I used to share a house with a huge, ancient dog named Major. Major would lie in the middle of the floor, an immovable mountain, where guests would have to step over him. You could vacuum around him. In fact, you could vacuum right over him. He wouldn’t move a muscle. “He must be deaf,” visiting friends would say. His owner would smile knowingly, walk to the kitchen, and pick up a bag of potato chips. Before she had finished one crispy, crunchy chip, Major would be standing hopefully by her side. Selective hearing: Lots of dogs have it. But lots of dogs, and some cats, also have true hearing loss, ranging from mild deficits to complete deafness.
Pet ears function basically the same as human ears. Sound sends vibrations down the ear canals to the eardrum, technically called the tympanic membrane. The vibration passes from eardrum to a bunch of little bones in the middle ear, then to the inner ear. In the inner ear a snail-shaped organ called the cochlea transforms the vibrations into nerve impulses that then travel along the auditory nerve to the brain. Voilà! Major hears that potato chip crunch … or not. When Major ignores you when you call him, can he really not hear? Or is he simply ignoring you?
Let’s start at the beginning with congenital deafness, i.e., pets that are born deaf. In puppies and kittens, the ear canals open up between 12 and 14 days, and hearing ability continues to mature until 6 to 8 weeks of age, by which time Baby Major should be able to hear just fine. But many breeds are prone to genetically linked deafness, often associated with particular coat colors. Merle or dapple in the collie, dachshund, Great Dane, and Shetland sheepdog. White in Jack Russell terriers. In Australian cattle dogs, deafness is most prevalent in females without facial “masks” or pigmented body patches. Other breeds predisposed to congenital deafness include Australian shepherd, beagle, border collie, Boston terrier, bull terrier, cocker spaniel, Dalmatian, English bulldog, English setter, foxhound, fox terrier, Norwegian Dunker hound (really, no joke, that’s a breed, though I’ve never met one), Old English sheepdog, and Scottish and Sealyham terrier. Border collies are also prone to an inherited adult-onset syndrome, in which they hear normally at birth but go deaf at 3 to 5 years of age. In cats, congenital deafness is associated with white coats and blue eyes. Puppies and kittens who are born deaf may be more vocal than their littermates, and more aggressive. They may be harder to wake up. If they are only deaf in one ear, signs may be subtle.
The more common form of deafness in dogs is called presbycusis. I just learned that word while researching this article. It’s from the Greek for “elder” and “ hearing.” Age-related hearing loss is usually caused by degenerative changes in the middle or inner ear, or the auditory nerve. Other things that can cause Major to go deaf over time can include recurrent ear infections, chronic exposure to loud noise, injuries, tumors, or even on rare occasions medications or anesthesia. I once treated a little dog whose owner insisted he went deaf immediately after we anesthetized him to clean his teeth. It was the first and only time I have seen this rare side effect to anesthesia, thought to be related to changes in blood flow. Happily that little dog’s hearing eventually improved.
The only definitive way to evaluate a pet’s hearing is the brainstem auditory evoked response (BAER) test, which actually measures electrical activity in the brain in response to sound. Few owners want to go to this length, so here are a few simple tests you can try at home. Make sure you are out of Major’s line of sight. Then make a loud noise and watch for a reaction. Try different-frequency sounds — bang two pots together, jingle your keys, hit a low drum, make a high whistle. Try rolling something across the floor like a small rock. Does he prick up his ears? Does he turn his head? Which way? Lack of reaction or an inability to orient or locate the source of a sound is suggestive of a hearing problem. I recently had a very astute client diagnose her dog’s ear infection by noticing that during their daily walk on the beach, the dog seemed unusually confused when being called. She would turn her head this way and that, as though she couldn’t figure out where her owner was. Sure enough, one ear canal was so inflamed it was virtually swollen closed. We treated the ear infection, and her hearing and behavior quickly returned to normal.
Animals that are born deaf often adjust very well, as do many that lose their hearing gradually, compensating by using sight, scent, and just sensing vibrations. When combined with other age-related issues, however, deafness can contribute significantly to disorientation in old dogs. People sometimes ask about hearing aids. Hearing aids are essentially just sound amplifiers. In animals with congenital deafness, the ear is totally deaf, so amplification doesn’t help. Dogs with other types of deafness often do have some residual hearing, and specialists have tried a variety of aids, but none have been consistently tolerated by the dogs, and none are commercially available. Cochlear implants, like those used for people, would work for many dogs, but due to the cost are not considered a viable alternative for pets.
Deaf pets should not be allowed to roam free, for obvious reasons, but they usually adapt well to their circumstances, relying on other senses to make up for their hearing loss. Most can learn to respond to hand signals, even some American Sign Language. Much as we joked about Major, the old boy really was hard of hearing, but he didn’t seem to mind. Maybe he could still hear the high-pitched crinkle of the bag. Maybe he smelled the potato chips. Maybe he just got up when anyone headed into the kitchen.