Infections with gastrointestinal nematodes (GIN) represent a major constraint in sheep husbandry. The present thesis investigates the control of these parasites by means of tanniferous fodder plants. Such alternative control strategies are urgently needed because of the emergence of nematode populations resistant to chemical synthetical anthelmintic drugs. Non-chemical control of GIN is also of crucial importance in organic agriculture, where the use of synthetical compounds is restricted.