At 28 years of age, Spot was enjoying a well-earned retirement. In the many years he had pulled a carriage for Horsedrawn Occasions, the Barnard family’s Derbyshire weddings and funerals business, the grey Gelderlander had never shown any problems with his ears, until one morning when his owner Elaine Barnard noticed some discomfort.
The pinna (the external, visible part) of Spot’s left ear appeared swollen and sensitive to the touch. Dr Regina Pereira, of Pool House Equine Clinic, identified a haematoma inside the ear, a soft bulge formed from blood gathering outside blood vessels, in this case between the cartilage and the overlying skin.
The origin of the haematoma was easy to find. The skin inside Spot’s ear canal was extremely inflamed — the top of the canal was completely closed, with swollen, infected skin pressing in from all sides. The fact that no drainage could occur from the ear canal was causing additional discomfort. Spot’s attempts to alleviate the pain by rubbing his ear against the stable wall had caused a blood vessel to burst and the haematoma to form.
After performing a minor surgical procedure to drain the haematoma from the pinna, Regina immediately commenced treatment of the infected skin. An aggressive programme consisting of both antibiotics and anti-inflammatories failed to settle the skin, however, so the decision was taken to admit Spot to the clinic for potential surgery.
The term otitis externa is used to describe inflammation of either of the two structures of the outer ear: the pinna or the ear canal.
The conical shape of the pinna is similar to an old-fashioned gramophone speaker and is excellent for capturing even the softest sounds, with horses able to hear faint noises from a considerable distance away. Comprised of cartilage covered by skin and hair, the pinnae are independently mobile — thanks to 10 different muscles involved in controlling their movement (compared with only three in humans).
The ear canal channels and amplifies the sounds captured by the pinna, transferring them to the ear drum and the middle ear beyond it, where they are processed. From where it starts at the pinna, the ear canal drops down almost vertically for around 5cm before turning at a 90° angle and travelling horizontally for another 2-3cm to the ear drum.
Otitis externa is less common in horses than in small animals, but it does occur and can be extremely debilitating and painful. The inflammation leads to crusting of the skin, itching, ear rubbing, resentment of the ears being touched or headcollars/bridles being put on, and tossing or weaving of the head.
Possible causes are:
- Sweet itch: This reaction to the saliva of the biting midge most often affects the mane and dock, but it commonly occurs on the ears. A good fly rug that covers the horse’s head as well as his body will help, along with an effective fly repellent and stabling at dawn and dusk when fly activity is prolific.
- Blackflies: Whereas midges will bite various parts of the body, the blackfly targets only the inside of the ears. Scabbing and crusting of the skin occurs as a reaction to bites, causing the horse to rub his ears and face in an attempt to relieve the irritation. The resulting abrasions provide access for bacteria into the skin, leading to painful secondary infection.
An affected horse may become head shy if steps are not taken to prevent blackfly bites. Fly repellent and cattle fly tags plaited into the forelock are helpful in countering this pest, but a well-fitting fly mask is often most effective. It is tempting to clip the hair from the insides of a horse’s ears. If he suffers from either midge or blackfly bites, it is better to leave hair in the pinnae to act as a protective blanket over the skin.
- Ear mites: The great majority of suspected cases of ear mites turn out instead to be due to either blackfly or sweet itch. The Psoroptes mite can live at the junction of the vertical and horizontal portions of the ear canal, however, where it feeds on skin scales. It can cause intense itching and distress, but fortunately is susceptible to the normal anti-parasitic treatments found in common wormers.
Since most horses in the UK are wormed at least once a year, this possibly explains why ear mites are rarely seen here.
- Aural plaques: These white, crusty patches, commonly found on the inside of the pinnae in horses of two years and over, are caused by a wart virus (papillomavirus) that is spread via blackfly bites. Aural plaques tend to improve gradually, sometimes resolving completely, but in certain cases remain for a lifetime. Resist the temptation to clean or apply any concoction to them, as this will only serve to make the horse head shy. Instead, take appropriate precautions against blackfly.
- Sarcoids: By far the most common skin tumour in horses, sarcoids are also caused by a papillomavirus spread by flies, which is why the ears are a common site. Sarcoids can present in five different forms, some of which do not involve breakage of the skin. However, the “fibroblastic” sarcoid takes the form of a bleeding mass that is hugely attractive to flies, causing further discomfort and distress to the unfortunate horse.
Various sarcoid treatments are available, but damage to the healthy tissue surrounding the sarcoid can occur as a result. Loss of tissue from the pinna can mean that the resulting ear is misshapen and disfigured. Those concerned about the cosmetic results may opt for a treatment that involves inserting radioactive iridium wires into the sarcoid for minutes at a time. This radiotherapy treatment can be very effective, but it is expensive and only a few facilities can provide this service.
- Squamous cell carcinoma: This is a particularly aggressive type of skin cancer. Eye and genital squamous cell carcinomas are probably the most common, but they can also occur in the ear.
The non-pigmented skin on the white-faced horse and excessive exposure to ultraviolet light (sunlight) are predisposing factors. Treatment is usually similar to that of sarcoids but may involve radical surgical resection (removal of tissue), which inevitably leads to disfigurement of the ear.
Clearing the way
In Spot’s case, we suspect that blackfly bites caused a secondary bacterial infection, creating a favourable environment for the development of chronic otitis externa.
As the medical treatment had been unsuccessful, Dr Andrea Giacchi of Pool House opted to perform surgical resection of the outer part of Spot’s vertical ear canal. This provided exposure to the horizontal canal to improve ventilation and, most importantly, drainage, allowing antibiotic treatment to work.
Ref Horse & Hound; 2 May 2019