How Often Should You Deworm a Horse in the U.S.?

For decades, many U.S. horse owners followed a simple rule: deworm every six to eight weeks. It was easy, predictable, and widely recommended. Today, that advice no longer reflects how parasites behave—or how horses stay healthiest.

Modern research shows that most horses do not need frequent deworming. In fact, over-deworming is now one of the biggest contributors to drug-resistant parasites, a growing problem across American barns and farms.

So how often should you deworm a horse in the U.S.?
The answer depends on age, parasite risk, management style, and fecal testing, not a calendar reminder.

This guide explains what a modern horse deworming schedule looks like, why it changed, and how to protect your horse without unnecessary treatments.