Health Concerns

Practical Genetics for Bull Terrier Breeders and Owners

Health Seminar presented to the Bull Terrier Club of America, October 10, 2002

Jerold S Bell, DVM, Tufts University School of Veterinary Medicine

To develop a healthy breeding program, you must choose your breeding stock, and their mates carefully. As stated above, the primary goal of dog breeding is to maintain and enhance the quality of the breed. You are not breeding a hip, a thyroid, or an immune system; you are breeding Bull Terriers. Conformation, temperament, working ability, and health must all be balanced in your selection. (See the article, “Choosing Wisely” in the April 2000 AKC Gazette for a more in depth discussion.)

The breeding goal of managing genetic disorders involves firstly, the prevention of affected dogs. Then, the goal is to decrease the (carrier) frequency of deleterious genes in the breeding pool. According to the AKC Canine Health Foundation, the most frequently occurring genetic disorders across all breeds are; epilepsy, hip dysplasia, hypothyroidism, cancer, bloat, heart disease, autoimmune disease, allergies, progressive retinal atrophy (PRA), patella luxation (slipping kneecaps), allergic (atopic) dermatitis, cataracts, and other eye diseases.

According to an online survey of Bull Terrier breeders, the number one health concern is kidney problems, followed by behavior problems, allergies/skin disease, heart problems, deafness, and orthopedic disease. The 1997 Bull Terrier Club of America Health Survey, conducted by Dr. Margaret Slater of Texas A & M University, asked breeders the disorders of particular concern to them. Number one was skin allergies (20.69%), followed by behavior problems (8.11%), deafness (7.71%), kidney disease (6.9%), cancers (3.65%), heart disease (3.02%), and skeletal disease (1.83%). These health concern lists parallel the list of disorders (based on frequency of diagnosis) from the health survey. This list includes half of the top ten disorders reported among all breeds. It also contains several disorders that are specific to Bull Terriers.

Skin allergies are a high frequency disorder across all pure-bred and mixed-breed dogs. If a dog has significant allergies, the hereditary component of this disorder should be considered. Such disorders should be considered a negative factor in selecting breeding stock. This is especially so if multiple siblings (littermates) have similar allergies.

Two categories of behavioral problems in Bull Terriers are aggression, and compulsive disorders. Owner perception of aggressive personality may be over estimated, if breeders are not diligent in screening perspective puppy buyers. If an owner is looking for a “Spuds MacKenzie” dog, but is not suited to a

Bull Terrier personality, they may believe that their dog is aggressive. Bull Terriers are not Golden Retrievers, nor do we want them to behave like one. Many dog owners are not good candidates to own a Bull Terrier. On the other hand, there are Bull Terriers with poor temperaments; characterized by severe aggression towards people, towards other dogs, extreme shyness, or volatile “lashing out” behavior. These extreme behaviors have genetic components, and should be selected against.

Compulsive behaviors, including spinning, tail biting, and flank sucking have been studied by Dr. Alice Moon-Fanelli at Tufts University. All of these behavioral disorders are related. Affected dogs can show several of these behaviors, and you can see multiple littermates affected with different behaviors. Based on electroencephalogram (EEG) examinations, and the response of affected dogs to different medications, there is some controversy as to whether these are true compulsive disorders, or petit-mal seizure disorders. Regardless, there is a strong genetic component to these behaviors, and this must be taken into account when considering breeding affected dogs or their close relatives.

Deafness is a genetic disorder seen with some regularity in the Bull Terrier. Deafness is associated with the extreme piebald pigmentation gene, and is most common in white Bull Terriers. Researchers have found that a lack of pigment (melanin) cells reaching the inner ear in the developing embryo leads to collapse and death of the nerve cells required for hearing. While the quantity of embryonic pigment cells is genetically controlled, the migration of these cells to the developing inner ear occurs by chance. If there are fewer pigment cells, there is a greater chance that some may not reach one or both ears, thereby causing deafness. This explains why deafness does not have a simple inheritance. A problem with controlling deafness is that for every bilaterally deaf dog, there are far more dogs who are deaf in only one ear. It is almost impossible to distinguish these unilaterally deaf dogs from bilaterally hearing dogs without electrodiagnostic testing (BAER test). It has been shown that unilaterally deaf dogs produce as much deafness as bilaterally deaf dogs, and must be identified and selected against for breeding. Dogs can be certified normal by BAER test at 6 weeks of age, before placement in breeding or pet homes.

Hip dysplasia does not appear to be a significant problem in the breed. Only 91 Bull Terriers have had hip radiographs submitted to the OFA for evaluation. 12.1% were rated as excellent, 62.6% were rated good, 16.5% were rated fair, and 8.8% were rated mildly dysplastic. There were no Bull Terriers rated moderately, or severely dysplastic. In the other OFA databases for Bull Terriers, there were 50 dogs evaluated for patella disease (all normal), 2 for elbow dysplasia (one normal, one dysplastic), and 48 submissions for cardiac disease (98% normal, 2% abnormal). Reported heart problems in the Bull Terrier include subaortic stenosis, congenital mitral valve dysplasia, and dilated cardiomyopathy. To get a clearer picture of these disorders in the breed, there must be a concerted effort for more screening by Bull Terrier owners.

Hereditary hypothyroidism is an immune-mediated disease, with autoantibodies being produced that are destructive to the thyroid gland. Measurable autoantibodies are only present during the period of thyroid destruction (usually sometime between 2-6 years of age). Annual testing for thyroglobulin autoantibodies should be done between these years. After the thyroid gland is destroyed, and the dog has low measurable thyroid hormone levels, there is usually no more measurable autoantibodies present. This is often misdiagnosed as idiopathic hypothyroidism, but in most instances is the end stage of hereditary autoimmune thyroiditis. This is why it is important to screen your dogs for measurable thyroid autoantibodies during the critical period to be able to properly diagnose the disorder, and utilize this tool in genetic disease control. The mode of inheritance of hereditary hypothyroidism has not been determined.

Hypothyroidism is reported at a frequency of 2.03% in the Bull Terrier Health Survey. Michigan State University (one frequently used endocrine testing facility) reports 4.3% of 854 Bull Terriers with measurable autoantibodies to their thyroid gland. The average for all breeds is 7.9%. While the level in Bull Terriers is less than the average of all breeds, this is a genetic disorder, and owners should test their breeding stock to prevent it’s spread in the population. Hypothyroidism is also linked to behavioral abnormalities in dogs.

Three different kidney disorders have been reported in Bull Terriers: hereditary nephritis, polycystic kidney disease, and age related kidney failure. Age related kidney failure is seen in most old dogs if they survive long enough for the kidney system to begin to fail. The other two problems are breed-related genetic disorders. Hereditary nephritis is an autosomal dominant disorder that causes kidney failure in adult dogs. Early screening for kidney disease involves running a test on the urine; a urine protein/creatinine ratio beginning at 6-12 months of age, through 4 years of age. A kidney biopsy at 3 years of age is a reasonable test for normalcy, although rare cases can have normal biopsy findings, but kidney failure at up to 8 years of age. Hereditary nephritis was originally described in Australian Bull Terriers, but is now being diagnosed with frequency in American dogs.

Polycystic kidney disease is also inherited as an autosomal dominant condition that causes renal failure in Bull Terriers. This condition was originally diagnosed in Australia, and appears to have originated from one family of dogs. The condition in America appears to be infrequently diagnosed. Diagnosis is confirmed by ultrasound examination of the kidneys.

Lethal acrodermatitis is a rare condition in the Bull Terrier caused by an abnormality in copper metabolism. The condition is not responsive to zinc supplementation.

The fact that we are listing all of these breed-related disorders does not mean that the breed is riddled with problems. These are just the problems that breeders should be vigilant about, and screen for in their breeding and pet dogs.

04062006 Reprint for www.btca.com