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A horse with head trauma induced by falling can have a traumatic brain injury or a fracture of the ossea part of the external ear canal. The aim of this study is to find the complications of a head trauma. The aim of the second study is to verify the deafness as a cause of behavioral disorder in horses. A three-year-old Hannoverian gelding fell down and injured the left lateral region of his head. After getting up the gelding had a bloody discharge out of the left ear. The neurological exam had shown slowly ear movements, painful left ear basis and left head tilt. The endoscopy of the guttural pouches was normal. The CT image detected a transversal fractur of the left osseus part of the external ear canal. Thirteen weeks after falling down the otoscopy of the cartilaginous and osseus part including the tympanic membrane of the right ear were normal (grading I/III). The protrusion caused by the fracture in the osseus part of the left ear prevented the view to the tympanic membrane. The epithelium of the osseus part was severe reddened and swollen which are signs of an acute external otitis. The threshold of normal hearing level of the right ear was 30 dB. The brainstem auditory evoked response (BAER) of the right ear showed prolonged latencies of wave III (2.95 ms, normal 2.86) and V (5.80 ms, normal 4.62) and interpeak latencies I-III (1.65 ms, normal 1.33) and I-V (4.50 ms, normal 1.76) which were showing a mild sensorineurale hearing deficit based on traumatic brain injury. This traumatic brain injury could induce an axonal damage of the brainstem auditory pathway. The threshold of normal hearing level of the left ear was 80 dB. BAER of left ear had no identifiable peaks and therefore no measurable latencies and interpeak latencies. These findings concluded to the diagnosis of sever conductive hearing deficit based on the protrusion in the left osseus part in this gelding with head trauma. The behavioral disorders of American Paint Horses were observed by the owners and these horses were refered to the equine medical clinic. The otoscopical findings of all horses were normal in the cartilaginous and osseus part (grading I/III). Achromodermia was found in all cartilaginous parts of the external ear canals. Only one horse had keratin scales around the entrance of the osseus part in both ears. All tympanic membranes were intact and transparent. The thresholds of normal hearing level on both ears of all horses were 100 dB. Absent peaks of the BAER and isoelectric lines were seen which characterize the sensorineurale deafness in all American Paint Horses. The sensorineural deafness was the reason of the behavioral disorder described by the owners. Horses with head trauma suffer from a traumatic brain injury. These horses could have a hearing deficit based on either due to a fracture of the osseus part of the external ear canal or an acute external otitis or both. Endoscopy of the guttural pouches, external ear canals and BAER should be done. Hearing deficit or deafness induce behavioral disorders which should know the owner. Horses with white head and blue eyes could have the genetical deafness. Deafness will be diagnosed with BAER. [ABSTRACT FROM AUTHOR]

The evaluation during the neurologic examination of hearing in horses generates only subjective values because the horse is turning the head and moves the ears towards the noise. Therefore the brainstem auditory evoked response (BAER) technique is very useful for evaluating the hearing in horses objectively. The aim of this study is to measure the BAER in horses with altered behaviour or lack of responsiveness to loud sounds. This has been effected on older horses, also on a horse with ceruminal occluded external ear canals and on a horse with colic surgery and bad prognosis during general anesthesia and euthanasia using T61®. Horses were sedated using detomidine (20 μg/kg bw i.v.) and placed in a stock or silent area. Needles were inserted subcutaneously on the median place of the vertex between the lateral canthus of the eyes, on the ventrocaudal area of the osseus part of the external ear canal on the top of Processus retrotympanicus on the left and right side, on the midline between the Os occipitale and Processus spinosus of the second cervical vertebra (ground). A click stimulus at 80 and 60 dB normal hearing level was applied ipsilateral and noise-masking sound at –35 dB normal hearing level was applied contralateral. An average of 2 000 responses of BAER was recorded over a 10 milliseconds epoch operated by the AEP-diagnostic system Corona. The latencies of peaks I, III and V were measured and the interpeak latencies between the waves I-III, III-V and I-V were calculated and saved by the AEP-diagnostic system. These measurements of five horses with altered behaviour and of one horse during euthanasia were compared with a control group of normal Warmblood horses (12 mares, 2 geldings, 2 stallions; mean age of 15 years, min 3 and max 19 years). The external ear canals were examined endoscopically before and they had normal findings (grade I) and the tympanic membranes were intact and transparent. The tympanohyoid and stylohyoid in the guttural pouches were normal too. The latencies in ms and interpeak latencies of the control group stimulated with 80 and 60 dB nHL ipsilateral are: peak I (left 1.49 ± 0.05, 1.79 ± 0.13; right 1.53 ± 0.09, 1.86 ± 0.11), III (left 2.81 ± 0.16, 3.27 ± 0.18; right 2.86 ± 0.20; 3.25 ± 0.18), V (left 4.60 ± 0.21, 5.05 ± 0.27; right 4.62 ± 023, 4.94 ± 0.26); I-III (left 1.32 ± 0.15, 1.48 ± 0.24; right 1.33 ± 0.15, 1.38 ± 0.20), III-V (left 1.79 ± 0.14, 1.78 ± 0.19; right 1.76 ± 0.24, 1.69 ± 0.28), I-V (left 3.11 ± 0.20, 3.26 ± 0.28; right 3.09 ± 0.19, 3.07 ± 0.27). A 20 years old Haflinger mare turned her head only to the left side when the owner called her. The peak amplitudes (I, III, V) and interpeak latencies (I-III, I-V) were reduced ipsilateral of the right ear. These are signs of a conductive hearing deficit and cochlear dysfunction or neural problem. The 25 years old Warmblood gelding which turned his head only towards very loud noises had reduced peak amplitudes and increased latencies (I, III, V) ipsilateral left and right. These are signs of conductive hearing deficit on both sides. No BAER (80 and 60 dB nHL) were detected ipsilateral on the left side on a 1.5 years old Warmblood mare which reacted only to very loud noises. These diagnostic findings explain deafness on the left ear. A five months old Warmblood stallion which responded only to very loud noises too, had prolonged latencies (I, III, V; 80 dB nHL) and unchanged interpeak latencies ipsilateral on the right ear. No peaks were detected stimulated by 60 dB. These are findings of a severe hearing deficit and cochlear dysfunction on the right ear. A five years old Warmblood mare had an altered behaviour with startling due to environmental noises. A complete obstructed osseous part of the right ear and a partial obstructed osseous part of the left external ear canal were seen endoscopically. Decreased peak amplitudes stimulated by 80 dB nHL and no peaks stimulated by 60 dB ipsilateral on the right side in comparison to the normal horse are findings with severe conductive hearing deficit on the right ear based on the complete obstruction. The applicated drug T61® used for euthanasia (30 ml/250 kg bw i.v.) under general anesthesia of a 19 years old Shetland pony gelding which had colic surgery and a very bad prognosis induced a complete loss of BAER which was a diagnostic finding of brain death within three minutes. In conclusion the testing of BAER in horses is an objective measurement of hearing and evaluates the physiology of the auditory pathway. The endoscopy of the external ear canal has to be done generally before BAER measurements! BEAR testing is indicated in horses with altered behaviour, head tilt, head shaking, temporohyoid osteoarthropathy, guttural pouch empyema, othematoma, melanoma, sarcoid or squamous cell carcinoma in the pinna or external ear canal, after surgery on the pinna or in the external ear canal, after treatment of Otitis purulenta externa or after surviving an encephalitis (West-Nile-Virus-, EHV-1-, Sarcocystis neurona-Infection). The BAER testing ought to be included into the pre-purchase exam plan/requirements! [ABSTRACT FROM AUTHOR]