Horse Side Vet Guide ®

Equine Health Resource

Deworming, Generally (Anthelmintics)

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There are 4 main classes of deworming compounds (anthelmintics) used to control internal parasites in horses: benzimidazoles, pyrantels, macrocyclic lactones (ivermectin, moxidectin), and praziquantel.

Different classes have different effectiveness against different types of parasites.

The usefulness of any anthelmintic medication depends not only on the effectiveness of the drug against a particular parasite species, but also on the drug’s pharmacology (how much of the chemical is exposed to the parasite in question and for how long), characteristics of the host animal (general health and immunity) and characteristics of the parasite (not only its susceptibility to the anthelmintic but also its location in the body and susceptibility at various life stages to the drug).

Keep in mind that no dewormer is effective if not used in conjunction with good management practices to reduce ingestion of infective parasite eggs or larvae.

Most anthelmintics are administered as oral pastes. In the past, injectable formulations (ivermectin) have been given to horses, but this has proven to be unsafe. Some anthelmintic formulations are available as granules to be top-dressed on feed. Continuous wormers are mostly pyrantel tartrate.

Oral paste wormers are dosed to horses by weight. In most cases, there is a weight measure on the packaging that allows accurate dosing.

YOUR VET’S ROLE

Determine the most appropriate deworming compound for your horses and the best timing of administration. This is done with fecal testing (fecal egg count reduction test).

YOUR ROLE

Horse owners play a vital role in the use of anthelmintic drugs. All anthelmintic drugs should be administered as part of a targeted deworming program along with management techniques to reduce intake of infective parasites.

You also need to properly provide fecal samples to your veterinarian to test the effectiveness of your parasite control program.

Related DiagnosesThis Treatment Might Be Used for these Diagnoses

Consider Potential Side Effects & Complications

Deworming compounds are generally safe medications. That said, each class of anthelmintic has different potential side effects at varying doses.

Moxidectin is the compound that is considered the most likely to cause side effects. It is not recommended in small or young horses, and can be easily overdosed. Side effects are neurologic in nature such as wobbliness, weakness, depression and even seizures.

Consider Reasons Not To Use This Treatment

Talk to your veterinarian about the benefits and limitations of each class of deworming products and what is best for your horses. Rotational use of dewormers is no longer recommended given the growing resistance in parasites. For this reason, veterinary guidance (combined with regular fecal egg counts to determine whether de-worming is necessary) is recommended. For more information, see the Terms & Topics that are linked to this record.

Is It working? Timeframe for effect

In most cases, it is difficult to tell whether or not a deworming compound is effective. In many cases, you will not see dead worms in the manure after deworming.

Just because a horse appears well does not mean that it does not have a large parasite load.

The only reliable way to determine the effectiveness of a particular deworming compound is to perform a fecal egg count reduction test (FECRT). A fecal egg count is performed on the horse. The dewormer is administered. Two weeks later, a second fecal egg count is performed. If the dewormer is effective, then the egg count of the second sample should be zero. Talk to your vet about creating a proper deworming protocol for your horses.

Questions To Ask My Vet

  • Which class of dewormer is the best choice for my horses?
  • How often should you do fecal exams?
  • What management changes should I make to reduce the worm burden in my horses?
  • When should fecal testing be performed to determine the effectiveness of my deworming program?
Bimedia Inc. Equimax® Paste (ivermectin 1.87% praziquantel 14.03%), Deworming
Bimedia Inc. Equell® Paste (ivermectin 1.87%), Deworming
Bimedia Inc. Bimectine® Paste (ivermectin 1.87%), Deworming
Bimedia Inc. Exodus® Paste (pyrantel pamoate), Deworming
Merck Animal Health Safe-Guard® Dewormer 20% Type A Medicated, Deworming
Merck Animal Health Panacur® Powerpac (10% fenbendazole), Deworming
Merck Animal Health Panacur® Paste (10% fenbendazole), Deworming
Merck Animal Health Safe-Guard® Equine Dewormer (10% fenbendazole), Deworming
Merck Animal Health Safe-Guard® Power Dose®, Deworming
Merial Zimecterin® Paste 1.87%, Deworming
Merial Eqvalan® Paste 1.87%, Deworming
Merial Zimecterin® Gold Paste, Deworming
Farnam Equi Aid Strongyle Wormer, Deworming
Farnam Equi Aid CW® Continuous Wormer, Deworming
Horse Health Horse Health Equine Ivermectin Paste 1.87%, Deworming
Farnam IverCare® Paste (ivermectin 1.87%), Deworming
Zoetis Animal Health Strongid® C (pyrantel tartrate), Deworming
Zoetis Animal Health Strongid® C2X™ (pyrantel tartrate), Deworming
Zoetis Animal Health Equimax, Deworming
Zoetis Animal Health Strongid® Paste (pyrantel pamoate), Deworming
Zoetis Animal Health Anthelcide® EQ, Deworming
Med-Pharmex Animal Health Iversol, Deworming
Zoetis Animal Health Quest®, Deworming
Zoetis Animal Health Quest® Plus Equine Oral Gel, Deworming
Zoetis Animal Health Quest® 2% Equine Oral Gel, Deworming
Zoetis Animal Health Strongid® T Suspension (pyrantel pamoate), Deworming
Zoetis Animal Health Anthelcide® EQ Suspension (oxibendazole), Deworming
Zoetis Animal Health Anthelcide® EQ Paste (oxibendazole), Deworming
AgriLabs Agri-Mectin® Paste 1.87%, Deworming
Aspen Veterinary Resources Ltd. Cooper's Best Equistrength™ Paste, Deworming
Durvet Animal Health Inc. DuraMectin™ Paste (ivermectin 1.87%), Deworming
Durvet Animal Health Inc. Pyrantel Paste (pyrantel pamoate), Deworming
Med-Pharmex Animal Health Ivermectin Paste 1.87%, Deworming
First Companion Iverchoice® Equine Paste 1.87%, Deworming
First Companion Ivermax® Equine Paste Dewormer, Deworming
First Companion Equistrength® Paste, Deworming
Henry Schein® Animal Health Parid EQ™ Liquid for Horses, Deworming
Henry Schein® Animal Health Parid EQ Paste™ 1.87%, Deworming
RXV Ivermax™ Equine Oral Fluid, Deworming
Phoenix Pharm Ivercide™ Equine Paste 1.87%, Deworming
VedCo ProMectin E™ Paste, Deworming
VedCo Equi-Phar ProTal™ Suspension, Deworming
Henry Schein® Animal Health Pyrantic Paste, Deworming
Merck Animal Health Panacur® Horse Dewormer Suspension 10%, Deworming
Merck Animal Health Panacur® Power Pac Equine Dewormer, Deworming
Merck Animal Health Safe-Guard® Equi-bits® Top Dress Pellets, Deworming
Equi Aid Strongyle Wormer Equine Anthelmintic, Deworming
Sparhawk Laboratories Inc. SparMectin-E, Deworming
VetOne Vetrimec™ Equine Oral Liquid for Horses, Deworming
VetOne Vetrimec™ Paste 1.87%, Deworming
Phoenix Pharm Anthelban® V, Deworming
Equi Aid CW® Continuous Wormer Equine Anthelmintic, Deworming
Vetoquinol USA Equimax (ivermectin/praziquantel), Deworming
Vetoquinol USA Exodus (pyrantel pamoate), Deworming
Vetoquinol USA Bimectin (ivermectin), Deworming
Durvet Animal Health Inc. Ivermectin Paste 1.87%, Deworming
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Author: Doug Thal DVM Dipl. ABVP

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