Out Cross for Improved Genetic Health?

Outcrossing could be key to better breed health

Created: 15/04/2015

BREED health could be improved through outcrossing, and the registration of those dogs, and kennel clubs imposing a limit on the use of stud dogs.

According to a new article in the online journal Canine Genetics and Epidemiology, public awareness, education, and ‘most importantly’ the support of breeders and breed clubs are significant factors in making these changes successful and common practice, and would compromise few breed Standards.

The writers go on to say a recent study found that 48 per cent of companion animal vets were advising clients against buying a pedigree dog due to inherited disorders.

Disorders

But rather than ‘abandoning’ – and losing – the breeds with the highest number of inherited disorders, a more realistic solution for the management of the most predisposed breeds would be to outcross with ‘closely-related breeds’ to reintroduce genetic variation, and combine this strategy with schemes to breed away from the most susceptible individuals ‘to ensure more genetically diverse future generations’.

The writers cite the Dalmatian Am Ch Fiacre’s First And Foremost who is 14 generations removed from a Pointer outcrossing and who was registered by the Kennel Club. The outcrossing rid that line of the gene which makes the breed prone to kidney stones, bladder stones and gout.

“Outcrossing would allow for genetic admixture but still work to maintain the standard characteristics of the breed,” the article says.

“For breeds without a small or decreasing population size it would be beneficial for kennel clubs worldwide to impose limitations on the number of offspring per stud, thus reducing the popular sire effect and promoting increased genetic variability on a population-wide scale.”

For rare breeds and those with small or decreasing population sizes, efforts should be made to mate sires and dams who are as unrelated as possible by considering ‘kinship coefficients’ calculated from pedigree information and also incorporating genotyping data as a standard genetic test for every dog registered, in order to monitor inbreeding on an individual level.

The authors suggest that the Dogslife project, which compiles health and life history information could be used as a model.

They also focus on ‘designer breeds’ saying there is a common misconception that because these originate from founders of distinct breeds they would automatically be healthier and less prone to inherited disorders. But while outcrossing can help it is important to maximise genetic variability and avoid lineages known to have a high prevalence of genetic diseases, for example hip dysplasia and various eye and joint diseases in the Labrador and Standard Poodle when creating a labradoodle, the writers say.

Careful consideration of lineages and thorough diagnostic screening and genetic testing of both sire and dam must be performed to ensure healthy puppies in future generations, the article states. “The hybrid vigour generated by this initial outcross would deteriorate beyond the first (F1) cross, and it would be critical that subsequent selection of animals for the ‘designer dog’ phenotype was carefully monitored to maximise genetic diversity and avoid known inherited conditions.”

Challenges


In the review the authors provide an overview of the ‘challenges’ breeders face to combat inherited disease. Incentive programmes, free diagnostic screening, and genetic testing days are already being implemented by breed clubs to help identify and diagnose inherited disorders in susceptible dog breeds, the writers say, but public awareness of the importance of testing needs to be much improved.

“Testing and screening programs are vital to understanding both the prevalence and susceptibility to developing disease and creating breeding strategies with the aim of significantly reducing inherited disorders. DNA tests for disease causing mutation(s) will be most informative and effective for disease management but must be combined with current screening schemes, pedigree information, and if possible genomic selection, to maximize the impact in significantly reducing the number of inherited disorders and improving overall health in pedigree dogs.”

Breeding selectively based on aesthetics and specific guidelines could have a detrimental impact on a dog’s wellbeing and overall health, particularly if it results in inbreeding or genetic bottlenecks, the writers state.

“Thus, creating new breeds for appearances may not be in the best interest of canine welfare, given our historical experience. Such schemes should take advantage of modern genetic technologies to ensure that known genetic variants are excluded and genetic diversity is maintained in their new lineages.

“There are already several dog breeds at a dangerously low population level in the UK.

“Instead of trying to make a new designer dog breed based on an arbitrarily chosen aesthetic we should focus on ensuring the future of our native established breeds, in addition to putting efforts into significantly reducing and eliminating the inherited disorders already present in purebred dogs.”