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).
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.
This Treatment Might be used for a horse exhibiting these signsRelated Observations
Related DiagnosesThis Treatment Might Be Used for these Diagnoses
Know Related Treatments
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?
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