Deafness in Canaan Dogs

Soon after I first came into Canaan Dogs I heard "rumours" that there had been a number of deaf Canaan Dogs born in the USA.  Whilst I now understand it is indeed true that there have been some born deaf, I have no idea of the details – how many nor their colouring.  A few years later I learnt of a deaf Canaan Dog in Europe. But it was not until 2004, when I detected a deaf puppy in one of my own litters, that I began to consider the situation seriously.

When Vicky was a couple of weeks old I became suspicious that she was sleeping to long and too deeply.  My first "serious" breed was the Dalmatian, and whilst I had never owned or bred a Dalmatian affected by deafness, my experience with sensorineural deafness within that breed made me consider that Vicky may be deaf.  There were no other signs, when she was awake she even appeared to react to noises, and somebody with no experience would probably not have noticed. At 6 weeks old I took her to the Animal Health Trust to have her BAER tested.  Sadly the test confirmed that she was bilaterally deaf (deaf in both ears).

Deafness can be unilateral (deaf in one ear only) or bilateral (deaf in both ears).  Whilst it can be found in a number of different dog breeds, the majority of research carried out so far has been with Dalmatians.

What is BAER testing?

Brainstem Auditory Evoked Response (BAER) tests became available in the late 1990s, and Dalmatian owners and breeders were the first breed to begin seriously testing their dogs in the UK.

Fine needles are placed under the skin of the scalp – one in front of each ear, one at the top of the head and one between the shoulders.  These needles are small electrodes that are connected to a special computer. This system detects electrical activity in the cochlea and auditory pathways in the brain.  It’s rather like how an ECG can detect the electrical activity of the heart.

Each ear is tested individually. Looking at the results in the diagram to the right; puppy 1 can hear in both ears; puppy 2 was deaf in the left ear, puppy 3 was deaf in the right ear and puppy 4 for was deaf in both ears.

It is a simple, quick test and, so far, although a puppy may wriggle purely in objection of being held still, none of the Canaan Dogs tested have needed to be sedated, neither puppies nor adults.

What causes deafness in dogs?

There are different types of deafness but, for the sake of clarity, in this instance we are discussing one of the most common forms of deafness found in dogs, hereditary congenital sensorineural deafness, which means that it is existing at birth or shortly afterwards.

Deafness has actually been associated with pigmentation patterns in dogs since 1896. However, as with many subjects, the cause of the deafness is not a simple one.

Whilst the exact mode of inheritance is not yet entirely understood, it is agreed that it involves the colour pattern that is genetically s^w, "extreme white", and possibly, but perhaps to a lesser extent, s^p, "piebald spotting", on the Spotting Locus. See Canaan Dog Colour Genetics for an explanation of colour and patterns in the Canaan Dog. Generally speaking, in Canaan Dogs these are dogs that are predominantly white with patches of colour.

Before a puppy is born colour pigment (melanin) migrates throughout the body, and continues to after birth.  A solid coloured dog has full pigmentation, while a dog of the extreme white colour pattern is caused by an absence of pigment cells, at the same time the patches of colour are fully pigmented areas. The spread of colour begins along the spine and progresses down the sides, and finally to the legs, tail and head. The white areas are simply where the melanin has failed to produce pigment.

Deep in the cochlea of the inner ear there are hair cells. Sound waves cause a vibration that bend these cells, and then neurons transmit this information as sound to the brain. The cochlear hair cells are nourished by melanin, and research has shown that it is essential for pigmentation to be present in order for the hair cells to survive. Without pigmentation they become damaged and die and deafness occurs.

It has been shown that in some dogs with white coat colour, the pigmentation does not fully reach these inner ear hair cells, and research shows that in these cases the lack of pigment is responsible for deafness, either unilaterally or bilaterally. What causes the failure of the melanin is unknown. It is understood that there are a number of different genes that cause lack of pigment, and probable that more than one of these are somehow linked with deafness. The fact that unilateral deafness occurs, and that pigment placement is usually asymmetric in dogs showing incomplete pigmentation, shows that there is a random element involved.

To summarise, we know that whilst the exact actual cause of deafness is unknown it is related to coat colour and has to be polygenic (more than one gene involved).

What about the Canaan Dog?

So the big question is, is the cause of deafness in Canaan Dogs the same as that in Dalmatians and other breeds and animals, i.e. related to the colour pattern and amount of white coat (the pigmentation)?

Of course, we cannot be 100% certain that it is, especially with so few dogs being BAER tested. However, when you look at the Canaan Dogs around the world that have been reported as deaf, and the few who have shown to be affected through BAER testing, you will see that they are all predominantly white, and none have been of the solid or Irish spotting pattern.

At this time I would therefore say that was pretty conclusive evidence that deafness in Canaan Dogs IS related to the extreme white, and possibly piebald spotting too.

So why haven't there been more deaf Canaan Dogs?

The Canaan Dog is a numerically small breed, add to that the number of dogs that are predominantly white is small so it is not surprising that there has been little evidence of deafness.

In Dalmatians, UK statistics report approximately 20% of dogs can be affected, that is either bilaterally or unilaterally deaf. Remember that that ENTIRE breed is genetically extreme white and that about 600 Dalmatians are registered a year with the KC.

Now consider that less than 20 Canaan Dogs a year are registered in theUK. Out of that 20 how many are patched, and out of those how many are predominantly white in pattern? 5 a year would probably be a very generous figure, although I have not studied the statistics as yet. IF there were to be the same percentage of affected in Canaan Dogs as the Dalmatian, that would mean 20% of 5 could be affected!

Then, of course, there is a certain amount of "luck" with which genes Mother Nature actually passes on.  For instance, I know Dalmatian breeders who have bred a number of litters over the years, yet have never produced an affected animal, yet another breeder may have just 1 litter and find that 2, maybe even 3 or more, are affected.  Nor are their any indications it may be familial (found more in one "line" than another).

Bearing this in mind, a breed may indeed go several years without a deaf puppy appearing.  As to how many Canaan Dogs are unilateral, we simply don't know because BAER testing has not been carried out and, although some like to think differently, it is impossible to tell a unilateral dog without testing.

What should breeders be doing?

First of all they should definitely be performing BAER testing on, at the very least, their dogs that are predominantly white. But it would be better still if all Canaan Dogs of every colour were to be tested, at least in the beginning.  This will show up any dogs that are just unilaterally deaf, which can NOT be diagnosed without BAER testing.

BAER testing all dogs will not only provide statistics for analysing, but will tell us if indeed there are more Canaan Dogs that are unilateral.

Should dogs be culled from the gene pool?

One breeder has rashly stated that all dogs that are related to the "affected" dogs should be removed from all breeding programmes. This would effectively eliminate the majority of the dogs in theUK, including dogs of their own breeding, from the genetic pool.

Is that a wise move, or simply a behaviour bordering on hysteria?   Let's look at this in proportion.

Canaan Dogs already have an extremely small genetic pool. Removing all related dogs to those found to be affected from the genetic pool, would greatly deplete what little genetic variation we have, forcing breeders to inbreed more and thus possibly increasing the number of dogs suffering from auto-immune related problems.  Can the breed truly afford to do that?

Whilst deafness should certainly not be taken lightly, I personally find it very sad that one person considers deafness, both unilateral and bilateral, to be for more serious than other health crippling and painful problems, such as masticatory muscle myositis or degenerative myelopathy, both of which have been seen in Canaan Dogs in the same number of those reported to be affected by deafness, i.e. 3.

If a person should feel that way, should we not therefore apply that reasoning to those who have been diagnosed with masticatory muscle myositis, or indeed any other disease?

Or, would it be far better to stop any "witch hunt" and begin to actually work on prevention by testing dogs, which the breeder concerned does not currently do?