1. Transit time of digesta, faecai volatile fatty acids (VFA) excretion and faecal output were measured in four pigs (initially of 90 kg live weight) fitted with chronic catheters inserted into the caecum.

2. Each pig was given a basal milk diet (20 g/kg live weight per d) for 30 d and then received successively four further treatments: the basal diet with bran (100 g/d), the bran-supplemented diet with a daily administration of neomycin (100 mg/kg orally and 100 mg/kg intracaecally), the basal diet with continuous intracaecal infusion of either saline (9 g sodium chloride/1) or with VFA solution (100 mM/h) at the same rate.

3. The mean retention time of the polyvinyl chloride marker was reduced from 98·6 h on the milk diet to 64·3 h on the milk + bran diet. This transit time was notsignificantly modified by neomycin treatment.

4. Daily faecal excretion of VFA was significantly affected by the diet: the additionof bran induced a 167% increase from the milk diet; neomycin treatment reduced VFA excretion with the bran-supplemented diet from 11·3 mM/d to 6·3 mM/d whereas during VFA infusion, excretion levels were twice those of the basal diet.

5. Infusion of VFA solution on the milk diet induced an 11% increase in transit time,without any change in faecal output and dry matter.

6. In conclusion, it is suggested that the decrease in transit time associated with bran supplementation is mediated by direct mechanical factors rather than fermentation products, including VFA.

1. The rate of elimination of administered Nτ-[14CH3]methyl histidine was used to assess the validity of Nτ-methyl histidine excretion as an index of muscle protein breakdown in poultry.

2. Broiler chicks (2–3 and 4–5 weeks old), laying hens, adult quail (Coturnix coturnix japonica), adult cockerels and turkey poults (2–4 weeks old) were tested.

3. All except the turkey poults showed quantitative recoveries of Nτ-[14CH3]methyl histidine within 1 week.

4. Turkeys showed a different pattern of Nτ-[14CH3]methyl histidine output; the mean total recovery after 14 d was less than 50% of the injected dose. The majority of the label remaining after this time was found in breast muscle.

5. All birds tested excreted Nτ-methyl histidine unchanged, although a small amount sometimes appeared as another metabolite.

6. No significant oxidation of Nτ-[14CH3]methyl histidine by broiler chicks, turkey poults or adult quail was found.

7. The results show that excretion of Nτ-methyl histidine is a useful measure of muscle protein breakdown in the domestic fowl and quail but not in turkeys.

1. Steers, equipped with simple rumen cannulas, were given diets of approximately equal parts of rolled barley and straw supplemented with urea. The diets provided sufficientestimated rumen degradable nitrogen (RDN: RDN: metabolizable energy values of 1:3) to maintain maximum microbial synthesis. In some experiments Na235SO4 was introduced into the rumen to label microbial protein.

2. Rumen digesta samples were taken before feeding and mixed rumen bacteria were separated from the solid (solid-associated bacteria; SAB) and liquid (liquid-associated bacteria; LAB) fractions of digesta. The most effective method of removing SAB from the fibre was a combination of homogenizing and pummelling. This process did not affect the physical form or chemical composition of the bacteria.

3. Samples of SAB contained significantly (P ≤ at least 0·05) less ash, total N, RNA and diaminopimelic acid (DAP) and significantly (P ≤ 0·01) more lipid than samples of LAB. Concentrations (g/kg dry matter) of ash, total N, RNA, DAP and lipid in SAB were approximately 87, 70, 35, 2.2 and 245 respectively. Corresponding values for LAB were 157, 80, 50, 3.8 and 124 respectively.

4. RNA-N: total N and DAP-N: total N values in SAB were significantly lower than those in LAB (P ≤ 0·05 and 0·02 respectively). 35S: totalN values were similar in both groups of bacteria. The importance of differences in constituent: total N values in the two groups of bacteria in relation to their use as indices of microbial protein synthesis is discussed.

1. Mineral balance and radioisotope studies have been carried out to test the adequacy of recent Agricultural Research Council (1980) recommendations for calcium and phosphorus for pregnant and lactating ewes. At the same time, Ca metabolism was compared throughout pregnancy and lactation in ewes restricted to these recommendations and in ewes given a plentiful supply of dietary Ca and P.

2. Irrespective of their Ca intake, ewes were unable to absorb enough dietary Ca in late pregnancy and early lactation to meet the high demands, and skeletal stores of Ca were mobilized to make good the deficit.

3. Whereas ewes given the plentiful intake absorbed enough dietary Ca in mid- to late lactation to replace their lost skeletal Ca stores, ewes given the restricted Ca and P intake did not and, at the end of lactation, were still in deficit of about 10% of their total body Ca.

4. Since Ca absorption in the restricted ewes occurred at the maximum efficiency (66%) expected from a hay and concentrates diet, the Agricultural Research Council (1980) recommendations for Ca, particularly in mid-to late lactation, must be inadequate.

5. It is suggested that in calculating requirements, allowance must be made for the inevitable loss and subsequent replacement of skeletal stores.

6. The endogenous faecal loss of Ca was found to vary in direct relation to the food intake, and the significance of this finding to calculations of Ca requirements is discussed.

1. Mineral balance and radioisotope studies have been carried out to test the adequacyof the recent Agricultural Research Council (1980) recommendations for calcium and phosphorus for pregnant and lactating ewes. At the same time, P metabolism was compared throughout pregnancy and lactation in ewes fed according to these recommendations and in ewes fed a plentiful supply of dietary Ca and P.

2. Bone mineral stores were mobilized in late pregnancy and early lactation, irrespective of the rate of P absorption. These stores were then replaced in mid- to late lactation in ewes given the plentiful Ca and P intake but not in the ewes given the restricted intake.

3. Results suggest that these changes in bone stores occurred as a result of changes in Ca requirements rather than in P requirements, and that accretion of P into bone or resorption of P from bone occurred merely as a conseqence of this change in Ca requirements.Immediate demands for P for maintenance and fetal or milk production do not reflect net Pdemands, which also take into account changes in bone P metabolism.

4. The rate of P absorption was directly related to net demands and the rate of endogenous excretion was inversely related to net demands.

5. Absorption and endogenous faecal loss of P were also both directly related to P intake.

6. A lack of dietary Ca, particularly in mid- to late lactation, makes it impossible to draw conclusions on the adequacy of the Agricultural Research Council (1980) recommendations for P. Results do suggest, however, that P requirements ought to be calculated according to net demands for P rather than immediate demands.

1. Twelve red deer stags (Cervus elaphus) penned individually from weaning were fed on a concentrate diet. Six stags received the diet to appetite throughout the study, and the other six were restricted to 70% of the intake of the first group during winter and then fed to appetite during summer.

2. The winter-restricted stags showed remarkable compensatory growth during summer. Compared with the unrestricted stags they showed greater food intake, greater daily live-weight gain and increased food conversion efficiency. Nonetheless, they failed to compensate fully for the previous undernutrition.

3. The hind-foot of the restricted stags failed to grow as long as that of the unrestricted stags.

4. Poor winter nutrition, particularly during the first year of life, and subsequent failure to compensate during the short periods of summer plenty, provides an explanation for the small mature size of wild stags in Scotland.

5. Although the winter-restricted stags were less fat both grossly and relative to body-weight than the unrestricted stags, both groups showed the same relationship of level of fatness to empty-body-weight. In both the groups of stags, extensive fat deposition began once they had reached about half their expected mature weight, a much later stage of development and age than in sheep and cattle.

6. The annual cycle of growth and appetite is considered to form part of a complex adaptive system to enhance survival in a harsh seasonal environment followed by a mild seasonal environment. On Scottish hills deer reach a size appropriate to their environment rather than their genetic potential size.

1. Rats were given diets containing (% dietary energy): 46 arachis oil (AO), 36 partially-hydrogenated arachis oil (HAO) + 10 AO, 36 partially-hydrogenated marine oil (HMO) + 10 AO, or 46 of a combination of rape-seed oils high and low in erucic acid (RSO + LERSO).

2. In the liver microsomes the content of arachidonic acid (20:4ω6) was reduced inthe groups given HAO + AO and HMO + AO.

3. The rates of Δ6-desaturation of linoleic acid into γ-linolenic acid (18:3ω6) and of Δ5-desaturation of dihomo-γ-linolenic acid into arachidonic acid were studied in vitro at two substrate levels: a high substrate level reflecting maximal microsomal desaturase activity in rat liver and a low substrate level reflecting desaturase activity under physiological conditions.

4. Dietary HAO, rich in 18:1 isomers, suppressed the Δ6-desaturase activity butnot the Δ5-desaturase activity. Dietary HMO, rich in 18:1, 20:1 and 22:1 isomers, reduced both Δ6- and Δ5-desaturase activities.

1. A study was made of nitrogen kinetics in the large intestine of sheep given 800 g chopped lucerne (Medicago sativa) hay/d. Four sheepwere continuously infused with (15NH4)2SO4 into the caecum and three other sheep were infused intravenously with [15N]urea. A digesta marker, 51Cr complexed with EDTA (51Cr-EDTA), was infused into the rumen of each sheep to allow estimation of the rates of flow of digesta constituents. Infusions were continued until tracer concentrations reached plateaux in digesta and blood pools, after which the sheep were anaesthetized and slaughtered.

2. Pre-infusion samples and samples on plateau were obtained before slaughter for subsequent analysis to give plasma urea and rumen ammonia-N concentration and enrichment. At slaughter, digesta were obtained from the ileum and segments of the large intestine. These were analysed for 51Cr-EDTA content and concentration and enrichment of ammonia-N, microbial N and non-urea non-ammonia-N (NU-NAN).

3. N flows in segments of the large intestine were calculated and represented in a quantitative eight-pool model.

4. Transfer of plasma urea across the wall of the caecum and proximal colon was negligible but there was an input of 0·8 g endogenous NU-NAN/d.

5. Flow of urea plus ammonia-N in digesta from the ileum into the caecum contributed 1·0 g N/d to the caecal ammonia pool.

6. Proteolysis and deamination produced a further 3·0 g ammonia-N/d in the caecum and proximal colon.

7. The net absorption of N between the ileum and the rectum was 2·8 g N/d but 3·0 g ammonia-N/d was absorbed from the caecum and proximal colon and, in addition, at least 0·9 g ammonia-N/d from the distal colon and rectum.

8. Ammonia-N was incorporated into caecal microbes (0·6 g N/d) and approximately 57% of the NU-NAN in caecal digesta was microbial N. The majority of the microbial N flowing from the caecum was excreted in faeces.

9. The rate of irreversible loss of urea-N from plasma, measured by intravenous infusion of [15N]urea, was 13·6 g/d. On average 83 (SE 6·8)% of the 15NH3 apparently absorbed from the caecum was incorporated into plasma urea; caecal ammonia contributed 9–19% of the N in plasma urea and 0·2–3·1% of the N in rumen ammonia.

1. Experiments were carried out in vivo to investigate the pathways of ammonia incorporation into rumen bacteria, bacterial fractions and free amino acids within the bacteria.

2. Steers were alternately given two isoenergetic, isonitrogenous diets containing the nitrogen mainly as either urea or decorticated groundnut meal (DCGM). At the end of each period on a given diet, a solution of 15NH4Cl was infused into the rumen and samples of rumen contents were removed at 2, 10, 20 and 90 min and 5, 10 and 24 h afterwards. Concentrations of ammonia and its 15N enrichment were determined and samples of mixed rumen bacteria were prepared. Bacteria were disrupted ultrasonically and separated into bacterial protein, cell wall and protein-free cell supernatant fractions. Amino acids were separated after hydrolysis and their 15N contents determined.

3. A rumen fluid circulation pump was developed so that representative samples could be taken at very short time intervals after the introduction of the 15N label.

4. Rumen pH changes, rumen fluid dilution rates and patterns of rumen ammonia concentrations were consistent with normal rumen metabolism. Net bacterial synthesis (as calculated from the net outflow of bacteria from the rumen) was significantly (P < 0·05) greater with the DCGM diet (12·4 g bacterial N/d) than with the ureadiet (9·24 g bacterial N/d).

5. With both diets the 15N label rapidly left the rumen ammonia pool and entered the rumen bacteria. Analysis of the bacterial fractions indicated that the label appeared rapidly in the protein-free cell supernatant fraction and more slowly in the bacterial protein and cell wall fractions.

6. With the DCGM diet bacteria apparently utilized intracellular label less efficiently than with the urea diet. The proportion of N in the protein-free cell supernatant was higher with the DCGM diet, suggesting increased levels of intracellular amino acids and peptides, following extracellular protein degradation.

7. Levels of enrichment of the amino acids alanine and glutamate in the protein-free cell supernatant fraction suggested that the enzymes alanine dehydrogenase (EC 1. 4. 1. 1) and glutamate dehydrogenase (EC 1. 4. 1. 2 and 1. 4. 1. 4) may be the major enzymes for assimilating ammonia when concentrations of soluble carbohydrate and rumen ammonia are high in the rumen.

8. The high levels of intracellular alanine are discussed with reference to publishedwork on the excretion of alanine by rumen bacteria.

1. The metabolic enzymes alkaline phosphatase (EC 3. 1. 3. 1), acid phosphatase (EC 3. 1. 3. 2) and isocitrate dehydrogenase (EC 1. 1. 1. 42) were measured in mucosal homogenates and these enzymes, together with glucose-6-phosphatase (EC 3. 1. 3. 9), were measured in homogenates of isolated enterocytes from germ-free (GF) and conventional (CV) chicks which were either fed continuously until they were killed or were subjected to a 16 h fast before killing.

2. The intestine of the GF chicks was generally lighter than that of the CV controls. The activity of alkaline phosphatase was greater in the mucosal homogenates of the CV chicks compared with the GF birds, but the concentrations of acid phosphatase and isocitric dehydrogenase were not different in the two groups. In the isolated enterocytes the concentration of all enzymes expressed per mg DNA, except alkaline phosphatase, was higher in the GF chicks. Expressed per mg protein there was no significant difference in enzyme activity in the two groups.

3. Fasting caused a reduction in intestinal weight and total mucosal protein in both groups but the reduction was greater in the GF chicks compared with the CV controls. In the GF chicks, fasting caused a significant fall in acid phosphatase and isocitric dehydrogenase activities of the mucosal homogenate, whereas in the CV chicks only acid phosphatase fell to a significant extent. In the isolated enterocytes feeding caused a marked fall in protein per mg DNA in the CV chicks; fasting tended to reduce enzyme concentrations in the GF chicks but to have less effect in the CV group except for alkaline phosphatase where there was a marked rise in activity.

4. It is suggested that the difference in enzyme activities in the mucosal homogenates and isolated enterocytes might result from (a) the presence of a much greater lamina propria in the CV compared with the GF chicks and (b) the greater mitotic activity in the fed CV chicks yielding a much larger number of smaller immature cells.