Effects of agro-ecological origin and harvest time of three medicinal plants on their anthelmintic efficacy

Gastrointestinal nematode infections, particularly those caused by Haemonchus contortus, remain a major constraint to livestock health and productivity. With the increasing prevalence of resistance to synthetic anthelmintics, the search for effective plant-based alternatives has intensified. This study presents the first systematic comparison of how agro-ecological conditions and seasonal variation influence both the phytochemical composition and the in vitro anthelmintic efficacy of three medicinal plants widely used in ethnoveterinary practice: Bridelia ferruginea, Mitragyna inermis, and Combretum glutinosum. Leaves from these plants were harvested across contrasting ecological zones of Benin during both the dry and wet seasons. Acetone–water extracts were prepared and evaluated for their ability to inhibit H. contortus larval migration. In parallel, total phenols, condensed tannins, and flavonoids were quantified using spectrophotometric assays. Phytochemical profiles varied significantly (p < 0.01) across both seasons and ecological zones, with generally higher concentrations of phenolic compounds recorded during the wet season (p < 0.05). In contrast, the strongest anthelmintic activity (≥ 25% and < 80% inhibition) was consistently obtained with dry-season extracts. Notably, extracts of C. glutinosum and B. ferruginea from zone IV achieved 65% and 75% inhibition, respectively, while M. inermis from zone II reached 60% inhibition at 600 µg/mL, with clear dose-dependent responses. Across nearly all zones, dry-season extracts outperformed their wet-season counterparts. Agro-ecological and seasonal factors affect both phytochemistry and anthelmintic activity; dry-season harvests in Sudano-Guinean and Sudanian zones maximize efficacy, supporting their use in sustainable parasite control for small ruminants in tropical regions.