Say goodbye to rotational deworming every six to eight weeks and hello to fecal testing! Vermont Large Animal Clinic-Equine Hospital can help you establish the most effective deworming schedule to minimize risk of parasitic disease and avoid drug resistance. VLAC-EH recommends collecting a fecal sample once or twice a year to perform a fecal egg count (FEC). Based on the results of the FEC, we will recommend a specific deworming plan to target the parasites shedding eggs into your horse’s feces and other silent invaders. The goal of FEC-informed plans are to reduce egg shedding and parasite transmission. The goal is not to obtain FECs of zero.
Collect one fecal ball in a ziplock bag labeled with your horse’s name, date of last deworming, and which product was used. The ideal time to perform a FEC is during the spring or fall. VLAC-EH avoids fecal testing and deworming during the winter in our practice area because parasites naturally reduce shedding and do not undergo larval development in cold weather. It is VERY important to perform the FEC at least four weeks after the egg reappearance period of the most recent dewormer. The egg reappearance period is different for each dewormer (e.g. 12 weeks after ivermectin, 16 weeks after moxidectin, and 9 weeks after fenbendazole or pyrantel).
CLASSIFY YOUR HORSE(S)
Horses fall into three categories based on FEC results: low, medium, and high shedders of strongyle eggs. Most horses are low shedders. These categories represent a horse’s strongyle egg shedding potential but do not correlate with likelihood of parasitic disease or overall health. Individuals in the same herd differ in their FECs and can change shedding categories when there are changes in health or herd conditions.
DEWORM BASED ON CLASSIFICATION
The parasites of most concern in adult horses are tapeworms and small strongyles. Tapeworms are common and widely distributed, have the potential to cause disease, and are difficult to diagnose with FECs. Therefore VLAC-EH recommends deworming with a praziquantel product at least twice a year. Ivermectin is the drug of choice for eliminating adult strongyles, whose eggs are found during FECs. VLAC might recommend deworming with another product to kill encysted small strongyle larvae if a horse is showing signs of parasitism (e.g. weight loss, diarrhea, intermittent colic). The parasites of most concern in young horses are roundworms; ask a VLAC-EH veterinarian about different deworming plans and medications for this population.
Examples of deworming plans for adult horses (more than 3 years of age):
TEST FOR RESISTANCE
VLAC-EH recommends testing for resistance if you have a whole herd of animals with high FECs. This is done by performing a pre-deworming FEC followed by a dewormer and a post-deworming FEC 10-14 days later.
Refugia are parasites (adults, eggs, larvae) not targeted by a dewormer during a deworming event; they do not undergo selection for drug resistance. We can maximize refugia and minimize resistance by only deworming low shedders biannually (not over deworming), avoiding larvicidal treatments in asymptomatic horses, deworming only a few horses in the herd at once, and deworming only during seasons when larvae are alive on pastures (spring, summer, fall). Another important part of parasite control is manure management, which does not require the use of dewormers.