Coefficient of Inbreeding (COI)
Inbreeding, put simply, is the mating of related dogs. 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.
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 are available on the Kennel Club website. The current average COI in Clumber Spaniels is 15.7%.
Essentially, the COI measures the common ancestors of dam and sire, and indicates the probability of how genetically similar they are.
25% would be the genetic equivalent of a dog produced from a father to daughter mating, or the mating of full-brother/sister
12.5% would be the genetic equivalent of a dog produced from a grandfather to granddaughter mating, or the mating of a half-brother/sister
6.5% would be the genetic equivalent of a dog produced from a great grandparent to great grandchild mating, or a first cousin mating.
0% indicates a dog that comes from two apparently unrelated parents, based on all available pedigree information
The COI calculator provides you with a percentage score; the lower the percentage, the lower the degree of inbreeding.
Inbreeding is accumulative, so if it has occurred to a significant degree over several generations, the inbreeding coefficient may exceed 25%. The higher the inbreeding coefficient, the higher the risk of health issues.
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.