Dog breeds are often recognized for distinctive traits – the short legs of a dachshund, the wrinkled face of a pug, the spotted fur of a dalmatian. Unfortunately, the genetics that give different breeds their distinctive traits are often the result of inbreeding.
In a study recently published in Canine Medicine and Genetics, an international team of researchers led by the University of California, Davis, veterinary geneticist Danika Bannasch shows that the majority of dog breeds are highly inbred, which adds to their overall disease and health care costs Lifespan.
“It’s amazing how important inbreeding seems to be for health,” said Bannasch. “Although 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 dogs of smaller size and without inbreeding are much healthier than larger dogs with high inbreeding. “
Inbreeding affects health
The average inbreeding, based on genetic analysis of 227 breeds, was close to 25%, or equivalent to sharing the same genetic material with a full sibling. These are levels well above what would be safe for humans or wildlife populations. In humans, high levels of inbreeding (3-6%) have been linked to an increased prevalence of complex diseases as well as other diseases.
“Data from other species, combined with a strong racial predisposition to complex diseases such as cancer and autoimmune diseases, underscores the importance of high dog inbreeding to their health,” said Bannasch, who also serves as the Maxine Adler Endowed Chair of Genetics at UC Davis School of Veterinary Medicine.
The researchers worked with Wisdom Health Genetics, a world leader in pet genetics, to obtain the largest possible sample size for analysis. Wisdom Health’s database is the largest canine DNA database in the world, helping researchers collect data on 49,378 dogs from 227 breeds – mostly from European sources.
Some breeds are more inbred
So what makes one breed of dog more inbreeding than another? Bannasch explained that it is often a combination of a small founding population, followed by heavy selection for certain characteristics of a breed – often based on appearance rather than purpose. While she was always interested in the population structure of some of these breeds, a few years ago she was particularly interested in the Danish-Swedish farm dog. She fell in love with its compact size, disposition and intelligence and eventually imported one from Sweden.
Bannasch discovered that due to their history with a relatively large foundation population of 200 and their breeding, Danish-Swedish farm dogs show a low degree of inbreeding based on function rather than strong artificial selection based on appearance. And according to the insurance health data on breeds collected by Agria Insurance Sweden and hosted online by the International Partnership for Dogs, the farm dog is one of the healthiest breeds.
The study also showed a significant difference in morbidity between brachycephalic (short skull and snout) and non-brachycephalic breeds. Although this finding was not unexpected, the researchers removed brachycephalic breeds from the final analysis of the health effects of inbreeding.
Preservation of genetic diversity
In the end, Bannasch said she was not sure whether there was a way out of inbred breeds. People have come to realize that it is misleading to create matches based solely on pedigree. The inbreeding calculators do not go back enough in a dog’s genetic line, and this method does not improve the overall high level of inbreeding in the population.
There are other measures that can be taken to preserve genetic diversity and health in a breed, she said. They include careful management of breeding populations to avoid additional loss of existing genetic diversity through breeder training and inbreeding monitoring made possible by direct genotyping technologies.
Outcrosses are suggested or already performed for some breeds and conditions to increase genetic diversity, but care must be taken to see if these effectively increase overall breed diversity and thus reduce inbreeding, Bannasch said. Particularly in the few breeds with low inbreeding, every effort should be made to preserve the existing genetic diversity.
Other UC Davis writers include Thomas Famula, Kevin Batcher, Noa Safra, Sara Thomasy, and Robert Rebhun. Wisdom Health Genetics contributors include Jonas Donner, Heidi Anderson, and Leena Honkanen.
This work was supported by the International Canine Health Award and the Maxine Adler Endowed Chair Fund.