Battling Bots

Bots are just one of the common parasites that can trouble your horse.

America’s Horse

Those yellow specks on your horse’s legs, nose and throat are bot fly eggs. The yellow and black honey-bee-size female bot flies, who lay 150 to 1,000 eggs between August and September (or until the first hard freeze), only lay their eggs on horses, according to Lee Townsend, an extension entomologist at the University of Kentucky in Lexington.

There are three species of horse bots: common, throat and nose. They are among the more than 150 species of common internal parasites that can infect horses. Because they lay their eggs where you can see them, they’re just more obvious about their attack on your four-legged buddy.

The common bot fly glues eggs to the hairs of your horse’s legs, Lee says. The throat bot lays eggs under the chin and lower jaw, while the nose bot prefers the hairs of the nose and lips.

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The eggs hatch after a two- to five-day incubation period, often stimulated by warmth and moisture from the horse’s tongue. Eggs of the other species may hatch without stimulation.

Newly hatched bot larvae enter or are taken into the mouth.

“They spend about three weeks in the soft tissue of the lips, gums or tongue, then migrate to the stomach or small intestine where they attach to the lining of the stomach,” Lee says.

The bots spend about seven months in the stomach before passing out in the manure. The mature larvae enter the soil below the manure pile and pupate. In two weeks or two months, depending upon the season, they emerge as adults, and the whole process starts over again.

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Bots don’t usually cause major health problems, although they can damage the lining of the stomach where they attach. They may also cause small areas of ulceration in the mouth, where the larvae burrow into the tissues for a time after the eggs are taken into the mouth, Lee says.

The effects of internal parasites on a horse range from a dull haircoat and unthriftiness to colic and death. Internal parasites lower the horse’s resistance to infection, rob the horse of valuable nutrients and, in some cases, cause permanent damage to the internal organs, he adds.

Physical control options during the during the summer include trimming or removing hairs with nits – or eggs – on them, using clippers or a bot knife. This must be repeated as eggs are noticed again on the animals.

“Several formulations of ivermectin, a dewormer and bot control product, are available and should be administered after fly activity ends for the season,” Lee says. “Since ivermectin has become such an easy deworming medication to obtain, bots are rarely found in properly dewormed horses.”

Managing Parasites

Chemical control using dewormers is just one part of a complete parasite control plan. As parasites are primarily transferred through manure, good management is essential. Here are some tips from the American Association of Equine Practitioners:

    • Keep the number of horses per acre to a minimum to prevent overgrazing and reduce pasture contamination with parasite eggs and larvae.
    • Pick up and dispose of manure at least twice a week.
    • Do not spread manure on fields to be grazed by horses; instead, compost it in a pile away from the pasture.
    • Mow and harrow pastures periodically to break up manure piles and expose parasite larvae to the elements (larvae can survive freezing, but they cannot tolerate extreme heat and drying for very long).
    • Consider rotating pastures by allowing sheep or cattle to graze them, thereby interrupting the life cycles of equine parasites.
    • Keep foals and weanlings separate from yearlings and older horses to minimize the foals’ exposure to roundworms and other parasites.
    • Use a feeder for hay and grain rather than feeding on the ground.
    • Remove bot eggs regularly from the horses’ haircoats (flea combs work well).
    • Consult your veterinarian to set up an effective deworming program for your horses.

Horse Owner Workshop Coming to Lexington to Celebrate WEG: A Winning Edge
Held in conjunction with the 2010 FEI Alltech World Equestrian Games™ and hosted by the AAEP, Alltech and Rood & Riddle Equine Hospital, achieving prime fitness in equine athletes will be the objective of The Winning Edge: Promoting Peak Performance in the Equine Athlete, a horse owner workshop. Horse owners and competitors will gain an understanding of industry issues and relevant health care information from veterinarians who have treated world champions. Hurry, registration closes September 7, 2010!

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