Trade-offs and benefits: implications of promoting a strong immunity to gastrointestinal parasites in sheep.

The search for sustainable control regimes for gastrointestinal nematode parasites in grazing livestock has resulted in strategies that include assisting sheep to promote a strong immune response. However, the immune response imposes a substantial nutritional cost to the animal which, when nutrient supply is limited, is likely to result in the diversion of nutrients away from productive function to immunological tissues. Therefore, this review examines the potential trade-offs between immune function and productivity that may arise in young grazing sheep. It is hoped that future manipulations intended to promote a strong immunity to gastrointestinal parasites in sheep may be able to minimize these trade-offs to ensure that the productivity of the host is not compromised.