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Intent on Buying a Purebred Puppy? Here’s How to Find a Healthy One.

A tool called the “coefficient of inbreeding,” or COI, can help you measure the risk that the puppy will have a genetic health problem.

buying a purebred puppy
When you’re buying a purebred puppy, it’s important to know the lineage. Photo: melissaleighstanley

Thinking of buying a purebred puppy?

If so, then take a few minutes to read this article. Seriously — it could save you from heartbreak.

When you fall in love with a particular breed, that puppy may carry an increased risk of genetic health problems.

For example, think:

Need I go on?

The Danger of Buying a Purebred Puppy

The reason is that creating the “look” of a breed means mating dogs who share a physical resemblance.

But an unwanted consequence is that the dogs are related.

If those ancestors share a “bad” gene coding for, say, hip dysplasia, then this gets passed down the line along with the breed’s looks.

A complication is that purebred dogs who appear fit and well may carry recessive genes for ill health. These recessive genes then show up when 2 dogs sharing the same gene are bred, resulting in 25% of the litter falling sick with that condition.

If your puppy is the 1 in 4 who develops debilitating hip dysplasia by the age of 3, then this matters — a lot.

If you’ve suffered the heartbreak of a gorgeous pet who becomes ill with a hereditary health problem, you’ll want to avoid this in future.

But how?

Actually, when you’re buying a purebred puppy, there are ways to predict a puppy’s health and therefore choose from a litter that’s statistically less prone to disease.

Here’s how …

Using Coefficient of Inbreeding when buying a purebred puppy
The coefficient of inbreeding (COI) can show how closely related the puppy’s parents are. Use it when you’re buying a purebred puppy. Photo: Alexas_Fotos

Coefficient of Inbreeding (COI)

If you take home one message about genetics, it’s that diversity is good.


In its simplest terms, when 2 healthy, unrelated dogs are bred, this gives the best chance of strong, genetically healthy pups.

But the other side of the coin is that breeding 2 closely related dogs magnifies hereditary health problems. Indeed, this risk can be measured and is called the “coefficient of inbreeding” (COI).

We can get as complicated as you’d like about genetics and the COI (homozygous, heterozygous anyone?), but instead let’s put things plainly.

COI and Its Interpretation

The COI measures how distantly related 2 parent dogs are and how many ancestors they share.

It is written as a percentage. The lower the number, the less closely related 2 dogs are:

  • So parent dogs with a 0% COI are totally unrelated — that’s ideal.
  • But parent dogs with a 25% COI would be like breeding brother and sister or father to daughter — not a good idea.
  • A 12.5% COI would be like mating grandfather and granddaughter — better, but still not a great idea.

Indeed, you can look at a breed as a whole to see how inbred it is. The Kennel Club has a slightly addictive Mate Select app for this where you put in the breed and see its overall COI.

Remember, a large gene pool will have a low COI, while a tiny gene pool has a high COI. So, in practical terms:

  • A breed with a low COI means it should be easy to find a completely unrelated dog to mate.
  • But a high COI means most of the dogs in that breed share lots of common ancestors.

Here are some of the breed COIs I looked up:

  • Pugs: 4.9%
  • Beagles: 9.7%
  • Poodles: 4.3% (Miniature and Toy); 2.3% (Standard)
  • Labrador Retrievers: 6.5%
  • Cavalier King Charles Spaniels: 6.3%

What It All Means When You’re Buying a Purebred Puppy

OK, let’s say that, unknown to you, the breeder is a cheapskate and breeds closely related dogs together.

Sadly, this increases the chances that you’ll be buying a purebred puppy with a genetic health problem.

One way of recognizing this before it’s too late is to study the pedigree papers of the parent dogs — but have you ever done that? It’s very complicated.

However, registered breeders in the United Kingdom, for example, have several generations of their dogs listed with the Kennel Club. This means all you have to do is visit the Kennel Club website and in the relevant section enter the pedigree name of both parent dogs, and presto: It generates a COI.

If that figure comes out at a scary 25%, then steer clear. And again, even a 12.5% COI is bad news, so choose accordingly.

Watch this news item on the problem Bulldogs are suffering because of inbreeding:

YouTube player

The COI Predicts but Doesn’t Guarantee

The COI is a great tool for avoiding inbred puppies, since these parents carry a greater risk of carrying bad genes, yet it doesn’t guarantee a healthy puppy (nothing can)

But team this up with buying from parents who are screened for genetic disease, and then you’re really a step ahead.

This type of screening that I’m talking about is different from the increasingly popular home DNA test kits you’ve probably seen advertised.

Genetic screening usually involves a vet visit and a blood sample (this is changing, with some specific screening tests now available as cheek swabs). The blood is then sent to a specialist genome lab where coding on the DNA helix is examined for sequences that spell trouble.

Why Screening the Puppy’s Parents Is Important

Many distressing diseases can be passed down from parent to puppy.

But some of these don’t develop until the parent dog is in middle or old age. Thus the dog produces the next generation before it’s realized they have the potential to pass on the problem.

It’s sobering to know currently there are around 350 inherited diseases that have been identified in dogs. That’s an awful lot of potential heartache right there if it means your cute puppy has an incurable metabolic disease, leading to a shortened life.

Now imagine the breeder knowing ahead of breeding whether the dogs will produce a healthy generation or not.

These tests check for errors or “misprints” on the DNA. If the potential parent tests positive for passing on a debilitating health condition, in theory, the breeder simply won’t breed that dog.

If you have a dog who went blind from progressive retinal atrophy or suffered premature arthritis, this has got to be good news for your next pup.

If everyone played by the rules, then certain genetic conditions could be gone in 1–2 generations.

Buying a Purebred Puppy
Ailments like skin allergies and hip and elbow dysplasia are sometimes genetic in certain breeds. Photo: Bieniu94

So, please do the following when you’re buying a purebred puppy:

  • Do some homework about the breed. Find out which diseases they are prone to.
  • Cross-reference this with a database that advises what genetic screening tests are available.
  • Then look for a breeder who breeds responsibly and has their parent stock screened for those problems.

Again, this doesn’t guarantee a rock-solid healthy puppy, but it certainly helps. When you select 2 unrelated, low-risk parents, then things look rosy for a strong puppy who grows into a healthy adult.

Of course, genetic screening tests for dogs cost money, so expect to pay more for the puppy — but what price can you put a price of peace of mind?

Useful Sites

To help you find that healthy purebred puppy, here are some useful sites:

Final Thoughts on Buying a Purebred Puppy

Besides all of the above, you’ll also want to actually examine the puppies.

The AKC Canine Health Foundation advises checking the following:

  • The skin should be free of parasites, hair loss, crusts or reddened areas.
  • The eyes, ears, and nose should be free of crust and discharge.
  • The nostrils should be wide and open.
  • None of the puppies should be coughing, sneezing or vomiting.
  • The area around the anus should have no hint of irritation or recent diarrhea.
  • Puppies should be neither thin nor potbellied.
  • The gums should be pink, not pale.
  • The eyelids and lashes should not fold in on the eyes.
  • By the age of 12 weeks, males should have both testicles descended into the scrotum.
  • Puppies should not be making loud breathing sounds, including excessive wheezing or snorting.
  • Puppies should not be limping or lethargic.

So, in short, when sourcing a healthy purebred puppy, find a breeder who screens for hereditary disease. Pop the parent dogs through an app that checks their COI. And then buy a puppy who’s only from unrelated (or very distantly related) ancestors, and be sure to inspect the puppy closely.


vet-cross60pThis pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed and updated Aug. 16, 2019.

If you have questions or concerns, call your vet, who is best equipped to ensure the health and well-being of your pet. This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis or treatment. See additional information.