Effects of parasitism on the nutrient economy of sheep: an overview

The experimental difficulties of qualifying the effects of gastrointestinal nematode parasitism on the nutrient economy of sheep from field and laboratory studies are discussed. The evidence available is reviewed and the conclusion drawn is that infection in the abomasum or small intestine induces protein deficiency while reducing supply through depression of appetite. It appears that the effects in susceptible animals-in lambs during the phase of initial acquisition of immunity and in ewes during the peripartum period - are largely reversible by protein supplementation. Quantified effects on mineral nutrition are few and are probably site-specific. The possibility that the host immune response per se may be implicated in the characteristic appetite depression is discussed. The need to understand the immune responseʹs demand for specific amino acids is emphasised, particularly if nutritional supplements are to be used effectively in parasite control. A better understanding of the post-ruminal supply of amino acid in grazing animals will also be needed.