Evaluation of three in vitro bioassays for measuring the anthelmintic activity of plant extracts containing condensed tannins

Abstract

Certain forages high in condensed tannins (CT) demonstrate anthelmintic activity, and appear to be a useful non-chemical adjunct to parasite control in small ruminants. In vitro bioassays have been used to evaluate this antiparasitic effect against several species of trichostrongyle nematodes. However, it remains unclear which in vitro bioassay is the most appropriate evaluation tool. The goal of this research is to evaluate different in vitro methods, and determine which are the most suitable for measuring the effective concentration (EC50) of these extracts. In this research, 3 in vitro methods (egg hatch assay (EHA), larval development assay (LDA) and larval migration inhibition assay (LMIA) were performed using CT extracts from 4 plants with Haemonchus contortus eggs or larvae. Of the 3 bioassays, the LDA yielded the most consistent results, and therefore, appears to be the most appropriate bioassay for measuring the antiparasitic activity of CT plant extracts in small ruminants.