17/02/2025
Well said
COI is not neutral – it is quite literally an expression of risk. Higher COI equals higher risk of an individual inheriting 2 copies of a recessive deleterious mutation. This risk is at the population level, meaning that not every high COI individual will be sick, but overall they have a higher probability of being sick than low COI individuals.
When you linebreed, any shared recessive deleterious mutations from the common ancestor are likely to show up in the offspring. Breeders often believe that they can use this as a strategy to “purify” their breeding stock of bad genes. But there are two flaws in this way of thinking. One, you have to produce sick puppies in order to even identify what genetic diseases your breeding stock is carrying. I don’t know about you, but I don’t see how intentionally creating puppies with potentially painful, terminal, or lifelong illnesses can be considered ethical. Second, animals simply have too many recessive mutations for us to eliminate them all using this method. The number of recessive genetic diseases that any one dog carries is estimated to be between 50 and 100. Most of these diseases will never show up in offspring due to their recessive nature, UNLESS linebreeding is done.
Many breeds end up playing whack-a-mole with recessive genetic diseases: as they inbreed to eliminate one disease, more pop up due to the increase in COI (and therefore risk). Our breeds with the highest average COIs, such as cavalier King Charles spaniels, Doberman pinschers, bull terriers, and Norwegian lundehunds, are riddled with severe genetic diseases, and the breeds now lack enough internal genetic diversity to select away from these issues.
Consistency absolutely CAN be achieved without inbreeding. Many guide dog breeding programs are now producing Golden x Lab crosses that have a higher success rate than either purebred. The key is to select breeding individuals who are highly similar in the areas you want to reproduce, but heterozygous in other areas. The clone-like sameness that seems to be expected in the show ring may not be possible without inbreeding, but there are many better paths to producing consistent, reliable dogs who perform their intended function.
