Frances O. Smith1, DVM, PhD, DACT; Jerold S. Bell2, DVM
Today's domestic dog originated with the domestication of the Grey Wolf between 15,000 to 33,000 years ago. Both genetic and archaeologic evidence indicate that humans domesticated wolves several times and mitochondrial DNA sequences show at least four distinct clades. Man selected among the canine population for the dogs that best suited their needs and for phenotypically desirable traits. Dogs were selected to hunt, guard, help, cart and pull, herd and just to love. Today we have over 400 dog breeds worldwide that range in size from just over a pound to over 200 pounds in weight and from 6 inches tall to over 38 inches at the withers.
Ancient mutations for the major canine inherited diseases occurred before dogs were separated into breeds and can be found in all breeds, designer breeds, and the mixed-breed population. Cross-breeding does not lessen the risk of producing genetic disorders caused by liability genes that are ancient in the canine genome. These include hip dysplasia, elbow dysplasia, patella luxation, thyroid disease, cancer, allergies, various cardiac, epilepsy and eye disorders, and many ancient testable mutations including forms of PRA and lens luxation.
The compartmentalization of genes into breeds and selection for morphological, health and behavioral traits caused different breed liability for the major inherited diseases. This also caused breed-specific genetic disease through the founder's effect or through linkage to selected traits.
There are three types of breeders of dogs:
The casual breeder either unintentionally allows their dog to get bred or plans an occasional mating.
The commercial breeder produces puppies for income. This includes large industrial operations, puppy mills, and Ma and Pa breeders who breed as a side occupation. They may produce pure-bred or designer-bred litters depending on market demands.
The breeders in the "Fancy" belong to breed clubs, show their dogs, and are more interested in breed improvement. They tend to be knowledgeable about breed health and genetic testing. They do not breed often and typically have waiting lists for puppies.
While knowledge of breed characteristics and participation in health testing are more prevalent in the "Fancy," there are breeders in all three categories that are health-conscious breeders, as well as those in all three categories that breed with no concern for the physical or genetic health traits that can befall the puppies that they produce. There is little correlation between the number of dogs owned by a particular breeder and the care, selection and health of the puppies that are produced. Breeder resources including financial capabilities, the physical plant, the employees and the commitment of the breeder result in optimal care for breeding stock and their offspring. This is not just a numbers game, it is about commitment and resources.
The OFA was organized as the not-for-profit Orthopedic Foundation for Animals, Inc. in 1966 as a screening registry for hip dysplasia. From that time to today, the OFA has expanded to become the world's largest genetic screening registry for testable hereditary disorders in dogs. The mission of the OFA is to promote the health and welfare of companion animals through a reduction in the incidence of genetic disease.
The OFA provides factual information on genetic disorders. Under the Education tab on the OFA website (www.offa.org) you will find several informative pieces including, "The Use of Health Databases and Selective Breeding" (www.offa.org/pdf/monograph_2012_web.pdf). You will also find an informative article from the Veterinary Journal entitled, "How the Orthopedic Foundation for Animals (OFA) is tackling inherited disorders in the USA: using hip and elbow dysplasia as examples" (www.offa.org/pdf/keller_dziuk_bell_vet_journal.pdf). As a private not-for-profit foundation, the OFA has funded nearly $3 million in research aimed at the identification, screening, and reduction of inherited companion animal disease.
The OFA offers radiologist screening for hip and elbow dysplasia, Legg-Calve-Perthes disease, shoulder osteochondrosis dessicans (OCD), tracheal hypoplasia, and spinal anomalies. It offers DNA-based genetic tests run by the University of Missouri Animal Molecular Genetics Laboratory for: primary lens luxation, liability for degenerative myelopathy, and several breed-specific disease mutations. Its genetic health registries include the above listed disorders, as well as eyes, patella, cardiac, thyroid, deafness, dentition, sebaceous adenitis, and other DNA-based genetic tests. Any genetic disorder with a test for normalcy is eligible for an OFA health registry.
A motto of the OFA is, "Heath-tested parents produce healthier puppies." Health testing is quality control. Breeding without health testing provides no selection for genetic health and propagates genetic disease. In no endeavor is quality control optional. Dog breeding does not have an exemption on quality control through health screening; however, most breeding is conducted without it. It is time for veterinarians to educate breeders and the public about the breeder responsibility to do genetic health screening on all prospective breeding dogs prior to mating.
The OFA Website
The OFA website provides powerful tools that help the breeder, veterinarian, and prospective dog owner in selecting for genetically healthier dogs. In the Reports/Statistics section of the OFA website, you can look up aggregate health test statistics for each individual breed (www.offa.org/stats.html). Under Disease Statistics you can look up the ranking of breeds for hip dysplasia, elbow dysplasia, patella, cardiac, and thyroid disease. For hips and elbows it shows the percentage of affected versus normal-testing dogs. Some OFA registries such as patella, cardiac and dentition are used primarily to register normal dogs, so these cannot be used to evaluate the frequency of abnormal-testing dogs in the breed. The OFA thyroid registry records the frequency of autoimmune thyroiditis through evaluation for thyroglobulin autoantibodies. For breeds that have DNA tests available, the OFA records the frequency of affected, carrier, and normal testing individuals. The OFA eye registry reports the results of all ACVO ophthalmologist examinations. These include examinations during eye screening clinics as well as regular appointments; so the registry statistics approximate the frequency of eye disorders in each breed.
The Survey section of the OFA website provides online health surveys for over 70 breeds (www.offa.org/surveys/index.html). They are available for any breed based on a request by a breed club. The health surveys are custom designed to record breed-related indices for disease, breeding, behavior, feeding, and any other aspect that the breed club deems important. Any owner can fill out a survey online as well as look at the aggregate results data.
Instructions for performing genetic screenings are available on the OFA website. Many genetic screening tests can be conducted at your local veterinary clinic. These include hip and elbow radiographs, thyroid profiles, patella palpation, heart auscultation for murmurs, and DNA collection for genetic testing at appropriate testing agencies. DNA required for testing can be collected through blood, cytology brush, or DNA cards that are available from the testing lab. The list of specific DNA tests that are available for breeds and disorders is constantly growing. The World Small Animal Veterinary Association (WSAVA) has a website hosted by the University of Pennsylvania that lists all available genetic tests, where the tests are run, as well as the peer-reviewed literature that you can research for further information. The website is: http://research.vet.upenn.edu/Default.aspx?TabId=7620.
The Clinics tab on the OFA website lists health screening clinics by date and location (www.offa.org/clinics.html). You can use these to find inexpensive clinics where owners can have their dogs screened for multiple body systems by boarded specialists. Another excellently maintained website hosted by a Cavalier King Charles Spaniel group lists all health screening clinics in North America (www.cavalierhealth.org/health_clinics.htm).
The CHIC (Canine Health Information Center) section of the OFA website lists the breed-specific pre-breeding health tests that should be performed for each breed as determined by the parent breed club (www.offa.org/breedtests.html). Over 175 breeds have their health test requirements listed here. Knowledge of breed-specific genetic test recommendations provides value to the client, patient and your practice. Included disorders specify breed predispositions which can assist you with differential diagnoses and treatments.
Veterinarians can use these breed-specific health testing requirements to advise their breeder clients on pre-breeding health screening. They can also be used to advise owner clients on what parental health testing results to inquire about prior to purchasing puppies. By asking for parental health test documentation, they are ensuring that they are purchasing from a health-conscious breeder.
When new puppies are presented to you for their first examination, your staff should instruct the owner to bring all of the paperwork that the breeder, store, or broker provided to them. Aside from the medical record, you should copy or scan any registration information, pedigree, breeder contact information, health testing documentation, and guarantees into the puppy's record. If health testing information is not provided in the paperwork, the parents of the puppy can be looked up on the OFA website by either their registered name or registration number (Quick search on upper left of OFA homepage). The OFA includes all registries, not just AKC-registered dogs. If health testing documentation is not found on the OFA website, then it is possible that some health testing was performed but was not submitted to the OFA. Provide your client with the breed's CHIC test requirement page and ask them to contact the breeder for any health testing documentation. If the breeder had health testing done, they will be happy to provide a copy of the official test results. If health test documentation is not available, then your patient did not come from a health-conscious breeder and there was no selection for genetic health.
The peer-reviewed literature shows us that designer-bred and mixed-breed dogs develop the common canine genetic disorders with similar frequencies as purebred dogs. Designer-bred dogs should have parental testing for each parent's breed-specific tests. If a dog is to be bred and there are no breed-specific testing requirements listed, then they should be checked for the morphologically appropriate disorders. These may include hips, elbows, patellas, cardiac, eyes, thyroid, as well as a medical history of allergies, epilepsy, gastric dilatation/volvulus, or other disorders with a hereditary basis. Pre-breeding health screening is like an equine pre-purchase examination. It evaluates the genetic health worthiness of the dog for breeding. If the public demands healthier dogs, then this is where it must occur.
Every Dog Has a Webpage
The most powerful aspect of the OFA website is the information available on individual dogs. Each dog has their own webpage searchable through their name (full or partial) or registration number (www.offa.org/search.html). Searching under a kennel name provides all of the breeder's dogs with their test results. On each dog's page is their identifying information, their picture (if submitted by the owner), their own test results, and the test results (if available) on their parents, offspring, full siblings, and half siblings through their sire and dam. These familial test result data are important when evaluating the risk of carrying liability genes for complexly inherited disorders. At the top of the dog's webpage is a link to vertical pedigrees which summarize the familial data for hips, elbows, cardiac, patella, thyroid, eyes, and degenerative myelopathy.
The individual dog's results for all but DNA tests represent its phenotype or physical expression of disease. The results of its close relatives provide data on the individual dog's genotype or the breadth of genetic disease liability it may carry. As more normal-result health screening tests are available on relatives, the risk of carrying disease liability genes diminishes.
As more genetic screening tests become available for dogs it is likely that many dogs will receive some kind of abnormal result. This does not always mean that they will develop a disorder or should be removed from breeding. Dogs testing as a carrier for a recessive disease-liability mutation can be bred to a normal-testing mate. No affected offspring will be produced and the carrier parent can be replaced in a breeding program with a normal-testing offspring. Dogs with mild disease (Grade I elbow dysplasia, mild hip dysplasia) who exhibit other quality traits that make them desirable as breeding dogs can be bred to dogs with normal phenotypes to improve the probability of producing normal offspring. The goal is for you to assist your breeder clients in improving the genetic health of their dogs with each mating.
The OFA health registries are semi-open, meaning normal results are openly reported, but the owner has to release abnormal results. Veterinarians should counsel their clients to initial the box for Authorization to Release Abnormal Results. No one plans to have a dog that is a carrier or affected with genetic disease. Failure to report abnormal test results, especially for dogs that will be used for breeding, has the potential to propagate the disease. It does not allow owners with relatives of the dog to properly evaluate the genetic risk of carrying disease liability genes. While the stigma of genetic disease used to lay with the owners of dogs with genetic disease, it now lays on the owners who hide the existence of genetic disease.
Abnormal test results for disorders that do not require OFA radiologist screening can be submitted to the OFA registries at no charge. These include thyroid, patella, cardiac, eyes, dentition, deafness, sebaceous adenitis, shoulder OCD, and all DNA-based tests. The owner should submit an application along with a copy of the official result form and initial to authorize release of abnormal results. If an owner wishes to release abnormal results from prior testing, there is a form under the Policies tab for moving information into the public domain. They will fill out the form to "Change from Semi-Open to Open Database."
Genetic testing is a responsibility of breeders. The release of all normal and abnormal test results is also an obligation of breeders who seek to improve the genetic health of their dogs, their relatives, and the breed. If a dog is used for breeding and does not have test results listed on the OFA website or official test documentation from the owner, it should be assumed that they failed their genetic screening tests or they are not owned by a health-conscious breeder. Your clients would do better to look elsewhere to breed or to purchase a puppy.
Dogs who are the offspring of parents who both tested normal for direct DNA tests can receive "Clear By Parentage" certification without having genetic testing themselves (found under the Policies tab: www.offa.org/cbp.html). To receive this clearance, the dog and both of its parents have to have DNA certification of parentage (through AKC parentage or other testing), and both parent's DNA test results must be submitted to the OFA registry.
Veterinarians are tasked with improving and maintaining the health of our patients. We should embrace our role to educate our clients and promote the purchasing and breeding of genetically healthy dogs. Much is written lately about the burden of the general practitioner to compete with vaccine clinics and big-box practices. Our greatest asset is the personal service that we can provide to our clients in managing the health of their pets. The OFA provides the educational resources and tools to assist us and our clients in this effort.