ALTHOUGH the skin is the most visible of the horse’s body structures it is also often overlooked. The skin is the largest organ in a horse’s body. The skin provides a strong barrier to challenges from outside the body and plays an important role as part of the immune system; it also helps control body temperature and makes vitamin D. In certain parts of the body the structure of the skin changes to perform specific functions, for example the hoof, chesnut and ergot are modified skin structures.

In spite of the exposed position of the skin, it is usually remarkably free of disease. However the skin is also the organ most likely to be damaged accidentally – cuts and scrapes are common and usually superficial. Infrequently, when more severe, these wounds may require suturing to close the wound. Bandages are also commonly used to protect wounds on the limbs and reduce movement which in turn aids healing.

There are only a few ways that the skin can react to injury and so many different diseases can have a similar appearance. The main presenting signs of skin disease are:

?Itching (pruritus) - horses may show excessive twitching or swishing of the tail, or rub, stamp, nibble or bite at their skin.

?Hair loss (alopecia) - can be due to self-trauma due to irritation, or due to diseases affecting the hair follicles.

?Exudation and crusting (dried exudate) - causing matting and tufting of hair, often due to bacterial or fungal infections.

?Excessive flaking or scaling of the skin - a frequent secondary feature of many skin disorders.

?Lumps (nodules) involving the skin - may be due to inflammatory conditions or sometimes tumour growth.

?Pigmentary alterations: Most commonly de-pigmentation of hair (leucotrichia) or skin (leucoderma), is due to injury or other causes of inflammation. Or, less commonly, increased pigmentation of hair (melanotrichia) or skin (melanosis), can infrequently be seen after the skin has been damaged by inflammation.

RINGWORM

Ringworm (dermatophytosis) can be quite common in racing establishments where young horses mix and are placed under stress by increasing exercise. Ringworm is a highly contagious fungal skin infection affecting many species including horses and humans (with a potential spread between species, called Zoonosis). In the UK, it is caused by the members of two groups of pathogenic fungi, microsporum and trichophyton species.

Young animals are more susceptible, probably because of reduced exposure to the fungus, but any age group may be affected. Horses can be re-infected, but these re-infections are usually of less severity and shorter duration.

?Clinical signs

The early signs of a ringworm lesion are a circular, tufted area of hair; most commonly seen on areas subjected to local trauma, such as from tack, horse clothing and riders’ boots. These tufted patches of hair stand up against the lie of the coat, and close inspection will reveal a cigarette ash-like deposit between the hairs. The hair in the centre will then be killed by the fungus and fall out to reveal scaly, flaking skin beneath.

These lesions may occasionally be itchy, and some will progress to show reddening around the scaly patch and these lesions often coalesce, losing their circular appearance, especially with further local trauma, from the girth or neck of a rug for example.

?Diagnosis

The presence of ringworm can be confirmed by microscopy of a skin scraping to look for spores or by culture on a special medium in the laboratory.

?Treatment

Ringworm is often a self-limiting disease with spontaneous remission occurring after a period of weeks. Its occurrence can be a sign of underlying immunosuppression in a racehorse due to the stress of the training environment. Treatment of any underlying disease in affected horses is indicated.

In a racing yard therapy is occasionally required as it can shorten the course, and reduce the severity of, the disease, as well as reducing environmental contamination and the spread of the problem to other horses in the yard. Topical treatment of the horse with antimycotic agents (anti-fungal agents) and an oral antimycotic agent may be prescribed for use in feed.

Current BHA rulings bar horses with active ringworm lesions from entering racecourse premises. Samples may be taken by the veterinary officer and sent to the laboratory to detect the presence of the fungus and, if present, the trainer would be fined.

?Preventative measures for ringworm control

All tack, rugs and grooming kit should be restricted to individual horses and regularly cleaned and sterilised with a fungicidal and sporocidal disinfectant.

MUD FEVER

Mud fever is a common condition of the lower limbs, especially the back legs, where the skin becomes inflamed and scabby with oozing serum; the coronet, pastern and heels of the foot may also become cracked. In severe cases the leg may swell and the horse may develop lameness. Often white limbs are affected first or more severely. It can be caused by a plethora of possible bacteria and occasionally fungal organisms.

Constant wetting due to muddy conditions in the winter is often a triggering factor, damaging the skin and allowing infectious organisms to thrive. Treatment consists of keeping the legs clean and dry removing scabs when suitable to do so. Flamazine topical cream contains silver sulpadiazine, an anti-bacterial component and the cream also moisturises and acts as a barrier for the skin. In more severe cases, systemic antibiotic therapy may be required to get on top of any bacterial colonisation.

RAIN SCALD

Rain scald is a very common condition in horses turned out over winter caused by dermatophilus congolensis. Skin wetting from rain, long dense hair coat and poor hygiene create an ideal environment for the bacteria to grow on the skin surface.

If one horse is infected, others may become infected too. Scabs cause pain and discomfort and removal of them is often resented and usually leaves a rosy-red area of skin. Treatment of rain scald involves keeping the skin dry after a careful warm water antibacterial wash. It is also important to avoid over-grooming while the skin heals; if the whole area can be clipped this will speed up the healing process. Rugs and blankets should be removed from the horse, as sweating without evaporation and extra warmth will simply encourage the bacteria.

Some cases are very difficult to manage, sometimes requiring courses of antibiotics, and affected horses may get repeated episodes.

FOCAL ACNE-LIKE DISEASE

Focal acne-like disease is when pustules or “spots” develop in the skin; there may be few or many lesions. It is usually caused by staphylococcal infection, and usually a painful dermatitis, most often affecting the back, loins, withers and neck of the horse. It is common in late winter and early spring.

The combination of a long winter coat, an emerging spring coat and heavy rugs contribute to its development. Once the condition starts it can be extremely painful; the horse may resent being handled or being washed. It is common for the affected areas to expand or seem to spread. In the same way it can spread to other horses.

Treatment is always difficult as the spots are so painful. Washing with warm water and an antibacterial shampoo is helpful. Hygiene is imperative to prevent spread on the horse or to other horses.

CRACKED HEELS

Cracked heels are relatively common in racehorses. They form on the back of the pastern just above the heel bulbs. They appear to be a multi-factorial disease. They almost solely appear in horses that are cantering and improve quickly if a horse stops cantering.

Prolonged periods of wet weather or wet conditions underfoot seem to increase the numbers of cracked heels. Feet that have been allowed to become too long or boxy seem to be predisposed to forming cracked heels as the poor foot balance causes folds of skin to form on the back of the pastern. Bacterial or fungal infection within these folds of skin cause greasy exudates and scabs to form and, in more severe cases, fissures in the skin form which are quite painful for the horse.

Treatment involves good hygiene cleaning and drying of the heels, attention to regular trimming and shoeing of horses and application of barrier creams for exercise. If the cracked heels become badly infected systemic antibiotics are sometimes indicated.

HIVES

Occasionally reactions in horses present as raised and sometimes itchy hives. They can occur in response to insect bites or allergic reactions. These are often transient in nature but can be quickly treated with anti-inflammatory steroid injections. The skin of a horse is a good general indicator of its well-being. As Mark often says: “Looks well, runs well.”

Here at Mark Johnston Racing every effort is made to keep the horses looking their best, and any ailments are investigated and treated promptly by the in-house vets and yard managers.

Neil Mechie is a graduate of the University of London and is in practice at Mark Johnston Racing. This article first appeared in the Kingsley Klarion.