified trainer or a veterinary behaviourist.
- Why does my rescue's result show unresolved ancestry?
- Unresolved ancestry is the part of your dog's DNA that couldn't be confidently assigned to a single breed, including small contributions too uncertain to report on their own. It's common in very mixed dogs and in dogs whose ancestry isn't well represented by modern breeds. It doesn't mean the test failed.
- Can a DNA test tell my rescue dog's age?
- No. A breed ancestry test doesn't read a dog's age. Our guide to whether a DNA test can tell a dog's age explains how age is usually estimated instead.
- Will a DNA test show if my rescue has health problems?
- No. The PuppyGenes report does not include genetic disease or health screening. Talk to your vet about your dog's health, especially in the first weeks after adoption.
From general to personal
See how this applies to your dog specifically.
Our at-home Complete Dog DNA Test adds your dog's own results to these tips across six report sections: breed ancestry, coat colour, physical appearance, temperament and size predictions, genetic diversity and oral microbiome. The report does not include genetic disease or health screening.