Some of the skin problems that can plague a horse in winter are ringworm, lice, and mites.
Ringworm is a skin disease caused by a fungus, and many kinds are contagious to other animals and to humans. The fungus sends out spores, which start new infections when rubbed into the skin. Brushes, tack, and other equipment used on more than one animal can spread ringworm.
After spores enter the skin, the fungal infection begins in a growing hair, causing it to break off just above the skin surface or in the outer layer of skin. Lesions appear within a week to a month as circular areas in which the hair falls out or breaks off. Sometimes thick crusts form. One type of ringworm produces small round lesions a quarter inch to an inch in diameter, eventually forming blisters that break and leave scabs. This form of ringworm causes intense itching and can be transmitted to humans.
Another type of ringworm (which can be spread by rats and mice as well as horses) creates lesions that appear on the forehead, face, or neck and sometimes at the root of the tail, but can spread to other parts of the body as well. The fungal growth expands from the center of each lesion outward, spreading from the edges. The lesions are gray and form crusts on their surfaces; broken off hair may protrude from the crusts. Another form of ringworm (which also affects dogs as well as horses and humans) produces small round lesions covered with tiny scales.
Incubation time for the various types of ringworm fungi can vary from as little as four days to as long as a month. If one horse in a group becomes infected, the fungus can spread to the rest, so take precautions to keep the other horses from getting it. Isolate an affected horse. Treat and disinfect saddle pads, grooming tools, and anything else that might be used on more than one horse. Treat the affected horse. Many topical medications (fungicides such as povidone iodine, chlorhexadine solution or ointment, or Captan) can be effective.
Some individuals seem more susceptible and get ringworm readily, while other individuals never do. Ringworm is most likely to appear in winter. Sunlight and heat inhibit the fungus.
Lice are also mainly a winter problem. Warmth and sunshine slow them down, and short hair does not provide a good environment for reproduction. They thrive in cold weather when hair is long.
Lice are tiny insects that spend their entire life cycle on the host. The eggs, called nits, are laid on the hairs next to the skin. Then there are three nymphal stages before the mature lice emerge to feed on the horse’s skin. Lice are transferred from one horse to another by direct contact or by harness, grooming tools, blankets, saddle pads, etc. Horse lice are not the same as cattle or human lice. Lice from other animals such as cattle will not infest a horse, nor is there any danger of humans getting lice from horses. A horse can get lice only from another horse or occasionally from chickens.
There are two basic kinds that infest horses: Hematopinus asini (sucking lice) and Damalinia (Bovicola) equi (biting lice). Sucking lice feed on the horse’s blood and in severe infestations can cause anemia due to extensive blood loss. Biting lice cause more skin irritation and itching as they feed on skin cells and secretions from oil glands in the skin. The horse may rub and bite at the affected areas, which may become hairless or raw.
You can usually see the lice if you raise the horse’s mane and part the hair underneath it with your fingers. The lice will be down on the skin between the hairs. A magnifying glass makes them easy to see. The hair comes out easily where lice have been feeding. Those areas often have greasy skin and heavy dandruff.
Horses rarely suffer lice infestations at pasture during summer; lice are mainly a problem in confined horses during the short, cold days of winter. Several sprays and dusts can help eliminate lice. If weather is cold, use a dust rather than a spray so the horse won’t become chilled. Follow label directions and treat the horse in an area where there’s no risk for contaminating feed or feeding areas. A second treatment two weeks later is needed to kill lice that hatch after the first treatment (the eggs may not have been killed). Brushes, blankets, or tack used on the infested horse also should be treated before being used again.
