I thought I would re-type this article out of "Bully Breeds-All About America's Favorite Dogs" for Scarlette. This will be word for word and quite long, but I think you and others with Deaf Dogs will find it quite interesting:
Although it is neither life-threatening nor life-shortening, bilateral deafness can have dire consequences. According to George M. Strain, Ph.D., associate vice chancellor for the Office of Research and Graduate Studies at Louisiana State University in Baton Rouge, Louisiana, "Unilaterally deaf [deaf in one ear] dogs can make great pets; however, bilaterally deaf [deaf in both ears] dogs present unique training challenges to overcome aggressive or anxious personalities that may result from their deafness. When startled, they bite in reflex, including family members, although not every deaf dog will develop these personality challenges."
Because of the bully breeds' forceful bite, bite injuries can be severe and the subsequent financial liability to the owner very costly. Bilaterally deaf dogs also live in some jeopardy because if they escape from the yard or leash-escape attempts are a common problem in bully breeds-they cannot hear oncoming traffic or their owners' calls. Dr. Strain recomments that breeders euthanise bilaterally deaf pups rather than place them.
Deafness has several causes: infection, blockage of the ear canal, trauma, poison, and genetics. With hereditary deafness, permenant and total hearing loss occurs either unilaterally or bilaterally when puppies are about 3 to 4 weeks of age. "There's a normal period of post-natal auditory development in dogs occuring before the ear canal opens, which happens at about 3 weeks of age," says Dr. Strain. "The dogs go deaf because the blood vessels in the inner ear (the cochlea) degenerate. When that happens, the nerve cells in the cochlea die, and irreversible deafness occurs."
The prevalence of total deafness in Bull Terriers is about 11%. Says Dr. Strain, "Deafness is about 10 times higher (19%) in white Bull Terriers. In colored Bull Terriers, incidence is about 2%." He adds, "Deafness associated with white [coat color] does occur in American Staffordshire Terriers and American Pitbull Terriers, but I have not seen it in enough to have any statistics. For that very reason my guess would be theat the prevalence is lower in those breeds-but not totally absent since I've seen it in both."
In young pups, unilateral and even bilateral deafness can be difficult to detect. "Bilaterally deaf dogs cue off the behavior of littermates," explains Dr. Strain. "If it's a feeding time and the other puppies scramble, they wake up the deaf puppy and it rins along with them. If the other puppies go chasing after something they hear, it will also follow along. But if the dog is sleeping by itself, it won't wake up in response to loud noises. A unilaterally deaf dog is ever harder to detect, as the only behavioral deficit is some difficulty in localizing where sound comes from." Consequently, many breeders test their puppies' hearing before placing them.
Although a general veterinary practitioner can make a presumptive (but not foolproof) diagnosis of bilateral deafness through behavioral testing, and electodiagnostic test called the BAER (Brainstem Auditory Evoked Reponse) can provide a definitive diagnosis of either bilateral or unilateral deafness. BAER equipment is available at most veterinary colleges and a few specialty veterinary practices. Specialists sometimes also offer hearing tests at dog shows. (A list of known BAER testing sites worldwide is posted at Dr. Strain's website, along with other helpful informations on deafness: www.lsu.edu/deafness/deaf.htm
Although the mode of inheritance for the defective genes is unknown, Dr. Strain, who has been researching deafness for 15 years, believes that both parents must contribute defective genes and that one of the involved genes is the piebald gene, the gene that makes white hair. "If the breeds have any white in the coat, they nearly certainly also have one of the versions of the piebald gene present," he explains. "To get all-white dogs requires that the gene be strongly expressed, so the deafness is probably therefore more likely in Bull Terriers and other breeds that allow all white." American Pitbull Terriers, American Bulldogs, and Staffordshire Bull Terriers all may come in all-white coats or combinations of white and other colors. Although all-white American Staffordshire Terriers are not allowed according to the breed's standard. up to 80% of the coat may be white. Dr. Strain continues, "White Boxers have a lot of deafness, white it is uncommon in the fawn, twany, or brindle colors. Parti-colored English Cockers have a good bit of deafness, while solids are essentially free of deafness. Increasingly stron expression [of the piebald gene] increases problems with deafness."
Dr Strain adds, "I believe there is an additional gene that regulates how strongly the piebald gene is expressed, and hence how likely deafness is to result." He is working on a study with Keith Murphy, Ph.D., associat professor, Department of Veterinary Pathobiology at Texas A&M University College, to identify the gene defect(s) responsible for deafness; the AKC Canine Health Foundation provides funding. Although the focus of Drs. Strain and Murphy's study is on Dalmations and English Setters, the research should benefit all breeds. Identify the mode of inheritance and the markers linked to the defective genes that cause deafness could lead to screening tests that identify clears, carriers and affecteds, permitting breeders to breed away from the problem.
In the meantime, Dr. Strain urges breeders to avoid breeding dogs that have a history of deafness in their lines. "The further you can get away from known producers of deaf offspring, the less likely you are to have deaf offspring," he says. "Remove from breeding all dogs affected with unilateral or bilateral deafness. Don't re-breed dogs and *****es that produce deaf puppies. Assume both the dog and ***** were contributors to the problem, because deafness appears to be either polygenic or recessive in mode of inheritance." he continues. "Look at siblings, parents, and other closely related kin of deaf animals as potential sources of deaf offspring. This is the only course presently available until we develop a blood test for carriers," Dr. Strein concludes.
Taken from Battling Genetic Disease by Marcia King...Pages 85-86 of Bully Breeds...All About America's Favorite Dogs.
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