Health Care Q and A

Q: Have you seen these little yellow eggs on your horse’s legs or stomach recently?

  • Answer
    heath-q-aThey are larvae produced by adult bot flies. We are seeing more bots this season than any other due to the extremely wet conditions. The adult bot fly lays yellowish eggs in the hairs of the forelegs, mane and flanks and sometimes between the mandible and chin or around the muzzle. When your horse itches or bites this area with their mouth, saliva provides the enzymes, moisture, and temperature that allows the egg to release it’s tiny larvae from the hair to which it was attached and be ingested by your horse. These larvae then spend the next 28 days burrowed in the mouth of the horse where they evolve and are then swallowed during a larval growth stage and attach to your horse’s stomach lining. There they mature and burrow into the lining of the horse’s stomach damaging tissue by consuming nutrients. After a few months, the bot larvae will then release their hold on the stomach lining, pass through the small and large intestines, and are deposited with the manure into your pasture. The bot is now in the pupae form and burrows down through the manure and into the soil. They will then mature and emerge as adult bot flies.

    Clinical signs of a bot larvae infection would be lethargy, pus pockets in the mouth and loss of appetite or colic. Larvae present in large numbers in the stomach can cause health issues such as blockages, ulcers, anemia, colic or even stomach ruptures.

    Treatment for bots is to first remove the eggs from the hairs by scraping them with a bot egg knife or old dull razor. When finished with this, be sure you dispose of these eggs where they cannot be ingested and wash your hands thoroughly as humans can be infected. We then recommend that you use an ivermectin or a moxidectin based dewormer such as Quest Gel. The horse should be treated within one month after eggs are seen during the early summer months. A second treatment should be administered in the fall to control the second and third stage larvae. If you are going to use Quest Gel, it is extremely effective for adult horses, but do not use this on foals or weakened horses. You also want to be sure to dose your horse correctly for their weight when using Quest Gel. We have seen bots on farms this year that we have not seen in over twenty years. So check your horse carefully and give us a call if you have any questions.

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