Equine Deworming Rotation Chart: Out with the old and in with the new

By: Dr. Lydia Gray

What is it?

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 comprehensive 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 deworming rotation chart and all horses were dewormed every two months, year-round, alternating between a benzimidazole, a pyrantel, and an ivermectin. But things have changed: now small strongyles are the number one parasite threat and parasites have developed resistance to the dewormers we’ve been using.

What can be done about it?

Fortunately, veterinarians have devised a new strategy in the war on parasites: targeted deworming. By performing a fecal egg count test, horses can be identified as low, medium, or high parasite egg shedders then a targeted deworming approach can be used. Using this method, low shedders might only be dewormed twice a year—at the beginning and end of grazing season—with a broad spectrum product that contains ivermectin or moxidectin and praziquantel (for tapeworms). Horses that shed moderate to high numbers of parasite eggs should be dewormed several times during the grazing season when parasite transmission is high.

What else do I need to know?

Change is hard, but by shifting to the targeted deworming approach owners will actually be doing a better job of protecting their horses from parasites and the problems they cause: colic, weight loss, loose stool, anemia, rough hair coat and other signs. Performing fecal egg counts to identify the high shedders in the herd, strategically deworming individual horses based on the number of parasite eggs they’re shedding into the environment, and keeping the environment clean by picking manure regularly from stalls, turnouts, and even pastures is a sound parasite control program for all situations.


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.