SAC Research

Host nutrition can indirectly affect gastrointestinal nematodes through its influence on host immunity. This is because expression of acquired immunity to parasites is often penalised 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 a wide range of 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.

• Short term grazing on chicory resulted in reduced level of parasitism in lambs (Athanasiadou et al., 2005; Tzamaloukas et al., 2005).
• Lambs reared on chicory without strategically used anthelmintics had lower faecal egg counts than their grass/clover grazing counterparts; they grew at similar rates as lambs reared on grass/clover following the strategic use of anthelmintics (Athanasiadou et al., 2007).
• Lambs reared on chicory had increased number of immune cells in their gastrointestinal tract compared to those reared on grass/clover, which indicates an additional effect of chicory on resistance to parasites (Tzamaloukas et al, 2006)
• 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.

Current work at SAC, funded by the Scottish Government, is investigating the interactions between the strategic combinations of various nutritional interventions for parasite control from parturition to weaning. Preliminary results show that the combined use of protein supplementation around parturition and chicory grazing until 10 weeks post weaning results in additive results when compared to either of the effects alone (Kidane et al, 2008) Furthermore, the interactions between nutritional interventions and host genetics in terms of worm resistance are also being investigated. The first results from this study are expected at the end of 2008.