DNA testing can provide useful information for all breeders
Testing our dogs’ DNA provides details on everything from ancestry in mixed breeds to disease mutations and genetic diversity in purebred dogs. Dr. Angela Hughes, Veterinary Genetics Research Manager at Wisdom Health, talks about the different types of DNA genetic testing.
“A breed is a specific combination of alleles,” Hughes said. “And 99 percent of the DNA in a Great Dane is the same as a Chihuahua. It’s that one percent that is so important.”
DNA Panel tests, Hughes said, test for genetic mutations. The Wisdom Health Optimal Selection panel tests for 180 different specific diseases that are broken out by which are identified and correlated within each breed.
Focus on genetic diversity.
“Studies show that losing genetic diversity causes loss of reproductive health, increased disease incidence, even decreased hunting ability,” Hughes said.
Purebred dog breeders are succeeding with test and replace breeding theories, Hughes believes. She referenced a study of dogs in the U.S., mixed breed and purebred, in which of all diseases tested for, 34 disorders were found only in mixed breeds, not in purebred dogs.
While Hughes acknowledges that “you can have healthy highly inbred dogs,” she notes that breeders have to be incredibly selective to achieve that.
“The average breeder doesn’t have the time and resources, the number of dogs necessary or enough information to be that highly selective,” Hughes said.
Genetic diversity in dogs will be different even in full siblings, Hughes said. For full littermates, on average, about 50 percent of the DNA is the same. This power of DNA testing, Hughes noted, is that it can help identify which of two dogs, similar in quality and pedigree, is the best match in terms of genetic diversity. Simple pedigree analysis and COI (coefficient of inbreeding) can’t provide that information.
Skip the Bottleneck
The diversity testing also helps avoid bottlenecks in a breed’s gene pool due to popular sire syndrome. She defines this as any sire with more than 100 puppies produced. In an example based on studies of Golden Retrievers in England, in a gene pool of six generations, with 31,259 individual animals represented, the testing revealed only 67 genetically unique individuals.
“DNA testing doesn’t tell you who to breed, it tells you who to breed to,” Hughes reiterated. “This is the last piece. Do all the other testing – conformation, temperament, health, function – then do this.”
Importantly, Hughes also noted that breeders should be careful to not lose the “essence of the breed” in search of genetic diversity.
“You want to move the needle,” Hughes said. “Just shift the curve in the direction of diversity.”
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BUSTING THE GENETICS MYTHS: DR JEROLD BELL
Last week we talked with Dr. Marty Greer about health testing 101. This week we’re taking the graduate course in genetics with Dr. Jerold Bell from Tufts University’s Cummings School of Veterinary Medicine.
Bell has some serious myth busting going on in this discussion that I think our listeners are going to enjoy.
MIXED BREEDS ARE NOT HEALTHIER
First of all, mixed breeds are not healthier than purebred dogs.
“The most frequent genetic disorders that we see in practice are seen equally between purebreds and mixed breeds,” Bell said.
Second, there is a heritability factor in many diseases we had not previously considered. Bell talks specifically about studiesindicating even something as seemingly obviously traumatic as cruciate ligament tears have a genetic component.
Third, all breeders should be health testing their dogs. The increasing number of DNA tests available enables breeds with simple recessive gene pairs creating disease to quickly and easily apply positive pressure to the pedigree. Breeding a quality carrier status animal to a clear, then breeding the resulting quality clear offspring, Bell said, will rapidly eliminate diseases such as a specific form of Progressive Retinal Atrophy.
“And that’s really the take home message for today,” Bell said. “Is that anyone that’s doing breeding must be doing breed specific genetic testing of the parents and if they’re not doing that then they should not be breeding. Then they are not an ethical breeder and not a health conscious breeder and there’s no place today for breeders that are not going to do that.”
Fourth, for complex inherited diseases, in which a combination of genes is causing a disease process to be expressed, the OFA/CHIC database offers the opportunity to research a “vertical pedigree” to study the incidence of disease in the entire family of the dogs being considered for breeding.
OFA IS FACEBOOK FOR DOGS
“So when you look up at dog’s web page on the OFA Website,” Bell said, “and this is Facebook for dogs, this is the dog’s own individual website. They can have their picture on there, it has all their information. It has all the information of the tests results from the parents from the siblings from the half siblings. … even in a normal individual that you’re looking at for breeding, if the parents or the parents’ siblings (indicate) more disease present, it tells you that you’re going to have a greater genetic load of liability genes for that particular disorder.”
Finally, using health testing *appropriately* is mission critical. Bell noted that breeders’ selection processes should emphasize only those diseases which are of concern within their respective breeds. He presented an outstanding webinar for the AKC Canine Health Foundation available here which goes in to even greater detail on this topic.
“…people might say that because (our dogs) purebred they have limited diversity and therefore they’re unhealthy,” Bell said. “And that is not true.’
We hope you enjoy this very rich conversation with Dr. Bell and are able to apply this knowledge in your own breeding programs.