Dogs and cats with unilateral deafness make excellent pets, with owners often unable to detect any impairment. However, owners of these animals should be discouraged from breeding them to prevent further affected animals and an ultimate increase in the prevalence of the disorder. Some animals will show directional localization deficits and may not awaken to sounds if sleeping with the good ear against the ground. Animals with late-onset acquired deafness generally adapt well, but precautions must be observed to prevent vehicular injury or death and bite injuries to humans, especially children, when deaf dogs are startled. Animals bilaterally deaf from both congenital and acquired causes place greater reliance on visual and vibratory sensory information to cope with the loss of auditory input. Dogs are easily trained to hand signals and other visual cues, such as flashing porch lights; some cats can similarly be trained. Obedience-training shock collars set to the lowest shock level can be used for recall of dogs.
Despite the worry of animal owners and those concerned with animal rights, the quality of life of deaf dogs and cats is not demonstrably diminished. Likewise, these animals do not have diminished mental capacities, any more than the average deaf or blind human has diminished mental capacity. The brain responds to the loss of a sensory modality by various forms of plasticity, whereby CNS structures that would have received input from that sensory modality constrict and adjacent structures expand to take advantage of the available space (Hata & Stryker, 1994).
A dilemma often occurs when bilaterally deaf puppies are identified in a litter. The official position of the Dalmatian Club of America is that such animals should be euthanized, and individual owners of other breeds often concur, but this position is not universally accepted. The recommendation for euthanasia is more difficult to accept after placement of a deaf dog in a home and the ensuing development of emotional attachments. Some variation may result from differences in personalities between breeds, but dogs that are bilaterally deaf from birth may develop anxious or aggressive personalities from continuously being startled. They are prone to vehicular deaths, may scare-bite, and require significantly greater effort to rear and protect. It is not uncommon for these animals to end up in animal shelters because of the inability of owners to cope with the deficit.
Genetic counseling for owners of at-risk breed dogs and cats will be difficult until the mechanisms of inheritance are identified or a DNA blood test is developed. In general, unilaterally deaf animals should not be bred, since they have the genetic defect and will pass it on to their offspring. Some breeders view hearing as just one of the spectrum of desirable or undesirable markers evaluated in breeding decisions, but the high prevalence of deafness in at-risk breeds suggests that a higher premium should be placed on hearing status for the overall benefit of the breed.