Don’t Fuck Your Siblings

The Ancients knew what happened when you inbred animals -- they could see it in their own flocks, and so laws were framed up to guard against it.

"Cursed be he that lieth with his sister, the daughter of his father, or his mother..."

— Deuteronomy 27:22

In the Kennel Club, of course, canine registrations are often closed with only 20-40 dogs on the roles, which means the gene pool can never expand and only get smaller, with disease, defect, dysfunction, and death to follow.

What’s the coefficient of inbreeding warned against in Deuteronomy?  

Lying with your sibling, or your parent, will generate a Coefficient of Inbreeding (COI) of 25 percent.

Is a 25 percent COI common in pedigree dogs?

It is.

In a December 2021 article in Companion Animal Health and Genetics entitled “The effect of inbreeding, body size and morphology on health in dog breeds “ the authors conclude:

“The average inbreeding based on genotype across 227 breeds was Fadj = 0.249 (95% CI 0.235–0.263). There were significant differences in morbidity between breeds with low and high inbreeding (H = 16.49, P = 0.0004). There was also a significant difference in morbidity between brachycephalic breeds and non-brachycephalic breeds (P = 0.0048) and between functionally distinct groups of breeds (H = 14.95 P < 0.0001). Morbidity was modeled using robust regression analysis and both body weight (P < 0.0001) and inbreeding (P = 0.013) were significant (r2 = 0.77). Smaller less inbred breeds were healthier than larger more inbred breeds.

“In this study, body size and inbreeding along with deleterious morphologies contributed to increases in necessary health care in dogs.” 

For the full study, see >> https://cgejournal.biomedcentral.com/articles/10.1186/s40575-021-00111-4

The “background” section goes over the basic history of dog breeding.  I have put in added carriage returns in order to make a solid block of text more readable on the internet:

“Most modern dog breeds were established within the last 200 years. 

“Dog breeds can be characterized by small numbers of founders, with strong selection for morphology, size and color. In addition, population bottlenecks due to historical events, and the introduction of closed studbooks in the last 100 years has shaped the formation of modern dog breeds. These factors have all contributed to high levels of inbreeding within breeds. 

“The level of inbreeding can be estimated using pedigrees, which were commonly used to determine the coefficient of inbreeding (Fp) within individuals and breeds; however, unless calculations include the complete pedigree, Fp may underrepresent the actual inbreeding by 5–10 fold. 

“More recently, measurement of genetic inbreeding levels through direct genotype-based methods has become a feasible option. Such approaches to determine inbreeding have provided evidence that dog breeds have levels of inbreeding that are considered extremely high (> 0.1) in other species and where the effects of inbreeding depression are expected to occur.

“There is evidence that high levels of inbreeding have consequences on health. Close inbreeding has a negative effect on litter size and neonatal survival.

“Domestication and breed formation have unintentionally increased the number of deleterious genetic variants within breeds.  Individual breeds also have strong predispositions to specific inherited diseases. The Online Mendelian Inheritance in Animals website (OMIA, April 2021, omia.org) currently catalogues 796 canine disorders and traits. Some of these have been found to be due to high allele frequencies of deleterious recessive mutations, while others have remained elusive and are likely polygenic in nature. Some of the breed disease predispositions may be due to concentrated genetic disease polymorphisms rather than segregating traits.  Consistent with this theory, mixed breeds have lower risk of diseases than purebreds….”

In the discussion section, the authors write:

“Breeds with higher inbreeding levels required greater amounts of veterinary care as did brachycephalic breeds and there were significant differences in required health care between FCI breed groupings. We identified a significant effect of both body size and inbreeding on morbidity across dog breeds with larger sized and more inbred breeds receiving more veterinary care throughout their lives.

“The inbreeding values within dog breeds were very high, with the mean being 0.24, just below the coefficient of inbreeding obtained from breeding full siblings. 

“The breeds with low inbreeding included recent cross breeds (Tamaskan Dog, Barbet and Australian Labradoodle) and landrace breeds (Danish-Swedish Farmdog, Mudi and Koolie), supporting the notion that high inbreeding is a result of closed stud books or small numbers of founders or both. It also demonstrates that it is possible to have consistent breed type without inbreeding.

“Similar to another recent study, brachycephalic dogs require more veterinary care than non- brachycephalic dogs. In addition, we identified that FCI group 2 breeds required the highest average number of veterinary care events. This group includes the larger molossoid dog breeds which others have previously identified as having higher mortality. The primitive FCI group 5 breeds had the lowest average morbidity of all the groups, which has not been reported previously, except for the Norrbottenspitz breed.”

As always, read the whole thing.