What causes deafness in Aussies? My friend had a litter of pups from a black tricolor male and blue merle female and two pups (a blue merle male and blue merle female) were born deaf. Neither parents are going to be bred again, but needing to know what exactly causes this major problem?
Merle to Merle probably and maybe the black tri color is not a real tri color.
I know what you are saying about there being a possibility of a cryptic merle, but I saw him many times and he is a real black tricolor Aussie. He didn't even have excessive white on him, just a little white trim and brown eyes. His parents were a merle bred to tri color.
Are the deaf puppies lacking pigment around the ears? That's usually the indicator of deafness. Merle to merle increases the chances of this happening but it isn't exclusive to double merle breedings only.
Cryptic merle is when a dog does not look like it is merle at all. Often the only way to tell if a dog is a cryptic merle, is to do color DNA testing on it. A lot of people think merle carrying dogs will always show at least one blue eye, but even that's not always true. I've seen a solid black Aussie with 2 dark brown eyes that was proven by DNA to be a cryptic Merle. The dog had no white or any other color other than black. He did not have a tail so it's thought there was merle on the tail, but docking it as a puppy removed it from sight. There is a photo online somewhere showing a black newborn Aussie pup with just a tiny grey blue spot on it's tail that shows how it can happen. Breeding merle to merle is common in Aussies and causes the pups to have all sorts of health problems. It's not always done on purpose either, accidents happen thanks to cryptic merles. Double merle dogs are usually mostly white and easy to tell they are double merle as such. Getting only deaf pups is actually good compared to how bad many double merle pups can have it. Some are still born or have so many health issues putting them to sleep is a more humane option.
However what is not a well know fact, is that the piebald gene also can cause deafness as it has excessive white. Lack of color pigment can be a far more serious issue than people realize. So if a dog has even a tiny bit of white, you might have a dog carrying piebald but not actually showing it, and if you breed it to another dog carrying it, you'll get pups with white piebald and the possible health defects that can come with it. In the end it really is best to have any dogs color DNA tested to be safe if you wish to breed them as it will save you trouble in the future.
I agree about cryptic merles not always being obvious. Had an e-friend with a Cardigan Welsh corgi that showed only a tiny spot of blue on the neck as a pup, which faded out as the dog got older.
Genetic testing is the safest way to go!
Like CrashKerry seems to be implying, doesn't have to be a merle-to-merle mating; the deafness seems directly associated with the pups themselves being merles. Long history of merles from all sorts of parental colour combinations in the assorted Collie breeds ( and Aussies are based on Collies). Where merle to merle breeding used to be avoided like the plague, for this and other health reasons.
DNA may tell you about the make-up of the pups and help you avoid it with future breeding; that's if the genome has been mapped in enough detail yet. But it can't neccessarily explain "Why ?" in the first place.
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