You are diligent in your attack on your horse’s load of internal parasites, routinely deworming per your veterinarian’s advice every 3-4 months and picking up manure from stalls and paddocks at least twice a week. Yet, you may wonder, “How well is my plan working?” It turns out there is a practical and easy means of determining this.
The starting point is to have your veterinarian run a fecal egg count (FEC) test to check for parasite eggs. If the sample comes back negative, then no eggs are being shed through the horse’s intestines at this time. Certain times of the year are more likely associated with eggs passed in the feces due to egg laying by adult worms and emergence of small strongyle larvae from their encysted state in the bowel lining. Parasite eggs are more commonly found in the feces in spring, summer and fall; winter not as much. It is best to check manure samples twice a year—spring and fall—especially if no eggs found are found in the initial test sample.
For fecal samples of horses that test positive for eggs, the number of eggs per gram of feces tells whether the horse is a low shedder, a moderate shedder, or a high shedder. Cut off for a low-shedding horse is 200 eggs per gram (epg); a high shedder has fecal egg counts of 500 or more epg. Medium and high shedders often need a stepped-up deworming protocol.
An additional step in determining if your deworming plan is working is to deworm an egg-shedding horse immediately after testing the fecal sample, then perform another fecal egg count two weeks later on a fresh manure sample. This procedure is referred to as fecal egg count reduction testing (FECRT). If the dewormer used reduces the parasite egg count by 90% or more, then that product is probably efficacious to continue to use on your farm as a dewormer.
Additional environmental management helps reduce the horse’s worm burden. If that deworming drug does not reduce the parasite egg load by at least 90%, then it is likely the worms have developed resistance to that specific product and other product choices should be pursued.
Once you have identified high shedders in your horse group, it is best to house them in areas separate from the others to minimize herd infection at least until you have that horse’s parasite load under control. High shedders might need more frequent deworming protocols—every two months for example—and might need administration of different deworming products or combination of dewormers. It is also important to evaluate those individuals for underlying pathologic conditions that could have affected their immune system.
Fecal egg count testing is non-invasive, and it is easy to have your vet perform this test. A bonus is that it is not expensive. In fact, it is a cost-effective strategy to help maintain your horse in the best of health.