Lice alert! - The Horse Owner's Resource

Lice alert!

Under the right conditions, any horse can pick up lice, and treating a case is a hassle. But you can take steps to prevent a serious infestation.
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It’s not a question of IF your horse will get lice, it’s WHEN your horse will get lice.”

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The text on the website seemed to shake its finger at me accusingly. This couldn’t be true. This couldn’t be happening to my horse ... could it?

I’ve owned horses for almost 20 years. I won’t suggest that I am an especially superb owner, but I do provide attentive care. For the past six years, my horses have lived at home with me on our small farm. Seven days a week, 365 days a year, I provide feed, supplements and fresh water; I groom; I turn out and bring in; I muck pastures, I muck stalls two to four times a day. I keep up with deworming and vaccinations, and my horses receive routine care from a veterinarian and a farrier. I spend one-on-one time with each of my horses daily. I probably give them far too many treats.

Like many horsepeople, I had always believed that lice occurred only on neglected horses, those who weren’t properly groomed or who were kept in unhygienic conditions. Certainly, I had never heard of any cases of lice among the many pampered horses I had known over the years. Yet here was the evidence right in front of me on the computer screen: The source of my Miniature Horse’s constant itching was, almost certainly, lice.

I was about to start learning quite a lot about equine lice---how to recognize a case and how to treat it. But as I did my research I also discovered many myths and misconceptions. While it is true that a serious lice infestation is more likely to take hold in an unthrifty or neglected horse, if there was one important lesson I learned, it was this: A case of lice can happen to any horse, even those who have good care and are otherwise healthy. What’s more, I was delighted to find ways to help prevent future outbreaks. And, I hope, so can you.

Catching the bugs

Lice infestation, called pediculosis, is common among horses all over the world, especially in temperate climates. Lice are tiny, wingless insects called ectoparasites---parasites that live on the exterior of the host. Two different types affect horses, distinguished by their source of nutrition.

Sucking lice (Haematopinus asini) feed on blood by embedding their mouthparts into the roots of a horse’s hairs. Generally, they prefer to be in areas where a horse has longer, coarser hair, such us under the forelock and mane, the tail and under the pasterns of long-feathered horses. These lice are about an eighth of an inch (1 to 2 mm) in length, with a large, broad abdomen behind a narrow, pointy thorax and head. Their color has been described as yellow-brown, dark nutmeg brown or dirty gray in color. To find them, part the horse’s hairs all the way to the skin. The insects will be stationary, not moving around.

In contrast, chewing lice, Bovicola (Werneckiella) equi (formerly Damalinia equi), tend to crawl around on a horse’s skin. These lice feed on the horse’s dander, and they prefer to live in the finer hair on the head and neck as well as in the mane and on the flanks and croup, and at the base of the tail. Chewing lice are smaller than sucking lice, and about a tenth of an inch (less than 2 mm) long, and are figure-eight-shaped, with a large, round head on a narrow thorax and wide abdomen. Their coloring ranges from cream-colored to yellow with dark crossbands.

Both species have a similar life cycle. They glue their eggs, called nits, near the base of the horse’s hair shafts. The tiny, whitish, semi-transparent elongated ovals can be seen by the naked eye; however, they are easier to spot with the help of a hand-held magnifying glass or a light microscope. Sucking lice nits hatch in 11 to 20 days, while chewing lice nits typically hatch after five to 10 days.

The immature nymphs resemble small adult lice and feed in the same way. Over the course of three to four weeks, a nymph will molt three times before becoming an adult louse. The adults survive to feed, reproduce and lay eggs for about one month. The total life cycle can vary between 20 to 40 days.

Lice cannot jump or fly, and it wouldn’t be unusual for multiple generations of the insects to spend their entire lifetimes on one animal. However, they can also spread easily to other horses in the herd---if horses rub against each other directly, or if one rubs against a fence post where another just left behind some nit-laden hairs. Lice can also be passed from horse to horse via shared tack or other grooming tools or equipment. In the right weather conditions, adult lice may be able to survive for two to three days on hard surfaces, and the nits can remain viable for about three weeks.

Lice aren’t usually passed from horse to horse on a person’s hands or clothing, but “it’s possible,” says Dana Bridges-Westerman, DVM, of Professional Equine Therapeutic Services in Monroe, Washington. However, if you know your horse has lice, she adds, “let people who come into contact with your animal [know] so they can take precautions not to spread it to another horse.”

Fortunately, you cannot contract lice from your horse. The lice that live on people are different species. “Horse lice are very specific to equids; they do not affect people, but they can affect mules and donkeys,” says Stephen D. White, DVM, of the University of California–Davis.

In general, ill horses and those whose immune systems are compromised by age, stress or other factors are more susceptible to a lice infestation. “Most horses have to be in a depleted state of health to be susceptible to lice,” says Brandi Holohan, DVM, of Pilchuck Veterinary Hospital in Snohomish, Washington. But there are exceptions. For example, a 2010 paper from North Carolina State University documents pediculosis in two research ponies. “These cases highlight the importance of recognizing the possibility of louse infestation even in healthy, well-cared-for animals,” the authors wrote.

Lice infestations can occur at any time of the year, but they are more common in the winter and spring, when equine coats are longer and thicker, and when blankets may hide the earliest signs of trouble. “Lower skin temperatures may also play a part,” says White.

Also, horses are more likely to be kept indoors during the colder months: “Lice occur in crowded, indoor conditions [and the winter] is when horses are most likely to be confined in close quarters,” he adds. “[Pediculosis is] less common in very warm, dry en-vironments where winters are not severe enough.”

Managing a case

Lice make a horse intensely itchy, and the first sign of the problem is constant scratching and biting at the skin. The rubbing is likely to quickly lead to hair loss (alopecia), usually appearing first on the areas where the lice occur: on the neck and head, around the base of the mane and tail, and along the flanks and sides. If the scratching goes on long or intensely enough, the skin may be rubbed raw. “They typically rub their face, mane and chest with less rubbing of the tail and hind end,” says Holohan. “They will rub until they bleed.”

The horse’s hair may become matted, or it may look ruffled, unkempt and “moth-eaten.” The discomfort may also make a horse anxious or irritable. A severe enough infestation of sucking lice may rob the horse of enough blood to cause anemia, which will make him lethargic and depressed with pale mucous membranes.

Although a number of treatments for equine lice are available over-the-counter, it’s a good idea to call your veterinarian if you suspect your horse has lice. He or she can confirm the presence of the parasites while ruling out other possible causes for similar signs. The veterinarian can also suggest the treatment best suited for your horse and the particular species of lice and offer a plan for preventing the parasites from spreading. Timing is important; the longer you delay treatment, the worse the case will get.

Substances that kill lice (pediculicides) come in a variety of forms, including sprays, wipe-ons, pour-ons, shampoos or powders. Common active ingredients include permethrin, cypermethrin and pyrethroids, which are used in fly sprays, as well as selenium sulfide, an ingredient in dandruff shampoos, and carbamate-based insecticides. These pediculicides work by directly killing louse nymphs and adults, but they do not harm the eggs. You’ll need to reapply the products over several weeks to kill any additional lice as they hatch.

Once my veterinarian confirmed that my horse had lice, she prescribed a topical permethrin powder. She opted for this product, she explained, because it is applied and left on, so it stays in contact with the coat longer than shampoo. (However, permethrin is toxic to cats, so either a product with a different active ingredient or a shampoo that rinses away might be a better choice if you have barn cats.)

If you’re dealing with sucking lice, another option is to administer a systemic avermectin, such as an oral ivermectin paste dewormer. This treatment approach is more effective against sucking lice because they ingest the pediculicide from the horse’s blood. “Oral ivermectin is less effective for biting lice,” says White.

Be sure to read and follow the instructions on the label of any product you use---including safety precautions. If you have any questions, ask your veterinarian; you may also find a toll-free information line on the label. You’ll find products for treating lice at most feed stores or from your veterinarian.

My veterinarian also stressed the importance of treating all four of the horses in my barn, even though the others showed no signs of lice. “Once there is an outbreak, all the horses should be treated regardless if they show clinical signs or not,” says Annette Petersen, DVM, of Michigan State University. So I applied the powder to all of my horses a total of five times, at seven- to 10-day intervals. It was late spring, and all of my horses were still in the process of shedding out their winter woolies, but I body clipped them all to make it easier for the treatments to reach the lice. Clipping also helps to deter the spread of lice through a horse’s coat because the lice prefer to be in longer hair. Of course, it is then important to clean the clippers between their use on different horses.

My veterinarian advised that I wear nitrile gloves---which are resistant to chemicals---as well as a dust mask while I applied the powder. It may have been overkill, but I also decided to wear protective eye covering as well as a disposable jumpsuit over my clothing while handling the permethrin powder.

Another important step in the treatment was to scrub and disinfect all of my grooming equipment, halters and other equipment that had touched my horses recently. “Combs and other grooming devices shared among horses should be cleaned with an approved product and, during a lice outbreak, dedicated to just one horse,” says White.

Cleaning stalls, as well as any areas in the paddock or pasture area where horses like to scratch themselves, is a helpful measure, but not as critical with lice as with contagious diseases. “Lice do not live very long off the horse,” says White, “so dramatic or severe cleaning of the environment is not necessary, although any of the topical products, such as permethrin sprays, if indicated on the label, could be used.”

Nevertheless, my veterinarian did suggest stripping all of my stalls and cleaning off debris, such as hair and cobwebs, that had stuck to the walls. Again, I went all the way, and with her instructions, I prepared a disinfecting bleach solution and sprayed down the surfaces of all of my stalls plus the area where I groom. I was extra careful to scrub places where my horses like to rub, both in their stalls as well as their favorite fence posts in the pasture. To speed things up, I purchased an inexpensive hand-pump weed-sprayer to apply the bleach solution, but an ordinary bucket and brush would work as well.

It was also wash time for all of my horses’ blankets. I used to launder their clothing only once per season, but from now on, I’ll do it more often. To disinfect, I’ll add color-safe bleach to the wash (although this will reduce any waterproofing treatment), and I’ll use very high heat with both washing and drying. In fact, some newer washing machines now feature an extra-hot “sanitizing” cycle that will kill lice nits as well as disease-causing microorganisms.

Preventive measures

Strategies for preventing lice from getting established on your horse revolve around keeping him clean and healthy---and closely monitoring his coat and overall health. You probably take the necessary steps to do that already. But constant vigilance is the key to catching and treating lice as early as possible and preventing the parasites from spreading around your herd. Here is a review of steps to take:

Groom regularly and thoroughly. Not only will deep brushing physically remove lice and nits, but the close monitoring of your horse’s coat will alert you to signs of the parasites as soon as they begin to appear. In addition to grooming, says Holohan, “bathing goes a long way to physically remove lice.” After grooming, clean the shed hairs from your brushes before stowing them away.

Keep separate grooming tools for each horse. Ideally, you’d have a separate set of brushes, rags and other grooming supplies for each horse in your care. Rolls of brightly colored electrical tape are one easy way to color-code and “tag” each horse’s gear so you can keep everything straight.

Clean tack and other equipment regularly. Blankets, saddle pads and other items that regularly touch your horse, especially in areas where lice lurk, need to be cleaned regularly. Blankets are generally washed after each season of use, but if your horse gets his especially messy, you might consider cleaning it as needed throughout the cold months.

If your horse becomes ill, keep an eye on his coat. “A healthy horse will resist parasitic infections,” says Bridges-Westerman, who lists “a healthy diet, regular fecal exams and parasite control” as primary preventive measures for lice. That said, a horse who is aging, ill or otherwise unwell may be more susceptible to the parasites. As you care for horses like these, keep a close eye on their coats for early signs of trouble.

Quarantine newcomers to the barn. Any new horse brought to your farm could potentially be carrying a number of parasites or contagious diseases. It’s always wise to keep the new arrival in a stall and turnout area separated at least eight to 10 feet from your current residents for two to three weeks to see if any signs of trouble will develop. It’s also a good idea to keep horses who travel frequently to shows or events apart from any “homebodies.” “It may be advisable to be on the lookout if a horse returning from a show within a few days shows any sign of itching,” says Petersen.

Avoid close contact with unknown horses. When you take your horse out to trails, shows or other places where he will encounter others, it’s always a good idea to prevent him from getting too close to strangers---both to prevent kicks, bites and unwelcome behaviors as well as lice and contagious diseases. However, you don’t really need to worry about picking up lice from stalls at showgrounds. “The risk is pretty low unless the horse stalled there previously was loaded with lice,” says Holohan. But if you’re concerned, she adds, you could spray the area with a permethrin product before putting your horse in it.

Be especially vigilant in winter. A number of skin ailments can develop unseen under heavy winter coats and blankets. Even if you’re not riding regularly in the cold months, it’s still a good idea to bring your horse into a brightly lit area at least every few days for grooming and a close inspection of the condition of the coat. “Warming the coat with a hair dryer will make [the lice] come out from hiding deep in the long winter coat,” says Petersen. “Clipping the coat may help if the local climate will allow it.”

I’ve made several changes since discovering my horse had lice. I live in a climate that tends to be cool and damp much of the year, so my horses had typically spent a good deal of time under blankets and sheets. Since dealing with lice in my barn, I don’t blanket as much as I used to, and when I do I keep my horses’ coats clipped shorter than before. Not only can shorter hair make it easier to detect lice, but because they prefer to live in long, thick hair, it can also deter them.

Almost daily now I part the hair on my horses’ manes and tails down to the skin, just to check for anything suspicious, and I use metal currycombs instead of the “jelly” style so I can really get through their coats when I groom. In addition, this spring I started using a long-acting fly repellent that also works against lice. So far we’ve had no further signs of trouble.

But the biggest and hardest lesson that I learned from my experience is, simply stated, lice happens---even to horses who are healthy and who receive attentive care throughout the day, each and every day. So the next time you’re grooming your horse, and you notice a small speck of “something” that makes you think, “Well, what is that? Dandruff? Shavings? Dust?” Take a very close look. It could very well be your first sign of horse lice.

This article first appeared in EQUUS issue #443. 

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