The origins
Inbreeding is defined as the result of sexual reproduction between two related individuals.
The inbreeding coefficient of a dog allows us to measure the relatedness of its ancestors and therefore the genetic diversity of the dog in question.
More precisely, its level of homozygosity is calculated (number of genes for which it has 2 copies of the same allele, which were transmitted by its 2 parents).
The more related the ancestors are, the greater this number will be.
The traditional method for measuring a dog's COI is to study its genealogy and estimate the degree of relatedness of its ancestors.
There are five-generation calculation methods for this, such as Wright's method. However, this method has flaws and is not very accurate.
This rate can also be measured directly in the dog's genome using genetic markers; this is called the genetic inbreeding rate.
With over 200,000 markers examined distributed across the genome, this test ensures that no large regions of inbreeding are hidden and provides the most reliable COI estimate possible.
It is thus possible to determine this coefficient very precisely for a given individual, as well as for the descendants of two parents whose genome has been analyzed.
This is the rate we indicate as the 'inbreeding rate' for each litter.
(note that there may be slight variation in this rate for puppies from the same litter due to genetic recombination).
We know that a marriage between Silver and Jorah would produce puppies with a 2% inbreeding rate, a marriage between Lisa and Jed a rate of 5%, a marriage between Willow and Grizzly 1%...
It is a valuable tool for the breeder to refine the choice of marriages and selection (it is sometimes useful to make marriages with a higher inbreeding rate in order to establish sought-after characteristics) and also for the person who wishes to acquire a puppy with full knowledge of the facts and does not wish to end up with a dog that is inbred at a high level.
A recent study shows that a 10% increase in inbreeding rate can lead to a 6% reduction in adult height and a reduction in life expectancy of 6 to 10 months.
It also negatively impacts litter size and fertility.
Generally, dogs with a high COI are at greater risk of having a reduced life expectancy and a higher incidence of hereditary diseases than a dog with a lower COI.
All individuals of the same breed are related to a greater or lesser extent, since inbreeding is essential to establish phenotypic characteristics specific to each.
But as we have seen, this also increases the likelihood of an individual inheriting 'defective' genes from their parents and therefore developing genetic diseases, and reduces their life expectancy.
For comparison with the rates of our litters, here are the average genetic inbreeding rates for dogs of the following breeds (source Embark):
German Shepherd 29% (this means that on average a purebred German Shepherd has an inbreeding rate of 29%)
Czechoslovakian Wolfdog 34%
Saarloos Wolfdog 36%
Researchers at the University of California studied the genomes of nearly 50,000 dogs from no fewer than 227 distinct breeds, noting an average inbreeding of 25%. The equivalent, for us, of a brother and sister sharing genetic material.
Much more, therefore, than what would be considered safe in humans.