Skin Skin Skin

Skin Conditions by Dr Ann Blackburne

The skin is the largest organ of the body and creates a protective layer between the environment and the horse. It is also the most visible organ and therefore any problems with your horse’s skin can be easily noticed. Skin lesions may be caused by infections, inflammatory reactions, tumours and even systemic illness can manifest as skin changes.

Rain Scald

Rain scald is the common term for “dermatophilosis”. This skin infection is caused by a specific bacterial organism that is commonly found on horses and/or the soil. Prolonged exposure to wet conditions is a key factor in the development of the disease. It is common to see certain horses predisposed to the condition repeatedly affected while other horses may remain unaffected. The classical features of “rain-scald” are matted tufts of hair crusting along the back and rump. While the lesions do not appear to be itchy they can be painful. These lesions can start as small crusts which progress to larger crusts with discharge. The most important aspect of treatment is removing exposure to moisture. If the horse remains dry, some cases may heal spontaneously. However, most cases will require treatment with a topical antibiotic product such as dilute iodine or chlorhexidine wash. Soaking the lesions for 10minutes during treatment will help to loosen the crusts and aid in their removal. When removing the crusts it is important to dispose of them well as they can spread the infection to other horses. Treatment should be daily for a week and then once to twice weekly until the lesions resolve. Some more severe cases will require treatment with systemic antibiotics and therefore need a veterinary consultation. It is also important to remember that if your horse is not responding to conservative treatment that the diagnosis may be incorrect and you may need a vet to have a look.

Ringworm

Ringworm is also named dermatophytosis and is a fungal infection in the top layers of the skin and hair. This is one of the most common skin diseases affecting stabled horses. It is often found in young horses and can spread via direct contact from horse to horse. Most commonly however, it spreads via contaminated grooming equipment, rugs and saddle cloths. Horses can take up to 4 weeks to show any signs of infection after exposure. Ringworm lesions appear as circular areas of alopecia (no hair) with scaling and crusting.  They can commonly be found in the girth /saddle region. Itchiness may or may not be present. Lesions can appear quite variable and can be confused with other skin conditions, therefore a veterinary consultation may be necessary to diagnose. Once diagnosed, treatment should begin to help accelerate the healing time and reduce spread of the infection to other horses and people. The horse should be shampooed with Malaseb wash one to two times per week for 2 weeks after the clinical signs have gone. This condition can spread from horse to person therefore strict personal hygiene is important when handling horses with the disease.

Greasy Heel

Greasy heel is a common term that actually represents a complex of diseases rather than a specific condition. It is an exudative dermatitis involving the skin over the back of the pastern and fetlock. Predisposing factors include moisture, repetitive trauma, low heel conformation and white socks. Organisms involved in the condition may be dermatophilus as well other bacteria and fungi. Greasy heel on white legs have a photosensitization component that causes a local inflammation. In the early stages there may be mild dermatitis and swelling of the back of the pastern. This is often followed by secretion and exudate formation creating large scab-like lesions. Treatment involves identifying the inciting cause and removing most importantly. Cleaning the area is important and clipping the hair may be necessary. It is essential to keep the area dry and to remove all sources of moisture. Medicated washes will help along with antibiotic cream with a corticosteroid in it to reduce the inflammation. Severe cases may need treatment with systemic antibiotics as well.

Contact Dermatitis

Contact allergies can occur in horses when the skin is in contact with various plants, chemicals and/or medications causing local inflammatory reactions. Skin lesions may appear as wheals, raised areas, reddened areas, exudation and may or may not be itchy. Some horses will get a reaction when exposed to a new plant or chemical for the first time; however horses can also develop contact hypersensitivity reactions after long-term exposure to tack, plants, bedding and shampoos etc. The muzzle or pasterns are often affected if plants are involved. Removing the causing agent is critical to effective treatment as well as topical antibiotic/steroid ointments and possibly systemic anti-inflammatory medication.

Qld Itch (“Summer Itch”, “Sweet Itch”)

Qld itch is a hypersensitivity reaction to the biting midge Culicoides. Insect hypersensitivity tends to be a seasonal problem, more commonly noticed during the summer months. It is often noticed in horses less than 4 years of age, however it can start at any age. This disease is extremely itchy and the lesions noticed are often due to self trauma from scratching. Affected horses can scratch off much of their mane and tail and have areas of alopecia (hair loss) across the midline of their back and ears. Horses that have been affected for years will tend to have thickened, dry scaly skin over these areas sometimes with a darker colouring to the skin. These typical lesions and seasonal incidence are suggestive of insect hypersensitivity, however there are occasionally other skin disorders including food allergy that may present similarly. Insect control is the crucial part of management of Qld itch and if done effectively will allow complete resolution of the disease. Regular use of a veterinary specific insect repellent as well as rugging and stabling often provides effective control. Secondary bacterial infections can occur and may also need to be treated. Some horses may also need treatment with systemic antiinflammatories/ long acting corticosteroids to help reduce the extreme itchiness seen with this disease.

Sarcoids

Sarcoids are unique skin tumours of the horse and are very common in horses less than 4 years old. They can present as single or multiple growths and can vary greatly in appearance. Some sarcoids may appear as raised wart-like growths while others may look ulcerative and appear similar to proud flesh. They can also appear as flat dry areas with crusts and alopecia (no hair) that may sometimes be confused with a fungal infection that does not respond to treatment. Sarcoids are commonly found on the head and on the legs or under the belly of horses. While sarcoids are not malignant, they are very persistent and can be locally aggressive. Surgical excision with good margins is the treatment of choice, however sometimes this is not possible due to location and size. Other therapies are available through veterinarians. We recommend the removal/treatment of all sarcoids.

Squamous Cell Carcinoma

Squamous cell carcinoma is a very common and aggressive tumour in the horse. Lesions can commonly be found on the head, third eyelid, genitalia and any unpigmented area of skin. This skin tumour can be malignant and may spread secondary tumours to other parts of the body. It is important to diagnose squamous cell carcinomas early and remove them with good surgical margins if possible.

Melanoma

Melanomas are benign or malignant tumours that arise from pigmented skin. They are common in older horses and are almost exclusively seen in grey horses. Melanomas are usually firm and nodular and may be alopecic, ulcerated and black in colour. They commonly develop around the base of the tail, around the throat area, and on the legs. Many melanomas will only be surgically removed if they are causing a problem due to size and location or if they are rapidly growing. Many horses can live with multiple melanomas for years without problem.

Proud Flesh

Proud flesh is the common term for excessive granulation tissue. This typically occurs on the legs and is secondary to a healing wound. It can be treated with surgical excision and the use of an astringent such as lotagen. Veterinary advice may be advisable for diagnosis as sarcoids can appear very similar to proud flesh.

Parasites: Onchocerciasis

Onchocerca is a parasite that infects horses worldwide. Adult worms live within the neck of the horse and larval stages of the worm migrate through the connective tissue and localize in the skin. Itchy skin lesions occur over the abdomen, head and neck. Lesions can be singular or widely spread and are often round, inflammatory lesions of alopecia, scaling and depigmentation. Treatment with an Ivermectin based parasite control product should resolve clinical signs.

Ticks

Ticks are a very common external parasite in certain geographical regions. There are multiple species of ticks ranging from paralysis ticks to cattle ticks. Adult horses can react to even very small larval ticks with large lumps and extreme itchiness. You may not be able to see the tick easily due to the small size, however one or multiple lumps may be noticed. Ticks can be controlled with a number of spray-on products available from most produce stores and veterinary clinics.

Nodular Necrobiosis (Equine eosinophilic granuloma)

Nodular necrobiosis is a very common skin disease in horses. While the disorder is not totally understood, it is probably related to a hypersensitivity to insect bites. It looks like small, circular, firm nodules (raised lumps). There may be one or multiple nodules that vary in size with no ulceration or loss of hair. Lesions occur most commonly on the withers and back and can also be seen on the face, rump, mane and girth area. Horses are not itchy or painful over the lesions. Skin biopsies may be necessary to differentiate this disease from others. Surgical excision is one treatment option; however injecting the nodules with corticosteroids may be less invasive and just as effective.

Photosensitisation

Photosensitisation can produce an inflammatory skin condition due to exposure to UV radiation (sunlight). Generally white areas of the horse that are sparsely haired or non-haired are affected. Pigmented areas will appear unaffected because they do not absorb the UV light. This condition can be caused by primary ingestion of a photosensitizing agent eg.toxic plants, certain drugs, or secondary to liver disease. Lesions will appear pink to red with swelling and progress to erosions and ulcers with crusting and scaling. These lesions can become very severe and affected areas of skin may slough. It is extremely important that a thorough investigation is conducted to identify and ideally remove the source of the photoactivating agent.

Selenium Toxicity

Selenium toxicity is a rare but serious condition where horses are over-supplemented or graze on certain plants that accumulate selenium from the soil. Horses become emaciated with a dull hair coat, lose hair from their mane and tail and may even slough their hooves.

Because the skin has a fairly limited repertoire of changes, many different conditions may appear superficially similar. Any given lesion may have multiple causes and once skin conditions become chronic they can appear very similar. It is therefore important to have a veterinarian take a look at any skin changes when you first notice them so that they can be correctly diagnosed and treated.