Are all Double Merle's Deaf/Blind/Both? No. It is possible for a Double Merle dog to not have hearing or vision issue but it is very uncommon.
Health Problems Associated With the Merle Gene
Among their findings, they recorded research on deafness in Dachshunds with the merle gene. One study reported 36.8% of Dachshunds with the merle coat pattern (Mm) suffered hearing problems ranging from mild to complete deafness.
There was no significant association with eye color or sex. Conclusions: Deafness prevalence in merle dogs was greater than that in some dog breeds homozygous for the piebald gene, such as the English Cocker Spaniel, but comparable to, or lower than, that in the Dalmatian and white Bull Terrier.
Double merles are born with or without their hearing deficiencies. If your double merle loses hearing later in life, it would be as a result of something unrelated to it being a double merle, such as old age or infection.
As stated above, deafness can be associated with the merle (dapple) gene, which produces a mingled or patchwork combination of dark and light areas overlayed on the basic coat color. This gene (M) is dominant so that affected dogs (Mm) show the pigmentation pattern, which is desirable in many breeds.
Double Merle dogs are highly likely to suffer from hearing and vision impairments and in some cases complete blindness and deafness. Deafness and hearing impairment happens due to lack of hair pigment produced in the inner ear. Double Merles can also be blind or have vision problems due to congenital eye defects.
When inherited in the homozygous state, the merle mutation causes dogs to be white and have an even greater incidence of deafness, blindness and sterility. The auditory and ophthalmologic abnormalities linked to merle are similar to those observed for the human auditory-pigmentation disorder Waardenburg syndrome.
Many people are unaware, but when two merles (of any breed) are bred together, each puppy has a 25% chance of being born as a double merle. These puppies have excessive white coloration – lack of pigment – and this coloration causes loss of hearing, vision, or any combination of the two impairments.
Some of the most commonly affected breeds are Dalmatians, Bull Terriers, Australian Cattle Dogs, English Setters, English Cocker Spaniels, Boston Terriers, and Parson Russell Terriers. Congenital deafness has been found in over 80 different breeds, but it may be found in any breed.
A double merle inherits the merle gene twice. One copy of the merle gene causes a marbling effect on the coat and creates lighter spots throughout the solid color coat. Image 1. In a double merle, the marbling/lightening effect is doubled and the coat becomes predominantly white.
Double merles, despite their deficiencies, are generally quite healthy dogs capable of living long, otherwise normal lives.
In fact, a dog without hearing can be even more loving, as he has learned to rely on his other senses. He will stick closer to you so that he can see your movements and snuggle up close so that he can feel your closeness. Never let deafness in your dog discourage you.
Merle dog breeds are more expensive for a number of reasons. For one, genetic testing is needed in every merle breeding to prevent a double-merle litter. Secondly, breeders may charge pet owners a premium for such an in-demand coat color.
The merle gene causes pets to have multicolored coats and striking blue eyes. Having the merle gene is great, but becomes problematic when two dogs with that gene are paired. Birth defects in litters can happen when two dogs with this merle gene are bred together, hence double merle breeding.
What is a double merle? A dog that inherits two dominant versions of M is a double merle. In Australian Shepherds these dogs usually will have excessive amounts of white, be deaf in one or both ears, and have serious and generally blinding eye defects. In a few severe cases the eyes have been missing altogether.
The merle gene is responsible for creating mottled patches of color in a dog's coat and blue or odd-colored eyes. However, merle is an incompletely dominant gene, so not every merle dog will have blue eyes. And while merle dogs often have blue eyes, they can also have one brown and one blue eye.
Cochleosaccular is the most common cause of deafness and is associated with coat color patterns. It is usually seen in dogs with the piebald color genes or merle color gene. It can cause deafness in either one or both ears and is seen more in association with blue eyes and a white coat.
Senile deafness develops gradually, typically occurring at about 13 years of age. Many older dogs lose their hearing but never become completely deaf; however, the loss that has already occurred is permanent. Temporary deafness is often the result of buildup within the ear canals.
The best age to test a litter is around 5½ to 6½ weeks of age (ear canals don't open until puppies are about 2 weeks old). The test can be carried out at any age after this, including on adult dogs. Many breeders wish to know the hearing status of their pups before they go to their new homes.
Australian Shepherd Health Issues. Australian Shepherds are generally healthy dogs with a life expectancy of 12-15 years.
Dogs with cryptic merle (also called phantom or ghost merle) typically display little to no merle pattern and some may be misclassified as non-merles. The cryptic merle alleles occur in the lower end of the range (typically from 200-255, however, this range and designation varies by study).
When two merle-patterned dogs are bred together, each puppy in the litter has a 25% chance of inheriting that gene from both parents. The resulting offspring is referred to as a double, or homozygous merle.
The extreme lack of pigmentation is what makes these dogs unhealthy and prone to multiple conditions. It goes along with: Hearing impairment – ranging from light deficits to complete deafness. Vision impairment – up to complete blindness.
Double merles have large amounts of white in their coat and deafness and eye abnormalities are common. All merles may have blue or partially blue eyes, and pink or partially pink noses. Merle can be completely hidden by recessive red, as recessive red dogs can't make eumelanin pigment and merle only affects eumelanin.
It is a common misconception that a dog with a merle coat must have hearing and seeing issues. The only time the merle gene causes a concern for health is when a dog is homozygous for merle, meaning “double merle.” The only way to get a homozygeous merle dog is to breed two merles together.