Horse Parasites Enjoy Winter, Too!

Horse with heavy winter coat.
Horse with heavy winter coat. Soren Juhl

Much attention is paid to internal parasites in horses, but external parasites are not only a nuisance, but can also be a source of serious health threats to horses. During cold winter months, most horse owners think that the cold will keep the parasites away, but some find happy camping grounds when hair is longer.

A horse bot fly.

A horse bot fly

The discomfort and health threats from ticks, lice, mites, and biting flies continue to affect horses in cold weather.
© 2015 by Janet Graham

In addition to the well-known threats from mosquitoes and ticks, the discomfort and health threats from lice, mites, and biting flies continue to affect horses during winter weather.


Two types of lice affect many areas. The biting louse and the blood sucking louse are the two types often found on horses. The blood sucking lice are more injurious because heavy infections mean a heavy loss of blood that may seriously weaken animals.

Lice occur in largest numbers in the winter months when the hair is long. Infections spread from animal-to-animal in adjacent stalls around managers.

Sucking lice are usually found on the head, neck, back and inner surface of the thighs. Biting lice may be found any where on the body, although they seem to occur in greatest numbers around the withers and the base of the tail. The biting lice feed on the hair and scales from the skin.

Mites - Horse Mange

Mites cause skin diseases known as mange, barn itch, scab and scabies. Transmission is by direct contact between healthy and infested animals, or by means of contaminated equipment.

Horses seek relief by rubbing affected areas of the body against any available object. The constant rubbing will cause skin to become swollen and inflamed and sometimes cause skin to rupture.

Biting horse flies

Several kinds of flies suck blood from horses. These include bot horse flies, horn and deer flies, stable flies and in some cases, black flies. The main damage that these flies do is annoyance to the horse although injuries to the skin from bites may become infected and some, such as the bot fly deposit eggs and developing larvae that invade the horse's skin and digestive systems.

Controlling these parasites leads to greater comfort and health for your horse. Methods vary, according to the individual parasite and many commercial products including shampoos, sprays, and insecticides are available aimed at external parasite control. In addition, horse owners should make sure that breeding sites for parasites are cleaned up regularly.

Updated article first posted in 2013

About the Author

Flossie Sellers

Author picture

As an animal lover since childhood, Flossie was delighted when Mark, the CEO and developer of EquiMed asked her to join his team of contributors.

She enrolled in My Horse University at Michigan State and completed a number of courses in everything related to horse health, nutrition, diseases and conditions, medications, hoof and dental care, barn safety, and first aid.

Staying  up-to-date on the latest developments in horse care and equine health is now a habit, and she enjoys sharing a wealth of information with horse owners everywhere..