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Starting from Scratch…

Starting from Scratch: A Brief Overview of Summer Skin Complaints

Luckily for us the skin is the largest organ in the horse’s body, which means that spotting the problems with it are relatively easy.  If only it stopped there! The difficulty, unfortunately, is not in spotting the problem but in diagnosing and treating the problem.  Skin problems in horses can be some of the most frustrating and time consuming for both owners and vets alike. This is in part, down to the fact that many skin diseases, such as allergies, have a complex cause so that one treatment option is not always available or possible.

The signs of the skin diseases can vary enormously, so for the sake of this article we will only focus on a few of the more common ones.  Some of the first signs of skin disease can include, but are not limited to:

• Redness

• Large, flat, circular swellings (wheals)

• Raised nodules (with or without crusting)

• Intense itching (pruritus); this can often lead to skin damage, hair loss, secondary infections, and thickened, wrinkled skin (hyperkeratosis)

Signs of allergic skin disease in horses often begin to appear in the spring and/or early summer and become progressively worse through the hotter months.  Often horses with this history are allergic to insect bites (insect hypersensitivity). The most common of these by far is “Sweet Itch” caused by the Cullicoides species; however, any insect can be responsible and more often than not a horse will be hypersensitive to more than one insect.

Insect Hypersensitivity (“Sweet Itch”)
The best way to prevent your horse showing signs associated with “Sweet Itch” is to prevent your horse from being bitten by these insects, or at least reduce the number of bites.  Management strategies that can be put in place to help stop this are:

• Stabling your horse from 4pm – 8am when the midges are at their most active

• Using long acting insect repellent

• A direct fan can be beneficial as insects can’t fly against a strong air current

• Keeping horses away from stagnant/slow moving water, as this is where midges breed

• Keep your horses skin covered

• Use medicated treatments, but these would need to follow strict treatment guidelines to retain effectiveness

• Feed supplements can be beneficial

• Homeopathic treatments are also available

• Speak with your vet for guidance on treatment options and management

Intradermal skin testing can also help to try and detect the insect or group of insects to which the horse is most reactive. If the causal problem is determined, then a personalised injection can be made for that horse. Approximately 50-70% of horses can show a positive result to treatment but it can take 6-12 months before you begin to see the full benefit; however, it is very expensive to carry out and does come with some risks.  Another option would be reducing the immune response from affected horses through the use of systemic corticosteroids or topical corticosteroids depending on the severity of the problem.

Possible other causes of urticarial skin reactions include:

• Immunological: 

1. bacteria and viruses

2. airborne agents (pollen, dust, chemicals, fungal/mould spores)

3. feeds (barley, haylage, hay, cereal is quite often linked to being the part of the cause

• Non-Immunological:

1. Heat/cold

2. Stress

3. Extreme light

4. Physical pressure

5. Heavy exercise (particularly in extreme weather)

Recurrent Urticaria
We can now have a look at a few other summer skin complaints in horses starting with recurrent urticaria.  This can be recognised by the sudden appearance of wheals/hives in the skin, some of which may coalesce, or grow together.  This response is often seen after interaction with allergens that may have been inhaled, ingested, or contacted in the environment.  The urticaria may disappear rapidly only to recur as quickly, or it may remain present for an extended period of time.  In these cases it can be very tricky to determine the exact allergen that is causing the issue, but possible diagnosis may be made through intradermal skin testing (IDST) or by trial and error.  The latter is a fairly tedious and time consuming process whereby all possible causes of a reaction are removed and the horse is kept on hypoallergenic bedding and a hay only diet and then each allergen is re-introduced individually.  This can obviously be very difficult to do in real terms but if possible can yield very accurate results.

Dermatophytosis (Ringworm)
Ringworm is characterized by annular (circular), patchy, coalescing, target lesions of hair loss with associated pruritus.  This skin disease is predominantly caused by the fungi Trichophyton equinum and T. mentagrophytes, however, Microsporum gypseum, M. canis, and T. verrucosum have also been isolated.  Diagnosis of ringworm is confirmed by the hair plucks from the lesions and culture of the fungal hyphae.  Transmission is by direct contact, grooming with contaminated instruments, or tack.  Treatment involves topical washes with fungicidal treatments, disinfection of all tack and equipment and isolation of the affected animals.

Dermatophilus (“Rain Scald”)
Dermatophilus or “rain scald” occurs in warm, damp conditions, for example, if a horse is turned out without a rug in rainy conditions for an extended period of time and their skin isn’t accustomed to this, or if a horse is left with a rug on in warm conditions for an extended period of time and sweats repeatedly.  It is caused by the bacterium Dermatophilus congolensis (the same bacteria involved in “mud fever”) but is often mistaken for a fungal disease.  The bacteria live on the outer layer of the skin and infection usually leads to large, scaly, crusty lesions, when these are removed the base of the hairs can be seen sticking through the scab.  In cases seen earlier then topical treatment and removing the scabs should be sufficient to treat the problem, but if the problem has progressed to the deeper structures then antibiotics may be required.

Your veterinarian should be an active partner in diagnosing and treating skin disease, particularly one that doesn’t resolve quickly.  By carefully examining your horse and following the progression of the skin lesions, you can help your veterinarian choose a place to perform a skin biopsy – the best diagnostic procedure for troublesome or persistent skin disease.  Once a diagnosis is made, then specific, targeted treatment can be instigated to resolve the problem.

 

James Evans BVetMed MRCVS Technical Manager Global Herbs 
James qualified from the Royal Veterinary College, where he then became part of the Equine Referral Hospital team as one of the Junior Clinical Training Scholars. He then worked at various practices in the Home Counties, working with some of the top polo teams, event, and competition horses in the world. It was during this time that James developed his interest in complementary medicine and nutrition and went on to develop extensive understanding of the needs and requirements of all varieties of horses. He is now the Technical Manager at Global Herbs Ltd. James is an FEI Permitted Treating Veterinarian, he presented his research project at the International Congress on Equine Locomotion in Stromsholm, Sweden and has also been published in the Equine Veterinary Journal.
He is also operates the advice line for Global Herbs and is available for technical advice on 01243 773363