Breeders of purebred dogs are faced with a conundrum. By striving to produce dogs possessing consistent and reproducible physical characteristics through line-breeding, they may be losing genes important for the dog’s basic function and health. When the practice of line-breeding is combined with the practice of eliminating dogs from their breeding program based on the results of DNA testing, you have a formula for disaster.
In this post, Carol Beuchat, PhD, vertebrate biologist and founder of the Institute of Canine Biology, explains why the use of DNA testing when making breeding decisions won’t necessarily result in healthier dogs. This post builds on a previous Healthy Dog Blog post by Dr. Beuchat entitled Using Genetics to Breed Healthier Dogs.
While it is true that genetic testing can prevent producing offspring with specific genetic disorders, genetic testing is not the way to healthier dogs. All dogs have recessive mutations (and so do we), and these little genetic accidents cause no harm as long as an animal has a copy of the normal gene. So we can pass these harmless DNA errors on to offspring just like any other gene, usually with no consequences because any particular mutation should only occur in just a few animals in a large population. But if an animal should happen to get two copies of a mutated gene, the normal gene is absent and whatever that gene is supposed to do won’t happen -a step in development, the production of some enzyme for digestion, a fatty acid needed to form cell membranes, a hormone to start lactation – the mission of that gene is thwarted and the animal has a genetic disorder.
Now, enter the breeder, who wants to breed for particular traits in their dogs. The easiest way to do this is to breed dogs that have those traits, and even better if the dogs are related so they have the same genes. This will make litters more uniform and increase the chances of getting the puppy you want with all the right traits. Inbreeding and line breeding are the tried and true ways to do this.But all dogs have mutations, and breeding to get the good genes from a relative will also give you the bad ones. Breeding to dogs with the same genes will produce puppies that are homozygous for those genes, whether they are good or bad. This is why genetic disorders in purebred dogs are increasing: as they become more inbred (more similar genetically), the chances of getting two copies of a mutation will increase. There’s no way around it; it’s just math.
So here’s the conundrum. Breeders should test their dogs for known mutations, so they can prevent producing puppies that will suffer from those disorders. But if after all testing is done, the breeder selects as a mate a closely related dog, they have eliminated the risk of one disorder that is known, and substituted a risk for a disorder that is unknown. Doing your DNA testing religiously then inbreeding is working at cross-purposes, and the closer the breeding the higher the probability you will get some problem that you really don’t want.
So the road to breed health is not genetic testing. DNA testing alone will not – cannot – make dogs healthier. Breeding practices that increase homozygosity – breeding to close relatives, will relentlessly, unavoidably, and inevitably destroy the health of the purebred dog. There’s no way around it; it’s just math.
Carol Beuchat, PhD is Founder and Scientific Director, Institute of Canine Biology (www.instituteofcaninebiology.org ) and member of the Department of Molecular and Cell Biology, University of California Berkeley. To connect with Carol on facebook go to: www.facebook.com/#!/carol.beuchat.9?fref=ts
