Co efficients of Inbreeding for Dummies


What is a COI?

COI stands for Co efficient of Inbreeding and is a statistical method of measuring the common ancestors of the dam and sire. It indicates the degree of genetic similarity they have. Putting this in to genetic language it is the probability of inheriting two copies of the same allele from an ancestor that occurs on both sides of the pedigree. These alleles are identical by descent. The COI can also represent the percentage of all the genes that are homozygous (both the same) So a COI of 10% means that 1 in ten of all the animal’s genes are likely to be homozygous. What started as a complex mathematical formula to make the calculations, can now be done at the touch of a button on a computer. It quite simply tells you the risk you take with a breeding.  The higher the COI, the greater the risk of inheriting two identical alleles by descent from the same ancestor.


Why does the COI matter?

In the early part of the last century animal breeders, particularly farmers, knew that breeding related animals produced consistent and predictable traits that were valuable to the breeder but, at the same time, there was some loss of well being Fertility was often lower, life expectancy was less and mortality higher. The farmers were very aware of both the risks and benefits of inbreeding. So the greater the inbreeding, the greater the detrimental effects.

When we consider the use of COIs in dogs it gives potential breeders a number that will indicate both the amount of benefit to be gained from a breeding as well as an assessment of the harmful effects. That is the risk.

Who is to blame?

We are in trouble now because for many years now breeders have striven to produce the perfect Beardie exactly matching the breed standard. We cannot apportion blame to anyone. Line breeding was recommended as best practice to produce a near perfect specimen. The knowledge of those early nineteenth century farmers was not appreciated by the late nineteenth century dog breeders.

How high should a COI be?

The deleterious effects of inbreeding may begin to be evident with a COI as low as 5%, and at 10% there will be an increase in the number of “bad” recessive gene mutations and a general loss of vitality. Carol Beuchat of the Institute of Canine Biology describes 10% as the ”extinction vortex

In other words if the level of inbreeding is above 10% we will begin to see all the problems facing the breed today. Smaller litters, a higher mortality, more auto immune conditions, male fertility reduced and more bitches failing to conceive.

How many generations are needed to calculate an accurate COI?

The more generations you consider the more accurate a COI will be. Five generations will give a very misleading result and all geneticists state a minimum of eight generations are required to do the calculation. It is also important that the pedigree is complete. Any missing data will distort the result and often give a falsely low reading. In future years as our record keeping improves we should have reliable data for 10 generations. This will give the most accurate figures. As the graph reproduced below shows there is a levelling off of the COI level above 20 generations and only a small rise between 10 and 20 generations.


What can we do to reduce COIs in the breed?

So for the future health of the Bearded Collie it is essential we try to reduce the number to single figures as quickly as possible and aim to get it down to below 6%.

Because the breed started with only a very small number of dogs, who fortunately were largely very healthy, it is important that every available good gene in the breed is preserved. This means extending our breeding horizons to lines not used for at least 6-8 generations, using pets who have been health tested clear, especially male dogs who previously would have been castrated. All planned matings should normally be expected to produce offspring with a COI lower than the parents. .

In humans it will be very rare to find the same individual on both sides of a family tree unless there are cousin marriages So the usual COI will be zero. Cousin to cousin marriages are banned in some countries as representing incest. Such relationships would mean the COI in any resultant child will be 6.25%. There is an increased incidence of congenital genetic disease in children whose parents are first cousins.

In dogs in the hypothetical situation that both dog and bitch have absolutely no common ancestors, if you mate a brother to a sister you will have a COI of 25%.  If you mate a Grandparent to a grandchild the resultant COI is 12.5%. If half siblings are mated again the COI will be 12.5%. A great grandparent to a great grandchild is 6.25%. In our real life situation with Beardie there will always be some common ancestors in the pedigrees so these close matings will actually have even higher COIs than if there were no common ancestors. Many of our Beardies today have COIs at 8 generations well above 25% This is most worrying and requires an urgent effort from us all to get this figure down year on year.

The future

An interesting study in standard poodles showed that dogs with a COI of less than 6.25% will on average have lived four years longer than poodles with a COI of over 25%

Whilst having a puppy with a low COI does not in any way guarantee a health puppy, having a high COI should always be a cause for concern.

In planning future breeding, it is essential that the all possible matings  are compared and the COIs calculated. The COI should be lower in each of the next generations. But remember the COI is only a tool and other considerations must be taken into account. Health, fertility, temperament should be top priorities because without those we have nothing.


Further Reading:


1)      Institute of Canine biology: Understanding the Coefficient of inbreeding: Beuchat Carol

2)      A beginners guide to COI; from dogbreedhealth.com


From top left to bottom right, naming dogs with COIs

CH Bravo of Bothkennar  12.5

Ch Osmart Bonnie Blue Braid  14.3

Ch Orora's Frank 15.3

Ch Potterdale Philosopher  20.5

Ch Potterdale Philanderer  23.2

Ch Gillaber Tillycorthie 34.3

Ch Gillaber Drummond 32.8

Ch Diotima Sea Wolf at Ramsgrove  32.3

Sw Ch Ramsgrove Ragthyme  28.0

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