Winter skin disease in horses

Woman_wHorse_Retouched_blogIt seems like just last week we were outside in short sleeves enjoying beautiful autumn days, but winter will soon rear its sometimes-ugly head in the Northern Hemisphere. With the cold season comes the host of winter dermatologic problems affecting our horses. The increased rainfall (for those not in the crisp, snowy northern U.S.), decreased sunlight, increased confinement and long hair coats of winter, predispose horses to a variety of issues from fungal infections to parasitic infestations.

Rain Rot, Pastern Dermatitis

Rain rot (rain scald) is a bacterial infection caused by the bacterium Dermatophilus congolensis.  This bacterium invades compromised skin and can result in large areas of hair loss and crusty scabs.  While generally not itchy, these lesions can be painful to the animal.  Treatment involves topical disinfectants, shampoos and sometimes antibiotics and immunostimulants.

When the same bacterium invades the pastern and coronet, the result is known as pastern dermatitis (mud fever, scratches).  Thick crusts form on the skin located on the back of the pastern and heels.  These painful scabs fall off to reveal inflamed skin beneath. Some horses are particularly susceptible to pastern dermatitis and can develop thickened scaly skin in the area with frequent exudate in scales forming. Most cases of pastern dermatitis will resolve when the horse is removed from wet environments, but cases may require treatment with immunostimulants, antibiotics, shampoos and antibiotic ointments.  Make sure to wear gloves when working with these horses as it is possible for humans to contract the infection.  Also, be careful to dispose of the scales and crusts coming off the horse as these can remain infective for an extremely long time.


Lice love the long winter coats horses grow and can be transferred directly from horse to horse or through shared equipment and tack. Affected horses are intensely itchy with rough coats and skin irritation. Two different species of lice commonly affect horses, Haemotopinus asini and Damalinia equi.

The sucking louse, H. asini, is found around the mane, forelock, tail and in the hairs near the hoof.  The biting louse, D. equi, is found on the sides of the neck and flank. Treatment is performed with insecticides and must be performed at two week intervals to make sure any emerging lice from deposited eggs are killed.  Affected horses should be clipped to minimize reinfestation.


Ringworm is caused by Trichophyton and Microsporum species of zoonotic fungi.  Zoonotic means the fungus can be spread from the horse to other species, including humans. This highly contagious condition spreads easily within a group of horses. Small raised areas of hair loss progresses to large areas with flaky scales and scabs forming. Most cases will resolve over several months, but most owners don’t wait that long due to the extent of hair loss and the possibility of infecting others.  Topical antifungal treatments and oral antifungals like griseofulvin are used for treatment along with frequent cleansing of affected animals. Good hygiene is particularly important when working with infected horses to minimize the spread of disease to other horses and the handlers themselves.


Prevention of all of these diseases revolves around maintaining healthy skin and a clean hair coat. Keeping horses out of deep, wet mud, getting them out in the sunlight when possible and working to promote active health throughout the winter, are all important in controlling skin diseases. Healthy horses with undamaged skin are much less likely to develop dermatologic diseases. Keep a close eye under those winter blankets for any problems, because early intervention is key to minimizing the effects of disease.

Joe Lyman


This blog was written by Neogen’s professional services veterinarian, Dr. Joe Lyman (pictured left).

For more information on Neogen’s animal safety division, see our website. 

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