How to Deworm Your Horse

Deworming your horse should be based on fecal egg count (FEC) results. This applies to all ages and breeds of horses. Our goal is to MINIMIZE how often we are using a deworming product for most horses.

Recent research into the current status of the effectiveness of our equine deworming products has revealed increased RESISTANCE to ALL of our available drugs. For instance:

Benzimidazoles (this includes Panacur and Anthelcide): All studies show resistance amongst strongyle parasites, and 3 out of 13 studies show reduced efficacy against ascarids. The PowerPac shows resistance at all larval stages, meaning a 5-day Panacur treatment no longer is effective against encysted strongyles.
Pyrimidines (Pyrantel, Strongid): 34 out of 37 studies showed NO EFFICACY of this type of drug against strongyles. Resistance of ascarids was observed in 4 out of 16 studies.
Macrocyclic lactones (Ivermectin, Moxidectin, which is Quest): 13 out of 57 studies showed resistance amongst strongyles. NO EFFICACY against ascarids or pinworms in 29 different studies.
Praziquantel: Typically, this is our only drug that has had any effectiveness against tapeworms. Now, in highly concentrated areas (like Kentucky), NO EFFICACY is observed in horse populations. They are seeing higher egg counts after treatment than before treatment.

Additionally, egg reappearance periods are decreasing, meaning the amount of time that the horse is shedding low parasite counts after deworming is becoming shorter. The parasites are reaching mature and reproductive stages faster than in the past.

Needless to say, this is all incredibly concerning. Experts state that "heavy intensity of deworming over the past decade has selected not only for drug resistance but also for strains of parasites with shorter life cycles that give them a survival advantage by increased egg production in a shorter time frame" (source: EquiManagement Spring 2024).

What Can You Do?

Here is a short list of important steps you can take to help decrease your contribution to resistance and protect your horse:

Stop buying dewormer at random from the store and giving it with no medical guidance. Deworming every other month or four times per year is no longer appropriate.
Get a fecal egg count performed, or even better, a fecal egg count reduction test. These tests help classify your horse as a high, moderate, or low shedder. A reduction test also shows whether the dewormer used was effective. Remember that susceptibility to parasites is individual—every member of the herd must be tested, as one animal is not representative of the whole group.
Practice environmental management: Parasites are primarily transmitted via ingestion of feces. Regularly clean up manure, drag and rest pastures, avoid overcrowding, and keep feed sources away from manure to reduce exposure.

It is important to note that zero parasites is not the goal. The focus should be on reducing high shedders and limiting exposure to vulnerable populations (young, old, and ill horses). It is essential to involve a veterinarian in your horse’s deworming plan to account for individual risk factors and environmental conditions.

Deworming Recommendations (Based on FEC Result)

Low Shedder (FEC Less than 200)

Spring: Panacur
Fall: Ivermectin or Moxidectin plus Praziquantel (Equimax or Quest PLUS)
Perform FEC at least once per year

Moderate Shedder (FEC 200-500)

Spring: Ivermectin
Summer: Panacur (fenbendazole) or Anthelcide (oxibendazole)
Fall: Ivermectin or Moxidectin plus Praziquantel (Equimax or Quest PLUS)
Perform FEC twice per year (spring and fall)

High Shedder (FEC Greater than 500)

Spring (March): Ivermectin
Summer (June or July): Panacur (fenbendazole) or Anthelcide (oxibendazole)
Early Fall (September): Deworm with Ivermectin if FEC is still high
Late Fall/Early Winter (November): Ivermectin or Moxidectin plus Praziquantel (Equimax or Quest PLUS)
Perform FEC 2-3 times per year (spring, summer, and fall)