Guide: coefficient of inbreeding
Coefficient of Inbreeding (COI) in Dogs: What Buyers Should Know
The coefficient of inbreeding, or COI, is a number that shows how closely related a dog’s parents are. A higher number means the puppy inherited more identical genes from both sides, which raises the chance of inherited disease. A large genetic study found that the average across 227 breeds was about 25 percent, the level expected from mating full siblings.
What the coefficient of inbreeding measures
Every puppy gets one copy of each gene from each parent. When the parents are related, some of those pairs are exact copies of a gene from a shared ancestor. The coefficient of inbreeding is the share of a dog’s genes expected to be identical in that way (Embark).
| Parents | Expected COI of the puppies |
|---|---|
| Unrelated | Close to 0 percent |
| Half siblings | 12.5 percent |
| Full siblings, or parent and offspring | 25 percent |
Real figures are often higher than a pedigree suggests, because dogs within a breed share many distant ancestors.
Why the coefficient of inbreeding matters for health
Harmful recessive genes only cause disease in pairs. So the more identical pairs a dog has, the greater the risk.
A 2021 study measured inbreeding from DNA in 227 breeds and compared it with insurance claims. The average was 24.9 percent. Breeds with lower inbreeding needed less veterinary care, and smaller, less inbred breeds were the healthiest of all (Bannasch and colleagues).
Pedigree COI and genetic COI
There are two ways to work it out.
- Pedigree COI is calculated from the family tree. It depends on how many generations are included, so it often underestimates.
- Genetic COI is measured directly from a DNA sample. It shows what the dog actually inherited.
A DNA-based figure is the more reliable of the two. In addition, it works for crosses that have no shared pedigree database.
What is a good coefficient of inbreeding?
Lower is better. The Institute of Canine Biology, a breeder education group, says harmful effects start to show at around 5 percent and become significant by 10 percent (Institute of Canine Biology).
Many purebred dogs sit well above that, simply because every dog in a closed breed is related to some degree. Therefore, compare a litter with its breed average as well as with the ideal.
The coefficient of inbreeding in doodles and other crosses
A first cross between two unrelated breeds usually has a low COI, because the parents share few recent ancestors. That is part of the idea behind hybrid vigor in dogs.
However, it is not guaranteed in later generations. If a doodle program relies on a small number of dogs, relatives end up being bred together, and the number climbs. So the question is worth asking even for a mix.
What to ask a breeder
- How are the two parents related, if at all?
- Do you know the genetic COI of each parent, or the expected figure for this litter?
- How many different sires and dams are in your program?
Embark panels report a genetic COI for each dog tested. So it is a number you can ask any breeder who uses Embark for, including us. See how we health test and what health testing before breeding should cover.
Related guides
- Puppy Development Stages: Week by Week From Birth to 12 Weeks
- How Many Puppies in a Litter? Averages by Dog Size
- Weaning Puppies: When It Starts and How It Works
- Early Neurological Stimulation (ENS) for Puppies: Does It Work?
- The Dog Heat Cycle Explained: Stages, Signs and Timing
See all our puppy guides, read about our health testing, or meet our Havapoo puppies for sale and Goldendoodle puppies for sale.
Sources
- Bannasch D, Famula T, Donner J, et al. Canine Medicine and Genetics, 2021. The effect of inbreeding, body size and morphology on health in dog breeds. pubmed.ncbi.nlm.nih.gov
- Embark Veterinary. What is COI (Coefficient of Inbreeding)?. help.embarkvet.com
- Institute of Canine Biology. COI FAQs: Understanding the Coefficient of Inbreeding. instituteofcaninebiology.org
Sources were checked on October 7, 2026.
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