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Inbreeding is at the foundation of the creation of domestic breeds, but it presents dangers. It is measured by a number that represents the percentage chance for an individual to inherit the same gene from both its father and mother when these parents share a common ancestor.
A question that breeders always ask is: what is the limit not to exceed? The answer is difficult because there is an important parameter in this calculation: the depth of the pedigree. The more generations that are considered, the more common ancestors are discovered, and the higher the inbreeding becomes.
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One primary consequence of this fact is that inbreeding levels are only compared at equal pedigree depth: a breeder who needs to choose between two males for his female runs a simulation of both litters at the same depth and compares them. For a long time, the pedigrees of the French Kennel Club included only three generations; today, this has increased to five.
The following calculation is generally made: with each generation, the influence of a common ancestor on inbreeding is halved. It has long been inferred that the inbreeding induced by individuals beyond five generations should be negligible.
For a long time I took this assumption for granted until computer tools allowed me to verify it. I am fortunate to have what I believe is unique in the world of dog breeding: a database containing absolutely all 5,400 dogs of the breed born since its re-creation starting in 1974.
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With a commercial program, it was easy for me to calculate three types of inbreeding for each dog: the complete inbreeding over all known generations, the inbreeding calculated over 5 generations, and finally the inbreeding calculated over 3 generations. By summing up the inbreeding coefficients of all the dogs of the year, we obtain the table below:
- in green: calculation done over all generations
- in blue: calculation done over 5 generations
- in yellow: calculation done over 3 generations
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It is observed that starting from the early 1980s, the inbreeding visible on the pedigrees of that time no longer reflects the actual inbreeding. It takes another 10 years or so before the visible inbreeding on the 5-generation pedigrees diverges from the real inbreeding.
These results lead to several observations and questions:
- Firstly, the French Kennel Club's decision to increase the depth of pedigrees from 3 to 5 generations is fully justified.
- Furthermore, the idea that inbreeding beyond 5 generations is negligible is invalidated. This is because with each generation, the number of ancestors doubles; thus, a common ancestor can appear multiple times in the pedigree, and while each contribution may be small, the multiplicity of these contributions eventually becomes significant.
Thus, we encounter genetic bottlenecks when top champions produce numerous offspring, whose descendants eventually interbreed. These champions appear multiple times in the pedigree, and the breeder who does not look beyond the pedigrees of their breeding dogs overlooks this inbreeding, which I have termed breeder myopia.
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There are two obvious questions that arise when faced with such a scenario:
- Faced with such a discrepancy, does monitoring inbreeding over 5 generations still make sense?
And the answer is: yes, more than ever. There exists residual inbreeding inherited from the history of each breed, especially from those champions that have heavily reproduced. This existing inbreeding cannot be changed. However, we can ensure not to add to it further. The inbreeding over 5 generations that can be calculated on the SCC website is therefore an important factor to consider before breeding a litter.
Nevertheless, the more genealogical information we have, the better. In our breed, breeders have been able to access their dogs' pedigrees since 2005. They quickly understood the importance of choosing less inbred breeding pairs, and we see the trend reversing as early as 2007. Without coercive measures, simply by informing breeders, we have managed to maintain the breed's good health. This is evidenced by Ignes de la Croix Saint Urbain's victory at the 2016 Open de France, the best French pointing dog of the year, an achievement unmatched in the breed's history!
- The second question raised is of a more general nature: if the known pedigree depth correlates with increased inbreeding, wouldn't we find extremely high levels of inbreeding if we knew the complete genealogy of our dogs? The answer is no, because there are mutations—random changes in the genome—that decrease inbreeding. These mutations are very rare, so within the lifespan of a breeder, they are not considered. However, on the scale of species evolution, they are significant. It's these mutations that ensure that over many generations, the contribution of common ancestors to inbreeding becomes negligible. Here, we're not talking about 5 or 10 generations, but rather 100 or even 500.
