Anthelmintic activity of forage chicory (Cichorium intybus) and field efficacy of ivermectin against gastrointestinal nematodes in Danish cattle

Parasitism with gastrointestinal (GI) nematodes is ubiquitous in grazing cattle and its control is critical to sustain satisfactory levels of animal health, welfare and productivity. Currently, conventional parasite control strategies relying exclusively on anthelmintic drugs are severely threatened by the development of anthelmintic resistance (AR) in bovine nematodes in several countries. In Denmark, cattle farmers and their veterinarians depend largely on macrocyclic lactones (ML), mainly ivermectin (IVM), for nematode control. However, no studies have evaluated the field efficacy of IVM against GI nematodes in Danish cattle. Alternative control approaches to minimize selection for AR and that can complement the use of the still effective anthelmintics in integrated control strategies are urgently needed. A promising complementary control strategy is to include bioactive forages with anti-parasitic effects in the animals’ diets. Forage chicory (Cichorium intybus) has demonstrated anthelmintic effects against sheep nematodes, but comparable evidence in cattle is absent. The direct anthelmintic activity of forage chicory has been associated with its content of plant secondary metabolites (PSM), particularly sesquiterpene lactones (SL). Still, no studies have investigated the content of SL in chicory used as anthelmintic forage and no evidence exists of a direct effect of chicory SL against parasitic nematode stages. Thus, the main objective of the present investigations was to contribute towards the integrated control of bovine GI nematodes by evaluating the field efficacy of ivermectin in naturally-infected Danish cattle and by exploring the direct anthelmintic activity of forage chicory and its SL against bovine nematodes in vivo and in vitro.