Evaluation of a feed-based control strategy for helminth infections in captive herbivores at Cabárceno Nature Park, Spain

The present study assessed helminth infection levels in captive herbivores at the Cabárceno Nature Park (Cantabria, Spain) and evaluated a control strategy based on fenbendazole administration over five consecutive days in selected species. Faecal egg counts were performed to quantify parasite burdens, and an egg hatch assay was used to determine benzimidazole resistance in strongyle populations. All herbivore species were found to be infected with at least one helminth parasite, with gastrointestinal nematodes accounting for 78.3% and trematodes for 21.7%. The highest levels of strongyle infection were found in young bison, with counts reaching 3,745 eggs per gram (epg), while a very high mean Trichuris spp. FEC (3,235 epg) was observed in young moose. The highest FEC reduction percentages were observed in waterbucks (93.3%) and adult elands (85.0%) infected by strongylids, followed by young moose infected by Trichuris spp. (77.4%) and adult Grevy's zebras infected with Fasciola spp. (72.2%). However, FEC reductions exceeding 95% were not achieved in any of the sampled species. The treatment protocol did not achieve a significant reduction in parasite loads, although strongyles remained susceptible to benzimidazoles. Therefore, the reduced efficacy observed in vivo was not due to anthelmintic resistance but rather to inadequate drug intake. These findings highlight the need for more targeted and effective parasite control strategies in captive wildlife, considering enclosure conditions and the practical challenges of drug administration.