Ruminants grazing on forages that contain condensed tannins (CT) have lower parasite burdens compared to those grazing on similar quality, tannin-free forages (Min and Hart, 2003). Evidence from previous grazing studies suggested that chicory, which contains only traces of CT, could also reduce the size of the parasite population carried by ruminants (Hoskin et al. 1999). Such bioactive plants may have direct anthelminthic effect on different developmental stages of the worms or indirect effects through nutritional improvement of host immunity. The purpose of this study was to determine whether short-term grazing of bioactive forages could affect either the established adult population or incoming infective larvae of Teladorsagia circumcincta a common abomasal parasite of sheep. The bioactive species tested were chicory (Chicorium intybus) and the CT-containing plants: lotus (Lotus pedunculatus), sainfoin (Onobrychis viciifolia) and sulla (Hedysarum coronarium).