Cassia fistula (Fabaceae): Botany, Secondary Metabolites and Anthelmintic Potential Against Small-Ruminant Gastrointestinal Nematodes

Gastrointestinal nematodes represent a major challenge to the health and productivity of small ruminants, particularly in the context of increasing resistance to conventional anthelmintic drugs. In this regard, medicinal plants are considered a potential source of compounds with antiparasitic activity. Cassia fistula L. (Fabaceae) is widely used in traditional medicine and contains anthraquinones, flavonoids, tannins, saponins, terpenoids, and other secondary metabolites. This narrative review summarizes the available information on its botanical characteristics, phytochemical composition, and anthelmintic potential against gastrointestinal nematodes of sheep and goats. A literature search was conducted in Scopus, Web of Science, PubMed, ScienceDirect, and Google Scholar for publications available up to August 2026. Studies addressing the phytochemical composition of C. fistula and its experimental anthelmintic activity against gastrointestinal nematodes of small ruminants were prioritized, while publications lacking relevant phytochemical or parasitological information were excluded. A total of 52 references were cited in the manuscript. Current studies report effects on egg hatching, larval development and migration, and adult survival; however, the experimental evidence remains limited and heterogeneous, with a predominance of in vitro assays and only a few in vivo studies. Differences in plant organs, extraction methods, concentrations, and parasite models make direct comparisons among studies difficult. Further research is therefore needed to standardize preparations, identify the metabolites responsible for the observed activity, and confirm their efficacy and safety in small ruminants.