Coefficient of Inbreeding

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The Coefficient of Inbreeding- what is it?

The Coefficient of Inbreeding (COI) is defined as “The proportion of all variable gene pairs that are likely to be homozygous due to inheritance from ancestors common to the sire and dam.” As such it is a measure of the relatedness of two dogs and is calculated by examination of pedigrees. Some breeders now use commercial pedigree programmes for pedigree analysis and generation. Many of these can perform the COI calculation and it is now appearing on some pedigrees. It is recommended the calculation be performed on 10 generation pedigrees for better accuracy.

To provide an understanding of the numbers that follow, breeding of uncle to niece gives a COI of 12.5%, first cousins 6.25% and parent to offspring or brother/sister is a 25% COI (note these figures assume uncle, niece etc to be unrelated). Dogs with a high COI (higher numbers) are the products of inbreeding or line breeding. So the average Australian Ridgeback is the product of an uncle to niece breeding. US dogs are more closely related, and Swedish dogs, less related.

There is little information about the COI and opinions vary on what is a “good” COI and how much inbreeding is appropriate.

The case for inbreeding

• Many breeders like to produce a consistent style or type of animal. Breeding related animals together is more likely to result in a more homogeneous litter.

• High quality closely related animals are often bred together with hope the genetic assortment will produce high quality offspring.

• Line breeding to a particular desirable animal improves the chances of producing an animal with the desirable attributes.

• Inbreeding may be performed to determine if genetic issues are to be found in a particular line- and if so, what they are.

• Breeders may prefer to work with lines where they know of the genetic problems- often meaning they stay within their own breeding program where genetic issues are better known. This results in a higher degree of inbreeding. Risks of genetic issues appearing can increasingly be offset by screening for these issues eg hip and elbow Xrays, testing for cardiac, thyroid, eye and ear problems.

• Outcrossed dogs are less likely to pass on their desirable attributes to their progeny ( )

That inbreeding is a common practice can be seen by the COI averages from the US and also in Australia.

The case against inbreeding

• Many of the problems with inbreeding are covered by the term known as “Inbreeding depression”. From a website on Siberian huskies:

“What is worse, unmistakable signs of inbreeding depression are surfacing in the breed: rising numbers of Caesarean births, smaller litters, lower birth weights, delicate nestlings prone to infection, etc. Breeders of domestic livestock - cattle, poultry, sheep - manage to run registries and maintain breed type without imposing the concept of absolute breed purity. They inbreed to fix desirable traits, as do dog breeders. Livestock breeders, however, do not try to pretend that they can inbreed forever without ill effects.” ( However, not all are in agreement with this concept and the issues associated with inbreeding depression have been challenged by data gathered from inbred populations of other animals (

• A study on the Rhodesian Ridgeback has shown that the higher the COI, the lower the life expectancy, and also noted the COI is increasing ( Similar findings have been reported in other breeds. John Armstrong of The Canine Diversity Project ( ) stated, "In general, the average poodle inbred < 6% will outlive those inbred over 25% (10 generation calculation) by about 3 years."

• Inbreeding reduces the genetic diversity of the resultant pups. If care is not taken, this can result in homozygosity of deleterious genes eg those producing defects that can impact on the health of the population ( It has been suggested that increasing autoimmune disease is being seen in dogs in a result of inbreeding (

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