ALL PUPPIES are BAER-tested at Ambajaye at seven (7) weeks of age. All breeding stock are also BAER tested and must have full hearing.
Congenital deafness is observed in more than 85 breeds of dog, including the Australian Cattle Dog (ACD) and the Australian Stumpy Tail Cattle Dog (ASTCD). The prevalence in ACD populations is as high as 15% (including bilaterally and unilaterally deaf dogs—this will be explained later), and although there is no data available on the prevalence in ASTCDs it can be assumed to be similar to that of ACDs for a number of reasons.
Firstly, ASTCDs share a common ancestry with ACDs and share other inherited conditions such as prcd-PRA and HD. Secondly, stumpy DNA and BAER test results have formed part of a ten year research program into congenital deafness at the University of Queensland. Lastly, there is anecdotal evidence of deafness within the relatively small gene pool of ASTCDs.
Congenital deafness is associated with the genetics of white pigmentation in dogs and other animal species. Much of the research undertaken has involved the Dalmatian, which records the highest prevalence of deafness and has comparable pigmentation and distribution genetics to the ASTCD.
A genetic marker for deafness has yet to be developed, despite decades of research into this area. It is therefore left to breeders to be mindful of the heritability of the problem.
Proven strategies to greatly reduce the incidence of deafness include:
- Removing affected dogs from the breeding population. Affected dogs are more likely to produce affected offspring. However, unaffected dogs can also produce affected offspring.
- Breeding away from pedigrees with a high prevalence
- Not breeding away from patches.
Identifying bilaterally deaf puppies (deaf in both ears) could be considered to be easy. Unfortunately even these puppies are not always identified by breeders and are sold to unsuspecting owners.
The main problem, however, arises from unilaterally deaf puppies (completely deaf in one ear only) as these dogs are considered to be ‘genetically’ deaf, although they can still hear much better than you or I (they will have an early, subtle problem with the direction of sound). The only way to reasonably identify a unilaterally deaf puppy or dog is to BAER test (brainstem auditory evoked response).
Studies have shown a significant relationship between deafness and parental hearing status. However, as mentioned earlier it is still quite possible to produce deaf progeny from parents with full (tested) hearing and, interestingly, two bilaterally deaf dogs can produce offspring with full hearing. This is why a simple Mendelian model of inheritance cannot be used to trace inheritance of deafness. Eliminating affected dogs from the breeding population has been proven to be the only way to drastically reduce the incidence of deafness within populations.
In studies of deaf ACDs (combining both bilateral and unilateral) the percentage with unilateral deafness was 84%. This means that without BAER testing these dogs could potentially remain in the breeding population, perpetuating the problem.
