How Often Should I Deworm My Horse?

Many opinions exist as to how often horses should be dewormed. What do you recommend?

Horse owners for many years dewormed horses every two months. This frequency, however, resulted in tremendous parasite resistance. In addition, researchers discovered that only 20 percent of the horse population carries about 80 percent of all parasites.

Perform Fecal Egg Counts 

For the above reasons, veterinarians recommend performing Fecal Egg Counts (FEC) in the spring and fall to determine the number of eggs a horse has in its manure. The FEC should be used to identify moderate and high egg shedders, with 200 to 500 eggs per gram, and over 500 eggs per gram, respectively. 

Today, most horse deworming programs target small strongyles and sometimes tapeworms in adult horses. Ascarids are the greatest problem in horses under the age of three. 

Deworming Adult Horses

Your will want to administer the following based on the FEC results:

Ivermectin and moxidectin for strongyles

Pyrantel pamoate, fenbendazole or oxibendazole for ascarids

Moxidectin and a daily feeding of Pyrantel tartrate for moderate and high egg shedders, administered three or four times a year.

Deworming Foals

Foals should be dewormed every two months during their first year:

2 months: double dose of Pyrantel pamoate    

4 months: Ivermectin

6 months: Pyrantel pamoate 

8 months: Ivermectin/praziquantel 

10 months: Fenbendazole

12 months: Ivermectin

Foals that live with a large number of foals or exist in the same pasture(s) used for foals year after year may be dewormed monthly with a single dose of Fenbendazole until they reach six months of age. 

In the past, horse owners and managers tried to rid every horse of all parasites, which is impossible. Today, the recommendation is to limit parasite infections so horses remain healthy.