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Equine Deworming

A horse receiving deworming medication
A horse receiving deworming medication

As fall arrives, and cooler temperatures are upon us, it is time to deworm our equine friends again. At this time of year, our aim is to eliminate a particular group of parasites that our horses have become exposed to over the summer. This will require specific medications. Of course we will always worry about the ever present small and large strongyles, and all of our deworming products will help to combat those. But this time of year, the two parasites in particular that we are targeting are bots and tapeworms. Bots are the larval stages of the botfly. These are honey bee-sized flies that glue their tiny eggs or nits to body hairs of horses, donkeys and mules.

Common horse bot eggs most often are attached to hairs on the forelegs but can be found on the outside of the legs, the mane, the face and throat, and on the flanks. Eggs of the horse bot fly hatch after a 2- to 5-day incubation period, often stimulated by warmth and moisture from the animal's tongue. Newly hatched bot larvae enter into the mouth where they spend about 3 weeks in soft tissue of the lips, gums, or tongue. The bots then migrate primarily to the stomach where they use sharp mouth hooks to attach to the stomach lining. Bots can damage the lining of the stomach or small intestine and can cause ulceration, they can interfere with the passage of food, or cause other gastrointestinal disorders.

They spend about 7 months there before passing out in the feces. The mature larvae enter the soil below the manure pile and pupate. In 2 weeks to 2 months, depending on the season, they emerge as adults. The adults do not have functional mouthparts so they cannot feed. Females go to horses only to lay their eggs. Most of the egg-laying is done during August and September but may continue until the first hard frost.

The bots cannot be detected with normal fecal tests. It is after the first few good frosts of the season that we recommend to treat horses with a product that combats these parasites.

The other group of parasites we are aiming to eliminate are tapeworms. Tapeworm eggs are passed with the manure of infected horses onto pasture, where forage mites ingest them. The immature tapeworm develops within the body cavity of the mite and is ingested by the grazing horse. When the horse digests the infested forage mite, the tapeworm is released and within 6-10 weeks develops into an adult that attaches to the horse’s intestine and the cycle starts all over again. These parasites are very difficult to detect using standard fecal flotation techniques. A link has been found between tapeworm infection and certain types of colic, and due to the difficulty in testing for it, it is recommended to treat the horse regardless of diagnosis.

The drug of choice for this tapeworm is Praziquantel, which is commonly found in certain combo products, such as Compounded Praziquantel-Ivermectin, Equimax, Eqvalan Gold, and Quest Plus. The other option is to use a double dose of Pyrantel Pamoate. Using the combo drug is convenient, as these also target bots, whereas the Pyrantel (Strongid or Exodus) does not.

As an aside, if you are concerned about roundworms in young horses, treatment for those pesky worms is best carried out with Pyrantel Pamoate (Strongid or Exodus), or Fenbendazole (Panacur). These parasites have become resistant to other dewormers. Please let us know if you have questions about these parasites in particular, as there can be some concerns when deworming heavily infected youngsters.

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