Australian Shepherds are one of many breeds that can be affected by careless merle-to-merle breeding (breeding two merle parents). Approximately 25% of the resulting litter could be born mostly white, generally with blue eyes, and generally can have hearing and/or vision loss. These "excessive white" merle puppies are called double merles, "lethal white" merles or homozygous merles (meaning they inherited a merle gene from both parents).
It was commonplace in the past (and is still fairly common today) that the white puppies would be culled (killed) at birth for being defective.
There are many myths surrounding double merle dogs. It is often believed that deaf/blind dogs are aggressive, unpredictable, untrainable, and prone to other health issues (even a shorter life span). None of this is true. Double merles (other than possible hearing and vision loss) are generally quite healthy dogs who live long lives. They are no more aggressive, unpredictable. or untrainable than a hearing/sighted dog. In almost every area, they have, in fact, excelled. Double merles often compete at the highest levels in agility and can be trained to pull carts, participate in K9 nosework, and can become therapy dogs, among many other things. The sky is the limit when training a double merle!
Double merle, Dakota (deaf/blind collie/Aussie mix), CGC
While double merles are quite amazing dogs, they do require homes that are able to handle a special needs dog (and contrary to another popular myth surrounding these dogs, homes DO exist that wish to take them in). Deaf or hard-of-hearing double merles need to be trained with sign language or hand signals. Vibrations and lights can also be used to train them.
Blind double merles would need auditory and scent cues placed around the home and during training. Care would need to be taken when changing the furniture in the home and any sharp edges at eye level would need to be moved or cushioned with bubble wrap or a towel. Deaf/blind double merles would need to be trained using touch signals and through scent cues. Stairs would be need to be baby-gated and/or a textured mat or scent placed before the doorway to alert the dog that something different is coming up.
Despite a few minor changes in how a double merle's environment is set up and how he/she is trained, owning and living with a double merle dog is an amazingly wonderful experience! They do not care that they cannot hear or see. They are just happy dogs who live life to the fullest!
For more information about Aussie health issues see the Australian Shepherd Health & Genetics Institute (ASHGI).
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