The use of tanniferous plants was suggested as a possible alternative option for controlling gastrointestinal nematodes of small ruminants. This experiment evaluated the possible in vitro effects of three phenological stages (Bloom, Seeds formation, Seeds) of Tunisian fabacae (Hedysarum carnosum Desf.) against Haemonchus contortus third stage larvae. The larval exsheathment assay (LEA) was used to determine the proportions (%) of exsheathment of three plant acetonic extracts at different concentrations (1200, 600, 300, 150 μg/ml). To confirm the role of tannins in the anthelmintic effects of extracts, polyvinylpolypyrolidone (PVPP) was used as deactivating chemical tannins. H. carnosum (S) showed the highest content of TP, TT and BA. The % of exsheathment was phenological stage, dose and incubation time-dependent (P<0.001). As the phenological stage advanced, the % of exsheathment decreased. After the addition of PVPP, the restoration of L3 exsheathment to values similar to those of control indicates that tannins are probably the main secondary compounds involved in anthelmintic effects. However, in vivo assays are necessary to confirm these results.
