Box 1: Use of Fecal Egg Counts


Purposes: To evaluate anthelmintic efficacy using the fecal egg count reduction test (FECRT).


To evaluate and monitor the strongyle egg reappearance period (ERP) of the most recently administered dewormer.


To determine the strongyle egg shedding status of the adult horse at the time of sampling (e.g., high or low shedder).


To determine the relative makeup of parasite burdens in foals and weanlings (i.e., whether the primary parasites are Parascaris spp., strongyles, or both).


Limitations: They do not detect immature or larval stages of parasites including migrating large strongyles and


ascarids, and/or encysted cyathostomins.


Egg morphology does not allow identification of large strongyles, nor species differentiation of small strongyles.


Tapeworm infections are often missed or underestimated by standard FEC techniques, and modified techniques are required.


Pinworm infections are usually missed since the eggs are adhered to the perianal region rather than being shed in the feces.


Fecal sampling and storage: Samples should be stored in airtight and leak-proof containers or plastic bags.


Collected manure should be as fresh as possible. Samples less than 12 hours old are acceptable but should be refrigerated immediately after collection (Nielsen et al., 2010b).


Refrigeration is always recommended for storage of fecal samples, but anaerobic storage at room temperature will also prevent eggs from hatching. Anaerobic storage can be achieved by squeezing all the air out of the bag, or by using a vacuum-sealing device.


Samples should preferably be tested within 7 days of collection, although there are indications that eggs can remain intact for longer if adequately refrigerated.


Fecal samples that are or have been frozen are not acceptable, as this will damage the eggs and decrease the recovery rate.


Diarrhetic samples are not acceptable for FEC but can be used for qualitative testing.


Microscope Use and Maintenance Make sure that microscope lenses are adjusted to the working distance offered by parasitology


slides used for the egg counts. Make good use of contrast (aperture condenser) to help visualizing morphological features.


To improve skills at parasite egg identification, several resources are available online and in textbooks. One should consider review by a veterinary parasitologist if questions arise.


It is recommended that microscopes be equipped with an ocular micrometer so that eggs and other questionable objects can be measured. Having measurements can greatly assist in the identification. Cheap digital cameras can be acquired with software allowing these measurements.


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