Understanding the coefficient of inbreeding in dogs
Every purebred dog is related to every other dog of its breed, at least a little. The coefficient of inbreeding in dogs, or COI, puts a number on how much. Used well, it helps you choose a sire that keeps your puppies healthier. This VerifiedStuds guide explains the number in plain language.
The coefficient of inbreeding, or COI, is the chance that a puppy inherits two identical copies of a gene from the same ancestor, one through each parent. It is written as a percentage. A COI of 0% means the parents share no known ancestors. Higher numbers mean closer relatives.
Mating
COI of the puppies
Unrelated parents
0%
First cousins
6.25%
Half siblings, or grandparent to grandchild
12.5%
Full siblings, or parent to offspring
25%
These figures assume the ancestors were not inbred themselves. In real pedigrees the same dogs appear many times, so the numbers stack up.
Most inherited diseases in dogs are recessive. A puppy is affected only when it receives the same faulty gene from both parents. Therefore, the more closely related the parents are, the more likely that becomes.
Inbreeding also has a general cost, which geneticists call inbreeding depression. Studies link higher inbreeding with smaller litters, more puppy losses and shorter lives. In short, a lower COI improves the odds, although it guarantees nothing.
There are two ways to measure it, and they give different answers.
Pedigree COI
Genetic COI
How it is found
Calculated from the family tree
Measured from the dog's DNA
Depends on
How many generations are counted
The actual genes inherited
Typical result
Lower, especially with few generations
Higher and more accurate
Where to get it
Pedigree databases and breed club tools
DNA panels such as Embark
A five-generation pedigree often shows a COI of only a few percent. However, it ignores everything earlier, including the small group of founders most breeds began with. As a result, DNA testing usually reports a much higher figure for the same dog.
A 2021 study led by the University of California, Davis measured genetic inbreeding in 227 breeds. The average was close to 25%, which is the level expected from a mating between full siblings. Only a handful of breeds averaged under 12.5%.
So a "low" number depends on the breed. In a breed that averages 30%, a litter at 20% is real progress. For that reason, many kennel clubs and geneticists give the same simple advice: aim for puppies below the breed average, and lower when you can.
As a rough guide used by many breeders, a pedigree COI under 5% over ten generations is considered low, 5% to 10% moderate, and above 10% high.
Calculate the litter, not the dog. The number that matters is the COI of the puppies from this pairing. A highly inbred stud can still produce low-COI puppies with an unrelated female.
Use the same method for every candidate. Compare ten-generation pedigree figures with each other, or genetic figures with each other, but never mix them.
Ask for a DNA-based match. Some labs predict the genetic COI of a planned litter when both dogs are tested.
Look for shared ancestors. Lay the two pedigrees side by side and mark names that appear in both.
Beware the popular sire. When one male fathers a large share of a breed, his descendants become hard to avoid a few generations later.
A low COI does not make a poor dog a good choice. Health clearances, temperament and structure still come first. In addition, a slightly higher COI can be a fair trade for a stud who is clear of a disease your female carries.
So use the coefficient of inbreeding in dogs alongside the breed's health tests. See the health testing guides and what makes a good stud dog. For lab options, read best DNA tests for dog breeders.
Shipped semen makes distant, less related sires practical. Our dog artificial insemination guide explains how. When you are ready, find a health-tested stud, compare prices in the stud fee guide, and take our questions to ask a stud dog owner. Stud owners can list their stud free.
What is a good COI for dogs?
Lower is better. Many breeders aim for a ten-generation pedigree COI under 5% to 10%, or at least below the breed average.
What COI do you get from breeding father to daughter?
25% if the dogs have no other shared ancestors, and higher if they do.
Why is my dog's genetic COI higher than the pedigree COI?
Pedigrees stop after a set number of generations. DNA measures all the inbreeding a dog has actually inherited, including from early founders.
Can a DNA test show a dog's COI?
Yes. Several breeder panels report genetic COI, and some predict it for a planned litter.
Is line breeding the same as inbreeding?
Line breeding is a milder form of inbreeding that repeats one ancestor further back. It still raises the COI.
Sources: ScienceDaily, majority of dog breeds are highly inbred (UC Davis study, 2021), Institute of Canine Biology, The Kennel Club (UK), inbreeding coefficient calculators.
Compare health-tested studs by breed, and ask owners for pedigrees and DNA before you book.