*** The BAER Test ***

Whether we like to admit to it or not, deafness is a problem witin our breed. Not to the same extent as it is in other breeds but a problem still. The exact genetic mode of inheritance in our breed is still unknown, and the debate as to whether the mode of inheritance in A.C.Dís is the same as that in Dalmatians still goes on. Hearing can be tested, but ,as always, we in North Queensland are once again penalised through distance. Brisbane is the nearest centre breeders can avail themselves of this fascility. Tina Sturre of Mackay has been trying to organise a visit to the north by specialists in this field of auditory deficiencies. Numbers are what will decide if she is successful or not, as costs will be decided accordingly. I must point out that the clear testing of the sire and dam of a litter does not mean that the puppies will automatically have full hearing.

The hearing test, known as the Brainstem Auditory Evoked Response (BAER) or Brainstem Auditory Evoked Potential (BAEP) detects electrical activity in the cochlea and auditory pathways in the brain, in much the same way that an antenna detects radio or TV signals or an EKG detects electrical activity of the heart. The response waveform consists of a series of peaks numbered with Roman numerals: peak 1 is produced by the cochlea, and later peaks are produced within the brain. The response from an ear that is deaf is essentially a flat line. Because the response amplitude is sosmall, it is necessary to average the responses to multiple stimuli (clicks) to unmask them from other related electrical activity that is also present on the scalp (EEG, muscle activity, etc.)

The response is collected with a special computer through extremely small electrodes placed under the skin of the scalp: one in front of each ear, one at the top of the head, and one between and behind the eyes. It is rare for a dog to show any evidence of pain from the placement of the electrodes - if anything, the dog objects to the gentle restraint and the irritation of wires hanging in front of its face. The stimulus click produced by the computer is directed into the ear with a foam insert earphone. Each ear is tested individually, and the test usually is complete in 10-15 minutes. Sedation or anesthesia are usually not necessary, unless the dog becomes extremely agitated, which can usually be avoided with patient and gentle handling. A printout of the test results , showing the actual recorded waveform, is provided at the end of the procedure. Test results are confidential, but annonymous details will be used in ongoing research for later publication and education of veterinary practitioners.

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PROGRESSIVE RETINAL ATROPHY



P.R.A.is an inherited disorder that effects the retina of the eye. There are two types or forms of P.R.A.: Central (CPRA) and generalised. The presence of P.R.A. is often noticed first as night blindness, or dogs that have particular difficulty with acute vision under dim light conditions. Unfortunately, P.R.A. often shows up in dogs after they have alreday produced offspring. Tests that certify a dog clear of P.R.A. do NOT certify it is genetically clear of the disorder!!

The reason behind this article was prompted by overseas buyers demanding P.R.A. and Hip Dysplasia certificates before purchase. Unfortunately neither is a genetic guarantee.

Submitted by John Chandler

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