1. Female hooded rats (65g) were maintained on a high-protein (HP) or low-protein (LP) diet for 2 weeks (ratio, energy supplied by utilizable protein: total metabolizable energy 10 and 3.5 respectively) and the oxidation of both L- and DL-[1-14C]leucine in vivo was measured in the fed and fasted animal.

2. Oxidation of leucine in vivo was reduced in the animals given the LP diet. Fasting caused an increase in the oxidation of the branched-chain amino acids.

3. Leucine-α-oxoglutarate transaminase (EC 2.6.1.6) and α-ketoisocaproic acid dehydrogenase were measured in both liver and gastrocnemius muscle from rats fed on the HP or LP diet. Enzymes were also assayed after a 48 h fast in a group of animals previously maintained on the HP diet.

4. The LP diet led to a fall in muscle dehydrogenase activity without any alterations in liver enzyme activity. Fasting also reduced muscle dehydrogenase activity but increased liver dehydrogenase activity.

5. The presence of a dehydrogenase in muscle and its ability to adapt to dietary stress at a time when the liver enzyme is unaffected suggests that muscle is the most important site for control of leucine oxidation.

6. Transaminase activity in muscle rose in the LP and fasted animals but the activity in liver was unchanged.

7. Oxidation, incorporation into protein of [U-14C]leucine and the pool sizes of free leucine in plasma and in the extensor digitorum longus muscles were measured. The rats were maintained under the feeding conditions described above. The ability of incubated muscles to incorporate [14C]leucine into protein in both the fasted animals and those fed on the LP diet was reduced. Oxidation of leucine in muscle was reduced in protein deficiency but there was little change in the evolution of 14CO2 from [U-14C]leucine on fasting.

8. The increase in pool size of free leucine in fasted animals is probably important in determining its rate of oxidation in muscle, as 14CO2 production was maintained despite falling activities of the dehydrogenase enzyme activity. The muscle enzyme accounted for 90% of the calculated body capacity for oxidation; activity in liver is insufficient to deal with normal rates of oxidation. Muscle enzyme is normally in excess of that required for the oxidation of branched-chain amino acids.

1. Chicks at 10 d of age were given diets containing all the nutrients known to be required, with L-amino acids in place of protein. Dietary supplements were added isonitrogenously.

2. Ox liver (100 g/kg) greatly improved the chicks' growth rate, whereas torula yeast (50 g/kg) was inactive. The activity of fresh moist liver was considered to be due largely to an organic factor, because of the inactivity of water and the low activity of liver ash.

3. The growth rates of chicks receiving diets based upon casein and isolated soya-bean protein were significantly improved by the inclusion of 100 g fresh ox liver/kg, but not of 50 g torula yeast/kg.

4. These results show that chicks receiving an amino acid diet require an organic growth factor (Progressin) that differs from the yeast factor required by rats receiving an amino acid diet.

1. Rats were given diets containing 200 g/kg of a complete or incomplete amino acid mixture or of high- or low-quality proteins. After 6 d the amino acid-incorporating activity of ribosomes from skeletal muscle and liver was studied.

2. The level of isotope incorporation relative to ribosomal RNA was similar for casein supplemented with methionine and for a complete amino acid mixture with the composition of whole-egg protein. Per wet weight of tissue there was a significant decrease after feeding with the complete amino acid mixture.

3. There was a significant decrease in activity after feeding with amino acid mixtures deficient in lysine, methionine or tryptophan. In skeletal muscle, but not in liver, the ribosomal activity was less than that obtained with wheat gluten. Activity per wet weight of both tissues was less than that obtained with wheat gluten.

4. Refeeding with methionine for 1 d resulted in complete restoration of ribosomal activity and activity per wet weight in skeletal muscle.

5. After lysine deficiency, protein synthesis per unit wet weight of both tissues and ribosomal activity in liver were not restored after 2 d of refeeding. Recovery of ribosomal activity in skeletal muscle was complete after 1 d.

6. Rats receiving the 200 g casein/kg diet supplemented with methionine at daily energy levels of 263, 176, 141 and 106 KJ (62.6, 42.1, 33.7 and 25.3 kcal) showed no changes in ribosomal activity, but there was a significant decrease in activity per wet weight when 106 KJ were given.

1. In order to reinvestigate the classical concept of specific dynamic action of food, the thermic effect of ingested glucose (50 g) or essential amino acids (50 g) or both was measured in seven healthy male subjects dressed in shorts, by using both direct and indirect calorimetry simultaneously. Experiments were performed under conditions of thermal comfort at 28°.

2. Energy ‘balance’ (heat production minus heat losses) was negative during the control period (mean heat deficit: −16.0 ± 0.8 kJ/m2 per h.

3. Metabolic rate increased 13.6 ± 1.8% after the glucose load, 17.2 ± 1.4% after amino acids, and 17.3 ± 2.9% after both glucose and amino acids: thus there was no additive thermic effect when both nutrients were given together.

4. In contrast to the metabolic rate, heat losses were not significantly altered after nutrient ingestion; consequently, the energy ‘balance’ became rapidly positive.

5. These results show that: (a) the food-induced thermogenesis, for a moderate energy intake, is less dependent on the nature of the nutrients than was classically admitted; (b) this increased heat production mainly induces changes in heat storage rather than in heat losses during the first hours following ingestion of a meal.

1. Samples of mixed bacteria were separated from rumen digesta taken from calves, kept out of contact with adult animals, and from sheep and cows.

2. For calves receiving a diet made up of equal amounts of roughage and cereals with 13–16 g nitrogen/kg dry matter, samples of mixed bacteria taken 4–6 h after feeding contained, on average, 140 g glucose in α-linked polymers (α-dextran), 25 g galactose and a total of 25 g other non-glucose, non-galactose sugars (mainly rhamnose, ribose and mannose) in combined forms per kg dry matter.

3. The α-dextran content of similar bacteria samples from sheep or cows receiving diets of similar composition was 70 g/kg dry matter. Samples from animals receiving all-roughage diets contained only 25 g α-dextran/kg dry matter, but those from cows given more than 70% of their ration as concentrates (mainly cereal) contained 150 g α-dextran/kg dry matter.

4. Addition of supplementary protein or urea to cereal–roughage diets given to calves greatly depressed the amount of α-dextran in the rumen bacterial samples to an average value of 60 g/kg dry matter.

5. Samples taken before a morning feed (i.e. after 16 h fasting) contained less α-dextran than samples taken 4–6 h after feeding for both calves and cows.

6. Under different conditions, variations in the amounts of galactose in rumen bacteria sometimes paralleled variations in α-dextran. Amounts of other non-glucose sugars did not vary greatly.

7. It was estimated, from a comparison of the compositions of rumen bacteria and duodenal contents, that, in the latter, the rhamnose, ribose and mannose came mainly from the bacteria, the arabinose, xylose and cellulose-glucose mainly from the diet and the galactose and α-dextran-glucose from both sources.

1. The effect of various dietary levels of molybdenum on uric acid and copper excretion was studied in experiments with four adult men given diets based on two sorghum varieties (Sorghum vulgare Pers.) differing widely in Mo content.

2. With a Mo intake of 160, 540 or 1540 μg/d the urinary excretion of uric acid was unaltered.

3. The excretion of Cu in urine increased with increasing Mo intake.

4. Cu-balance studied with high- and low-Mo diets showed that with a high-Mo diet urinary Cu excretion increased but faecal Cu was unaffected. This indicates that dietary Mo had no effect on Cu absorption.

5. The high serum concentration of Cu with diets high in Mo indicates that Mo either mobilizes tissue Cu or inhibits Cu uptake, or both.

1. The nutrient content of battery, deep litter and free range eggs from domestic hens under systems of management typical of those used in the commercial production of eggs was studied from January to March 1968.

2. Monthly samples of eighteen eggs, supplied by six centres, were homogenized, freezedried, ground and stored at −15°. Their contents of moisture, nitrogen, amino acids, fats, fatty acids and cholesterol, ash, sodium, potassium, calcium and iron, thiamin, riboflavin, nicotinic acid, pantothenic acid, folic acid, vitamin B12, tocopherols and retinol were determined. The mean values for eggs from each system, each centre and each quarter of the year were calculated.

3. For many nutrients, no significant difference between systems was detected; the greatest variations occurred in the content of some vitamins. Free range eggs contained more vitamin B12 than deep litter or battery eggs and more folic acid (Lactobacillus casei assay) than battery eggs. Differences in tocopherol and cholesterol contents were complicated by system-by-centre interactions. There were also small differences in calcium and iron contents.

4. Riboflavin, folic acid (Lactobacillus casei) and vitamin B12 were the only nutrients which were observed to vary with the time of year in the eggs from all systems of management. Major differences were found in the vitamin content of eggs from different centres.

5. Though the differences in vitamin B12 and folic acid contents which result from the different systems of management are of little significance in an average mixed diet, they would be measurable for some individuals who may depend on eggs as an important source of these nutrients.

1. Acetate, propionate, butyrate and glucose were each administered intravenously (2.09 MJ (0.5 Mcal)/d) to lambs on either high-concentrate (HC) or high-roughage (HR) diets in two experiments with 4 × 4 Latin square design. During a control period all animals received a saline infusion.

2. In lambs on the HC diet glucose was the most effective metabolite tested for improving nitrogen retention. Acetate was 51%, butyrate, 75%, propionate, 90% as effective as glucose in promoting N retention. Propionate infusion was most effective in increasing N retention in lambs on the HR diet. Acetate was 60%, butyrate, 75%, and glucose, 80% as effective as propionate. Glucose infusion did not lower plasma urea N (PUN) concentration in lambs receiving the HC diet, but the three volatile fatty acids (VFA) did lower it (P < 0.01). All energy sources significantly reduced the PUN concentrations with the HR diet, but differences between sources were not significant.

3. Plasma concentrations of valine, isoleucine, leucine and phenylalanine were depressed to 57, 71, 89 and 90% of their control values during glucose, propionate, butyrate and acetate infusion. Plasma concentrations of lysine and methionine were significantly decreased from control values (P < 0.05) but there was no significant difference between energy sources. Lysine, valine, isoleucine and leucine were significantly (P < 0.01) higher in lambs given the HR diet than in lambs given the HC diet. The concentration of alanine was greater (P < 0.05) during glucose infusion than during acetate and butyrate infusions, indicating net synthesis of alanine and possibly other non-essential amino acids during glucose infusion, since the plasma free amino acid N concentration increased despite decreased concentrations of plasma essential amino acids during glucose infusion.

4. The results indicated that glucose and propionate were superior to acetate and butyrate as energy sources for protein formation.

5. The poor relationship between PUN and N balance and plasma free essential amino acids suggested that PUN concentration may have been inappropriate to assess the protein status under some dietary conditions.

1. In one experiment according to a latin square design five sheep with fistulas in the abomasum and terminal ileum were given diets based on barley. Five diets were compared, one without protein supplementation, two with different levels of fish meal and two with combinations of fish meal and urea.

2. The amount of non-ammonia crude protein passing through the abomasum and removed from the small intestine increased linearly with fish-meal supplementation but the only effect of supplementation with urea was to increase the crude protein removed before the abomasum. It was concluded that urea did not appear to have a sparing effect on the degradation of dietary protein.

3. Seventy-eight lambs were used in a second experiment. They were given thirteen diets made up from a basal barley diet and different combinations of fish meal and urea.

4. Digestibility of organic matter and efficiency of food conversion increased with each level of fish-meal supplementation. The effects of urea supplementation on organic matter digestibility and efficiency of food conversion depended upon the level of fish meal in the diet and at the highest level of fish-meal supplementation there were no effects.

5. The maximum digestibility of organic matter (about 820 g/kg) could be achieved both with urea alone and fish meal alone and was attained at a lower level of nitrogen in the diet with urea. In contrast, the maximum food conversion efficiency that could be achieved with a fish-meal supplement was much greater than could be obtained with a supplement of urea alone.

1. Ruminal metabolism of labelled phenylacetic acid, 4-hydroxyphenylacetic acid, indole-3-acetic acid, glucose, shikimic acid, phenol, and serine was studied in vitro by short-term incubation with special reference to incorporation rates into aromatic amino acids.

2. Earlier reports on reductive carboxylation of phenylacetic acid and indole-3-acetic acid in the rumen were confirmed and the formation of tyrosine from 4-hydroxyphenylacetic acid was demonstrated for the first time.

3. The amount of phenylalanine synthesized from phenylacetic acid was estimated to be 2 mg/1 rumen contents per 24 h, whereas the amount synthesized from glucose might be eight times as great, depending on diet.

4. Shikimic acid was a poor precursor of the aromatic amino acids, presumably owing to its slow entry into rumen bacteria.

5. A slow conversion of phenol into tyrosine was observed.

1. Protein digestibility of two proteins was measured when these proteins were given together and separately to rats.

2. The influence of carbohydrates on protein utilization (true protein digestibility, biological value and net protein utilization) was also studied. Autoclaved potato starch was replaced by increasing amounts of glucose, sucrose, fructose and lactose respectively. Glucose, fructose and sucrose appeared to have no specific influence on protein utilization when given in increasing amounts and when compared with autoclaved potato starch. Higher concentrations of lactose, however, caused diarrhoea.

3. The true digestibility of the protein components in a mixture was directly related to the true digestibility of each protein component, including proteins of low digestibility.

1. Iron absorption from rice-containing meals was measured by red cell utilization of radioactive Fe in sixty-six volunteer multiparous Indian women.

2. In all the studies salt added during the cooking process was used as the carrier for supplemental inorganic Fe and ascorbic acid.

3. Intrinsic Fe in the rice and supplementary inorganic Fe were absorbed to the same extent, with a wide range of absorption values.

4. There was a striking difference between the mean absorption of a 3 mg dose of ferrous Fe given to fasting subjects in a solution containing 30 mg ascorbic acid and that of Fe in a rice meal (48.7 and 3.5% respectively).

5. When ascorbic acid was added during cooking there was a threefold increase in the absorption of both intrinsic Fe and supplementary Fe when a sufficient quantity (60 mg) was present.

6. It is concluded that the Fe nutrition of rice-eating communities could be improved significantly by the addition of ascorbic acid to the diet.

1. Studies have been made of the effects of different concentrations of either free or esterified linoleic acid on the biohydrogenation of linoleic acid by rumen micro-organisms in vitro. A comparison has been made with the changes which occurred in the fatty acid compositions of rumen free fatty acids and plasma triglycerides of sheep given intraruminal infusions of linoleic acid or maize oil.

2. In the in vitro experiments, with increasing concentrations of 18:2 added as the free fatty acid, a decreasing proportion of this 18:2 was hydrogenated to 18:0 and trans-11-octadecenoic acid accumulated. The accumulation of large amounts of trans-11-octadecenoic acid was accompanied in all instances by the accumulation of a conjugated diene identified as cis-9, trans-11-octadecadienoic acid. There appeared to be a product–precursor relationship between the conjugated diene and the trans-11 monoene.

3. When linoleic acid was presented in vitro as the triglyceride, the extent to which hydrogenation occurred was, in all instances, greater than when equivalent amounts of 18:2 were presented as the free acid. Only small amounts of the cis-9, trans-11 diene were detected, and there was no apparent product–precursor relationship between this conjugated diene and the C18 monoenoic acids. The C18 monoenoic acids that accumulated consisted of both cis and trans isomers; the cis isomers consisted largely of cis-9- and cis-11-octadecenoic acids, which together comprised about 30% of the C18 monoenoic acids present.

4. The infusion of free linoleic acid into the rumen of sheep resulted in an increase in the proportion of total 18:1 and a decrease in the proportions of 16:0 and 18:0 in the total rumen free fatty acids. This increase which occurred in the concentration of 18:1 consisted predominantly of the trans-11 isomer. A concomitant increase in the concentration of the C18trans-11 acid was observed to occur in the fatty acids of the plasma triglycerides. Infusion of maize oil into the rumen of sheep resulted in little change in the fatty acid compositions of either the free fatty acids in the rumen or the triglycerides of the plasma.

5. The findings in vitro and in vivo are discussed with reference to each other and with reference to the possibility that biohydrogenation of 18:2 derived from the triglyceride proceeds by a different pathway from that of 18:2 presented as the free acid.

1. Heat losses associated with the utilization of metabolizable energy for synthesis of protein and of fat during growth were studied in Zucker rats selected for normal leanness or congenital obesity.

2. Measurements of energy and nitrogen balance were made on groups of four lean and four fat rats offered food ad lib. and kept at 22°. Balance trials were also conducted on groups of fat or lean rats offered restricted amounts of food at two levels and kept at 22° or 28°. The medium rations offered to fat and lean rats were the same. The energy and N contents of fat and lean rats were determined by carcass analysis at 35 d and at about 90 d of age.

3. At ad lib. intake, fat rats ate 38% more than lean rats. Heat losses and N balance were similar. When fat and lean rats were pair-fed, heat loss and N retention were lower in fat rats. Absolute values and changes during growth of heat loss (kJ/rat per 24 h) were closely correlated with values obtained for N balance.

4. Carcass analysis showed that energy retention in protein was, on average, 75% in lean rats but only 14% in fat rats. Estimates of energy retention from slaughter experiments and balance trials agreed well, but marked discrepancies existed between the different estimates of N retention.

5. The net efficiencies of utilization of metabolizable energy for growth in lean and fat rats were 0.485 and 0.614 respectively. The energetic efficiencies of net protein synthesis and net fat synthesis were estimated to be 43 and 65% respectively.

6. The interactions between appetite, growth and activity in the development of obesity in the Zucker rat are discussed.

1. The effects of the protein content of the diet on the vitamin B12 concentration of serum and of various tissues were studied in rats by means of microbiological and radioisotopic techniques.

2. Protein starvation reduced tissue weights and nitrogen contents, serum protein concentrations and haemoglobin values.

3. The vitamin B12 contents of the serum and of several organs and tissues were greater in the protein-starved animals for reasons that remain unexplained.

4. The retention of radioactive cyanocobalamin per g fresh weight was significantly greater in liver, kidney, spleen and brain in the protein-depleted rats than in those given adequate protein. However, the total tissue retention was not significantly different between these groups, so that there was a greater capacity for tissue binding and for body conservation of vitamin B12 in the protein-starved animals.

1. Ten severely malnourished children were studied.

2. During recovery the mean energy intake was 916 kJ (219 kcal)/kg per d when the children were fed ad lib. on a high-energy milk preparation.

3. When a lower-energy milk preparation was given ad lib. the children voluntarily increased the volume consumed but the mean energy intake fell to 703 kJ (168 kcal)/kg per d.

4. After recovery the children no longer consumed an increased volume when the lower-energy milk preparation was offered.

5. The results provide further evidence of the importance of feeding with a high-energy preparation for the treatment of malnutrition, and demonstrate that additional benefits can be obtained by offering such mixtures ad lib.

1. A method was developed for the estimation of tryptophan in purified proteins or in feeding-stuffs. Samples were hydrolysed by autoclaving them with barium hydroxide in polypropylene flasks or tubes. Excess Ba was precipitated as the hydroxide by cooling, and hydrogen sulphide formed during hydrolysis was removed under reduced pressure. Tryptophan was assayed colorimetrically with dimethylaminobenzaldehyde by comparison with tryptophan standards carried through the complete procedure.

2. The method was applied to purified proteins, to analysed materials and to a wide range of samples. Results agreed fairly well with published values for purified proteins, though rather less well for the samples analysed by other workers. Reasons are discussed. The samples examined gave results in the expected range.

1. Preruminant calves, some of which were equipped with re-entrant cannulas in the small intestine, were given liquid feeds in which various starches, maltose or lactose formed the sole source of carbohydrate.

2. The sugars left the abomasum at the same rate as a water-soluble marker but the starches were greatly delayed. Little starch left the abomasum until about 5 h after feeding. Examination of abomasal contents 0.5 h after feeding showed the starch to be associated with the casein clot.

3. Amounts of starch, maltose and lactose removed during the passage of digesta through the small intestine were about 60, 43 and 97% of intake respectively, with no marked difference with age between about 7 and 16 weeks.

4. No change in blood glucose was apparent in calves given starch-containing feeds. The possible effect of the retention of dietary starch in the abomasum in minimizing blood glucose responses is discussed.

1. Pigs from 20 to 47 kg live weight were given a wheat–safflower diet supplemented with either 0, 2 or 4 g L-lysine/kg either once daily or in six equal portions at intervals of 3 h.

2. The addition of lysine at both levels significantly (P < 0.001) increased growth rate, feed conversion and lean content of the ham.

3. Frequency of feeding had no effect on the response of pigs given the control diet.

4. A significant interaction (P < 0.05) between frequency of feeding and lysine supplementation occurred for growth rate. Growth responses to the supplements of 2 and 4 g L-lysine/ kg with once-daily feeding were only 43 and 69% of those achieved under the frequent-feeding regimen.