1. Ewes were made hypocupraemic by feeding a copper-deficient diet and the subsequent responses in plasma Cu obtained when Cu was added to the diet were used to assess the biological availability of the added Cu.

2. The uniformity of responses was investigated by repleting thirty-six ewes for 33 d on two occasions with a standard diet containing 5.0 mg Cu/kg dry matter (DM). The mean responses were 0.36 and 0.33 mg/l and the coefficient of variation was approximately 53% on each occasion. The marked individual differences were largely repeatable, the correlation coefficient (r) within individuals being 0.68 (P < 0.001).

3. A dose: response relationship was investigated by giving five groups of seven ewes diets containing 2.7, 4.2, 5.7, 7.2 or 8.7 mg Cu/kg DM for 33 d. Each increment in dietary Cu above 4.2 mg/kg significantly increased the response in plasma Cu. The relationship between plasma Cu response (y, mg/l) and Cu intake (x, mg/d) after 21 d was y = 0.0871x−0.250 (r = 0.99; 3 df).

4. The source of individual variation was investigated by comparing the responses of three ‘slow’ and three ‘fast’ responding ewes from Expt 1 to Cu given as a continuous intravenous infusion at rates of 0.05–0.3 mg/d. The relationship between plasma Cu response (y) and infusion rate (x, mg/d) after 17 d, was y = 2.135x –0.156 (r = 0.86; P < 0 .001). The regression coefficients for ‘slow’ and ‘fast’ responding ewes were similar, as was their metabolism of intravenous 64Cu, suggesting that the individual differences were due to differences in absorption rather than in the metabolism of absorbed Cu. Faecal endogenous Cu excretion was estimated to be 0.127 ± 0.019 (mean ± SE) mg/d.

5. The relative responses to oral and intravenous Cu were used to estimate the true availability of dietary Cu; in one experiment it was 4.1% and for individual ewes in another experiment, availabilities ranged from 4.5 to 11.4%. The figures are compared with assessments by conventional techniques.

6. It is concluded that the repletion technique provides a sensitive means of assessing the availability of Cu in ruminant diets.

1. Results from metabolic balance studies in young adult men were examined for the relationships between the concentration of serum urea (SUN) and the efficiency of dietary nitrogen utilization. A total of 231 separate balance periods were included in the analysis. Net protein utilization (NPU) was used as an index of dietary protein quality.

2. Protein intake ranged from 0·27–0·73 g/kg body-weight per d in the various experiments. There was a highly significant negative correlation between NPU and urea levels. The relationship was: NPU = 1·23–0·029 × SUN (mmol/l) (r = −0·89).

3. These results are considered in relation to the evaluation of protein quality in adult humans.

1. Developing rats were growth-retarded during gestation and the suckling period by underfeeding their mothers from mating. After weaning, all animals were fed ad lib.

2. At 18 weeks each male was paired with another male for 10 min on 4 consecutive days. Tests 1 and 2 were with males of like-treatment group and tests 3 and 4 with males of unlike-treatment group.

3. Pairs of previously undernourished rats boxed and fought more often than pairs of controls. In the mixed pairings of tests 3 and 4 the previously underfed animals initiated contact more frequently than did their control partners.

4. Evidently there is a lasting effect of early nutritional deprivation on inter-male social behaviour, especially when both of the animals interacting are of the previously undernourished type.

1. A study was made of factors affecting the plasma concentrations of free amino acids (PAA) and urea (PU) in calves receiving approximately equal daily amounts of concentrates (flaked maize and protein supplements) and straw, the former at 10.00 and 17.00 hours, the latter at 17.00 hours only.

2. For calves receiving a diet containing 20 g nitrogen/kg dry matter in which the protein supplement was decorticated, extracted groundnut meal (DCGM) (diet A) there were marked increases in PAA and PU about 1–2 h after a morning feed, then a fall in these values 2 h later to a level which was maintained for the next 3 h. No similar changes occurred after the evening feed. Samples taken 3 h after the morning feed were used in subsequent comparative experiments. There was much more variation between animals than within animals in total PAA, PU and the concentrations of most individual amino acids in these samples.

3. Total PAA and most individual amino acid concentrations were not appreciably affected when the DCGM intake was reduced to give 10 g N/kg dry matter in the diet (diet C), but PU was halved. When maize gluten replaced DCGM as the protein supplement at the higher N intake (diet B) then PU doubled, but again total PAA and most individual amino acid concentrations were little affected. Exceptions were arginine, which was halved, and leucine, which was doubled.

4. Infusions of more than 4·4 g L-methionine/d into the abomasums of calves (110–160 kg live weight) receiving diet A led to a marked increase in plasma methionine concentration. This was considered to correspond with the point at which methionine requirements were met. Using a chromic oxide marker to estimate flows of methionine and cystine from the rumen to the duodenum, it was calculated that under these conditions the methionine requirement was 9·8 g/d, with a cystine flow of 4·9 g/d. Similar calculations showed the corresponding value to be 7·5 g/d with a cystine flow of 2·8 g/d for calves receiving diet C.

5. Infusion of increasing levels of L-lysine into the abomasums of calves (110–160 kg live weight) receiving diet B led to a progressive increase in plasma lysine concentration. There was no consistent change in the rate of increase with increasing amounts infused. Estimated lysine requirement appeared therefore to be less than the flow of lysine from the rumen to the duodenum under these conditions (18·8 g/d).

1. The subcellular distribution of copper, zinc and iron was investigated in liver and kidney homogenates from Cu-deficient and control rats. The supernatant fraction contained most Cu and Zn in control animals, but the highest proportion of Fe was in the microsomal fraction.

2. Cu deficiency reduced the concentration of the metal in all fractions, but the depletion was most severe and developed most rapidly in the supernatant fraction, indicating that the soluble cytoplasm is the site of Cu storage in the cell. The Fe content of the liver increased during Cu deficiency with Fe being deposited preferentially in the mitochondria.

3. All the Cu and most of the Zn in liver and kidney supernatant fractions occurred in four protein-containing fractions that were of similar molecular weights in both organs. A fraction of molecular weight 30000 was primarily concerned with Cu storage in mature rats.

4. The reduction in liver Zn during Cu deficiency appeared to be the result of impaired intestinal absorption and it is suggested that a small amount of Cu facilitates the absorption of Zn.

1. Sterol metabolism was studied in rats fed on a semi-synthetic fibre-free diet and in rats fed on diets containing cellulose (200 or 100 g/kg) or sugar-cane fibre (bagasse) at the same levels.

2. Rats fed on the diets containing cellulose or bagasse produced significantly greater quantities of faeces than did rats fed on the fibre-free diet.

3. Rats given bagasse excreted more bile acid and more neutral sterol in their faeces than did rats fed on cellulose or on the fibre-free diet.

4. After 28 d, hepatic synthesis of cholesterol (from acetate) and cholesterol 7α-hydroxylase activity were significantly higher in animals fed on bagasse than in animals fed on the other two diets.

5. No significant differences in serum cholesterol levels were seen in rats fed on any of the three diets.

6. Food consumption was not substantially altered by the inclusion of bagasse or cellulose in the diets, although the efficiency of foodstuff utilization was generally lower.

7. Bagasse adsorbed substantial quantities of cholic acid in vitro, whereas cellulose did not. The lignin fraction prepared from bagasse contributed only slightly to the total bile acid-binding capacity of bagasse.

8. The results are discussed in the light of possible effects of dietary fibre on sterol metabolism in man.

1. The effect of folic acid deficiency on collagen formation, with respect to the level of collagen-protein synthesis and the extent of collagen-proline hydroxylation, has been studied. A folic acid-free diet containing 10 g sulphasuxidine/kg was used to induce folate deficiency in young male rats. Animals were judged folic acid-deficient on the grounds of retardation of growth, characteristic haematological changes and the urinary excretion of formimino-L-glutamic acid.

2. From isotope incorporation studies it was found that folic acid deficiency caused a marked impairment in collagen synthesis. It was shown, however, from the use of pair-fed control animals, that this was due in part to a reduced food intake accompanying the vitamin deficiency. The further reduction in synthesis in addition to that attributable to inanition was considered to arise from an involvement of folic acid in general protein synthesis, since it was found that the synthesis of elastin and non-collagenous skin proteins was similarly impaired.

3. Reduced synthesis of collagen was not considered attributable to lack of hydroxylation of peptidyl proline that may occur in ascorbic acid deficiency. Hydroxylation of collagen- and elastin-proline was only very slightly impaired in folic acid deficiency. It was concluded that, at least when ascorbic acid is present, folic acid is not directly essential for the hydroxylation, in vivo, of peptidyl proline. The results support the view that ascorbic acid participates direct, in vivo, in this hydroxylation rather than indirect by simply maintaining an adequate level of reduced folates. They do not, however, exclude the possibility, arising from the known ability of tetrahydrofolate to participate in the hydroxylation of collagen proline in vitro, that when both ascorbate and folate are present, the latter may, in some measure, share in the role of reducing agent in the hydroxylation of peptidyl proline in vivo.

1. Young steers were fed either 20 or 4 h before exposure to a thermoneutral or a moderately cold environment. Measurements were made of total oxygen consumption (total VO2), respiratory quotient (RQ) and hind-leg blood flow (leg Q) and oxygen uptake (leg VO2). The arteriovenous difference in plasma concentrations of individual volatile fatty acids (VFA) across the leg was also measured. Net exchange and fractional uptake of VFA by the leg were calculated from these results.

2. Cold exposure doubled total VO2, significantly decreased the RQ and caused 3-fold and 10-fold increases in leg Q and leg VO2 respectively in both 4 h- and 20 h-fed steers. Arterial plasma concentrations of total VFA (which was more than 95 % acetate) and net leg uptake of VFA also significantly increased in both groups. Cold had no effect on the fractional uptake of VFA by the leg.

3. Feeding shortly before the experiment caused a significant increase in total VO2 in thermoneutrality only, and in RQ, arterial plasma VFA and net VFA uptake by the leg in both environments. There was a significant decrease in the fractional uptake of VFA by the leg.

4. Calculations suggest that although circulating acetate could, in theory, supply over 60 % of the energy required by the hind leg in the resting, fed animal, less than 30 % of the increased requirement of the shivering leg could be supplied by acetate during acute cold exposure, even shortly after feeding.