Nutrition Affects Parasites

Notes For Researchers

Host nutrition can directly or indirectly affect gastrointestinal nematode parasites. Direct effects are related to ingestion of plant secondary metabolites (PSM) with anti-parasitic properties (Coop and Kyriazakis, 2001).

Since most PSM are also anti-nutritional factors, the consequence of their ingestion for the parasitised host needs to be considered within a trade-off framework (Athanasiadou and Kyriazakis, 2004; Houdijk and Athanasiadou, 2003). Parasitised hosts could obtain a net benefit from the PSM consumption if anti-parasitic effects outweigh their anti-nutritional effects. Indirect nutritional effects are related to nutritional sensitivity of host immunity to parasites.

Expression of acquired immunity to parasites is often penalized at times of nutrient scarcity, and it is postulated that this is because scarce nutrient allocation is prioritized to growth and/or reproductive functions (Coop and Kyriazakis, 1999, Houdijk et al., 2001a). Indeed, an increased supply of protein, from various protein sources reduces the level of gastrointestinal nematode parasitism in both growing and periparturient hosts (see Houdijk and Athanasiadou, 2003; Kyriazakis and Houdijk, 2006 for recent reviews).

Recent research at SAC has investigated direct and indirect effects of host nutrition on parasitism in sheep:

·     Lambs reared on chicory without strategically used anthelmintics had lower faecal egg counts than their grass/clover grazing counterparts, and grew at similar rates as lambs reared on grass/clover in the presence of strategically used anthelmintics (Athanasiadou et al., 2004). 

·     Short term grazing on chicory has the potential to results in reduced worm burdens (Athanasiadou et al., 2005; Tzamaloukas et al., 2005). 

·     Scarce protein supply is directed towards milk production rather than to immunity to nematode parasites in lactating sheep (Houdijk et al., 2003)

·     The degree of breakdown in immunity to parasites is larger in twin-rearing ewes than in single-rearing ewes (Houdijk et al., 2001b)

·     Improved protein nutrition in twin-rearing ewes can reduce nematode egg excretion and worm burdens within a matter of days (Houdijk et al., 2006)

·     The presence of body protein reserves in pregnant ewes reduces nematode egg excretion at times of limited protein supply from the diet during lactation (Houdijk et al., 2001c).

·     Reduced nematode egg excretion at times of high protein supply concurs with elevated concentrations of globule leukocytes in the abomasal mucosa (Houdijk et al., 2005).

A strategic combination of these direct and indirect effects of host nutrition would greatly contribute towards a non-chemical, sustainable parasite control in systems of ruminant production. It is anticipated that such nutritional control will be part of an integrated approach for parasite control, e.g. together with genetic selection for increased resistance, vaccination and biological control, rather than being used in isolation.