Using fecal egg count tests correctly can yield valuable information for identifying anthelmintic resistance and deworming individual horses selectively. | Michelle Anderson/The Horse

Simple solutions to common problems veterinarians and technicians encounter when performing FECs

Fecal egg counts (FECs) are the foundation of modern equine parasite control programs. Counting those parasite eggs reliably to obtain the information you need to make smart deworming decisions, however, can be frustrating. In this article Martin Nielsen, DVM, PhD, Dipl. ACVM, EVPC, Schlaikjer Professor of Equine Infectious Diseases in the Gluck Equine Research Center at the University of Kentucky, in Lexington, offers solutions for seven common problems equine practitioners and their technicians encounter when performing FECs.

Problem: My clients don’t understand the purpose of FECs.

Solution: Review the frequently updated AAEP Internal Parasite Control Guidelines to brush up on your basic internal parasite ­knowledge.

Nielsen co-authored the AAEP’s guidelines, which outline the main goals of FECs:

1. Performing fecal egg count reduction tests (FECRTs) to monitor anthelmintic (dewormer) resistance among both small strongyles (cyathostomins) and ascarids (Parascaris spp).
2. Identifying animals in need of anthelmintic treatment as part of a targeted anthelmintic treatment protocol. Such surveillance-based control regimens eliminate rote deworming, with the goal of preserving effective chemical anthelmintics.
3. Identifying the presence of ascarid eggs in young stock and deworming affected animals when indicated with an appropriate anthelmintic.

Have FECs performed at least twice a year on all adult horses. This allows you to classify horses based on their egg shedding level, because not all horses shed parasite eggs to the same extent. Research shows a small percentage of horses, dubbed “high shedders,” are responsible for excreting the bulk of the eggs on a farm. This is the 80/20 rule: Twenty percent of the horses on a farm shed 80% of the eggs.

Low shedders have fewer than 200 eggs per gram (EPG) of feces, whereas moderate and high shedders have more than 200 and 500-1,000 EPG, ­respectively.

“The main aim of the FEC is to identify the low and the high shedders,” says Nielsen. “The medium shedders between 200 and 500 EPG aren’t as important.”

Problem: I don’t know which horses to deworm based on the FEC.

Solution: Focus on moderate/high shedders at appropriate times of