Gastrointestinal nematode parasitism constitutes the major challenge to the health, welfare and productivity of grazing ruminants. The development of nematode resistance to anthelmintics - the traditional means for their control - has forced us to consider alternative means for parasite control. Here we evaluate the opportunities for nematode control that arise from the manipulation of the ruminant host's nutrition. By definition, an increase in nutrient supply will enable hosts to direct extra nutrients towards the replacement of damaged tissues and allow them to produce in the presence of nematode challenge (resilience). Host nutrition can also shift endocrine settings in favour of immune responses and importantly, enhance their ability to deal with the parasites (resistance). The latter effect appears to be more targeted towards the acquired rather than the innate immune response. There are several instances where host (protein) nutrition appears to enhance the effectiveness of the immune response, by increasing or maintaining humoral and mainly cellular acquired immune responses. The same effects on host resistance and resilience can be achieved through the indirect effects of plant secondary components (PSC) on the digestive and metabolic processes of the host. However, PSC can also have direct, damaging effects upon the nematodes and thus directly reduce the nematode population resident in the host. Unfortunately, PSC may also have negative effects on the host itself. Such negative effects will have to be offset against the positive consequences that arise directly or indirectly from the effects of PSC on the parasites. We conclude that host nutrition can affect both the resistance and resilience of ruminant hosts exposed to parasites, through a number of routes. Exploitation of these effects should lead to a more holistic approach to the control of nematodes in ruminants, leading thus to a lower input from and reliance upon antiparasitic drugs in ruminant production systems.
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