Martin Nielsen, DVM, PhD, Dipl. EVPC, ACVM, assistant professor in the University of Kentucky Department of Veterinary Science at the Gluck Equine Research Center, lectured on parasite control in young horses at the 6th annual Kentucky Breeders’ Short Course, held Jan. 24 in Lexington, Kentucky.

Nielsen emphasized the significance of anthelmintic resistance during his presentation and highlighted the various dewormers that have the greatest and poorest effect today.

Traditionally, farm managers have opted to apply year-round treatments at regular intervals, often referred to as rotational deworming. Veterinarians and caretakers believed this provided continual protection from parasites. Nielsen referenced a study conducted by the National Animal Health Monitoring System in 1998 that showed United States horse farms using an average of four or more treatments per year. Similar international studies show South African and British farms using an average of five to seven treatments per year.

“But change is coming,” Nielsen said. “We did not eradicate a single parasite species. We have instead encountered the dreaded ‘R’ word–resistance. There is no single drug that guarantees full effect