1.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 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 5'CrC1,-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 < 0.05) in N retention and increased ( P < 0.05) flow of N at the ileum. The increase in N flow at the ileum of infected lambs was greater ( P < 0.01) at weeks 11-13 of dosing (infected-control 3.6 g N/d (standard error of difference (SED) 0.57), P < 0.01) than at weeks 5-7 of dosing (infected -control 1.5 g N/d (SED 0.57), P < 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 < 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. It was calculated that to account for the extra non-ammonia-N (NAN) flow at the ileum up to 3-5 g NAN/d during weeks 5-7 of dosing and 15-20 g N/d during weeks 11-13 of dosing could have entered the small intestine as mucin and sloughed cells.7. The results seem to indicate that the nutritional penalty associated with the development of resistance to infection is greater than that associated with the primary infection.

1. The relation between the level of food intake and gastrointestinal motility and digesta flow in the abomasum and small intestine was studied in sheep fitted with nichrome-wire electrodes in the gut wall, an abomasal and a duodenal catheter and a terminal ileal cannula.2. Abomasal volume and outflow were calculated from CrEDTA dilution in six sheep and small intestinal transit time by the passage of Phenol Red in ten sheep.3. The frequency of the migrating myoelectric complex of the small intestine was not altered by the level of food intake but the duration of the periods of irregular spiking activity, the amplitude of abomasal activity and the frequency of duodenal rushes were decreased as the level of food intake was decreased.4. There was a linear relation between the level of food intake (FI) and abomasal outflow (mean with SEM:327 (69) ml/h for each kg FI/d; P < 0.01), and abomasal volume (mean with SEM: 344 (50) ml/kg FI per d ; P < 0.001), without any significant change in the half-time of marker dilution in the abomasum. Small intestinal transit time decreased with an increase in food intake (mean with SEM: -54.9 (5.6) min/kg FI per d ; P < 0.001). 5.It is concluded that abomasal volume and the rate of digesta flow from the abomasum and along the small intestine are linearly related to the level of food intake.

I. Three experiments wereconducted with sheep given spring-harvested dried grass (SHG) and autumn-harvested dried grass (AHG). The first was a calorimetric trial to determine the metabolizable energy (ME) content of each grass and the efficiency with which sheep utilize their extra ME intakes above the maintenance level of intake. The second examined the relative amounts of extra non-ammonia-nitrogen (NAN) and individual amino acids absorbed from the small intestine per unit extra ME intake as the level of feeding was raised from energy equilibrium (M) to approximately 1.5 M. The third was a further calorimetric trial to investigate the effect of an abomasal infusion of 30 g casein/d on the efficiency of utilization of AHG.2. The ME content of the SHG (11.8 MJ/kg dry matter (DM)) was higher than that of AHG (10.0 MJ/kg DM). The efficiency of utilization of ME for productive purposes (is. above the M level of intake; k,) was higher when given SHG (k, 0.54 between M and 2 M) than when given AHG (kf 0.43 between M and 2 M). Consideration is given to the possibility that the higher efficiency of utilization of ME in sheep given SHG may be related to the amounts of extra glucogenic amino acids absorbed from the small intestine which provide extra reducing equivalents (NADPH) and glycerol phosphate necessary for the conversion of acetate into fatty acids.

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