Deafness isn’t commonly recognized in horses. Dr. Gary Magdesian (School of Veterinary Medicine, University of California, Davis) said it can be difficult to tell if a horse is deaf. “Causes of deafness in horses include genetics, head trauma, middle or inner ear infection, brain diseases, and a syndrome called temporohyoid osteoarthropathy. An adverse reaction to gentamicin, a commonly used antibiotic in horses with serious infections, is another possible cause,” he said.
THO is a degenerative process in the joint between the hyoid apparatus (bones that supports the tongue) and the skull. “During this degenerative process excessive bone builds up, which can cause compression of the 8th cranial nerve, which is responsible for hearing,” he explained. Another cause of deafness that probably occurs but has not had much research is age-related hearing loss in older horses. Since humans and other animals tend to lose hearing as they get older, we assume that horses do also.