Hearing Tests (BAER)
A BAER (Brainstem Auditory Evoked Response) test is the only 100% reliable method for determining that an animal is deaf (or for measuring the extent of its hearing loss). It is a procedure using computers to record the electrical activity of the brain in response to sound stimulation. This is the same test used to check the hearing of human infants, and measures the same range of hearing. This means that the test does not measure the full range of canine hearing, but it will tell you if your dog or cat has hearing within the typical range (some dogs will test as “deaf,” but will still be able to hear very high pitches).
The test is not painful and can be performed on any dog/cat over six weeks of age (ear canals don’t open until they are about two weeks old). Sedation is usually not necessary, but some animals (especially puppies) don’t like being restrained, or having wires hang from their face, so it can be easier while they are sedated. A clicking sound is directed into the ear through a foam insert, earphones, or headphones and the brain’s response is recorded. Each ear is tested individually and the test generally lasts for only 10 to 15 minutes.
What are the Uses of BAER Testing?
- Early diagnosis of hearing loss secondary to cochlear agenesis/degeneration.
- Assessment of brainstem (caudal part of the brain) function.
- Conductive hearing loss which is the result of a dysfunction of the external ear canal and middle ear space.
- Sensorineural hearing loss which is the result of dysfunction of the cochlea, cochlear nerve or central auditory pathway.
Hearing Loss in Puppies
We test litters of puppies who are prone to having hearing loss such as Dalmatians, English Setters, English Cockers, Australian Cattle dogs, Jack Russell Terrier, and other breeds. The best time to test is at seven weeks of age. Dogs can lose hearing up to 16 weeks of age, so retesting before breeding if we get a questionable reading on the first test or if the owner notices and problems, is not an uncommon practice.
If a puppy tests negative in one or both ears, usually nothing can be done to regain hearing if they suffer from cochlear degeneration. The ears are checked for any type of infection, which can interfere with the test, but congenital deafness cannot be restored. Chronic ear problems can cause thickening of the ear canals and cause poor signals to the brainstem, which would cause poor hearing and a questionable test. In this situation the patients will often be retested after being treated appropriately.
Most responsible breeders of dogs who are at high risk for congenital deafness will test liters of puppies before selling them.
A dog that seems to be able to hear but cannot locate where the sound is coming from may be affected by unilateral hearing loss (hearing in one ear only). A BAER test can confirm this and identify the affected ear.
We recommend a book “Living with a Deaf Dog” by Susan Cope Becker. This book gives some training techniques to help an owner who takes on the task of a deaf dog.