Your Dog's Health Screening Documentation

Not so long ago, the only way for a breeder to know what genes—good and bad—her dogs carried was to breed the dogs and watch the offspring. Now science has expanded the tools available to the responsible dog breeder. As more knowledge is gained, breeders will have better and better tools at their disposal to eliminate or control many serious inherited disorders from their dogs.

Whether we want to reduce the occurrence of a problem trait, or increase the occurrence of a desirable trait, we need to know its mode of inheritance—that is, how the trait is inherited. We also need to know how to identify the trait as early as possible in puppies. Sometimes that can be done just by looking at the puppy—if we're concerned about color or markings, we can see those very early in the puppies of most breeds. Your dog's underlying genetic makeup is his genotype. The traits that we can physically see make up the dog's phenotype. Phenotype usually reflects a combination of genes and environmental factors that affect development. For instance, your dog's potential adult size is determined by his genes. But his adult size is also affected to some extent by the quality of food you give your dog, his general health during his growth phase, and sometimes other environmental factors.

The modes of inheritance have not yet been determined for many traits thought to be inherited. Interestingly, some traits that appear in more than one breed are not always inherited in the same way in the different breeds, and the traits sometimes behave differently from one breed to another. Finally, although many problems occur in multiple breeds, some occur only in a handful of breeds, and some breeds simply never inherit certain disorders.

New tests to detect problems are being developed every day, and the number of inherited disorders for which breeders can have their dogs screened is rapidly increasing. Until recently, it has been difficult (if not impossible) to eliminate diseases that are passed on by dogs who do not have the symptoms of the diseases. Now, however, DNA can be used to determine not only if a dog has some disorders, but also if he carries the genes for those disorders. As scientists learn more and expand the number of tests available, breeders will be able to screen all breeding animals and prevent transmission of many more inherited disorders.

Not all inherited disorders can be detected or prevented through testing, but you greatly increase your chances of getting a healthy pet if you insist on seeing the parents' screening test certificates. Let's look at the common inherited disorders for which tests are now available.

Hip Dysplasia

Dogs are prone to a number of inherited defects of the skeletal system. The most prevalent of them is canine hip dysplasia (CHD), a malformation of the hip joint. CHD cannot be detected by watching the dog move, so don't be misled by anyone who claims she doesn't need to x-ray her dogs since she can see that they're okay. Not all breeds are prone to CHD, but many are. If you've chosen a breed in which CHD occurs, be sure to see certification showing that the parents are free of hip dysplasia. Preferably, the puppy's grandparents and great-grandparents will also be certified free of CHD, as well as siblings in each generation and prior offspring if they have any. In other words, you want to see as many relatives as possible certified free of CHD.

The OFA rates hip structure by evaluating x-rays. The dog must be at least 24 months old when x-rayed in order to be certified, although preliminary evaluations can be made earlier. Dogs that are considered free of CHD are rated Excellent, Good, or Fair. Dysplasia is also ranked at three levels of severity.

The Pennsylvania Hip Improvement Program (PennHIP) uses a different method, also requiring x-rays, and can evaluate puppies as young as four months. PennHIP provides two numbers. First, they provide a distraction index for each hip that indicates the laxity, or looseness, of the hip joint. Laxity is considered an accurate predictor of degenerative joint disease. Second, PennHIP provides a percentile score showing where an individual dog ranks in relation to all members of his breed that have been evaluated by PennHIP. The percentile ranking may change as more dogs are tested, but the laxity index will not.

Some breeders now use PennHIP, but most use OFA. A few use both systems. Several other programs are also available, a few of them limited to single breeds, so once again, you need to do some research to determine what's appropriate for your chosen breed. Whatever system is used, your breeder should show you an original certificate or copies of original certificates verifying that the parents are free of CHD. You can also use your potential puppy's pedigree (which the breeder should be happy to provide prior to selling you a pup) to verify OFA or PennHIP certification.

Other Orthopedic Problems

Elbow dysplasia refers to inherited elbow disease, consisting of one or more problems in the elbow joint. Usually, a dog with elbow dysplasia in one elbow has it in both. Symptoms of elbow dysplasia include lameness, faulty movement as the dog tries to compensate for elbow pain by turning his front toes inward, and limited range of motion in the elbow. Symptoms usually appear in puppyhood; the exact age depends on the individual's particular problems as well as environmental influences, such as weight and exercise. In breeds that are prone to elbow dysplasia, breeding animals should be x-rayed and found free of elbow dysplasia before being bred.

A cushion of cartilage protects the ends of a dog's long leg bones. Although it protects the bone, the cartilage itself can be injured, particularly in a large, active, young dog. If the cartilage in the joint cracks and tears, the dog has osteochondrosis (OC). If bits of cartilage break free and float in and around the joint, the dog has osteochondrosis dissecans (OCD). OCD usually affects the shoulder or elbow, but may also occur in the hip or knee, causing inflammation of the joint (arthritis), lameness, and swelling of the joints (especially after exercise). OCD is usually quite painful. Symptoms usually appear when the dog is between four months and one year old. Research suggests that a dog must inherit a predisposition for OCD, which is then brought on by trauma, usually in the course of normal exercise.

As I write this, the OFA is conducting research on OCD, but at present there is no standardized screening test for the disease. If you're considering a breed in which OCD commonly occurs, ask the breeder about the incidence of the disease in your potential puppy's relatives. Your best bet is a pup with no close relatives affected by the disorder.

The patella, or kneecap, is located in the stifle joint in the dog's hind leg. If the patella luxates, it slips out of its normal position and locks the leg straight, which is painful and potentially crippling. Patellar luxation is a problem in many toy breeds as well as some larger breeds. A veterinarian can check for patellar luxation even in young puppies. Dogs with luxating patellas should never be used for breeding. If you're considering a breed prone to this disorder, ask to see either OFA certification or a letter from a veterinarian certifying that the parents have normal patellas. If possible, ask that your puppy be examined by a vet before you bring him home, or retain the option of returning him for a full refund within a certain time if your own vet finds his patellas to be abnormal during his first puppy exam.

Other orthopedic problems occur in some breeds and affect different parts of the skeletal system, including the spine and various joints. Learn about your breed, and if it is prone to any of these disorders, insist on seeing the appropriate documentation before you buy your puppy.

Inherited Eye Disease

Inherited eye disorders affect many breeds. If eye diseases are a problem in your chosen breed, be sure to see documentation of an eye examination within the previous year. Ask about the grandparents of the puppy as well; hopefully, there is evidence that they also passed yearly eye examinations until at least six or seven years of age. In some breeds, the puppies, too, should have their eyes examined at a specific age, so find out whether that is recommended for your breed. All eye examinations should be done by an American College of Veterinary Ophthalmologists (ACVO) board-certified specialist. General practice vets don't have the special training or the equipment necessary to administer a thorough eye examination.

The Canine Eye Registry Foundation (CERF) maintains a registry of purebred dogs that have been examined by ACVO Diplomats (members) and found to be free of major inherited eye disease. CERF also issues certificates to those owners who submit the results of the ophthalmologist's exam. However, many breeders prefer to see the actual examination form rather than a CERF certificate, because the ophthalmologist may note certain conditions that would not prevent a dog from getting a certificate, but which are of concern to careful breeders. In any case, you should see originals or copies of either a CERF certificate or a certification of eye examination by a veterinary ophthalmologist.

Testing for Other Inherited Disorders

So is that it? Watch out for orthopedic and eye problems and you're home free? Well, no, not quite. Some breeds are prone to inherited heart defects; blood disorders; kidney, liver, and lung disorders; diabetes; and deafness. The incidence of cancer is very high in some breeds. Idiopathic (inherited) epilepsy occurs in a number of breeds. A few breeds even have their very own inherited disorders that occur in no other breeds.

Unfortunately, no tests have been developed yet for some of these problems. Your best approach is to read as much as you can about the breed, find a breeder you trust, and ask her what she's doing to control the problem in her puppies. Ask for evidence of testing where that is possible, and find out as much as you can about relatives of the pup you're considering.

Remember, though, that there are healthy dogs out there! It's well worth the extra time and effort it takes to find a breeder who does everything humanly possibly to produce healthy pups from healthy parents.

Excerpted from The Complete Idiot's Guide to Getting and Owning a Dog © 2003 by Sheila Webster Boneham, Ph.D. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.

To order this book visit the Idiot's Guide web site or call 1-800-253-6476.