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PUREBREEDS AND GENETIC DISEASES....

Posted Jun 12 2011 12:00am

Well, some of you are already on your vacations (possibly with your pets) and some of you are still looking forward to getting away for some fun time this summer.  Regardless of your travel plans, be sure to check in with Helpful Buckeye each week for the latest issue of Questions On Dogs and Cats.

Desperado and Helpful Buckeye will be traveling this next week, although this trip is more for family medical reasons than for pleasure...helping Helpful Buckeye's dad get organized in the face of some health issues.  However, I won't leave our readers high and dry without your weekly fix of Questions On Dogs and Cats.

We've added another feature to our blog offerings.  A "Blog Archive" is now available in the column to the left.  You can click on the weekly issues from the most recent month and then from each whole month back to the beginning of this year.  Before that, you can click on each year.  Remember that for specific topics, you can look through the list called "Labels"...also in the column to the left...and click on whatever topic interests you.

Over the last couple of years, Helpful Buckeye has received some e-mails with questions about certain breeds of dogs and any particular diseases that are associated with those breeds.  I've answered those questions on an individual basis but it now appears that this would be a good topic for our weekly discussion.


The subject of genetics first aroused my interest as an undergraduate student as part of my zoology major.  That interest continued into graduate school and veterinary medical school.  The study of genetics at that time was almost rudimentary compared to what is known today.  The many disciplines of genetics have allowed scientists to delve into
the aspects of gene expression and to find a lot of answers to questions about why certain diseases are seen more often in certain breeds of dogs than others.  From the studies of Thomas Hunt Morgan on fruit flies 100 years ago through the findings of Watson and Crick about the structure of DNA to the science of today, geneticists and molecular biologists are able to help us understand how a Golden Retriever can have a genetic eye disorder and how a white cat with blue eyes can be deaf.  I'm not trying to make geneticists of any of you (I'm not one either) but I think most of our readers will find this information pretty interesting.  If you have any questions on this material, don't hesitate to send an e-mail to me at: dogcatvethelp@gmail.com  

Purebreeds and Genetic Diseases
The Humane Society of the United States has published this very informative article that provides a nice overview of this topic:
The Purebred Paradox


Is the quest for the "perfect" dog driving a genetic health crisis?


by Carrie Allan


In the days leading up to the annual Westminster Kennel Club Dog Show, the hotels around Madison Square Garden in New York City fill up with owners, handlers, and hundreds of purebred dogs. They come from around the country, spiffed up and ready to shine: prancing white poodles with their fur teased into towering pompadours, basset hounds with their ears held up in shower caps to keep them from dragging on the ground, bright-eyed Chihuahuas peering eagerly out of fancy carriers.


For these show dogs, who must be registered with the American Kennel Club, this is the Oscars—“the symbol of the purebred dog, in show rings as well as in millions of television homes across America,” according to its marketers. They vie for a hierarchy of awards: best of breed, best in group (sporting, herding, hound, toy), and, most prestigious of all, best in show.


In an interview filmed during the show this February, Kimberley Meredith-Cavanna explained the criteria that she and other judges consider when determining how closely these premium pooches match the “ideal specimen” prescribed by each breed’s parent club. “We’re looking to see what its head should look like, its eye set, its proportions, its size, how the dog moves, and how it should be built,” she said.


While it may seem as though contestants are competing against each other, they are actually judged against standards written by the clubs and ratified by the AKC: Are this dog’s ears long enough to make her an ideal beagle? Is that one’s head big enough to make him a prime example of English bulldog-ness? Does this Rhodesian ridgeback have the correct symmetrical ridge of hair along her spine?


Watching the lively animals in the ring, how can a dog lover not be charmed? Westminster and other shows like the annual AKC/Eukanuba Championship have a loyal following among breeders and casual dog lovers alike.


But the shows are not without their critics. Though the dogs who compete at Westminster are beautiful and most are likely healthy, the rise of such spectacles—and judging measures that in some cases emphasize appearance over welfare—has been blamed for a host of genetic health problems facing scores of breeds today.


Brachycephalic (or short-faced) breeds like bulldogs and pugs suffer from breathing problems; Great Danes and other large dogs from joint problems; long dogs like dachshunds and basset hounds from back problems; wrinkly-faced dogs like boxers and shar-peis from skin and eye problems. And due to prolific production to meet public demand, the most coveted dogs tend to have the most genetic disorders; Labrador retrievers, who’ve topped the AKC’s popularity list for 19 years, are prone to around 50 inherited conditions.


The stories of those who fall in love with these animals, only to watch them suffer, are often heartbreaking. On New Year’s Eve, Janice Pfeiffer’s dog Daisy suddenly “started yelping really loud,” says the New Hampshire resident. “It turned out she had a seizure, and she recovered from the seizure on the floor, and crawled into a corner and just looked glassy-eyed.”


An MRI revealed the painful truth about the Cavalier King Charles Spaniel Pfeiffer had bought at a pet store: At less than a year old, Daisy had syringomyelia, a condition in which fluid-filled cavities occur within the spinal cord near the brain. In severe cases, a dog’s brain swells beyond the space provided by her skull. Some studies have indicated that, due to its prevalence in the breed’s gene pool, 30 to 70 percent of Cavaliers will develop the condition.


The Genetic History of Man’s Best Friend


Once upon a time, people believed that purebred dogs were naturally healthier than mixed breeds. How have we arrived at a point where it may be safer to presume the opposite?


Like humans, dogs are diverse in appearance—perhaps one of the reasons we love and identify with them. But that wasn’t always the case.


All dogs share ancestry with the wolf, but since their domestication at least 15,000 years ago, they’ve been selectively bred by people to assist with herding, hunting, and—in the case of the Pekingese—warming the laps of Chinese emperors. For the better part of canine history, the physiques of breeds were driven by dogs’ role as working animals, a classic example of the dictum that form follows function.


As that role diminished and pet keeping became common, dogs began to be bred more for appearance. You can see the resulting diversity any time you go to the dog park and watch an amorous Chihuahua trying to make time with an embarrassed St. Bernard, while a baffled Afghan and whippet look on. They’re all dogs—but if you didn’t know that, you might believe they were different species.


The thought wouldn’t be unreasonable. A recent study in The American Naturalist compared the diversity in the dog to that across the entire order carnivora. They found more difference between the skulls of a Pekingese and a collie than between those of a walrus and a coati, a South American member of the raccoon family.


Left to their own devices, dogs will be dogs—and will eventually intermingle enough to level out extreme differences within the species. Natural selection ensues and hybrid vigor results: Witness the similar color and size of mutts in Mexico and other countries where they’re allowed to roam. To protect particular characteristics, though, breed enthusiasts have long guarded a highly controlled process, regulating genetic lines and creating registries that stipulate which animals can be bred to produce more of the same type.


But therein lies the problem: The more limited the number of mates, the greater the chance a dog will be bred with a relative who shares similar genes. Genetic diseases are caused by recessive genes, so a good gene from one parent will trump a bad gene from the other. But if both parents have a bad gene—such as one that predisposes them to hip dysplasia or blindness—the likelihood of a sick puppy increases.


“What happens when you have a small and inbreeding population is that the probability of two negative recessive genes finding each other increases as the gene pool chokes down to a smaller and smaller pool,” says Patrick Burns, a Dogs Today columnist who frequently writes about genetic health issues on his blog, Terrierman’s Daily Dose.


A closed registry that allows no “new blood” into the mix exacerbates the problem, he argues: “In many AKC dogs, the founding gene pool was less than 50 dogs. For some breeds, it was less than 20 dogs.”


Standard Problems


This year’s (2010) Westminster champion, a Scottish terrier named Sadie, hails from one of these tiny gene pools and is “very heavily inbred,” says Burns. The limited ancestry for AKC-registered Scotties, he adds, helps explain why 45 percent die of cancer.


“We do not need to have a closed registry to keep a breed,” Burns says, pointing out that breeds existed long before there was an organization to track them. “We did not create the dogs we love in a closed registry system—we have only ruined them there.”


Some breeders would doubtless disagree with Burns on this issue. But the inherent difficulties of protecting the health of a breed within a closed registry are exemplified by a project undertaken by the Basenji Club of America, which has in the past requested that its stud book be opened temporarily to bring in healthier animals.


Genetic problems in registered Basenjis were detected in the 1970s, when many of the small curly-tailed dogs known for being “barkless” began suffering from hemolytic anemia. After a test for the disease was developed, breeders tried to protect the gene pool through euthanasia of affected dogs, says club president Sally Wuornos. But eliminating dogs with hemolytic anemia left a much smaller number of registered Basenjis. And many of the remaining animals now displayed a different problem, a kidney disease called Fanconi syndrome. By addressing one disorder, the breeders had unwittingly amplified another.


Instead of repeating past mistakes and culling Fanconi carriers, the club received the AKC’s permission to open the Basenji registry to dogs from countries with no AKC-accepted registry. Since then, Basenji lovers have brought dogs back from isolated areas in the Congo and successfully integrated these healthy animals into the breeding pool.


Obtaining such permission to bring in new genes is unusual. Many breeders and clubs employ less dramatic measures: They pair mates who are healthy. They keep dogs with known disorders out of their breeding stock. They insist on conducting available genetic tests.


Yet in spite of these efforts, purebred health problems have continued and in some cases worsened. While genetic testing has made precautionary measures possible for some breeds in recent decades, people have been breeding dogs for centuries. Much damage has already been done. The modern German shepherd provides a classic example: One of the breed’s primary disorders, hemophilia, is thought by most experts to have spread almost entirely through the descendants of a single popular stud dog born in 1968 in Europe.


Though veterinarians learn about such problems in school and see them in their practices, even they are sometimes still surprised by their prevalence. When veterinarian Paula Kislak adopted retired racing greyhounds, she assumed the breed “at the very least was physically strong because it was being bred for athleticism,” she says.


But because many racing greyhounds are killed when they cease performing on the track, few people knew of their genetic issues. As her dogs aged, “they were getting some really serious conditions in a proportion that was much higher than … the general population,” says Kislak, a member of the Humane Society Veterinary Medical Association’s leadership council. “The oncologists were seeing a lot of osteosarcoma. In fact, 50 percent of the greyhounds I’ve had have died of some sort of cancer.”


A Shot Across the Bow


While pet owners have been dealing with these issues relatively quietly for decades, the documentary Pedigree Dogs Exposed recently brought them to the forefront.


Broadcast in the U.K. in 2008, the film was critical of the Kennel Club, the British equivalent of the AKC, and showed purebreds with a range of health problems. Among its revelations: The 2003 champion of Crufts, the country’s most prestigious dog show, was a Pekingese who had to be photographed sitting on ice blocks because his flat face made him so prone to overheating. The film showed images of certain breeds in the early 20th century alongside pictures of the same breeds today, demonstrating how a century of selecting for looks had lengthened the back of the dachshund, rounded the skull of the bull terrier, and dropped the hindquarters of some German shepherds into an almost froglike stance.


The filmmakers interviewed the RSPCA’s chief veterinary adviser, Mark Evans, who noted that his group was extremely concerned about “the very high levels of disability, deformity, and disease in pedigree dogs.” According to the documentary, sickly purebred dogs were costing British owners 10 million pounds a week in veterinary fees.


In response, the Kennel Club and the Dogs Trust—a charity that, along with the RSPCA, had been critical of the club’s policies—jointly commissioned an independent inquiry led by Cambridge University professor emeritus Sir Patrick Bateson. The resulting report largely confirmed the documentary’s findings, concluding that inbreeding, selecting for extreme characteristics, and the practices of mass breeding facilities known as puppy mills were negatively impacting dog welfare.


Describing the tension at the heart of the issue, Bateson wrote, “To the outsider, it seems incomprehensible that anyone should admire, let alone acquire an animal that has difficulty in breathing or walking. Yet people are passionate about owning and breeding animals which they know and love, even though the animals manifestly exhibit serious health and welfare problems.”


Britain’s Kennel Club has since banned the registration of puppies from closely related parents (matings of fathers and daughters, for example) and revised many breed standards, adding language to emphasize health and soundness, says the group’s public relations manager, Heidi Ancell.


Many of the standards, she says, were amended to ensure they don’t encourage extreme features. The Pekingese standard now specifies that a “muzzle must be evident.” The bulldog’s standard calls for a “relatively” short face, stipulating that pinched nostrils and heavy wrinkles over the nose should be severely penalized by show judges—who have in the past rewarded high marks for such features.


Some breed clubs have welcomed the changes; others have protested. But in the United Kingdom, at least, there seems to be momentum for change. Whether that momentum will gather steam in the U.S. remains to be seen.

This should be enough to stoke your interest in this subject.  Even if you don't have a purebred dog, you will know someone who does.  Come back and see us next week for the 2nd installment of this topic.
Remember to NEVER bite off more than you can chew....


~~The goal of this blog is to provide general information and advice to help you be a better pet owner and to have a more rewarding relationship with your pet. This blog does not intend to replace the professional one-on-one care your pet receives from a practicing veterinarian. When in doubt about your pet's health, always visit a veterinarian.~~
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