School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, Australia
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BAER Hearing Testing: Is one in the hand worth the cost?

Deafness is a serious problem in Australian Cattle Dogs (unilateral + deafness is around 15%) and appears to be multi allelic and/or have varying degrees of penetrance with modifiers. That means you can mate two deaf dogs and get puppies with bilateral hearing. It is, however, clear that including dogs that are unilaterally deaf or totally deaf increases the frequency of the disease causing alleles in the breeding population. Much genetic work needs to be done in this area.




Like many breeders interested in bettering their chosen breed, I endeavour to be thoughtful about mating. I aim to improve the breed whilst, concomitantly, reducing the prevalence of genetically inherited diseases. However, as many breeders will testify, this can be a delicate balance. In my opinion, the only certainty is that reliable information is a key to progress. In this short article I question whether short-cuts in determining disease states are worth the price of admission.

Congenital hereditary deafness is a problem for over 35 breeds of dog. Deafness can be unilateral (affecting one ear) or bilateral (affecting both ears).

Deafness is the inability to hear and can be caused by either conduction or neurologic abnormalities. Conduction deafness is caused by abnormalities of the pinna (external ear), ear canal, tympanic membrane (eardrum), auditory ossicles or middle ear. Neurologic or sensorineural deafness is caused by abnormalities of the inner ear, auditory nerve or in the brain itself.

Recent work suggests that there could be more than one form of congenital deafness in dogs. The gene Mitf has been identified as a cause of white spotting and extreme white spotting in some breeds of dogs including the Dalmatian and Bull Terrier. In the Stumpy-Tail Cattle Dog, white spotting is an autosomal recessive trait with incomplete penetrance that maps to chromosome CFA10.

A BAER test is the only 100% reliable method for determining that a dog is deaf (or for measuring the extent of its hearing loss). BAER (pronounced "bear") stands for "Brainstem Auditory Evoked Response" and is a procedure using computers to record the electrical activity of the in response to sound stimulation. The waveform represents specific anatomical points along the auditory neural pathway: the cochlear nerve and nuclei (waves I and II), superior olivary nucleus (wave III), lateral lemniscus (wave IV), and inferior colliculi (wave V).
One simple device that is routinely used for testing puppies is the BAERCOM™. My question, and the discussion that I hope to provoke here, is how accurate and sensitive is this device as compared to the more expensive and sensitive equipment that resides in a subset of facilities?

The UFI website states “The BAERCOM includes only the minimum functionality required to test for hearing ability and eliminates functions that are unnecessary for this purpose. It does not have the extensive capabilities of the more expensive audiological testing machines”. Currently it costs US $2250.

An unfortunate case of circumstance
Following the untimely death of a cornerstone breeding female and the disruption of breeders agreement I decided to mate a female I had on my “reserve list”. This female had many meritorious characters, but she was diagnosed as unilaterally deaf at 8-weeks using the BAERCOM™. The male I selected has full bilateral hearing according to the BAERCOM™. The same individual did not test these dogs.

To complicate matters, the female now lived across the continent in Perth while the identified male two-hours drive away from her. Armed with all the information and cautionary genetic notes about the possibility of congenitally deaf puppies, we waited for her to come into season.

Following progesterone testing she was whisked away to meet the future sire. Introductions were brief and the fertilization was completed without regard to romance.

Two months later five puppies were born into a welcoming household. The diligent owners then planned microchipping, vaccinations and BAER testing with the local veterinarian at 6-weeks of age.

Crisis! The BAERCOM results suggested that two puppies had normal hearing, two were unilaterally deaf and one was bilaterally deaf. As it was reported to me, the vet suggested that the two unilaterally deaf pups should be retested at 8 weeks. The vet wrote “deaf” on the paperwork of one female pup. She was not microchipped as euthanasia was considered a possibility.

The severity of the results caught both the Perth household and me by surprise. As a non-expert in interpreting BAERCOM results, I sent the reports to multiple specialists including Professor George Strain (Louisiana State University).

Here is his response in full (reprinted with permission)
First, the device used to test these dogs, called a BAERCOM, has a long history in my experience of providing equivocal recordings and misdiagnoses based on what I contend are poor recordings from an unreliable a system that is not reliable in the hands of most users. I see many results sent to me by doubting owners. The recordings frequently are full of artifact that can obscure results (visible to a limited extent on Plain Maverick and Blackbutt), and it is not possible (last I knew) to adjust the display gain of the output. The relative low cost of these units makes them attractive, but I don’t think you get your money’s worth with them, and there is no training in BAER testing to accompany purchase. Training in human applications is not adequate.
That said, none of the tracings you sent appear to show hearing in either ear. However, without having been present at the testing and being able to produce a clearer output, I cannot say so with certainty.”

Far from feeling overwhelming dismay when I read the email I saw a spark of uncertainty concerning the robustness of the results. Some may argue that this makes me a “glass half full” person but my optimism was subsequently validated.

Next, I contacted Dr’s Susan Sommerlad and Caroline O’Leary in Queensland as they have been studying deafness in Australian Stumpy Tail Cattle Dogs. I made this contact as a geneticist because I know that a single litter containing bilaterally deaf, unilaterally deaf and normal hearing puppies can be invaluable in identifying specific DNA mutations that cause disease.

To resolve the hearing conundrum, or at least validate the results, I made an appointment to retest at Murdoch Vet Hospital (http://www.murdoch.edu.au/Services/Veterinary-Hospital/). The pups were 8-weeks of age when they were retested. At Murdoch, Dr Mandy Burrows and her proficient and professional team had been in contact with Dr’s Sommerlad and O’Leary and we planned to collect blood from all the puppies and the dam. Two days prior I had collected a cheek swab from the sire of the puppies so this could be included in the research program.

Dr Burrows and her team retested each of the puppies and the dam using the more sensitive and sophisticated Nihon Kohden MEB 9200K, Neuropack M1 testing unit. Four of the five puppies and the dam were diagnosed to have normal bilateral hearing. The fifth pup, previously reported to have normal hearing with BAERCOM testing, was now found to be abnormal in one ear.

Compiled, these results show 4 of 5 puppies and 1of 1 adult’s showed conflict between the results. While it is unlikely that a single source of error can be identified, the three compounding factors are age of puppies (6 cf 8 weeks) machine (BAERCOM cf Nihon Khoden), and operator (Perth Vet cf Murdoch Vet Hospital).

Costs and Benefits
A puppy’s ear canals don’t open until they are about two weeks of age and BAER testing may be done on puppies as early as six weeks. However, some breeders suggest that an 8-week test is more robust. Sedation is usually not necessary, but some puppies don’t like being retrained, or having wires hanging from their face, so it can be performed while is sedated. Dr Burrows sedated the puppies prior to testing.

One has to assume that, during its development, the BAERCOM device was compared against a “gold standard” method of measuring hearing in dogs. The results of that testing are typically published in the manual supplied with testing devices. Devices that fare poorly in these initial tests are typically not released onto the market. So, check your manual if you own a BAERCOM.

A good manual will also provide guidelines for interpreting the output of the device – what response pattern or amplitude of response would represent intact hearing versus deafness. As with any diagnostic test, there will always be two risks - falsely diagnosing deafness and falsely claiming normal hearing. The manual should explain the likelihood of making these two mistakes, when the test is administered correctly. The implications are clear to any breeder. Ask to see the manual if somebody else tests your puppies.

But, naturally, even a good test can fail under certain circumstances. Check that the measurement of hearing was made accurately – the machine was properly calibrated, the electrodes were correctly placed, the tester was adequately trained in administration and interpretation of results. Some say that the lack of training is a serious issue with the use of the BAERCOM. As with your own health care, it is always wise to watch the testing closely, ask questions along the way if you are not sure things are being done properly, ask for a full explanation of the results and what was the basis for the tester making his/her decision of deaf/not deaf. If deafness is identified, don’t be afraid to get a second opinion or ask for a retest on a different day. Either way, a positive or negative test on two separate occasions is more likely to be true than a single test.

 

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