What are fecal egg counts used for?


The best use of fecal egg counts (FEC) on a sheep/goat farm is to determine resistance to dewormers, identify resistant (and susceptible) animals, and monitor pasture contamination. By themselves, fecal egg counts are not a reliable measure of worm burden. Generally, they should not be used to make individual deworming decisions, unless other information is available.

A fecal egg count is a quantitative measure of how many worm eggs a sheep/goat is passing in each gram of its manure. You get a number like 1000 eggs per gram of feces (EPG). Fecal egg counts are performed by veterinarians, state diagnostic labs, and independent laboratories. You can also learn to do your own fecal egg counting.

Before and after fecal egg counts can be used to determine dewormer resistance. Collect fecal samples from 10 or more animals. Each sheep/goat needs to have a fecal egg count of at least 250 EPG. Higher is better. Ten to 14 days later, collect samples from the same animals. Compare the fecal egg counts. A fecal egg count reduction of less than 95% means dewormer resistance is present. Less than 70% is problematic from a treatment standpoint.

Fecal egg counts are being used increasingly to select small ruminants for resistance to parasites. Sheep/goats that have good FAMACHA© scores and don’t require deworming may still be shedding a lot of eggs onto the pasture. They are “resilient” but not necessarily resistant. It is estimated that approximately 30% of the flock/herd is responsible for shedding 70% of the eggs onto pasture (and vice versa). Parasite resistance (fecal egg count) is a moderately heritable trait. It may be less heritable in goats.

To select for resistance to parasites on your farm, you need a contemporary group of animals to compare. A contemporary group is a group of animals (ideally 20 or more) of similar age and type that have been raised the same. Selection for resistance to parasites is not for the faint hearted. In order to make accurate selection decisions, you need sufficient exposure to parasites. The group average FEC should be at least 500 EPG, preferably higher. You also need a significant spread in fecal egg counts, e.g., 0 to 4000 or 250 to 6000 EPG. Some farms struggle with having enough exposure to parasites to be able to accurately select for parasite resistance. In fact, the more successful you are at controlling parasites (limiting exposure), the harder it is to select for resistance.

Several universities are now offering low-cost ($5/sample) fecal egg counting for the purpose of genetic selection and fecal egg count reductions. Go to https:/www.wormx.info/lowcostfec to learn more.


Additional reading
Why do sheep and goat fecal egg counts? - University of Rhode Island
What do fecal worm egg counts tell us? - Ohio State University
Fecal egg counts: uses and limitations - What Works With Worms