Lice and ticks and horses

Horse Health: Horses that have stressed immune systems are more vulnerable

Lice and ticks are unwelcome guests on horses and donkeys, taking up residence in the warmth of their thick winter coats with peak infestations occurring during the late winter and early spring.

Horses infested with lice are intensely itchy, and often the first sign of trouble is a tattered hair coat — or perhaps extra dandruff or “scurfy” stuff noticed during grooming. As infestation progresses the hair coat becomes increasingly matted, unkempt, and “moth eaten.”

Horses become anxious and irritable, scratching, rubbing, and biting at the skin. This behaviour quickly leads to hair loss/alopecia, scarring and inflammation of the skin, and self-mutilation. With severe infestations horses may lose condition and become depressed and lethargic.

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Generally horses that have immune systems depleted from stressors such as overcrowding, underlying health issues, poor feed quality or age are the most susceptible to infestations. However, even healthy well-cared-for animals can become infested as the little parasite is not too terribly choosey as to who it infests.

Lice are predominantly found under and around a horse’s forelock, mane, tail, and the feathering of the lower limb. If present, the lice can be found by parting the hair of the horse and examining the skin and coat with the aid of a light source and, if available, a hand-held magnifying glass. Fully grown, the louse will be only two to four millimetres in length, making them slightly difficult to detect with the naked eye.

Two types of lice infest both horses and donkeys — the sucking louse and the chewing/biting louse. The sucking louse is the larger of the two lice with a dark nutmeg to dirty grey-coloured broad body and a long pointy narrow head. Their mouthparts are adapted to piercing the horse’s skin and sucking blood. With severe infestations, blood loss can be substantial, causing the horse to become anemic and weak.

The smaller chewing/biting louse is yellow brownish in colour with a wide body, marked with dark cross-bands. Its head is broad and rounded with a snubbed nose. These lice feed on the dander, scales, and scurf of the horse’s skin. In contrast to the stationary sucking louse the chewing louse is active, crawling around on the horse’s skin.

Both species of lice have a simple life cycle. They glue their tiny cream-coloured eggs, called nits, near the base of the horse’s hair shafts. The young hatchlings, called nymphs, mature into the adults within two to four weeks.

Lice are easily spread from one animal to the next through direct contact. They can also be easily transferred between horses by things the horses have direct contact with such as shared grooming tools, tack, and/or a favourite scratching post.

Lice need the warmth and food supply of their host and are unable to survive off the host for much longer than two to three days. Therefore severe cleaning of the environment with infestation is not necessary however, a thorough cleaning of those things in close contact with the horse, such as grooming tools and blankets is advisable. Fortunately lice are host species specific, which means horse lice prefer horses and will not infect humans, dogs, cats, etc.

The only approved product for the treatment of horses with lice is a pesticide dusting powder; it is the treatment of choice under winter conditions.

All other products are used in an off-label or extra-label manner and veterinary supervision is advised, if chosen. Control of lice is challenging because pesticides kill the lice but not the eggs.

Therefore re-treatment will be necessary two to three weeks later to successfully kill the hatchlings. Be generous with the dusting powders, taking precautions not to inhale the dust and using gloves to work the dust thoroughly into the thick winter coats. All horses in contact with the infested horse may need to be checked and treated if necessary.

For reasons not completely understood, a few animals remain as a reservoir for a small population of surviving lice, despite treatment. These animals can then reinfest larger numbers of animals when conditions become opportune.

Horses in Alberta can also occasionally get winter ticks. The preferred habitat of the winter tick are members of the deer family such as deer, elk and moose. Horses are marginal habitat for the winter tick so numbers of individual ticks generally remain low.

The adult female tick lays eggs in the vegetation and the infective larvae gather on plants in hopes of catching a ride on a suitable host as it passes by in the brush. Once on the host, the larvae engorge on blood meals and mature into the adult form around March and April.

The females become grossly engorged with blood before dropping off onto the ground to lay eggs and begin their cycle over once more. Engorged female ticks can swell to two cm in size, and look similar to a purple grape with eight legs. When present, these ticks can be found under the mane, near the withers or in the ear. The winter ticks pose no major threat to horse or human health and can easily be removed with a pair of tweezers, ensuring to remove all of the embedded mouthparts.

About the author

Contributor

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

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