Seasonal occurrence of gastrointestinal helminths in a feral horse population from a Mediterranean mountain ecosystem

Gastrointestinal helminth infections are widespread in free-ranging horses, but information on their seasonal occurrence in Mediterranean mountain ecosystems remains limited. We investigated gastrointestinal helminth occurrence in a feral horse population inhabiting the Sierra Nevada Natural Space, southern Spain, using faecal egg counts and molecular detection of Strongylus vulgaris . A total of 166 faecal samples were collected from 61 individually identified horses during four seasonal campaigns between spring 2024 and winter 2025. Strongylid infections were highly prevalent throughout the study, with sample-level prevalence ranging from 95.2 to 100%, while S. vulgaris was detected by PCR in 86.4–100% of faecal samples across seasons. In contrast, S. vulgaris PCR status was not significantly associated with faecal egg counts after accounting for season and repeated sampling. These findings provide a seasonal baseline for gastrointestinal helminth infections in an unmanaged feral horse population and highlight marked seasonal variation in strongylid egg shedding in a Mediterranean mountain ecosystem.