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 effect of high dietary vitamin A or tocopherol, or both, on lipid absorption and secretion in the gastrointestinal tract and on serum and hepatic lipids was determined in the chick.

2. High dietary vitamin A increased secretion of cholesterol, bile acids, phospholipids and fatty acids to the duodenum, and tocopherol enhanced cholesterol and bile acid secretion to the duodenum. No differences in over-all absorption were observed.

3. Serum cholesterol was depressed by vitamin A and hepatic lipids were enhanced, except phosphatidyl choline which was depressed. Tocopherol increased hepatic triglycerides and cholesterol.

4. In vitro fatty acid synthesis from lactate by liver homogenates was enhanced by vitamin E and cholesterogenesis enhanced by both vitamin A and tocopherol. Δ9 Desaturation was also enhanced by vitamin E.

5. It is concluded that both vitamin A and tocopherol affect the hepatic synthesis and catabolism of cholesterol and that vitamin E also influences fatty acid metabolism.

1. Two experiments are reported. In Expt 1, five male lambs of 26–33 kg were used to measure basal nitrogen excretion when the lambs were entirely sustained by an intraruminal infusion of 450 kJ/kg body-weight0·75 per d of volatile fatty acid (VFA) and were receiving no protein. In Expt 2, which was a conventional growth trial, the response to fish meal (66 or 132 g dry matter/d) of lambs given a control diet of sodium-hydroxide-treated barley straw was measured.

2. In Expt 1 the mean basal N excretion of the lambs was 429 (SE 21) mg N/kg body-weight0·75 per d. This exceeds current UK standards for the amino acid N of microbial origin which would be made available to the normally-fed host animal at a maintenance level of metabolizable energy intake.

3. In Expt 2 there was a clear growth response to the fish meal, which was greater (P < 0·05, single-tailed test) than that to be predicted from the energy content of the fish meal. There was no effect of fish meal on the voluntary intake of the basal diet, but there was a suggestion that the digestibility of the basal diet was improved.

4. It is concluded from Expt 1 that the basal requirement for amino acid N by lambs is three- to fourfold that currently recommended in the UK. This higher basal requirement should have resulted in a marked response to supplemental protein in Expt 2. The fact that the growth response in Expt 2 was less than anticipated may have been due to a combination of a slightly lower basal N excretion than that found in Expt 1, a higher yield of amino acids of microbial origin than current UK standards predict, and possibly to a change in the body composition of the lambs.

1. A fluorescent high-molecular weight lipid–protein aggregate was isolated from the cytosol of chick intestinal mucosa or liver by gel filtration on columns of Sepharose 4B or 6B.

2. This aggregate exhibited carotene-cleavage activity.

3. On incubation of this aggregate, dissociation occurred and low-molecular weight fractions containing Cu and Zn and exhibiting carotene-cleavage activity were found. This fraction appeared on sodium dodecyl sulphate polyacrylamide electrophoresis to have a molecular weight of 7000–11000 and resembled the previously described Cu chelatins in amino acid composition.

4. Carotene cleavage may be effected by a copper–zinc metalloprotein of low-molecular weight, associated in intestinal cytosol with a lipid–protein aggregate.

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. For a period of at least 2 weeks before an experimental collection each of four young steers received total daily intakes consisting of approximately (g/kg) 600 straw and 400 concentrates with the nitrogen provided mainly as urea and in which the main energy source was starch (tapioca) for diet 1 and glucose for diet 2. Concentrates were given twice daily at about 09·00 and 17·00 hours, straw at 17·00 hours only. The value for the ratio, rumen-degradable N: metabolisable energy (g/MJ) in the daily intake was estimated to be approximately 1·2.

2. On the day that an experimental collection was to be made the urea normally given in the feed at 09·00 hours was labelled with 15N. This urea and sometimes the appropriate energy source were added either as a single dose (SD) at 09·00 hours or in three equally-divided doses (DD) at 09·00, 11·00 and 13·00 hours. Treatments, given in a Latin-square design, were: (A), starch (SD)+ urea (SD); (B), starch (SD) + urea (DD); (C), glucose (SD) + urea (DD); (D), glucose (DD) + urea (DD). Doses of polyethylene glycol (PEG) and 144Ce (as cerous chloride) were given as markers with the urea.

3. After these doses were given, samples of abomasal and duodenal digesta were taken periodically for 72 h. It appeared that virtually all the PEG had left the rumen by this time and mean recovery of 144Ce relative to PEG was approximately 90%. From recoveries of non-ammonia-15N (microbial 15N) at the abomasum, estimated relative to PEG, values for mean fractional efficiencies of conversion of urea-N to microbial-N were calculated to be 0·59, 0·59, 0·40 and 0·41 for treatments A, B, C and D respectively. Values for treatments A and B were significantly greater than those for treatments C and D but no other differences were significant. Examination of duodenal samples led to similar conclusions.

4. It was concluded that starch was a more suitable energy source than glucose for maximal capture of ammonia-N for microbial synthesis but that spreading the urea and glucose doses in an attempt to match energy and ammonia release rates had no significant effect on capture efficiency.

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. Vitamin E and selenium deficiencies were produced in the Pekin duckling (Anser cinerens) and were characterized by the development of lesions after 14 d in gizzard, intestine, heart and skeletal muscle.

2. The activities of glutathione peroxidase (EC 1.11.1.9), using hydrogen peroxide and cumene hydroperoxide as substrates, glutathione-S-transferase (EC 2.5.1.13), superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6) were measured in homogenate supernatant fractions of liver, heart, intestine, gizzard and skeletal muscle of deficient ducklings and of control birds given vitamin E or Se or both.

3. Glutathione peroxidase activities were dramatically lower in tissues of Se-deficient ducklings, and this was unaffected by vitamin E. No adaptive changes were seen in the activity of the other enzymes, even after 21 d when the deficiency was severe.

4. It appeared likely that the variability of the enzyme activities, other than glutathione peroxidase, in the different tissues studied might explain differences among the tissues in susceptibility to peroxidative damage.

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. Six protozoa-free steers with simple rumen and abomasal cannulas were given basal diets consisting of a concentrate mixture of flaked maize and tapioca with either barley straw (BS) or alkali-treated barley straw (BSA). Other diets used were supplemented with urea (BSU and BSAU respectively) or contained fish meal in place of tapioca BSF and BSAF (respectively). The diets were given in a 6 × 6 Latin square design. Diets were isoenergetic and provided sufficient metabolizable energy (ME) to support a growth rate of approximately 0·5 kg/d. Basal diets, urea- and fish-meal-supplemented diets had estimated rumen-degradable nitrogen (RDN): ME values (g/MJ) of 0·5, 1·2 and 0·8 respectively. 103Ruthenium and polyethylene glycol were given as flow markers, and flows (g/24 h) at the abomasum of organic matter (OM) and carbohydrate components were calculated.

2. True digestibility coefficients of OM between mouth and abomasum were significantly greater for diets containing alkali-treated straw (approximately 0·63) than for those containing untreated straw (approximately 0·55) but were not significantly affected by N supplementation.

3. Digestibility coefficients of the neutral-sugar components of dietary polysaccharides between mouth and abomasum were 0·28, 0·34, 0·31, 0·23, 0·31 and 0·87 for mannose, galactose arabinose, xylose, cellulose-glucose and starch-glucose respectively for diet BS. Corresponding values were 0·37, 0·42, 0·56, 0·51, 0·40 and 0·88 for diet BSA. All but the mannose and starch-glucose values were significantly greater for the latter diet. N supplementation also led to increases in digestibility of all neutral sugars except mannose and starch-glucose. Fish meal produced a markedly greater effect than urea but only significantly so for cellulose-glucose. Thus, the highest digestibilities were seen for diet BSAF and were 0·68, 0·67, 0·74 and 0·64 for galactose, arabinose, xylose and cellulose-glucose respectively. Of all these sugars xylose consistently showed the greatest response in digestibility to sodium hydroxide treatment or N supplementation.

1. The dietary requirements for protein and amino acids of the growing gosling (0–7 weeks) were calculated according to body composition, maintenance needs and the absorption rate of amino acids from feeds.

2. The diets were formulated by least-cost linear programming, using the calculated requirements for amino acids, with or without minimal glycine + serine requirements. The diets formulated without minimal requirements of glycine + serine were supplemented with various amounts of glycine, and fed to growing goslings.

3. The calculated requirements for protein and essential amino acids were lower than those suggested for growing broilers and turkeys. The requirements (g/MJ metabolizable energy) at 0–2, 2–4 and 4–7 weeks of age respectively, were: lysine 0·88, 0·48, 0·43; methionine + cystine 0·48, 0·38, 0·29; protein 14·5, 9·3, 7·6.

4. The goslings did not respond to glycine supplementation of the diet.

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. A method is described whereby a large quantity of rumen microbial dry matter of high purity was isolated from whole rumen contents obtained from abattoirs, by means of a continuous process of one filtration through four sieves followed by three differential centrifugations.

2. The contents of ash, carbohydrate, lipid, nitrogen, RNA, DNA and individual amino acids of the three centrifugal fractions are given and compared with values summarized from more than sixty published reports on the chemical composition of rumen micro-organisms isolated from both whole rumen contents and pure cultures.

3. The amino acid composition of isolated rumen micro-organisms, in particular that of the bacteria, was found to be remarkably constant.

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.

Four experiments were conducted with eighteen lambs sustained entirely by intragastric nutrition at gross energy inputs varying from 430 to 860 kJ/kg live weight0·75 (W0·75). Isolated rumen micro-organisms (RMO) were infused into the abomasum in quantities varying from 0 to 2 g digestible N/kg W0·75 to assess the increase in N balance as a result of increasing RMO input when N was limiting.

The over-all utilization of N from RMO (RMO-N) could be described by the equation y = 0·543 x −0·457, residual SD = 0·037, where y is the N balance and x is the abomasal input of RMO-N, both expressed in g/kg W0·75. Thus the coefficient of efficiency of utilization of infused RMO-N was 0·543 (SE 0·008). The coefficient of efficiency of utilization of RMO-N truly digested (i.e. the biological value) was 0·659 (SE 0·015).

The RMO-N input (mean with SE) at N equilibrium was 0·843 (0·009) g/kg W0·75. The true digestibility of RMO-N was 0·813 (0·004). The urinary N excretion when no N was infused was 0·329 (0·008) g/kg W0·75 and the N excreted via the faeces with zero N input was 0·036 (0·009) g/kg W0·75.

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.