In vitro evaluation of anthelmintic activity of various tannin structures against Cooperia oncophora

To prevent the spread of resistance among gastro-intestinal nematode populations, the use of bioactive tannin-rich plants is currently investigated as an alternative to the exclusive use of anthelmintic (AH) synthetic drugs. Studies of AH effects on cattle nematodes using tannin-rich legumes such as Onobrychis viciifolia have been carried out in vitro but the contribution of all structural parameters from their condensed tannins has not yet been completely elucidated. The aim of this study was to investigate the relationship between structure and AH activity in vitro. A series of condensed tannins extracts and fractions from various plants was chosen according to their monomeric composition (prodelphinidin/procyanidin ratio) and additionally characterised for their degree of polymerisation (mDP) and cis/trans ratio by thiolytic degradation. These tannins were examined for their AH activity against Cooperia oncophora using the Larval Feeding Inhibition Assay (LFIA) and the Larval Exsheathment Inhibition Assay. Preliminaries results from the LFIA showed a positive correlation between AH activity and increasing prodelphinidin/procyanidin and cis/trans ratios of the tested tannins, respectively. The variation in mDP between plants was very limited and the influence on AH activity could not be assessed. These findings should be confirmed by further in vitro assays including others tannin fractions. Moreover, hazelnut skin crude extract presented a total inhibition of larval exsheathment at 600 lg/ml suggesting that some agro-industrial resources may be helpful in sustainable control of cattle nematodes.