Inside your horse’s ears

 

The ears are the source of relatively few problems in the horse

The equine outer ear includes the pinna (the flap of the ear) and the external auditory canal (the cuplike ear canal). The pinna collects soundwaves and channels them from the external auditory canal to the middle ear, where they meet the tympanic membrane (the eardrum) and cause it to vibrate. Here the ossicles (the auditory bones) transmit the tympanic membranes’ vibrations to the inner ear. The inner ear, which is made up of the auditory nerve, cochlear and vestibular labyrinth, transfers the waves into nerve impulses, which are sent to the brain’s hearing centre.

Though the ears are just as complex as in most mammals (including humans) and have a large opening which is exposed to the air, they are the source of relatively few problems in the horse. This is great news for horses, but does mean that we, as owners, can easily overlook the ears as a source of problems in the horse. Below we list a few of the conditions that can affect the ear, and discuss what can be done about them.

Insect-induced dermatitis

This is a hypersensitivity to midge bites. The bites themselves occur all over the body, but bites close to the ears can trigger this condition in the ear itself. The body does not react to the bite itself, but in fact to the saliva of the insect. The saliva causes an immune response, which ultimately results in an inflammatory reaction. The ears look scabby and you may be able to see spots of blood where the insects have bitten.

Insect-induced dermatitis is fairly easy to manage by using insect protection, such as long-lasting fly sprays, medications applied to the skin and fly masks with ear protection. Badly affected horses may actually need oral anti-inflammatory treatment to relieve their symptoms.

However, the problems that the bugs cause can extend beyond simple irritation. Biting midges can spread a papillomavirus that results in the appearance of crusty plaques (also known as aural plaques) inside the ear. Some of these plaques are simply unsightly but others will cause severe ear sensitivity and even headshaking. These plaques can be treated with creams, but it is essential that insect control is implemented to reduce the chance of reoccurrence.

Diagram of the ear cavity

Ticks

Some tick species will attach and feed on the horse’s inner ear. This can cause the horse to become very sensitive around the ears, and make him resistant to wearing a bridle, halter or anything that fits over the poll area.
Several species of tick can actually live in the ear canal for prolonged periods. These are more difficult to detect, often until you start to see ticks hatching right out of the ear! If ticks are suspected and nothing obvious can be seen, horses can be sedated to allow the vet to do a thorough examination of the ear area.
Thankfully ticks are relatively simple to remove, although an infestation (attachment of more than a few ticks) does require a vet’s care. Treatment includes applying medication, usually pyrethrin-based, to the ear of a sedated horse. This should obviate the need to remove the ticks physically. The ticks should release their hold in response to the medicine and then the horse will be able to shake them out himself. It is usually advised to treat these ticks at least once more after the initial treatment, to ensure that all ticks have been eradicated.
Sometimes these ticks may have resulted in a secondary infection of the ear with a bacteria, virus or fungus, and this may need veterinary attention. Therefore, if the horse does not appear to improve after a couple of treatments for ticks, it is worth returning to the vet to look for other issues. If the infection is of the outer portion of the ear, it can be easily managed by the owner by administering antibiotics, antifungals, steroids and/or anti-inflammatories prescribed by the vet. An inner ear infection is more complex to manage and veterinary assistance will be required.
Prevention of tick infestation includes outfitting the horse in a fly mask that protects the ears. Some fly sprays are also useful in repelling ticks.

Did you know?

Horses, in addition to hearing through their ears, can also pick up vibrations in the ground through their teeth while grazing. These vibrations are then transmitted to the inner ear through the jawbone.

Text: Dr Lizzie Harrison

The full article appears in the April/May issue of HQ (132) > Shop now