Module 3: The Quantitative Fecal Exam
Module 3.1: The Quantitative Fecal Exam
The fecal smear (dry and wet techniques), sedimentation, and fecal flotation techniques can indicate if an animal is harboring internal parasites. However, these tests do not provide an estimate of the number of ova or oocysts in a known amount of feces, as they are qualitative tests. Egg-counting techniques, otherwise known as quantitative fecal exams, allows for an estimate of the number of parasite structures (eggs or oocysts) within a known amount of feces. Quantitative information can assist in determining anthelmintic efficacy, as well as estimating pasture contamination. However, egg counts from an individual animal at a particular point in time are of limited value – results will vary depending on factors affecting egg/oocyst production. On the other hand, quantitative approaches, when used in a well-designed experimental or clinical study, can provide significant information.
The two most common quantitative fecal techniques used in veterinary medicine are the McMaster’s and Wisconsin techniques. Over the years, scientists and diagnosticians have made improvements on the original techniques described at their initial development and you will see these techniques referred to as “modified”. A specific mass of feces and volume of flotation solution are measured out before conducting the test for all quantitative techniques. We can estimate the total number of eggs per gram (epg) of parasitic ova in the fecal mass being floated by knowing the specific fecal mass and fluid volume. This number can help estimate pasture contamination of ova and when used before and after anthelminthic administration, help identify potential resistance in a nematode population. Setting up an experiment or clinical trial for the determination of anthelmintic resistance using specific experiment design and quantitative fecal techniques is called a fecal egg count reduction test (FECRT).