The practice of treating all horses every six weeks with rotational dewormers is no longer recommended. Previous deworming practices have allowed resistant worm populations to grow. The goal with deworming is to treat the right horse at the ideal time for the parasite load it’s carrying. If your horse is on a daily dewormer, it’s still important to have your veterinarian perform a fecal egg count twice a year during spring and fall.

Fecal Egg Count Tests are performed to determine if you have resistant worms on your farm. This test involves running fecal egg counts before deworming, then running them again following treatment. Horses are classified as high, medium, or low shedders based on the results of the test.

Young foals are generally more susceptible to parasites than adult horses because of their immature immune systems. Additionally, foals are uniquely susceptible to certain parasites that generally do not affect adult horses--specifically strongyloides (threadworms) and ascarids (roundworms).