4.2. Interpretation of the FECRT For good reliability of the FECRT, it is recommended to count an average of 40 eggs/horse pre- treatment in the group. An egg counting technique with a low multiplication factor will count more eggs than one with a higher multiplication factor, and this can be especially useful in scenarios where FECs are generally low.


Uncertainty in the group mean FECR should be calculated with 90% confidence intervals, which quantify the variation of the data and are measures of the precision of the efficacy estimate. An online interface for analysis of FECRT data is available from the University of Copenhagen: https://www.fecrt.com/. With this calculation, each mean FECR will have an upper and a lower confidence interval limit. The interpretation of the FECRT results is based on these confidence limits. It is important to note that a diagnosis of resistance only means that the efficacy is reduced from the expected, and that drug-resistant worms are infecting the horses. However, efficacy might still be fairly high if resistant worms are present in a low frequency, or efficacy may be almost zero if resistant worms are present in a high frequency.


Evidence of good efficacy: Evidence of resistance: Inconclusive:


The lower limit is above the lower threshold. The worst possible efficacy is still within the acceptable range.


The upper limit is below the upper threshold. The best possible efficacy is still less than the expected efficacy for that drug.


Both limits fall outside the thresholds. The data are too variable to make a clear determination of adequate efficacy or resistance.


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