Hair Loss in Itchy Horses August 29 2018

by Michael Lowder, DVM, MS

Everyone at the barn is talking and your horse has it. But what is it? They walk around the corner talking and pointing at 'Trigger' like he is from Mars!

Hair loss is a common finding among horses during the summer months. Lesions can range from a single blemish to a general spottiness. Some areas may include scaling, irritation, and even seeping sores due to secondary bacterial infection. Some skin conditions appear to be extremely itchy and others are just imperfections in your otherwise healthy equine.

Hair Loss in Horses

Before a diagnosis can be made, a complete history and physical exam is necessary. Once all information has been gathered, a list of the possible causes (commonly referred to as ‘rule outs’ or differentials) for the hair loss can be formulated. Again, the history is an important element of diagnosis. Some of the pertinent questions regarding the condition include:

1. How long has the hair loss been occurring?

2. Does it itch?

* If so, was it itching from the beginning?

3. What treatments have you tried?

* Did they help?
* If so, for how long?

4. Is the horse currently on any treatments?

5. What changes in the environment and/or feed have occurred?

6. Are any other horses affected?

Once it has been determined if itching (pruritis) is involved, then the rule outs can be divided into two groups: itching and non-itching. We will cover the itching diseases this week.

Hair Loss In Itchy Horses

1. Culicoides hypersensitivity

2. Cutaneous onchocerciasis

3. Fly dermatitis (Horn flies are common)

4. Pinworms (oxyuriasis)

5. Lice (pediculosis)

6. Mange

7. Chiggers (trombiculid)

8. Ringworm

Culicoides hypersensitivity is one of the most common summer skin diseases. This condition, often referred to as “sweet itch”, is an insect hypersensitivity to the Culicoides species of fly (often called sand flies, “no-see-ums” or midges). They are active during the summer, thus would not be a cause of hair loss in the cooler months. Hair loss is common on the neck, face and underside of your horse. It is also manifested as tail rubbing resulting in the classic “rat-tail” appearance. Itching can be mild to moderate in most cases.

Pinworms (oxyuriasis) are generally seen in stabled horses and are easily treated with a good dewormer (ivermectin or pyrantel). Pinworms cause a persistent irritation to the anus and tail head.

Tail rubbing may be a learned behavior, and some horses will rub their tail out of habit. The best prevention is placing them in the pasture or installing a board (a 2×6 parallel with the ground) in their stall about 8-10 inches below the tail head. Doing so will keep your horse’s tail head off the wall.

Cutaneous onchoceriasis is a parasitic disease that can cause bald spots on the horse’s face, neck and belly with mild to moderate itching. It is infrequently seen this day and time due to the effectiveness of the ivermectin-based dewormers.

Fly dermatitis is very common in horses that are pastured with cattle or in stables with poor fly control. Although a fly problem is easily observed, it is often hard to control. If flies cause your horse’s skin condition, you must eradicate the flies in your stable. Treatment without fly control is fruitless.

Lice infestation (pediculosis) is usually observed during the winter and spring months when your horse has a long winter coat. Treat the environment (stall, brushes, and tack) with water based insecticides twice a week for two weeks. Deworm your horse with an ivermectin product once, then four days later, and again two weeks later. Itching and hair loss is moderate to severe.

Mange! Oh what a dreaded word. It brings the worst to mind and rightfully so. There are four basic types of mange that horses get: chorioptic, demodectic, sarcoptic and psoroptic.

Chorioptic mange is commonly referred to as ‘foot or leg’ mange and is most frequently seen in draft or draft type horses. Affected horses will have extreme itching of their legs.

Demodectic mange is rare in horses. Horses generally show signs of alopecia (hair loss) and scaling of the head, neck and withers. Itching is variable with each individual. There is no effective treatment in large animals. Spontaneous resolution may occur.

Sarcoptic mange is a very uncommon contagious disease of horses. Again, these horses itch like crazy. The mite is usually on the head and ears but may infest the entire body. Treat with an ivermectin product once every two weeks for three treatments.

Psoroptic mange has been eradicated in horses in the United States. The major clinical signs in horses are intense itching. The mite is commonly found around the ears.

Chiggers are most commonly seen in horses that have been in wooded areas, but the mite may plague horses that are taken through infested fields. Chiggers are active in the late summer or early fall.

Papules may be found on the face, neck, legs, and belly of the horse. Affected areas may or may not itch. Close examination of a papule will show the red mite at its center. The disease is self-limiting due to the short life span of the mite. Note that horses may become re-infested if kept on the same infested pastures.

Ringworm (dermatophytosis) is a superficial fungal infection of the skin. It is most often found in young horses but can be seen in any age horse. Lesions are most commonly seen on the head, neck, shoulders, and sides of the chest. Initial infection in the horse may look like an allergic reaction in the sense that there are small circles of ‘erect’ hair. Within 1 or 2 days, these circles will progress to the more characteristic lesions with scaling, crusting, and hair loss. About one third of horses have itching associated with this condition.

This disease is self-limiting in most cases but can be treated with various products. Ringworm is contagious to stablemates and their human companions. Sunshine is a good old-fashioned treatment.

Now you can see the complexity in diagnosing what condition your horse may have.

Article courtesy of: Horse City


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