Scratches — several names, several causes

Due diligence Once the horse is placed in a favourable environment 
a variety of treatments can be undertaken

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Scratches, greasy heel, mud fever, mud rash, or equine pastern dermatitis are all various names for a skin condition that occurs on the backside of a horse’s pastern. The area of skin on the underside of the pastern becomes inflammed and ulcerated, oozing and weeping to form scabs and crusts.

The thick, crusty, black scabs often coalesce in a linear fashion across the back of the pastern region resulting in the name “scratches.” As the lesion progresses, crusty, black scabs become generalized across the back of the pastern, occasionally including the bulbs of the heel and/or fetlock. If left untreated lameness may occur. This location is particularly tender, continually flexing as a horse moves.

Horses with white feet seem to be more prone to scratches as unpigmented skin is more sensitive to environmental agents than skin of a darker colour.

Scratches has many contributing factors and generally investigation is necessary to uncover the actual problem that initiated the skin condition. Fungi and bacteria bear the brunt of the blame, yet that an infection exists is only partially true. Often underlying causes occur first, weakening the immune system, and so creating an opportunity for the existence of fungi and bacteria to take hold.

Weak immune systems, overactive immune systems, photosensitivities, allergies, poor or improper nutrition, dietary intolerances, overburdened livers and even copper deficiencies can predispose a horse to scratches. Since the skin only has a limited number of ways to express irritation it means that a myriad of conditions can present themselves as scratches.

Horses living in unrelenting wet or muddy conditions are especially vulnerable to the development of scratches. The incidence of scratches also increases during July and August when morning dews are heavy. Dampness softens the delicate pastern skin, weakening skin barriers. In addition a fungus found on mature clovers favours these environmental conditions, exposing the horse to a greater-than-normal fungal burden.

Treatment

Due diligence is often required to uncover the underlying conditions that contribute to and masquerade as scratches. Some cases are simple and respond to good hygiene. Removal of the horse to a clean, dry area brings relief to the sensitive skin. Additionally, it is advisable to remove affected horses from pastures laden with clovers and alfalfa as some horses can develop scratches from a dietary sensitivity to such legumes. Clinically this sensitivity can appear as scratches.

Once the horse is placed in a favourable environment a variety of treatments can be undertaken to care for the skin lesion itself. Salves and ointments containing antibiotics, anti-fungals, carrying agents such as DMSO, and anti-inflammatories can be used as medications.

Another equally effective method is to apply a poultice bandage to the area, drawing out inflammation and toxins. Although it is tempting to clean the affected area of scurf and scabs, it can be very painful for the horse. A soothing poultice bandage will soften the crusty debris, allowing for a thorough cleansing of the affected area once the bandage is removed. While medicated salves and ointments can effectively treat the affected region it is helpful to remember that symptoms may continue to reappear until the underlying problem is addressed.

Since bandages hold in dampness it is best to minimize their use. Once the affected area is clean, creams used to treat diaper rash in babies can be applied to the affected skin to form an effective soothing barrier from dampness until the horse fully heals.

About the author

Contributor

Carol Shwetz is a veterinarian focusing on equine practice in Millarville, Alberta.

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