Dog inbreeding contributes to increase in disease and healthcare costs

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Dog breeds are often recognised for distinctive traits. Unfortunately, the genetics that give various breeds their particular attributes are often the result of inbreeding, a US study has found.

In the study—published in Canine Medicine and Genetics—an international team of researchers led by University of California, Davis, veterinary geneticist Dr Danika Bannasch show that the majority of canine breeds are highly inbred, contributing to an increase in disease and healthcare costs throughout their lifespan.

“It’s amazing how inbreeding seems to matter to health,” Dr Bannasch said.

“While previous studies have shown that small dogs live longer than large dogs, no-one had previously reported on morbidity, or the presence of disease. This study revealed that if dogs are of smaller size and not inbred, they are much healthier than larger dogs with high inbreeding.”

The average inbreeding based on genetic analysis across 227 breeds was close to 25 per cent, or the equivalent of sharing the same genetic material with a full sibling. These are levels considered well above what would be safe for either humans or wild animal populations. In humans, high levels of inbreeding have been associated with increased prevalence of complex diseases as well as other conditions.

“Data from other species, combined with strong breed predispositions to complex diseases like cancer and autoimmune diseases, highlight the relevance of high inbreeding in dogs to their health,” Dr Bannasch said. 

The researchers partnered with Wisdom Health Genetics, a world leader in pet genetics, to obtain the largest sample size possible for analysis. Wisdom Health’s database is the largest dog DNA database in the world, helping researchers collect data from 49,378 dogs across 227 breeds—primarily from European sources.

So, what makes a dog breed more inbred than others? Dr Bannasch explained that it’s often a combination of a small founding population followed by strong selection for particular traits in a breed—often based on looks rather than purpose. 

The study also revealed a significant difference in morbidity between brachycephalic (short skull and snout) and non-brachycephalic breeds. While that finding wasn’t unexpected, the researchers removed brachycephalic breeds from the final analysis on effects of inbreeding on health.

Measures that can be taken to preserve the genetic diversity and health of a breed include careful management of breeding populations to avoid additional loss of existing genetic diversity, through breeder education and monitoring of inbreeding levels enabled by direct genotyping technologies.

In the few breeds with low inbreeding levels, every effort should be made to maintain the genetic diversity that is present.

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