A large number of FEC techniques are available today, and the choice of technique will depend on the purpose of the count (Nielsen, 2022a). Appendix A contains a protocol for the McMaster technique, which is the most useful technique in equine veterinary practice. The McMaster is useful for monitoring strongyle egg shedding status and presence of ascarids, while other techniques may offer better accuracy and precision, which would make them better choices for the FECRT. In recent years, automated image-analysis based egg counting techniques have been made available and validations demonstrate good precision of some of these (Cain et al., 2020), suggesting that these could be useful as well.
3.3. Strongyles Strongyle FECs are used to estimate the level of strongyle egg shedding contributed by each horse in a given herd, and to evaluate treatment efficacy with the fecal egg count reduction test (FECRT, see this section). Quantitative performance is summarized for two commonly used techniques in Table 1. The Wisconsin technique is generally not considered suitable for equine usage due to its low accuracy and precision. For identification of high strongyle shedders, techniques with moderate to high accuracy levels are recommended.
Table 1. Accuracy and precision levels for determining equine strongyle fecal egg counts for two commonly used manual fecal egg counting techniques.
Technique
McMaster Wisconsin
Multiplication factor
25, 50 1
Accuracy1 Low Precision2 References
Moderate-high Moderate Noel et al., 2017; Cain et al., 2020 Cain et al., 2020
Low
1 Accuracy is a measure of how close the test measurement is to the true fecal egg count. 2 Precision is a measure of how close repeated measurements are to each other.
Strongyle egg counts typically follow an overdispersed distribution within herds of horses with most horses shedding low or moderate levels and a minority of the horses being high strongyle shedders. This is often described as the 20/80 rule, since 20% or less of the horses in each herd excrete 80% of the total egg output (Kaplan and Nielsen, 2010). Furthermore, research has documented that mature horses have a strong tendency to consistently maintain the same level of strongyle egg shedding across time (Nielsen et al., 2006; Becher et al., 2010; Scheuerle et al., 2016). Therefore, FEC testing is recommended to identify high strongyle shedders within a herd and treat them appropriately. FECs can be determined year-round, and there are no fluctuations in reliability across seasons.
3.4. Ascarids Ascarid shedding is most often limited to specific age ranges and varies widely over time, which means that there is no long-term shedding consistency in individual horses. Thus, the most important applications of ascarid FECs are 1) qualitative detection of infection (positive/negative) and 2) treatment efficacy evaluation (see FECRT section). There is very limited validation information available on the performance of various techniques for ascarid FECs; therefore, no specific technique can be recommended at this time. A recent study suggested that the McMaster technique performed with good precision for determining ascarid FECs (Ripley et al., 2023).
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