Through in vitro studies, Molan et al. (2000) showed that the tannin, extracted from forages such as sulla (Hedysarum coronarium) and Large Bird́s-foot-trefoil (Lotus pedunculatus), inhibited the development of T. colubriformis eggs to the larvae stage (L1) and of the L1 to infectant larvae (L3) stage. Larva motility was also reduced. These authors, therefore, suggested that forages containing tannins can alter the life cycle of nematodes of sheep and reduce pasture contamination with infectant larvae