The BAER Test
BAER (brainstem auditory evoked response) is a diagnostic test for hearing whereby a dog is fitted with a sound source in the form of earphones with foam inserts that extend into the ear. The device emits a sound and the response is detected by tiny electrodes that have been placed at specific sites on the dog’s head and shoulders. The BAER detects electrical activity in the cochlea of the ear as well as in the auditory pathways of the brain, much like an EKG detects electrical activity in the heart. The resulting waveform definitively shows the extent and degree of a dog’s hearing loss and is used to evaluate a dog’s hearing status. The procedure is painless, but occasionally dogs will object to wearing earphones and being lightly restrained; in extreme cases they are muzzled or sedated, though this is rarely necessary. Results are available on the spot.
While curious pet owners sometimes seek confirmation of a hunch that their dog is deaf, BAER testing is used routinely by breeders, primarily those whose breeds are susceptible to congenital deafness. Coat-color-related deafness is associated with some white-coated and merle breeds, such as Dalmatians and Australian Shepherds. (To find out which breeds are most affected, see Louisiana State University’s Dr. George M. Strain’s comprehensive list.)
Inside the ear, the organ of Corti includes a layer of cells, the stria vascularis. The job of these cells is to secrete a factor that keeps hair cells healthy within the ear. If the stria vascularis cells are not pigmented, they are defective and lead to hair cell death within a puppy’s first few weeks, resulting in deafness. Unfortunately, this takes place in the inner ear and is, therefore, not visible to the eye; often, it is not obvious that a puppy is deaf. Deaf puppies may play harder than their littermates (because they cannot hear the yelps they inflict); also they may be hard to wake, or be seen to be following cues from the other puppies. Hunches must be confirmed with BAER testing.
Those who train working dogs also utilize BAER testing. These dogs need to be able to hear in both ears in order to localize the source of a sound. A dog can be unilaterally deaf (deaf in one ear), so that he can still hear but cannot tell where the sound is coming from. Others whose dogs experience chronic ear infections may seek BAER testing to find out how much hearing loss their dog might have experienced as a result of infection. BAER testing is also used to aid in the diagnosis of more serious medical conditions, such as vestibular (inner ear) disease or brain tumors.
BAER testing can be done only at one of the centers that specialize in the test. (Click here for a list of BAER testing sites.) However, BAER testing is occasionally available at “health clinics” at major dog shows.