Fecal Egg Count (FEC) is a technique that veterinarians can use to help monitor your horse’s internal parasite levels, determine the efficacy of current deworming treatments, and can aid in future decisions with when and how to treat your horse. In addition to helping owners better target unwanted worms it can also help avoid unnecessary treatments which save money, and helps limit our impact on wormer resistant parasites.
An FEC is a simple test performed on fresh manure and is examined by a veterinarian or lab technician. The FEC test is quantitative versus qualitative in that the results are reported as the number of eggs per gram (epg) of feces as opposed to a straight forward positive v.s. negative result for worms.
The most common procedure in determining a FEC used by veterinarians is the McMaster technique. This technique involves taking a weighted sample of manure and diluting it allowing the eggs to float. Once the prepared fecal mixture has been allowed to float using a McMaster’s slide, the tester will begin counting the number of eggs found in each chamber under a microscope. These results will be averaged, and multiplied by a dilution factor which gives a result expressed as eggs per gram (epg) of feces.
Working with your veterinarian you can schedule the best time for your FEC based on your goals, region, and current parasite concerns. Parasites typically reproduce when the weather warms-up during spring and early summer. As spring and early summer marks the beginning of the parasite season it is one of the best times to test. Performing an early spring fecal egg count test on your horse allows you to set a parasite burden baseline for treatment and future testing comparisons.
Once you have performed your initial FEC it is best to confer with your veterinarian for the best deworming plan. They may suggest performing another FEC two weeks later to measure the effect of the deworming treatment. The initial FEC and retest can be compared to give better insight into the effectiveness of the treatment, whether there seems to be treatment resistant parasites, and a good idea of your horse’s parasite baseline.