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Deafness in Ferrets

Misty being tested with BAER equipment (Yup, deaf as a post!)

 

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Deaf Daisy, a black-eyed marked white

Flower, with the Waardenburg stripe, but not deaf, only hard of hearing

Zeus, with the Waardenburg stripe, and completely deaf

© Erika Matulich, Ph.D.

I was once watching eight of my ferrets play in the living room, when the trash collector outside dropped an entire Dumpster—with a terrific bang! I jumped a foot high, and seven ferrets immediately scattered and hid. The eighth, Bobbin, stood in the middle of the floor with a puzzled look, as if to ask, "Hey! Where did everyone go?" That's when I knew Bobbin was deaf, which is fairly common in ferrets.

Linked to coat pattern
Deafness in ferrets is usually a genetic defect caused by Waardenburg syndrome, which results in the underdevelopment of the hearing mechanism of the inner ear. In ferrets with Waardenburg syndrome, deafness is genetically linked with white markings on the face. Generally, this affects ferrets with "blaze" markings (a white "badger stripe" on top of the head and a white bib) and those with "panda" markings (a white head and bib, with no mask). It's estimated that 75 percent of badger and panda ferrets are deaf.

Waardenburg syndrome can also be present in dark-eyed whites like Bobbin. (Albino ferrets—also called red-eyed whites—have abnormally small hearing mechanisms in their middle and inner ear; they can be hard of hearing but are not usually deaf.) Unfortunately, the attractive color patterns of dark-eyed whites, badgers, and pandas make these ferrets highly sought after, and breeders do not always test for deafness, which can be difficult to determine.

Diagnosing deafness
Determining if your ferret is deaf will take skill and observation, especially because hearing ferrets can be unresponsive to certain sounds. However, deaf ferrets have a couple characteristics that can help with the diagnosis: They are easily startled if approached from behind, and they are often more vocal than hearing ferrets. When startled, many deaf ferrets will express surprise by screaming.

All ferrets are sensitive to movement and vibration, so if you clap your hands or stamp your foot to determine deafness, your ferret may be reacting to the movement of your body, or to the vibration in the air or on the floor, rather than the sound. My favorite in-home test is to place a vacuum cleaner in the room with the ferrets, stand where they can't see you, and then plug in the vacuum cleaner to turn it on. In most cases, the hearing ferrets will dash away (or attack the vacuum), and the deaf ferrets will wonder why everyone else left!

There are also scientific tests for deafness. The hearing test known as the brain-stem auditory evoked response (BAER) or brain-stem auditory evoked potential (BAEP) is potentially useful in determining deafness in ferrets. This is a test performed routinely by reputable breeders of Dalmatian dogs to determine the extent of hearing loss or deafness in their breeding stock. The procedure is not painful, and no sedation is necessary. Most veterinary colleges of medicine at universities have the testing equipment, as do some individual clinics.

The test detects electrical activity in the inner ear and brain in much the same way that an antenna detects radio signals or an EKG detects the heart's electrical activity. Electrodes are placed around the ear and on the head, and send pictures of "hearing" to a computer. The series of peaks on the waveform correspond to the response of the inner ear and the brain. The response from a deaf ear is a flat line.

Challenges and rewards
Deaf ferrets pose potential behavioral and training problems. Deaf mother ferrets may be more likely to injure their babies, because they can't hear them cry. Deaf ferrets also seem to be more prone to biting, given that they are easily startled and will immediately try to defend themselves. Additionally, they are more difficult to train, because they do not respond to your voice commands.

Because of the challenges posed by deaf ferrets, particularly for beginner owners, responsible breeders should be more careful about breeding for color patterns not associated with hearing problems.

Deaf ferrets do respond to lots of love and treats, and can even be trained to respond to hand signals. I have had several deaf ferrets, and they don't seem to mind at all that they can't hear. Misty, my deaf blaze, is the alpha ferret in my household—over 10 other ferrets! She loves to play, bounce, hide, eat, snooze, and snuggle with her hearing buddies.

The pigmentation-hearing link Dutch eye doctor P. J. Waardenburg was the first to notice a link between hearing problems and pigmentation. Waardenburg syndrome shows up in humans as well as in ferrets, dogs, cats, mice, and other animals. Humans with eyes of different colors often have hearing problems. People with Waardenburg syndrome may also have a white forelock of hair, and their hair may turn gray prematurely. Deafness is far more common in white cats than in those with other coat colors. According to the ASPCA Complete Guide to Cats, 17 to 20 percent of white cats with nonblue eyes are deaf; 40 percent of "odd-eyed" white cats with one blue eye are deaf; and 65 to 85 percent of blue-eyed white cats are deaf.