Tuesday, April 28, 2015

X -- X-Rays and Genetic Tests

First and foremost, I'd like to call bullshit on "hybrid vigor" -- the idea that mixed breed dogs are healthier because they avoid recessive genes found in purebreds. A 2013 study published by UC Davis dispels this myth. The truth is, all dogs -- much like all humans -- have dominant and recessive genes. And some of them come with some pretty nasty traits. Hip dysplasia, epilepsy, heart diseases and cancer attack mixed breed dogs with the same fury as purebred dogs. Thanks to modern medicine there are genetic tests available for some of these diseases. Responsible breeders are using these tests to keep debilitating recessive genes out of their lines.

Hip Dysplasia is a hereditary condition that causes the hip joint to form improperly. It's seen mostly in large and giant dogs, both purebred and mixed breeds. It can also be found in medium sized dogs as well. Because the joint is loose, the dog's leg bone moves around too much, causing painful wear and tear. Dysplastic dogs may appear stiff or sore in the hips when getting up, may be hesitant to stand on hind legs or climb stairs and may limp or "bunny-hop" when walking.

X-rays are used to determine whether or not a dog is dysplastic. Responsible breeders check their dogs for hip dysplasia before ever breeding them. One of the biggest organizations testing for dysplasia is the Orthopedic Foundation for Animals (OFA). Dogs 2 years old and older are x-rayed by their regular vets and the x-rays are sent away for evaluation. The OFA scores hips as excellent, good, fair, borderline dysplasia, mild dysplasia, moderate dysplasia and severe dysplasia. Only dogs with excellent, good or fair hips are bred. The OFA also tests elbows. Elbow scores are either pass or fail. OFA scores can be found online and are available to the public. All you need is a dog registered name or registration number to see the results. Look here to see the score for Jedi's mother's hips. (Spoiler alert: they're excellent!)

Another common test is for Degenerative Myelopathy (DM). This is a disease of the spinal cord and peripheral nerves. The initial symptoms of DM include loss of coordination in the hind limbs, wobbling when walking, rear feet knuckling over or dragging, and mild weakness in the hind end. As DM progresses limbs become weaker and the dog has difficulty standing, loses control of its bladder and bowels, and develops weakness in the front limbs as well. The disease is more common in several breeds -- including German shepherds and corgis -- but it's seen in all dogs, mixed breeds as well as purebreds. The typical age of onset for DM is between 8 and 14 years old, and the dog is often paralyzed in the hind end within a year.

A genetic mutation has been identified as a major risk factor for development of DM, and there is a genetic test available for this mutation. The test is simple and can be taken either from a blood sample or cheek swab. Either a dog has it (+/+) doesn't have it (-/-) or is a carrier (+/-). Determining the probability of producing a dog that may have DM is as easy as using the Punnett Squares we learned in high school biology class. Responsible breeders do not breed DM positive dogs.
 
Many breeders have eye tests done through the Canine Eye Registration Foundation (CERF). These tests check for a whole host of eye problems including: eyelid conformation abnormalities, persistent pupillary membranes, retinal dysplasia, choroidal dysplasia, progressive retinal atrophy and cataracts. Breeding and potentially-breeding dogs are tested yearly. A passing score is only valid for 365 days because some conditions don't present themselves until a dog is older.

This is not an exhaustive list. Different breeds are concerned with different genetic disorders. The National Club for each breed will have more information about the concerns of that particular breed. And don't be afraid to ask a breeder which genetic tests her dogs have had and why. A responsible breeder would be happy to discuss them with you! -- K

Tomorrow's Topic: You Should Know . . .