Equine parasites have been implicated in horse colic but deworming a horse with a heavy parasite burden is a colic risk, too. And now we're starting to see parasite resistance resulting from the unintentional misuse of chemical dewormers. To keep your horses healthy and ensure the continued effectiveness of important deworming chemicals, keep worm burdens low, reduce the spread of parasites through sensible pasture management and treat only the horses that truly need treatment.