A proper parasite control program is essential to the health of your horse. The two broad categories of parasites that affect horses are internal and external parasites. Commercial deworming products are aimed at controlling internal parasites such as nematodes (worms.)
Types of internal parasites include the following:
- Bots (stomach bots):The tiny yellow "seeds" that are often found on horses' lower legs are the eggs of botflies. These eggs are consumed by the horse through licking and grooming of itself. They mature in the stomach, causing irritation and sometimes even an obstruction. Bots are controlled by products that contain ivermectin as the active ingredient.
- Large and small strongyles: Large strongyles are worms that cause internal blood loss as they feed on the lining of the intestine. They also cause damage to the arteries through which they migrate during their life cycle.
Small strongyles do not migrate outside of the intestinal tract, as large strongyles do. They cause diarrhea, which in turn leads to dehydration and sometimes even death, especially in young horses.
- Pinworms: Pinworms migrate through the horse's body to the anus and deposit their eggs, causing irritation. This causes the horse to rub its hindquarters, resulting in a hair loss around the tailhead.
The type of deworming schedule your horse should be on depends heavily on the environment in which it lives. There are two main types of deworming products: those that are given quarterly and those that are given daily (pyrantel tartrate or Strongid.) Horses that are housed on pasture that has been in use for several years, or those that are pastured with a large number of other horses may benefit from daily deworming. This is in addition to deworming with an ivermectin
- containing product in the spring and fall. Daily deworming is necessary due to the large number of worm eggs that will be present in high-use pastures. (More horses = more manure = more worm eggs.)
Pfizer
Animal Health
An effective deworming program for horses that are rotated into new pastures periodically or small herds on large pastures would be a rotational deworming program. This consists of biannual deworming with both an ivermectin and a product containing an active ingredient other than ivermectin. (These two products should NOT be given at the same time, however.) Rotating products is important because over time parasites can build up resistance if the same active ingredient is used over and over.
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