A fecal egg count test is part of the usual equine health services offered by veterinarians. This simple test is inexpensive, yet can provide a substantial amount of information regarding the health of the horse and also help assess how effective their deworming program is. However, there are still limitations to this kind of testing ; there are different factors that may influence the results, which make it not completely reliable when it comes to measuring the parasite burden in a single horse or a whole herd.
Parasite Eggs and Horses
In the past, when there weren’t many classes of deworming agents available, horse owners are mostly troubled by large strongyles or bloodworms. These parasites can severely harm the horse, attacking their internal organs and cause various health problems and even death.
However, large strongyles today are not as notorious as they were in the past because they have been managed properly with the availability of different deworming options that are capable of targeting both adult and immature stages of the parasite. Most of the eggs gathered from a fecal egg count test are usually those belonging to one of the small strongyle species – the cyathostomins. Cyathostomins come in 52 different species but only 12 are predominant and account for a huge percentage of infective parasites carried by horses today. When a fecal egg count is positive, it is most probably an infection caused by one of the 12 species. However, for horses that do not receive regular and updated deworming treatments, positive results may indicate presence of different equine parasites including large strongyles, small strongyles, and ascarids or roundworms.
The fecal test only measures the presence of the eggs of those aforementioned parasites, but it cannot specifically determine the species of strongyle that dwell inside your horse. There are more specific tests that should be performed by a veterinarian.
Interpretation of Results
When a fecal egg count test is performed by your vet, they are trying to check the quantity of parasite eggs found for every gram of manure, with results read as eggs per gram. There are no standards set to determine if the results are good or bad, but traditionally, when the value reaches 200-500 eggs per gram of manure, treatment is very necessary.
However, these results were considered an alarming reading considering that large strongyles from 50 years ago were quite common and having a reading of 200 eggs/gram would mean that the infection has reached its critical level. Today, a result of 200 eggs/gram are considered relatively insignificant since it sometimes mean that there is only a small amount of small strongyles present – which does not necessarily mean that your horse has a serious clinical disease.
Results from FEC can also be used by your veterinarian to assess the effectiveness of a deworming protocol for an individual horse or the herd. For instance, if the FEC reading before treatment is 400, the veterinarian may initiate a second test after several days of being treated with a deworming agent. If the result shows a significant reduction in the FEC result following treatment, then the deworming program is considered effective.
Relying too much on fecal egg count tests can unfortunately be misleading. There are cases where heavily burdened horses harboring a type of infection can yield a negative to low result. Conversely, horses that are properly managed can be very healthy despite the positive results shown in an FEC test.
What are the Factors that Affect the Results of the Test?
The test comes with its own set of limitations and it is something to bear in mind for horse owners. For instance, small strongyles in horses of North America may shed eggs following a seasonal pattern. The results will show that the eggs will be in greater quantities during spring for horses located in areas with northern climates. The results could reach its peak in late summer and autumn and may be reduced during winter. The opposite thing can be said about the Southern areas, where the result is at its peak during winter.
Another factor that can affect FEC readings is the phenomenon called hypobiotic cycle. Small strongyle larvae have the ability to become encysted in the intestinal lining of the horse. They bury themselves in the tissue and form a protective cocoon around themselves and go into a dormant state. Horses that harbor encysted small stronglye larvae will produce a low FEC reading since these larvae (in that particular state) do not shed eggs and if the horse is treated, only the adult parasites are killed off. In time, these encysted forms will break out from their dormancy and become adults and once again start the cycle.
Using FEC as Protection Against Parasites
Making your horse 100% free from parasites is not achievable through any parasite protection plan. In fact, there is no scientific evidence that a zero FEC reading is necessary for foals to develop normally or for adults to stay healthy. The main objective of a parasite protection plan is to maintain a low level of parasite burden in horses instead of completely eliminating the parasites. This is to avoid over treating and further expenses for parasite control, as well as giving the horse’s immune system time to take over the infection if they become overwhelming.