When designing a horse deworming program it is important to get advice from your local veterinary practitioner. The ideal program for you will depend on many factors including your geographic location and the exposure your horse has to parasites transmitted by other horses. In warm, wet climates it is necessary to administer deworming medications more frequently than in dry areas or locales where hard freeze is common during the winter. Unfortunately there is no one “best” program or even a “best” program for a specific geographic region, because there are too many other variables. Horses in a boarding stable, sharing paddocks, stalls, and pastures with a constantly changing group of neighboring horses that are not dewormed at the same time will need to be dewormed with much greater frequency and with a wider variety of products than horses in more isolated situations.

Using an aggressive deworming protocol such as those designed to rid a horse of encysted small strongyles is not without risk because a horse with a heavy parasite load may have large die-off of small strongyles resulting in severe intestinal inflammation, colic, and diarrhea. The American Association of Equine Practitioners¹ recommends starting with a fecal test just prior to deworming. This will establish parasite load and help your local vet determine the program that will work best for you. Deworming programs nearly always include at least twice-yearly use of ivermectin or pyrantel pamoate along with other products as needed (such as praziquantel to treat tapeworms). Adult horses are often treated with ivermectin in the fall, after the first hard freeze, and again in the spring, in mid-fly season, to effectively treat bots in addition to the many other parasites ivermectin controls. Although ivermectin is labeled² for foals as early as 6 weeks of age, many vets recommend using pyrantel pamoate on foals and their mares because young foals are susceptible to round worms.

Regardless of the deworming program instituted, timing of administration is extremely important. One equine practitioner³ recommends the following deworming program compliance tips:

• Buy the whole year's supply of horse dewormer at once. You will be less likely to miss a critical deworming date if you have the product on hand.
• Label each tube with each horse's name and the date to be given.
• Keep your horse dewormers handy, but store them out of reach of children and pets.
• Post a calendar prominently in your barn. Clearly mark the day before each deworming day to give you time to prepare. On the scheduled day, set the dewormer out where you can't miss it.

The bottom line is that it is essential to get advice from your local veterinarian regarding the deworming program that will be best for your situation.

Remember to store your deworming products where they will not freeze. Keep your horse dewormers handy, but store them out of reach of children and pets.

1. Chamberlain L. Ask the vet: Deworming April 07.  2007;  Available at: http://www.aaep.org/ask_the_vet_questions.php?category_id=81; Accessed February 15, 2008.
2. Bimeda. Bimectin Product Insert; 2004.
3. Hayes KEN. Design a top-notch deworming program. Horse & Rider (June 1999);  Available at: http://www.equisearch.com/horses_care/health/deworming/eqdeworm321/; Accessed February 15, 2008.