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Inbreeding – using COIs

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What is inbreeding and how can it impact health?

Inbreeding, put simply, is the mating of related individuals – those individuals with common ancestors. High levels of inbreeding can impact the health of individual dogs, as it increases the chances of a dog being at risk for both known and unknown inherited disorders. It could also have an impact on the breed as a whole, for example, a reduction in litter size and fertility.

It is impossible to make precise predictions about the exact impact that inbreeding has on an individual dog, but we do know that, as the degree of inbreeding increases, the risk of having a serious and harmful impact on the breed as a whole will increase.

How can you measure the degree of inbreeding?

The degree of inbreeding can be measured by using a Coefficient of Inbreeding (COI). This is the probability that two copies of the same variant at a gene have been inherited from an ancestor common to both the sire and dam. The lower the degree of inbreeding, the lower the inbreeding coefficient.

Inbreeding Coefficient Calculators

The Kennel Club's free online health resource, Mate Select, provides breeders with inbreeding coefficient calculators for all dogs found on the Kennel Club's Breed Register. These calculators use all pedigree records stored on the Kennel Club's database to calculate the result, for:

Use any of our inbreeding coefficient calculators here.

How many generations of pedigree information are used to calculate the COI?

Each of these COI calculators use all available, electronically held, pedigree information and does not limit the number of generations used, making each calculation as precise as possible. It is crucial to find out how many generations of pedigree information were used for the calculation you have just carried out. The number of generations – and how complete they are – is available for individual calculations and is provided on the bottom right hand corner on Mate Select.

Putting your dog’s COI result into perspective

The COI calculator provides you with a percentage score; the lower the percentage, the lower the degree of inbreeding.

Therefore, an inbreeding coefficient of:

Inbreeding is accumulative, so if it has occurred to a significant degree over several generations, the inbreeding coefficient may exceed 25%.

What is the annual breed average COI and how is it calculated?

Each COI calculation is accompanied by annual breed average. This figure is provided to enable breeders to compare any potential matings to the average of the rest of the breed to allow them to put their COI into perspective.

This annual breed average is calculated each June using Kennel Club registered dogs born in the UK between January and December of the previous year. Using this data is a more effective means of monitoring yearly change than by using the average of all living dogs in that breed.

In smaller breeds, if no dogs have been born in that year, the annual breed average will default to the last year in which a calculation could be performed. In breeds where there is no available annual breed average data for the past five years, the annual breed average will display as N/A. This may include breeds where no dogs have been born in the UK for five years or more, or some newly recognised breeds.

Prior to June 2014, the breed average COI was calculated to include dogs registered in a year as well as dogs born in a year. It was decided that using dogs born in the UK was a more accurate and useful figure.

Breeding advice

When choosing a potential mate for your dog, the Kennel Club recommend that breeders use Mate Select to calculate the inbreeding coefficient of the puppies that could be produced from a hypothetical mating.

The current Kennel Club breeding guidelines are that, where possible, breeders should produce puppies with an inbreeding coefficient which is at, or below, the annual breed average and ideally as low as possible. The annual breed average is recalculated each year and is shown to you each time you use the COI calculators.

A note of caution about using COI calculators

Dogs that have been imported may only come with a three generation pedigree, and so it may be difficult to calculate an informative COI.  When looking at any results on the Kennel Club COI calculators, it is important to check the “About this calculation” section (on the right hand side of the page) to see how many generations have been used for calculation.  If this indicates that only the first 3 generations are fully complete, you may wish to use the COI result with care. If additional pedigree information or inbreeding resources are available to you, then you may wish to consult these.

Making balanced breeding decisions

As well as considering the implications of a dog’s inbreeding coefficient, there are other equally important factors to consider when deciding whether two dogs should be mated together, such as temperament, genetic diversity, conformation, other available health test results, the general health of the dogs etc. Your breeding decisions should always be well balanced and take into consideration the qualities and compatibility of both the sire and dam that you are considering.

Can COIs guarantee the health of future puppies?

Breeders should be aware that the inbreeding coefficient is a measurement of risk and does not guarantee that puppies produced will, or will not, have any inherited health conditions. The higher the inbreeding coefficient, the higher the risk of health issues.

Will the Kennel Club still register puppies with a higher than average inbreeding coefficient?

The Kennel Club will still register the puppies of a mating which results in an inbreeding coefficient which is higher than the annual breed average, but it is recommended that you consider a different pairing, all other considerations being equal. If you do go ahead with the mating and plan to use any of the puppies for breeding in the future, it is strongly recommended that you take extra care to choose a highly unrelated mate that will result in puppies with an inbreeding coefficient well below the breed average.

To help reduce the highest degrees of inbreeding, the Kennel Club does however not register puppies produced from a mating between father and daughter, mother and son, or brother and sister, save in rare exceptional circumstances for scientifically proven welfare reasons.