Coefficient of inbreeding (COI) in dogs and cats – a full discussion

At first glance this is a daunting and off-putting topic. However, we have Ben, the TikTok vet to ease us into the discussion 😎. He’s great and thanks Ben. He has a nice video of the COI of the most inbred pedigree dogs available in the UK. It is a very good start. This being a website mainly about cats, I wondered how cats compared to dogs on the COI scale. Of course, there is a pretty wide variation between breeds but in general the criticism of the cat and dog fancy (breeders, clubs and show organisers) is that their creations are too inbred.

Ben said: ‘To get a COI of 50 percent…you’d have to mate two full siblings together, for three generations in a row, to accumulate more inbreeding.’

COI - coefficient of inbreeding
COI – coefficient of inbreeding. Image by MikeB.

The inherent problem is that the cats and dogs have to be inbred to ‘fix’ their appearance as per the breed standards. It just depends on how inbred. The more inbred the higher the COI and the higher the COI the more unacceptable the breeding is and the greater the propensity for severe health problems euphemistically described by the umbrella term “inbreeding depression”. It is a balancing act.

RELATED: Over 370 genetic diseases affect dogs.

Ben’s explanation of COI and some seriously inbred dog breeds in his video Researchers have identified JUST HOW inbred our dog breeds are – and you would be shocked #learnontiktok #dogsoftiktok #benthevet #doghealth #fypp ♬ Aesthetic – Tollan Kim


Note: this is an embedded video from TikTok. I can’t guarantee that it will work for a long time. If it is broken – sorry.

COI means

“[COI] calculates the probability that two copies of a gene variant have been inherited from an ancestor common to both the mother and the father.” – Kennel Club.

Observations on the video

I have found some useful input on acceptable levels of inbreeding – acceptable COIs – from the premier UK cat association, the GCCF. Here it is in a table. Use the slider below the spreadsheet to see the bit on the RHS.

The table is clear in its conclusions. The ideal is a COI below 10%. A “higher end” COI would be a 25% and anything around 40% is a result of breeding which “should not be undertaken”.

Towards the end of Ben’s video, he points out six dog breeds which are all over 40%. These are: the Airedale, Cavalier King Charles spaniel, English setter, Pug, Scottish terrier, Irish wolfhound

The average COI for dog breeds is 25%. That is the average and it is at the higher end of inbreeding. This is the same amount of inbreeding as two siblings i.e. a brother and sister mating and procreating. It is that close in terms of inbreeding. Something which you simply wouldn’t go near in human society as it is unacceptable. In the world of cats and dogs matings between siblings is apparently acceptable but at the higher end of COI.

It should be noted that sometimes wild cat species inbreed due to small populations living in fragmented habitats. But they are not as inbred as these dogs. The Florida Panther (puma) is an example of a wild cat species affected by inbreeding as they are cut off from the main population of pumas in the USA.

Balancing act

It seems to me that breeders have to find an acceptable balance between fixing the appearance to meet the breed standard while ensuring as best as possible that the breed is healthy. The truth is, though, that appearance is more important than health which is why the COIs are higher than they should be for dogs at an average, as stated, of 25%. Dogs as Ben mentions are also breed for function which is why purebred dogs have been around much longer than purebred cats.

The University of Montréal has a page on interpreting inbreeding coefficients. They state unequivocally that, “It is advised to maintain a coefficient of inbreeding that is below 10% which should allow a number of desired traits to be fixed without allowing the undesirable effects of inbreeding to become too pronounced.

And they go on to add that “incestuous crosses resulting in offspring with coefficients of inbreeding above 12.5% should not be performed”. Clearly, too many dog breeders are running unacceptable selective breeding programs.

What about cats?

Searching the Internet for specific COIs concerning individual cat breeds does not produce a result. Perhaps the cat fancy is hiding this data?

I have managed to find a study regarding inbreeding of cat populations in Poland. This may provide us with some sort of feel for the COIs of cat breeds in other countries. And the news is good from Poland because in an assessment of 26,725 cats from seven breeds based upon information provided by the Association of Purebred Cat Breeders in Poland indicates that “the average inbreeding coefficient [COI] exceeded 5% only for Siberian and Russian breeds”.

Interesting to note that British cats which I presume you mean the British Shorthair had COIs upwards of 38%. Although the lower and it was 0.1%.

With respect to Maine Coon cats in Poland, they concluded that there was poor record-keeping which made their task difficult. They came to the conclusion also that there was an average COI of over 11% for a group of 19 males and a COI of 7.8% for 21 females.

In their study there were 1786 Siberian cats. They found that there was zero inbreeding for 638 kittens with an average COI of 7.36%. The impression I get is that in Poland purebred cat selective breeding does not produce COIs which are in general unacceptable. They appear to be below 10% normally. This, according to the GCCF is acceptable.

In a study entitled: “Statistical analysis in support of maintaining a healthy traditional Siamese cat population” they found that the COI of Siamese cats was 12% (1998-99).

Springer (a science website) states that “The Russian breed had one of the highest proportion of inbred individuals (71.41%)”. It is unclear what this means as the breed is not stated and the percentage relates to the number of inbred cats but how inbred?

I really don’t have any more information on pedigree cat COIs. The information might be on the internet somewhere it is tucked away if it is an I can’t find it.


My tentative conclusion from his online research is that dogs are more inbred that cats. And some dog breeds are dangerously inbred and suffering from consequential serious health issues.

All cat breeds have some health issues related to inbreeding. It is part and parcel of the cat fancy. It just appears to be less concerning than for dogs. Dogs have been artificial bred for far longer than cats: around 20,000 years or more compared to less than 9,500 for cats when the wild cat was first domesticated and probably for no more than 4,000 years when ancient Egyptians were engaged in breeding for sacrifice.

Below are some more articles on inbreeding depression.

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