Inbreeding and line breeding: What you need to know – Croney Research Group


Humans developed dog breeds for specific physical and behavioral characteristics. Most of this selection happened over the last 200 years or so. Creating breeds required starting with a limited pool of dogs with certain desired traits. Dogs from that original group and their offspring were bred together, ensuring consistency in appearance and behavior. However, breeding dogs from a small founding group limits genetic diversity.

Inbreeding and line breeding

Inbreeding is the mating of dogs who have one or more ancestors in common. First-degree relatives share 50% of their genetic material and include parents/children or siblings; second-degree relatives share 25% of their genetic material and include grandparents, half-siblings, or uncles/aunts.

Line breeding is a form of inbreeding, but usually, these mating pairs are not first- or second-degree relatives. The result of either type of breeding is mating dogs with genetic similarity.

A limited gene pool increases the risk that puppies will be affected by diseases. This is especially true for recessive conditions. Keeping levels of inbreeding low supports genetic diversity and can improve welfare.

What is a recessive condition?

Dogs inherit copies of genes from both parents. Recessive conditions occur when a dog inherits two faulty copies of a gene. Dogs with one faulty copy are carriers. Carriers usually do not have the condition or disease, but you cannot know if they are a carrier without a genetic test. If both parent dogs are carriers of the disease (each has one copy of the faulty gene) then it would be expected that 1 out of every 4 of their puppies (on average, 25%) will be affected by the condition.

What is the coefficient of inbreeding?

The coefficient of inbreeding, or COI, is a measure of how related an individual’s parents were. It tells you how similar their genetics are. The COI can range from 0 to 100%. A higher COI means the dog has a higher risk of inheriting recessive genetic conditions. Some commercial genetic tests provide a dog’s COI in their results which can help inform breeding decisions.

Why is inbreeding a concern?

Multiple studies have shown that inbreeding can lead to:

  • smaller litter sizes
  • more difficulties during pregnancy
  • greater neonatal puppy mortality
  • a shortened lifespan

In short, it’s not good for the health of dogs or your breeding program!

What’s a good COI?

Most conservation programs aim for a COI of less than 10%. Rates above this are associated with inbreeding depression (reduced survival and fertility). Unfortunately, for many dog breeds, the average COI is higher than 10%.

What you can do

  • Test your breeding dogs for identified recessive conditions, especially those that are common in your breed (s). Look for testing companies that can also provide a dog’s COI.
  • Breed pairs of dogs with relatively low COI for the breed.
  • If you have dogs who are carriers for a recessive condition, only breed them with clear dogs.
  • Do not breed carriers to other carriers or affected dogs.
  • Talk to a geneticist (veterinarian or PhD) who can help you make breeding decisions based on the dogs in your kennel. Many testing companies offer genetic counseling.
  • Do not remove dogs who are carriers from your breeding pool without talking to your veterinarian or a geneticist.





For more information, see our article on Pre-Breeding Health Screening & Testing for Dogs

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Topic(s): Bare Bones Basics, Breeder Resource, Genetics, Health, Reproductive Healthcare