Horses grazing lush green pastures paint an idyllic picture. But things might not be as serene as they seem—these animals could be ingesting harmful parasites with each bite. Researchers have shown that on most horse farms the vast majority of “internal” parasites lurk in pastures, waiting to be consumed.

The objective of parasite control programs is to interrupt transmission by targeting specific parasites at the proper times, which vary by climate. Because worms have developed (and are continuing to build) resistance to deworming drugs, horse owners should investigate other feasible options for parasite control—for example, pasture management.

Martin Nielsen, DVM, PhD, Dipl. EVPC, an assistant professor in parasitology at the University of Kentucky’s Maxwell H. Gluck Equine Research Center, in Lexington, says horse owners are becoming more interested in pasture management for parasite control, even though there’s little scientific information to guide them in their efforts. “This is an area that hasn’t been studied lately,” he says. “For several decades we didn’t think we needed to do any pasture management.” Rather, horse owners assumed they could depend on deworming drugs.

“Now we are waking up from that and facing many questions,” he continues. In this article we’ll address some of those questions and describe ways you can manage your property to reduce worm loads