Congenital Deafness in Dogs
Congenital deafness occurs as a result of degeneration of sensory inner ear structures in one or both ears within a few weeks of birth. It can result in total permanent deafness in both ears (bilateral) or in one ear (unilateral). This is a hereditary condition and is believed to be linked to coat colour as breeds with white coats and blue eyes are most affected e.g. Dalmatians, Bull Terriers, Australian Cattle dogs. Research with these breeds has shown that if even one parent is unilaterally deaf the chances of any offspring being unilaterally or bilaterally deaf are almost doubled. Breeders are therefore advised to have the hearing status of both breeding dogs and litters assessed.
Bilateral deafness can usually be identified by behavioural traits but unilateral deafness is more difficult to detect. Most breeders are aware of the importance of hearing testing however the effectiveness of the ‘test’ used varies considerably. Some DIY tests involve clapping hands, hitting saucepans and even calling a mobile phone placed in the puppies’ basket. The main flaw in all of these techniques is that they will not determine unilateral deafness and even bilateral deaf pups could simply be following the responses of their siblings or responding to vibration. The only 100% accurate way of determining deafness is with a Brain Auditory Evoked Response (BAER) test. This uses a computer-based system which records electrical activity in the inner ear and auditory pathways in the brain. The BAER test is completely painless and can be carried out on puppies after five weeks without an anaesthetic. Older pups and adult dogs however may need to be sedated.
At the R(D)SVS we hold regular clinics where owners and breeders can bring their puppies or adult dogs for BAER testing. We see mainly Dalmatians, bull terriers and border collies and our results show an incidence of over 14% dogs and puppies either bilateral or unilateral deaf. This is an average figure which varies considerably between breeders. Our first case at Edinburgh was a Dalmatian bitch that had perfect hearing. Her owner has gone on to breed successive litters from her all with 100% normal hearing. This breeder operates a careful breeding plan where the dogs mated with her bitch have all been previously BAER tested. C onversely we have had litters of puppies from other breeders in which only 47% tested normal with 53% being either bilateral or unilaterally deaf.
Unilaterally deaf dogs can make good pets but breeders are strongly advised to have them spayed/neutered as these dogs will pass on their deaf genes. It is only by continuous and dedicated testing by responsible breeders that the incidence of deafness within affected breeds will be reduced.
If you require further information our contact details are as follows:
Royal (Dick) School of Veterinary Studies
Hospital for Small Animals
Easter Bush Veterinary Centre
Telephone: 0131 650 7650