Sustainable nematode parasite control strategies for ruminant livestock by grazing management and biological control

Internal parasitism constitutes one of the greatest disease problems in grazing livestock worldwide. Control of these parasites is now becoming a serious concern, particularly in the small ruminant industries, due to the widespread and rapid development of resistance to chemotherapy. The broad-spectrum drugs (anthelmintics) used in the control of nematode parasites fall into just three classes viz. the benzimidazoles, imidothiazoles and macrocyclic lactones. Resistance to all three drug classes now occurs in the major nematode parasites of sheep and goats throughout the world. This is largely the result of a more-or-less complete reliance on anthelmintics for worm control. By analogy then, any specific parasite control method may be unsustainable when used in isolation. The more choices and the greater variety of controls used in combination, rather than relying almost solely on anthelmintics, the longer effective worm control can be expected. Grazing management strategies and biological control offer two non-chemical methods of parasite control, which have proven effectiveness. These should form part of integrated nematode parasite control programmes for grazing livestock with the objective of maintaining long-term sustainability.