Patchy Hair Loss

I noticed that my Arabian mare was missing a patch of hair under her mane at the beginning of the summer. Since then, the spot has gotten larger. What causes this? How can I treat it?

Hair loss in the horse can be caused by something simple, such as environment and temperature, or it can be caused by a more serious dermatophyte (fungus), such as ringworm, that invades the hair follicles of the skin.

There are three phases of hair growth in the horse. Anyone who has clipped his or her horse closely in the winter months, or has clipped the hair from around a wound, has noticed how the hair has a growth period (anagen), a resting period (telogen), and a time when the horse sheds as new hair arrives. Generally, it takes three to six weeks for hair to grow after it has been lost, although that time varies in each individual and is dependent on genetics. Horses will shed their hair seasonally as a result of changes in the length of daylight. Adjacent hair follices tend to be in different phases of the growth cycle, so that no obvious shedding or bare spots are observed. You are used to seeing such cycles, but what happens when suddenly your horse has a completely bare spot?

If the area of hair loss is under the mane, it could be for a very benign reason encountered by many stables during the summer. Excessive sweating during hot or humid times of the year will occur where heat is trapped under the mane. Sweat is absorbed by the keratin layer of the epidermis, and the hair follicles remain moist for the duration of the hot weather. That moisture causes the hair follicle to soften and release the hair.

The high protein and salt content in the horse’s sweat also can dry in contact with the horse’s skin and cause irritation, which can lead to hair loss as well.

Hair loss due to heat and sweat also is commonly observed on the faces of horses, around the eyes and the ears. This pattern of hair loss is many times the result of some horses’ aversion to having their faces washed during a bath or after hard work. The sweat and dirt accumulate, spurring the loss of hair, and the horse appears as if he is wearing gray goggles.

Proper management, careful grooming, and thorough weekly washing of the horse can help prevent hair loss due to the aforementioned reasons. However there still are many horses which might glow with regular care and grooming, but lose areas of hair anyway. The owner, while doing his/her best to prevent the cycle, might eventually have to accept this as normal for the horse. Horses with long manes for show purposes, like the Arab mentioned in the question, might fare well with their manes French-braided to avoid having the heat trapped against the neck. Small individual braids will break the hair, but a French braid directly down the top of the neck that is redone every few days will keep long manes intact.

Other, more serious hair loss can stem from dermatophyte infections. If there is crusting associated with hair loss (along the leading edge of the bald area), the owner might be dealing with a dermatophyte such as ringworm. Before purchasing and applying products for these conditions, you should make sure that is, in fact, the cause of the hair loss. Your veterinarian will pluck some hair and put it in dermatophyte test media (DTM). This substance costs around three dollars for a jar and has a color indicator that will decipher whether the fungus is the airborne type that lands on hair all the time, or if it’s a serious dermatophyte that requires more rigorous treatment.

There are a number of topical antifungal agents that will help with ringworm and other fungi, most of which are available over-the-counter from your drugstore or pharmacy. Some veterinarians use iodine or prescription anti-fungals. It is not recommended to use home remedies such as Clorox, as these agents will burn the skin.

For proven ringworm, a problem arises when topical anti-fungal ointments sit on top of the skin and surrounding hair and do not reach the hair follicle, where it is needed. A soft toothbrush will solve this matter if used to brush the medication in at the base of the hair. Here are the steps for effectively treating a fungal condition:

  • Wash the area with Palmolive dishwashing liquid (the green formula), as other brands are too drying on the skin, or use a commercial horse shampoo without additives that might irritate the skin.
  • Dry the area with a clean towel.
  • Using the soft toothbrush, brush the medication in to the affected area, making sure that the medication is not just "sitting on top" of the area.
  • Most importantly, communicate with your veterinarian about the condition and avoid home remedies. Your veterinarian will be able to advise you on the best course of treatment for your horse’s individual hair loss problem.

About the Author

Susan L. White, DVM, MS, Dipl. ACVIM

Susan L. White, DVM, MS, Dipl. ACVIM, is a professor at the University of Georgia College of Veterinary Medicine.

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