The University of Kentucky maintains a unique herd of horses that hasn't been dewormed since 1979.

According to Martin Nielsen, DVM, PhD, parasitologist at the University of Kentucky Gluck Equine Research Center, while the horses have a lot of parasites, they are healthy.

He and his team recently published a study describing parasite infection patterns in these horses over the course of a calendar year. Some of the findings include:

• Mare pregnancy, foaling and lactation did not affect parasite fecal egg counts.
• There were no differences in parasite egg shedding between seasons.
• Horses had antibodies to the bloodworm (Strongylus vulgaris) throughout the year, and the parasite was steadily detected in fecal samples.
• Mares passed these antibodies onto their foals through the colostrum.

"We learn so much from this unique herd of horses,” Nielsen said. "First and foremost, they remind us that parasitism is a natural state, and that worms only extremely rarely cause disease or ill-thrift.”

Nielsen said that several of the findings made in the study were surprising. Seasonality in parasite egg shedding had been reported in other countries, and many people had speculated that pregnancy and foaling could affect parasite transmission.

"This study demonstrates the importance of investigating these things properly, and this research herd offers excellent opportunities for doing so,” he said.

The full scientific paper can be found at: https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-022-05168-z?fbclid=IwAR2PwNPek2qaxPZOxvao5NeTXhbyelYrjaULSzujBGh_oygZAOXPxxqDZLY

Martin Nielsen, DVM, PhD, Dipl. ACVM, Schlaikjer professor of Equine Infectious Disease at the University of Kentucky Gluck Equine Research Center, provided this information.