Treatment efficacy of pyrantel, fenbendazole and macrocyclic lactones in equine strongyles in Germany using FECRT and the model eggCounts

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BACKGROUND: Reduced anthelmintic efficacy against small strongyles in horses is a widespread problem, yet recent data is scarce. AIMS: This paper aims to investigate the current status of anthelmintic efficacy in the field in Germany, specifically focusing on pyrantel. METHODS: The study included 1670 horses for which a total of 1913 dewormings were analysed. Of these, 1682 were performed with pyrantel, 56 with fenbendazole, 162 with macrocyclic lactones and 13 with other compounds (e.g. herbs). The faecal egg count reduction (FECR) was calculated with two methods, the faecal egg count reduction test (FECRT) and the statistical model eggCounts. In interpreting the results, we adhered to the guidelines of the American Association of Equine Practitioners (AAEP) and the World Association for the Advancement of Veterinary Parasitology (WAAVP). RESULTS: Overall, 1156 dewormings (68.7 %) with pyrantel, 12 (21.4 %) with fenbendazole and 159 (98.1 %) with macrocyclic lactones were scored with a FECR >95 %. Pyrantel is classified as 'low resistant' with both FECRT (UCL/LCL: 91.1/89.5) and eggCounts (88.7/88.1), fenbendazole as 'resistant' with FECRT (65.0/49.1) and eggCounts (50.4/42.9), and macrocyclic lactones as 'susceptible' with FECRT (100.1/99.0) and as 'low resistant' with eggCounts (99.8/99.5). CONCLUSION: Whereas treatments with macrocyclic lactones were sufficiently effective, the majority of fenbendazole treatments showed insufficient efficacy. For pyrantel the results confirm reduced treatment efficacy in 31.3 % of the treatments. Nevertheless, most treatments remained effective. Consequently, pyrantel should be continued to be used for treating strongyle infections. A control of treatment efficacy 10-14 days after administration of the anthelmintic should become standard practice.