There is an increasing resistance in equines to their deworming medication, making it more and more difficult to accurately treat and control parasites in horses. Veterinarians must work in concert with horse owners to create and implement an effective deworming strategy. Knowing which horses should be treated, what medications and dosages are most effective, and the best timeline for deworming and collecting fecal samples post-deworming will all work together to help veterinarians and owners alike to better treat horses.Mountains Photo
Which Horses Should be Treated for Worms?
The current recommendation for equine deworming is that horses should be treated if they show signs of heavy parasite load. Fecal egg counts are used to determine low, moderate, or high egg shedders and those horses who have moderate or high egg shedding should be treated immediately to prevent escalation and transmission of the infestation.
High egg shedders will need more than one or two treatments per year. On the other hand, low shedders likely only need one or two treatments per year maximum. Young horses are more susceptible to parasite infections and should be wormed at least four times in the first year of their lives.
Which Medications Should be Used to Effectively Deworm Horses?
Before you decide which medication to prescribe your patient, you must determine which type of parasite has taken hold. Prescribing the wrong deworming medication or the strongest medication available as a blanket treatment will help build the parasites’ resistance to deworming treatments.
Ivermectin and moxidectin are the best choices for controlling strongyle parasites, while pyrantel, fenbendazole, and oxibendazole are good for treating ascarids in young horses. Ivermectin resistance is common in ascarids, so be sure to use a different deworming medication, especially in young horses where parasite infection is much more likely.
Remember, the goal is not to rid a horse of all parasites – that pursuit easily results in overmedication and treatment-resistant parasites. Rather, the goal is to limit parasite infections so your horse patients can remain healthy and stave off illness.
When Should You Deworm, and When Should Fecal Samples be Taken Post-Deworming?
There is no need to deworm during the coldest temperatures of winter or the hottest temperatures of summer because parasites cannot reproduce in these temperature extremes. Deworming should be viewed as a yearly cycle during which medication is given when worm transmission is most probable, thus reducing the likelihood of overgrowth and illness.
Fecal samples are required to test the dewormer’s effectiveness. However, samples must be taken at appropriate times:
There is no one-size-fits-all deworming program for horses. Parasite control requires some thought and advance planning when setting up an effective program. With increasing resistance to dewormers, it is important that veterinarians understand the best ways to prevent and treat these infections without increasing resistance further.
Be aware of your timing when deworming horses, of which horses need to be dewormed, and of how frequently those horses need to be dewormed. For more information contact EPC to speak to our experienced veterinary pharmacy staff.