Table 2. Efficacy thresholds and recommended group sizes for FECRT testing of equine cyathostomins (small strongyles).
Upper threshold Lower Threshold Group size1
Group total eggs counted1
Ivermectin/Moxidectin 99.9% 92% 5
200 1 Based on counting a minimum of 40 eggs/horse pre-treatment
Table 3. Efficacy thresholds and recommended group sizes for FECRT testing of equine ascarids. Ivermectin/Moxidectin 99.9% 90% 5
Upper threshold Lower Threshold Group size1
Group total eggs counted1 200 1 Based on counting a minimum of 40 eggs/horse pre-treatment
4.4. Treatment check with fewer than five horses? While a FECRT should optimally follow the guidelines summarized above, it can still be meaningful to evaluate the treatment efficacy in scenarios with fewer than the recommended number of animals, or with fewer eggs counted pre-treatment. However, in these scenarios, results should be interpreted with more caution due to a higher potential for variability and uncertainty. Furthermore, results are more likely to fall in the inconclusive category when group sizes are small.
Even though it would not be considered a true resistance test, it can still be useful to perform a treatment check on a single horse in situations where this is the only animal available for testing, such as a newly arrived horse in quarantine. In these cases, a general guideline is that any anthelmintic should reduce both ascarid and strongyle fecal egg counts by more than 95% at 14 days after treatment. For a single horse, we must rely solely on the arithmetic mean reduction, since it is not possible to calculate a confidence interval. Again, the number of eggs counted pre- treatment will largely affect the reliability of the result.
As a rough guideline, more than 40 counted eggs can provide a reasonably meaningful test, while 20-40 counted eggs can be expected to be moderately useful. Fewer than 20 counted eggs may not provide reliable results. If a low number of eggs is counted, a result indicating high efficacy could easily be attained due to variance, thus, such a result should be interpreted carefully. However, since the expectation is for high efficacy when resistance is not present, and since dead worms do not shed eggs, a result from a single horse that yields poor efficacy can be reasonably assumed to be due to resistance.
Benzimidazole 99.9% 90% 5
200 200
Benzimidazole 99% 90% 7
280
Pyrantel pamoate 98% 80% 7
280
Pyrantel pamoate 99.9% 90% 5
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