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. 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. 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. 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. 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. 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.

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. An experiment was conducted with three sheep maintained entirely by intragastric nutrition to estimate the digestibility of isolated individual constituents and amino acids (AA) of rumen micro-organisms (RMO) in the small intestine.

2. Five levels of RMO were infused into the abomasum. The apparent and true disappearance of the individual components were measured by regression of abomasal input on the passage at the ileum.

3. The true digestibility values of N, AA-N, DNA and RNA were 0·82, 0·85, 0·81 and 0·87, respectively.

4. The digestibility of individual AA varied between 0·80 and 0·88, the only exceptions being diaminopimelic acid (0·37), histidine (0·68) and cystine (0·73), which were significantly lower than the average (0·847).

5. The endogenous components in the ileal fluid in sheep given protein-free infusions, expressed in mg/kg live weight0·75 per d, were total N 42 and AA-N 20.

1. To estimate the tryptophan requirement of the kitten, six male and six female kittens were presented diets containing 0·7, 0·9, 1·1, 1·3, 1·5 and 3·0 g tryptophan/kg diet for six experimental periods lasting 10 d in accordance with a 6 × 6 balanced Latin-square design.

2. Mean daily weight gain and nitrogen retention (N intake minus urinary and faecal N) plateaued at 1·1 g tryptophan/kg diet indicating that the minimal tryptophan requirement of the kitten was 1·1 g/kg diet.

3. Plasma tryptophan concentration exhibited a marked increase at dietary tryptophan concentrations above 1·3 g/kg diet.