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Dealing with internal parasites is not the most enjoyable part of horse ownership, but it’s critical to the health and well-being of your equine companions. Left unchecked, gastrointestinal worms can wreak havoc on your horse’s health, causing weight loss, lethargy, colic and even permanent damage to internal organs. With so much information and misinformation out there about deworming, understanding parasite control can seem daunting. No need to be overwhelmed! We’ve put together a simple FAQ and helpful guide to inform you about worms, their effects, and what type of dewormer will most benefit your horse.

So, how does my horse even get worms?

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Most worms are transmitted to horses through infected pasture. As a horse grazes, he inadvertently ingests eggs or larvae that have been deposited into the pasture via the manure of an infected horse. Within the horse’s digestive tract (and sometimes lungs), those eggs or larvae will mature into adult parasites. Eggs produced by the adult parasites will be shed in the feces of the host horse, increasing the worm load in the pasture and potentially infecting other horses.

What are the signs that my horse has worms?

Depending on the worm type and worm load, signs can be as subtle as seeming a little “off” or as severe as ulcers or colic. If your horse demonstrates any of these symptoms, parasites may be the culprit:

  • Weight loss
  • Lethargy and weakness
  • Lack of appetite
  • Poor performance
  • Diarrhea or constipation
  • Poor growth in foals
  • Dull coat
  • Colic

Do all horses have worms?

Pretty much. Worms are a normal occurrence in horses at all stages of life. A low worm load will have little or no effect on a horse’s health, but a high worm load can cause serious health issues.

Gross. What types of worms could be living in my horse?

The six most common types of internal parasites are large strongyles, small stronglyes, ascarids, pinworms, tapeworms and stomach bots.

  • Large stongyles—Also known as red worms or bloodworms, large strongyles are among the most harmful worms for horses. The S. edentates and S. equinus species are blood feeders that can cause anemia and weakness, and the S. vulgaris can cause arterial blockage leading to intestine damage and even rupture.
  • Small strongyles—Also known as small red worms, small strongyles or cyathostomins feed on gut lining and material in the large intestine which can cause mild ulceration, weight loss and diarrhea. Larvae can encyst themselves in the intestinal walls, so when treating for this parasite, use a dewormer that is effective against encysted small strongyles.
  • Ascarids—Also known as roundworms, ascarids are particularly large worms that can be especially problematic for young horses. At the larval stage, they can migrate to the lungs and cause respiratory issues. Adult worms can cause impactions that require surgery.
  • Pinworms—Female pinworms lay their eggs outside the anus of a horse, causing discomfort, itchiness and hair loss. As horses try to relieve the irritation by scratching themselves, they may cause wounds to the base of their tail.
  • Tapeworms—Tapeworms are transmitted to horses through forage mites, which horses ingest while grazing. Forage mites serve as an intermediary host to tapeworm larvae, which then develop into maturity in the horse’s gut. Adult worms can typically be found in the upper intestines, where their presence can cause intestinal blockage and even rupture.
  • Bots—Female bot flies lay their eggs on horse coats, which are then ingested during grooming. Activated by saliva, the eggs molt into larva in the horse’s mouth then migrate to the stomach. In the mouth, bots can cause damage to the tongue and gum tissues; in the stomach, they can cause irritation and ulceration.
Everything is included in this complete pre-paid test. All you need to do is collect 1-2 tsp. of stool sample, place it in the enclosed kit and mail via first class US Mail to the Perfect Pet Products Veterinary Lab. Once received, the test will be processed within 24 hours.

Everything is included in this complete pre-paid test. All you need to do is collect 1-2 tsp. of stool sample, place it in the enclosed kit and mail via first class US Mail to the Perfect Pet Products Veterinary Lab. Once received, the test will be processed within 24 hours.

How can I find out what type of worms my horse has?

A fecal egg count test can provide a wealth of information, including whether your horse has worms, which kind, and suggestions for which dewormer to use. Your veterinarian can perform the test or you can test with a convenient at-home kit that is then analyzed at a veterinary laboratory.

I tested my horse and know the worms he has. What type of dewormer should I use to control of them?

Great! You took the first step in treating your horse for worms. Refer to the chart to identify which type of dewormer addresses your horse’s needs.

Drug ClassBrand NameParasite Affected

Benzimidazoles

Panacur Paste Equine DewormerSafe-Guard Equi-BitsSafe-Guard Equine Dewormer Paste

Large and small strongyles, encysted cyathostomes, pinworms, and ascarids

Macrocyclic Lactones

ZimecterinBimectin Paste; Eqvalan // Quest Gel Horse Dewormer

Large and small strongyles, small bloodworms, ascarids, bots, threadworms, pinworms, hairworms, lungworms, and large mouth stomach worms // Large and small strongyles, encysted cyathosomes, ascarids, hairworms, pinworms, large mouth stomach worms, bots, and tapeworms

Tetrahydropurimidines

Strongid Paste

Large and small strongyles, pinworms, and large roundworms

Isquinoline-pyrozines

Quest Plus Gel Horse DewormerZimecterin Gold

Large and small strongyles, ascarids, hairworms, threadworms, stomach worms, lungworms, bots, pinworms, and tapeworms

How often should my horse be wormed?

The best resource for developing an effective deworming schedule is your veterinarian. If you have any questions about creating or enhancing your parasite control regimen, reach out to your veterinarian. 

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