Out with the Old Horse Deworming Schedule & Rotational Chart

Updated June 28, 2024

A woman deworming a bay horse — Veterinarians recommend a baseline of one to two dewormings per year for all adult horses, plus additional treatments for high parasite egg shedders.

Deworming Schedules: Then vs Now

Back in the 70s, over-the-counter paste dewormers had just come on the market and were an excellent way for owners to protect their horses from the number one parasite threat: large strongyles.

Because dewormers then weren’t as effective as they are now, veterinarians advised owners to switch between the different classes of dewormers so that all species of parasites would be controlled. Therefore, every barn posted a rotational deworming schedule, and most horses were dewormed every two months, year-round, alternating between a benzimidazole, pyrantel, and ivermectin.

But things have changed. Now small strongyles pose the largest threat to adult horses and many parasites have developed resistance to the dewormers we’ve been using.

Fortunately, veterinarians have devised a new strategy in the war on parasites: targeted deworming. By performing a fecal egg count (FEC) test, horses can be identified as low, moderate, or high parasite egg shedders, and then a targeted deworming approach can be implemented.

Determining a Deworming Schedule for Your Horses

A pile of horse manure in a grass paddock — A fecal egg count (FEC) test can help identify horses as low, moderate, or high parasite egg shedders.

Modern, veterinarian-recommended methods involve all adult horses being dewormed once or twice a year— at the beginning and end of parasite transmission season.

Horses that shed moderate to high numbers of parasite eggs should have additional deworming treatments during the grazing season when parasite transmission is high. You can identify whether your horse needs more than two dewormings per year with a FEC performed twice per year (the recommended amount for all adult horses).

Change is hard, but by shifting from a schedule of blindly rotating anthelmintic products to a targeted deworming approach, owners will do a better job of protecting their horses from parasites and the problems they can cause

Ask the Vet Video on When to Deworm a Horse

In this Ask the Vet video, Dr. Lydia Gray answers a horse owner’s question on which months are best to deworm horses, mules, and donkeys.

SmartPak strongly encourages you to consult your veterinarian regarding specific questions about your horse's health. This information is not intended to diagnose or treat any disease, and is purely educational.