Endoscopic findings of the external ear canal in a group of clinically normal horses and horses with head shaking or vestibular disease.

Since there is a lack of information about the normal appearance or pathological findings of the equine external ear canal (EEEC) and tympanic membrane (TM), we aimed to find a practical way to perform the otoscopic examination in standing, sedated horses. Therefore, we worked with common veterinary video endoscopes, which are normally used for gastroscopy or bronchoscopy. Both ears each of 38 randomly selected, chemically restrained horses were otoscopically examined. 33 of those horses had no history or signs of potentially ear-associated diseases. However, two horses with vestibular disease and three horses with head shaking were included in the otoscopic examinations. We created references of the normal appearance of the EEEC and TM on the basis of the characteristic anatomical landmarks, degree of debris, amount of keratin scales, shape of the intersection between the cartilaginous (CEEC) and osseous (OEEC) portion of the external ear canal, shape of the OEEC, formation of the keratin layer and its integrity, epithelium colour of the OEEC, and complexion of the TM. With this information, we were able to visualise tympanosclerosis in two equine eardrums, as well as low-grade to severe external otitis in three horses. Severe bilateral external otitis combined with temporohyoid osteoarthropathy (THO) was found in one of those horses. A foreign body was found in one OEEC. This study shows that otoscopic examination is a basic, easy to perform and beneficial diagnostic procedure for a complete work-up of ear-related diseases, such as THO, facial nerve paralysis, vestibular disease, head-shaking or head trauma. Plus, regarding animal welfare, well being of horses is highly influenced by noise exposure. Therefore research on equine audiological aspects needs to be promoted. The standardized otoscopic examination provides an important basis for further research on aural diseases.