The influence of increased feeding on the susceptibility of sheep to infection with Haemonchus contortus

Previous research has shown that supplementing the diet of growing lambs wi th urea enhances their ability to withstand gastrointestinal infection with the nematode Haemonchus contortus. This study compared lambs given two dif ferent amounts (x 1 and x 1.5) of the same urea-supplemented diet. One diet ary allowance was sufficient to allow uninfected lambs to gain approximatel y 400 g/week without adverse clinical signs. In contrast half of the H. con tortus infected lambs on this dietary allowance had to be humanely killed b efore the end of the experiment due to severe anaemia and anorexia. All inf ected lambs on this dietary allowance showed decreased mean red cell volume s and decreased plasma albumin concentrations indicating inadequate replace ment of red blood cells and plasma proteins last during the infection. The remaining lambs were offered proportionately 0.5 more of the same dietary a llowance. Among lambs an this dietary allowance, there were very few differ ences between uninfected and infected sheep in clinical signs and growth ra te. Therefore, dietary allowances that are adequate for uninfected lambs ar e not necessarily sufficient for infected lambs. As nearly all grazing lamb s are infected with nematodes, dietary recommendations should take parasiti c infection and its nutritional demands into account.