A purge dewormer should be given before the daily dewormer program is started. However, also of concern in adult horses are bots, tapeworms, and encysted small strongyles. Treatment for these parasites can be part of the two-month interval rotation program or can be given in addition to a seasonal or daily program. Ivermectin alone is highly effective against bots infections. It should be given in the spring, after bot eggs are produced, and again in the late fall, to remove any bots picked up during the grazing season.
Tapeworms can cause intermittent colic.
A horse may have tapeworms even if no eggs are found in a fecal test. However, Dr. Hutchens advises always consulting your equine veterinarian before using doses higher than the label recommendation. Moxidectin, a new drug on the market, or high doses of fenbendazole are effective against encysted small strongyles. Moxidectin is also reported to be effective against roundworms, small and large strongyles, pinworms, bots, hairworms, and stomach worms. It has been shown to be effective against strongyles for up to three months in adult horses, a month longer than the standard two-month dosing interval.