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
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
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.