Aussie Genetics Fact Sheet: Pigment &
by C.A. Sharp
Not every form of deafness is pigment-related. However, this is the most likely cause of congenital hearing loss in Australian Shepherds.
Homozygous merles and dogs which have extensive white markings on their heads, especially on or around the ears, may suffer some degree of hearing loss due to lack of pigment in the inner ear. The degree of hearing loss can vary and may occur only in one ear. A BAER test may be necessary to determine the degree of loss.
Pigment cells play an important part in the process of translating the
mechanical vibration that is a sound wave into the electrical impulse which can travel via nerves to the brain. The inner ear contains a tiny organ called a cochlea. It is shaped
rather like a snail's shell. It contains a fluid and is lined with tiny hair-like structures called cillia. Sound vibrates the air. The vibrations travel through the ear canal and ultimately vibrates the fluid within the cochlea. Those vibrations wiggle the cilia, which connect with nerve endings.
A pigment cell plays a key role in connecting each cilium to it's
corresponding nerve. It "translates" the mechanical vibration
into a electrical impulse. If it is absent, this translation can't
take place. The more pigment cells that are missing, the greater the
Dogs with considerable amounts of white on or immediately surrounding the ear are more likely to also be lacking pigment within the ear.