In the world of Weird Dog Facts That Don't Make Any Sense, did you know that most white-coated dogs are deaf?
No wonder ol' Snowball never seems like he's listening to you.
Approximately 85 different dog breeds have been reported to carry the DNA that causes congenital deafness.
There's a lot of scientific mumbo jumbo about the recessive deafness gene, and how it gets passed from one dog to another, and so on. But the truly interesting thing is, we commonly see deafness in dogs with white-pigmented skin. (So, their skin; not their fur).
In order to understand how a dog's coloring affects his hearing, we need to review how hearing works.
When sound waves reach you, they enter the ear canal and strike the eardrum. The eardrum vibrates like a gong, causing the ear ossicles (middle ear bones) to vibrate as well. The vibration reaches the fluid-filled, spiral-shaped cochlea of the inner ear, creating waves.
All this commotion causes a pressure change and forces the cochlea’s tiny hair cells to move. These hair cells are connected to the auditory (hearing) nerves, which spark a nerve impulse down the auditory pathway that connects to the brain.
OK. Stay with me here...
White-coated dogs carry the piebald gene, which is demonstrated by their predominantly white coat and often blue eyes. The piebald gene results from the absence of melanocytes, the cells which create pigment. Melanocytes are the part a dog’s DNA that determines his hair color, eye color, etcetera.
When a dog is born without the genetic material to create melanocyte cells, a white coat — and usually blue eyes — are the result.
And here's where it gets interesting. The genetic ability to create pigment, and the genetic ability to hear, come from the same stem cell source.
If a dog lacks the cells required to determine hair and eye color, then he also lacks the special layer of inner-ear cells required to hear. So his whiteness doesn't cause his deafness; it's just an indicator of the same genetic anomaly.
The following breeds are most commonly deaf due to the piebald gene:
- English Bull Terriers
- English Setters
Apart from the piebald gene, congenital deafness is also linked to the merle gene, which causes a dog to have a mottled ("merle") coat and blue or odd-colored eyes.
(Fun fact: Blue eyes are not a true eye color, but rather result from a lack of color-producing pigment within the iris. The lack of pigment on the iris suggests a lack of pigment cells throughout the body, including the inner ear.)
Dog breeds that are commonly affected by the merle gene are:
- Old English Sheepdog
- Dapple Dachshund
- Australian Shepherd
- Border Collie
The only way to effectively test a dog’s hearing is through a Brainstem Auditory Evoked Response test (BAER) test.
A veterinary professional will attach electrodes to the skull and measure the electrical activity within the brain. The technician will make a series of clicks that are passed through headphones placed on the dog’s ears. When the dog hears a sound, a connection is made by nerves to the brain. This ear-to-brain connection is the electro-activity that can be measured by the BAER test.
A series of waves will display on the BAER test screen in a dog with normal hearing, but very few, if any, waves will appear in a deaf dog. BAER tests can determine whether a dog is deaf in one ear (unilateral deafness) or both ears (bilateral deafness).
So. If you own a white-coated, blue-eyed dog that never seems to heed your commands, don't be mad — he might be deaf!