Hereditary diseases are prevalent in both pure-breed dogs and mixed-breed dogs. Breeding practices are closely linked to the incidence of hereditary disorders. Many hereditary diseases are progressive and without complete cures, which leads to difficulties for the dog, often from a very early age.
Understanding hereditary disease information and applying good breeding practice have an impact on the health of the breed in general. Therefore it is extremely important that vet teams have a good understanding of their role in improving genetic health in dogs, and are able to use their knowledge to educate breeders and encourage the use of good breeding practices.
The Role of Vets and Vet Nurses
Vet teams are exposed to many health conditions in dogs, and hereditary diseases make up a large proportion of health issues in dogs. There are several ways in which vet teams can assist in improving genetic health for dogs.
Diagnosis.
Vet teams have the opportunity to treat dogs from a young age during check-ups, and are therefore well-positioned to seek early signs of diagnosis for hereditary diseases, or to do screening for young puppies.
Treatment and care.
Although many hereditary diseases do not have complete cures, many have treatment options to alleviate symptoms. Vet teams can provide these treatments for relief of symptoms, and can also provide care information to pet owners to assist in creating a healthy, comfortable lifestyle for dogs.
Control and prevention.
Vet teams can assist in running screening programs for hereditary diseases. By understanding the biological basis of hereditary diseases, vets and vet nurses are also better positioned to advise dog breeders on good dog-breeding practices and educate breeders to breed healthier dogs and help lower the prevalence of hereditary disease in dogs.
Vets can also make recommendations for a dog diagnosed with a hereditary condition to be desexed to prevent it from participating in breeding programs. This can help prevent the inheritance of the condition in its puppies.
Background of Hereditary Diseases
Genetic diseases are caused by mutations in genes (DNA). Hereditary diseases are genetic diseases that are transmitted from parents to children. When breeding occurs, the offspring receives half its DNA from the mother, and the other half from the father. This means that the breeder dogs’ genetic information directly impacts the likelihood of a disease being present in the puppies.
Some genetic mutations are not visibly expressed as a phenotype (traits). For example, the mother and father both have a genetic mutation that does not cause any disease symptoms in them, however if the offspring receives these mutations from both parents, the disease may become apparent. In this case, the parent dogs are known as ‘carriers’.
Running genetic tests and looking at a breeder dog’s family history can give an indication of whether the breeder dog is affected by a disease or is a carrier for a disease.
Not all hereditary diseases are prevalent across all dog breeds. For example, degenerative myelopathy is a progressive neurological condition that most commonly affects German Shepherds. Being aware of disease prevalence in certain breeds will lead to better decision-making when breeding dogs. This will also be helpful in providing pet-care information to pet owners.
It is also important to note that whilst genetic factors play a large role in the causation of hereditary diseases, many of these diseases are complex diseases, meaning environmental factors (such as diet, exercise etc.) also impact the onset and severity of the disease. Therefore, combining genetic information in dog breeding with care-taking tips for pet owners is necessary for having a healthy dog.
Recommendations for breeding stock selection
Based on hereditary disease information, here are some important considerations to keep in mind when choosing a breeder dog. Vets and vet nurses can advise dog breeders of these considerations and encourage them to follow these tips.
Choose healthy dogs.
Where one or both breeder dogs have a mutation in their genes causing disease, it is more likely for this disease to be inherited by their puppies. This applies similarly to situations where one or both breeder dogs are carriers of a disease. Therefore, there should be an increased selection of healthy dogs for breeding.
Avoid choosing dogs with extreme traits.
This tends to cause exacerbation of that trait in their puppies. An example of this is where two short-statured dogs are bred together, their puppies often show patellar luxation, a condition where the kneecap pops out of place when the knee is flexed, causing dislocation of the leg.
Avoid inbreeding.
Inbreeding refers to the breeder dogs being closely related to each other, meaning their DNA sequence will be more similar than unrelated dogs. This increases the chance of their puppies being affected by a hereditary disease, particularly if one or both of the breeder dogs are carriers of a disease.
DNA Testing in Dogs
Since genetic mutations are not always expressed visibly, genetic screening is encouraged to test for genetic disease in both potential breeder dogs, and also for newborn puppies. The goal is to exclude dogs carrying genetic mutations from breeding programs to prevent inheritance of the mutation.
DNA tests can be completed using samples of cells from the dog. These samples are usually collected by rubbing a sterile brush along the inside of the dog’s cheek to collect cells from that area. Sometimes, a blood sample is collected for larger DNA samples. The sample will then be sent to a lab for testing.
The DNA test will look for any mutations present that have been known to associate with hereditary diseases.
A breed-specific DNA test can also be run. This test will look for genetic mutations that are associated with conditions common in a specific breed. Hereditary diseases are not equally prevalent in all dog breeds. This test can be useful if the dog being tested is of a breed that is commonly diagnosed with certain hereditary diseases.
DNA testing is not 100% accurate, but can provide a high degree of accuracy in determining potential genetic risks in dogs.
Common Hereditary Diseases in Dogs
Listed below are three common hereditary diseases in dogs. Vets and vet nurses are likely to encounter dogs with these conditions. The application of good breeding practice is a good starting point to decrease the prevalence of these diseases. Importantly, there are also care-taking practices which can be implemented to relieve or prevent aggravation of symptoms for dogs diagnosed with these hereditary conditions.
Hip Dysplasia
Hip dysplasia, a deformity of the hip that occurs during growth, is the most common hereditary musculoskeletal disorder in dogs. Research in a range of populations, including a veterinary teaching hospital and in the United States and Canada, have found the overall prevalence of hip dysplasia in dogs to range from 15.56% to 19.7%. This condition most commonly affects large dogs such as German Shepherds, Retrievers, and Great Danes.
The hip joint is made of the head of the femur and the socket of the pelvis. During growth, both should grow at the same rate. When the growth rate is not the same, the result is a loose hip joint which causes symptoms such as difficulty rising, laying down, or jumping.
Since his dysplasia typically affects large dogs more severely than small dogs, it is recommended that dogs diagnosed with this condition be kept at a normal weight during growth to minimise the effects of the disease.
Mitral valve disease
Mitral valve disease accounts for 80% of heart diseases in dogs. The mitral valve is the valve between the left atrium and left ventricle of the heart which prevents blood from flowing backwards. In dogs with mitral valve disease, the valve becomes thicker and floppier, leading to backward blood flow. Clinical treatment such as drug treatment is available for mitral valve disease. It is also recommended that dogs diagnosed with this condition maintain a low-salt diet.
Dog breeds that are more at risk of this disease are smaller dogs such as Cavalier King Charles Spaniels, Chihuahuas and Pomeranians.
Brachycephalic Airway Syndrome
Brachycephalic airway syndrome refers to a collection of abnormalities in the upper airway of brachycephalic dogs–dogs with short skull bones, leading to a ‘pushed-in’ appearance of the face and nose. These dog breeds include Bulldogs, Shih Tzus, and Pugs, among others.
Symptoms of brachycephalic airway syndrome include difficulty breathing, noisy breathing, coughing, and being prone to overheating. It is recommended that dogs diagnosed with this condition are to avoid over-exercising or being overweight.
These symptoms are directly related to the selection of traits during the breeding of brachycephalic dogs - the ‘flat-face’ look that is desired causes a disproportion between the size of the skull and the soft tissue of the nose and pharynx. A direct effect of this disproportion is the many of the physical abnormalities which underlie the effects of this disease, including abnormally narrow nostrils, an elongated soft palate and a narrower trachea, all of which impact proper air flow and breathing.
Conclusion
Hereditary diseases are prevalent across pure and mixed-breed dogs. Being aware of hereditary information and applying it to dog breeding by selecting healthy breeder dogs and avoiding inbreeding will help to decrease the prevalence of hereditary diseases. Vets and vet nurses should take opportunities to educate and advise dog breeders about this information and work together to achieve the common goal of breeding healthy dogs.
References
Leroi G (2011) ‘Genetic diversity, inbreeding and breeding practices in dogs: results from pedigree analyses’, The Veterinary Journal, 189(2):177-182, doi:https://doi.org/10.1016/j.tvjl.2011.06.016.
Loder R and Todhunter R (2017) ‘The demographics of canine hip dysplasia in the United States and Canada’, Journal of Veterinary Internal Medicine, doi: 10.1155/2017/5723476.
Rettenmaier J and Keller G and Lattimer J and Corley E and Ellersiek M (2002), ‘Prevalence of canine hip dysplasia in a veterinary teaching hospital population’, Veterinary Radiology & Ultrasound, 43(4):313-318, doi: 10.1111/j.1740-8261.2002.tb01010.x.
Schachner E and Lopez M (2015) ‘Diagnosis, prevention, and management of canine hip dysplasia: a review’, Veterinary Medicine (Auckland), 6:181-192, doi:10.2147/VMRR.S53266.