Dog breeds must be “rebooted” through careful cross-breeding to save them from ingrained health problems, a leading expert has said. From French bulldogs with spinal and respiratory issues to cavalier King Charles spaniels with skull malformations and heart problems, many breeds are prone to specific disorders. But while efforts have been made to breed healthier pedigree dogs by screening for problematic traits, the approach has limits. Clare Rusbridge, a professor in veterinary neurology at the University of Surrey, said many diseases arose from a complex array of genetic variants, while the gene pool of breeds was often so small that there were simply not enough unaffected individuals to breed from. “There needs to be an acceptance of allowing new genetic material in,” she said. A case in point, said Rusbridge, was the cavalier King Charles spaniel, a breed that has high rates of a spinal disease called syringomyelia – a painful condition called Chiari-like malformation that occurs when the skull is too small for the brain – and heart problems. “They all have a heart murmur by 10 years old, and most of them die from mitral valve disease,” Rusbridge said. The concerns are so great that in 2022 Norway’s supreme court banned the breeding of the cavalier King Charles spaniel. While scientists have discovered cavalier King Charles spaniels with genetic variants that protect them from myxomatous mitral valve disease (MMVD), Rusbridge said their rarity meant it would be more fruitful to cross them with other breeds that have protective variants to produce dogs with better health. The offspring could then be crossed back into the original breed. “The reality is it doesn’t take many crossbreeds before you get back to a dog which looks like the original,” Rusbridge said. She is adamant the approach does not mean doing away with beloved dog breeds, or creating designer pooches. Instead, the idea is to save them. “Reboot the breed,” she said. Crucially, Rusbridge added, such efforts must involve the formation of crossbreed registries, and a route by which later generations can be registered as pedigree members of the original breed. The approach has already been adopted in several Nordic countries, with Finland launching separate outcrossing projects for the cavalier King Charles spaniel and the French bulldog. “Altogether, there have been or are ongoing at the moment over 10 official cross breeding projects in Finland,” said Kaisa Gold, secretary of the scientific committee of the Finnish Kennel Club. Lena Gillstedt, a breeder involved in an outcrossing project run by the Swedish Cavalier King Charles Spaniel Club, said: “Of course, there are some breeders who are sceptical and even negative. But overall, the consensus among breeders has been very high.” She added that so far six litters had been born and more were on the way. But not everyone is convinced. Michael Levy, chair of the UK-based Cavalier King Charles Spaniel Club, said although the organisation watched such efforts with interest, they “currently do not see this as a solution to some of the health issues we face with our popular breed”. He added: “As with any breeding, selection is of the utmost importance and health is the priority always in those selections. Health testing is conducted and encouraged by all the breed clubs.” He said his club strongly advocated that breeders DNA test their dogs for MMVD, while a new scheme would start soon to reduce the prevalence of syringomyelia. The UK Kennel Club said it had accepted outcrossing projects, similar to those in Finland, for various breeds over the years – although none have included French bulldogs or cavalier King Charles spaniels – and had a pathway back to pedigree status. But Dr Joanna Ilska, genetics research manager at the Kennel Club, said there must be robust evidence and a plan in place to maximise the chances of outcrossing improving health and ensure improvements were successfully spread through the breed. “We continue to urge breeders to participate in health screening their dogs prior to deciding to breed and the Kennel Club has developed a number of tools to not only help breeders make responsible decisions, but also to collect data, which is vital for future actions and solutions to protect dog health,” she said. Rusbridge said a more proactive approach was needed, noting that at present it is up to breed clubs to push for outcrossing projects with the Kennel Club. “Attitudes across the board need to change,” she said.