Deafness & Piebald Animalsby Kat Walden
The bull terrier is one of several piebald dog breeds that exhibits varying degrees of hereditary deafness.
Piebald is a word originating from the 1580s, originally referring to the bicolored plumage of the magpie. In earlier times, bald meant spotted or white, and the word magpie meant of mixed character." By its strictest definition, piebalds are only of black-and-white coloring. Today, the term piebald can apply to any number of animals including dogs, horses, pigs and even ball pythons.
It's All in the Genes
Some describe piebalds as animals with white pigmentation, while others refer to it as a deletion of color. Piebald coloring occurs as a result of a combination of genetic factors, including a DNA variant in the micropthalmia associated transcription factor (MITF) gene. The effects of this variant differ between dog breeds, and the result depends upon how many copies of this genetic variant a dog has in his DNA. For example, in dogs such as the collie, Great Dane, Italian greyhound or Shetland sheepdog, one copy of the MITF variant will produce a dog with some white in his color pattern. A dog of these breeds with two copies of the MITF variant, meaning he has inherited it from both parents, will have extreme white coloring, perhaps showing only a single spot of color on his body or on his head. Dogs such as the boxer or bull terrier with two copies of the MITF variant are solid white.
Why Colorless Ears Cause Deafness
Hereditary deafness can occur in more than 100 different dog breeds but appears with more frequency in dogs with the piebald or merle coloring gene, the Dalmatian presenting the highest percentage of deafness. In fact, pigment-related deafness is the most common cause of deafness in dogs and cats. In order for an animal to hear, sound vibrations travel through the outer and middle ear, then detected by the cochlea and transduced by neural hair cells. These transduced vibrations travel via the eighth cranial nerve through the head, eventually finding their way to the thalamus and the primary and secondary auditory areas of the temporal lobe. The nerve cells of the cochlea rely on high potassium levels in the fluid surrounding them to survive. One of the known functions of melanocytes in the blood vessels is to maintain those potassium levels. When those pigment-producing cells are absent, such as in the case of piebald animals, the auditory nerve cells die off, causing deafness. The condition normally develops between one and three weeks following birth and can affect one or both ears.
If you suspect your piebald dog is deaf, a simple test you can perform at home is to step quietly behind him and clap your hands together sharply, once, to test his response. You can also ask your veterinarian to perform a test called the brainstem auditory evoked response, or BAER. Small electrodes are placed beneath the skin of the dog's scalp, then, via computer, your veterinarian can see and measure the dog's response to auditory stimuli.
Caring for Your Deaf Dog
Love and empathy are the best things you can provide your deaf dog. With much patience, teach him simple hand signals he can see from a good distance away so you can communicate with him. When you enter his area and he's not looking at you, make him aware of your presence by tapping him gently on his shoulder. You can do the same to make him aware when you're leaving. Stomping on the floor might get his attention, and consider using a flashlight to signal him, day or night. Never allow him to remain outside unsupervised unless he is in a fenced yard that you know is secure.
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