AAEP’s Parasite Control Guidelines
AAEP’s Parasite Control Guidelines
Commonly used strategies for parasite control in adult horses are based largely on knowledge and concepts that are more than 50 years old. However, much has changed in this time, necessitating a re-examination of recommendations for parasite control.
In response to this need, the AAEP’s Parasite Control Subcommittee of the Infectious Disease Committee in 2013 produced a comprehensive set of recommendations for helping veterinarians develop improved strategies and programs for parasite control in horses of all ages. In 2019, these guidelines went through a rigorous review with the committee and former subcommittee and were updated.
It is important to keep in mind that the information contained within these guidelines are suggestions; there are many variations of these suggested programs that will still meet the same goals and follow the same principles. Ultimately, each farm (with veterinary guidance) should develop its own program tailored to the specific needs of the farm and each animal. There is no such thing as a “one size fits all” program.
Guidelines are specified separately for adult and young horses (less than 3 years). All treatment and non-treatment recommendations are made within the context of a preventive program where fecal egg count (FEC) surveillance is being performed.
Read Parasite Control Guidelines.
Visit AAEP's Parasite Control Guidlines webpage
Equine Deworming Plan
Equine Deworming Plan
The recent increase in parasite resistance to commonly used deworming products has left the equine community concerned and in search of ways to slow down, if not reverse, the alarming trend. As parasites can pose a very serious threat to a horse’s health, including fatal situations, it is apparent that the commonly accepted approach to parasite control should be reconsidered. For example, the so called dewormer “rotation” is no longer an acceptable practice.
Strongyles, roundworms, bots, pinworms, and tapeworms are some of the parasites that veterinarians and horse owners deal with. Some of these can be identified easily, others not so much. That is why every treatment should start with analyzing fecal samples. The test is relatively inexpensive, and can provide a solid basis for choosing the right product that will ensure an effective deworming treatment. Every horse from the herd should be tested, but if the group is very large, then a proportionate test group may be used to gather samples from. The fecal test should be done once a year or at least every other year.
Statistically, horses can be categorized as follows:
| Number of eggs in a gram of fecal matter (EPG) | Category | Proportion relative to the herd |
|---|---|---|
| More than 600 (up to 3,000) | Heavy shedder | 20% |
| 200 - 500 | Moderate shedder | 30-40 % |
| 0 - 100 | Light shedder | 40-50 % |
If you test the whole herd individually you may find that not all horses carry the same amount and/or type of parasites. Some horses will carry a lot of worms and others much less. This is due to individual immunity, genetics, exposure level, and a variety of other factors. It may be a good idea to group horses based on the parasite type of infestation they have. This may help prevent further transfer of eggs and larvae between individuals.
There is no longer any fixed time chart or an ideal schedule for equine deworming. Instead, a proper deworming program will be based on the level of infestation and on the climate in your area. It is strongly recommended to perform a treatment after the first killing frost in the late fall to control bots and another round in the spring with a praziquantel- containing dewormer, which will provide a solid tapeworm control program. Note that this is the minimal treatment for the so-called light shedders.
| Category | Recommended frequency of deworming per year |
|---|---|
| Light shedder | 2 times per year (or no treatment at all) (late fall after the first killing frost and spring) |
| Moderate shedder | 3 – 5 times per year (late fall after the first killing frost and spring , plus when needed, usually in the summer season in the warm environments) Will benefit from one additional treatment during the main season of pasture transmission –spring through autumn in the North; autumn through spring in the South* |
| Heavy shedder | 5-6 times per year (approximately every other month) Intensive treatment required all through the main seasons of transmission* |
Always consult your veterinarian before treatment. Fecal testing can help determine the right product and the most effective way to treat your horses. The currently preferred drugs are pyrantel (not effective for tapeworm or bot treatment), ivermectin, moxidectin, and praziquantel (effective against tapeworm).
*Craig R. Reinemeyer, DVM, PhD, The Horse.com, “What is your Horse’s Fecal Egg Count Telling You?”, April 17, 2017
Resistance
Resistance
Resistance is the ability of worms in a population to survive treatment by a particular deworming chemical. Resistance grows when parasites survive treatment, and then pass the ability to survive on to their offspring.
Factors that influence resistance growth1:
- Under dosing.
- Deworming frequency.
- Using dewormers that do not kill resistant parasites.
Resistance can be reduced by:
- Use the proper dose and ensure the horse ingests the full dose.
- Deworm only when needed.
- Use dewormers that are effective. Studies have shown certain deworming classes, e.g. benzimidazoles have a high rate of resistance2.
80% of horses in a recent study3 whose weights were set visually were underestimated. Optimally, weigh your horse. This can be done when trailering, weigh your vehicle with your horse and without (scales can be found at feed mills, truck stops etc). If a scale is unavailable, weight tapes use a combination of a horse’s girth and height to estimate weight. Use care, weight tapes can be inaccurate for foals, miniatures and heavily muscled and high withered horses.
Know how many pounds the dewormer treats. This varies by brand, by as much as 20%. Round up to the nearest measurement and securely lock the syringe mechanism in place for that dosage.
Be sure once administered the horse ingests the full dose. This can be aided by raising the horses head and stroking under their jaw. Apple flavored dewormers can increase the ease of dosing, this can help reduce spit outs and other activities that prevent a full dose from being ingested.
- Sangster NC. Pharmacology of anthelmintics resistance in cyathostomes: will it occur with the avermectin/milbemycins? Vet. Parasitol. 1999; 85: 189-204.
- Kaplan RM. Anthelmintic resistance in nematodes of horses. Vet. Res. 2002; 33: 491-507.
- Asquith, R. Johnson, E. Kivipelto, J. and Depew, C. (1990). Erroneous weight estimation of horses. Proceedings of the annual convention of the American Association of equine practitioners. 599-607.