Ten 5-month-old lambs (29 (SE 1.2) kg), reared parasite-free and prepared with rumen duodenal and ileal cannulas, were paired and given rations of Ruminant Diet AA6 (90 g/kg live weight0.75) by means of continuous feeders. From 6 months of age one of each pair was dosed daily with 2500 Trichostrongylus colubriformis larvae for 14 weeks. Untreated animals received the amount of ration consumed by their infected pair-mates the previous day. 2. During three periods, [1) the week before and the first 2 weeks of dosing with infected larvae, (2) during weeks 5-7 and (3) during weeks 11-13 of dosing) all lambs underwent a series of experiments to determine their nitrogen balance, the amounts of N leaving the small intestine, the amount of 51CrCl3-labelled plasma protein leaking into the small intestines, and the disappearance of 35S-labelled bacteria from the small intestine. 3. The infection caused varying degrees of feed refusal in all infected animals. As a result the values for N balance and for the flow of N at the ileum during the latter two periods were regressed against dry-matter intakes for each group in each period. 4. The infection caused a reduction (P less than 0.05) in N retention and increased (P less than 0.05) flow of N at the ileum. The increase in N flow at the ileum of infected lambs was greater (P less than 0.01) at weeks 11-13 of dosing (infected-control 3.6 g N/d (standard error of difference (SED) 0.57), P less than 0.01) than at weeks 5-7 of dosing (infected-control 1.5 g N/d (SED 0.57), P less than 0.05). 5. There were no between-treatment or between-period differences in the disappearance of 35S-labelled bacteria from the small intestines of infected or control lambs, but the infection did cause an increase in plasma N leakage during both periods. During weeks 5-7 and 11-13, plasma N leakage in infected lambs was 1.1 g N/d (P less than 0.01) and 1.7 g N/d (P = 0.056) respectively higher than that in the control lambs. 6. A proportion of the endogenous secretions which enter the small intestine is likely to be resorbed before the ileum.(ABSTRACT TRUNCATED AT 400 WORDS)
