Inbreeding and linebreeding



Among breeders, "inbreeding" usually refers to mating first-degree relatives, or sometimes second-degree relatives. "Linebreeding" usually refers to milder inbreeding, such as mating cousins or half-cousins.  

The degree to which the coefficient of inbreeding accumulates for each match

Selective linebreeding over multiple generations is a method used to create various dog and cat breeds by crossbreeding individuals with desired appearance and personality traits to establish predictable characteristics. However, this limited genetic diversity causes harmful recessive genes that were masked by healthy dominant genes to pair up and lead to various genetic diseases. Furthermore, certain practices, such as the excessive use of show-winning sires for breeding, further undermined genetic diversity and spread genetic diseases throughout the breeds.

Traditionally, breeders have calculated COI based on 5 to 10 generations of pedigree information; however, because this does not go back to the breed founder, it tends to be lower than the genome-wide COI, which traces back to the time of breed inception. Therefore, genome-wide COI is considered a more accurate method for calculating COI.

The average genome-wide COI of Dobermans is about 40%, which is 15% higher than the COI of those born from first-degree relatives matching.

Some people think that inbreeding in breeds usually refers to breeding between parents and children or siblings. Sometimes, that method was used in the process of creating breeds in the 19th to early 20th centuries; But personally, I don't consider mating between immediate family members to be the primary cause of the severe lack of genetic diversity observed in some breeds. The process of creating a breed takes decades. However, when they only rely on mating first-degree relatives to create breeds, the COI increases by 25% in the first generation, by 50% in the second, and reaches 100% by the fourth generation. This method will make the pedigree collapse even before the breed is even established.

In fact, accumulated linebreeding and popular sire syndrome over several generations can sufficiently increase the average COI by 20%, 30%, or even 40% over decades, and I consider them to be the main cause.



So, do you think there are solutions to increase the genetic diversity of the breed?

I think that:
- Since dog and cat breeders deal with life, they should be taken more seriously (not just a hobby) and held to higher standards.
- The participation of experts in veterinary medicine and genetics should be increased.
- Tests capable of verifying genome-wide COIs for dog breeds should be widely used among dog breeders (and I hope that tools similar to Embark (but for cats!) develop for cat breeders to easily know the average genome-wide COI of each cat breed; That will help cat breeders and the future of cat breeds)
- Openness to discussions regarding outcrossing is particularly important, given that experts use that method to restore endangered wildlife populations. Outcrossing discussions should be opened even in dog breeds that do not have a severely high COI and incidence of specific diseases, to prevent increasing their COI and specific disease rates in future.

And personally, I think using dogs/cats outside the studbook (including mixed-breed dogs with more than 85-90% of a specific breed's DNA) for breeding that are healthy and have similar appearances and personalities is also a good idea.

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