In a recent study published in Canine Medicine and Genetics, an international team of researchers led by veterinary geneticist Danika Bannasch of the University of California, Davis shows that the majority of dog breeds are highly inbred, contributing to increases in disease and healthcare costs affecting their breeds Lifespan.
“It’s amazing how important inbreeding seems to be to health,” Bannasch said in a statement. “While previous studies have shown that small dogs live longer than large dogs, no one had previously reported morbidity or the presence of disease. This study found that when dogs are smaller and not highly inbred, they are much healthier than larger highly inbred dogs.”
Average inbreeding based on genetic analysis in 227 breeds was nearly 25%, or the equivalent of sharing the same genetic material with a full sibling, the study found. These are levels well above what would be safe for humans or wildlife populations. In humans, high levels of inbreeding (3-6%) have been associated with an increased prevalence of complex diseases as well as other disorders.
“Data from other species, combined with strong breed predispositions to complex diseases like cancer and autoimmune diseases, underscore the importance of high levels of inbreeding in dogs to their health,” says Bannasch, who also serves as the Maxine Adler Endowed Chair in Genetics at UC Davis Faculty of Veterinary Medicine, said.
The researchers worked with Wisdom Health Genetics, which has the largest canine DNA database in the world, to obtain the largest possible sample size for analysis. Researchers collected data from 49,378 dogs from 227 breeds, mostly from European sources.
Bannasch explained that it’s often a combination of a small founding population followed by strong selection for certain characteristics of a breed – often based on appearance rather than purpose. Unfortunately, the genetics that give different breeds their distinctive characteristics are often the result of inbreeding.
While she has always been interested in the population structure of some of these breeds, a few years ago she became particularly interested in the Danish-Swedish farm dog. Bannasch discovered that Danish-Swedish farm dogs have a low level of inbreeding based on their history of a relatively large founding population of 200, and they were bred for function rather than heavy artificial selection for appearance.
According to Breed Insurance Health Data collected by Agria Insurance Sweden and hosted online by the International Partnership for Dogs, the Farmdog is one of the healthiest breeds.
The study also showed a significant difference in morbidity between brachycephalic (short skull and muzzle, like pugs) and non-brachycephalic breeds. Although this result was not unexpected, the researchers removed brachycephalic breeds from the final analysis of the health effects of inbreeding.
In the end, Bannasch said she wasn’t sure there was a way out of inbred breeding. Inbreeding calculators do not go back far enough in a dog’s genetic lineage, and this method does not improve the population’s overall high level of inbreeding.
However, there are other measures that can be taken to maintain a breed’s genetic diversity and health, she said. These include careful management of breeding populations to avoid additional loss of existing genetic diversity through breeder education and monitoring of inbreeding levels made possible by direct genotyping technologies.
Every effort should be made to preserve the genetic diversity that exists within the few breeds with low levels of inbreeding, the report said.
Other UC Davis authors include Thomas Famula, Kevin Batcher, Noa Safra, Sara Thomasy, and Robert Rebhun. Wisdom Health Genetics contributors include Jonas Donner, Heidi Anderson and Leena Honkanen.
