What is a fecal egg count?
A laboratory test that counts worm eggs present in a manure sample to assess internal parasite burden in horses and livestock.
A fecal egg count (FEC) is a laboratory diagnostic that quantifies the number of internal parasite eggs shed in an animal's manure. The test involves collecting a fresh manure sample, processing it in the lab using flotation or sedimentation methods, and counting eggs under a microscope. Results are reported as eggs per gram (EPG) of feces, which indicates parasite load intensity.
In horses and livestock, FEC testing guides deworming strategy by identifying which animals carry significant parasite burdens and which do not. Rather than treating all animals on a set schedule, veterinarians use FEC results to implement targeted deworming, reducing unnecessary medication and slowing anthelmintic resistance development. Animals with low or undetectable egg counts may not need treatment, while those with elevated counts receive appropriate deworming protocols.
The test is especially valuable for grazing operations where pasture management and herd health intersect. Young stock, pregnant females, and animals under stress typically shed higher egg counts, so FEC testing helps prioritize treatment decisions. Results inform decisions about which animals to treat, which drug class to use, and when to retest for treatment efficacy. Large animal and equine veterinarians commonly recommend FEC testing as part of annual wellness exams and parasite management plans.