1. Changes in strength of cotton, Italian ryegrass leaf, hay stem and barley-straw stem on immersion in the contents of the reticulo-rumen, at two sites in the rumen and at one site in the reticulum, for periods of up to 56 h were measured using a cow on a hay diet. Specimens of the fibrous materials were immersed in the rumen digesta in such a way that they were not damaged by agitation or by rumination.

2. Load-to-fracture and elongation were measured on a machine using a constant-speed cross-head at a strain of about 10−3/s. The ratio strength:density (breaking load/mass per unit length) was determined.

3. Leaf of Italian ryegrass and stem of hay and of barley straw had strengths of about 37, 150 and 210 MN/m2. They lost strength at different rates when immersed in the rumen digesta, the times to half strength being in the ratio grass: hay: straw = 1:1.9:3.8. The similarity of this ratio to that for total time for eating and ruminating as given by Balch (1969), namely 1:2.0:3.5, for similar materials was noted.

1. The kidneys of normal rats were analysed for water, fat, protein, RNA and DNA, at 10, 21 and 36 d after birth. The effects on growth caused by two types of malnutrition were investigated.

2. An increase in the RNA:DNA ratio was demonstrated between 10 and 36 d, contrary to previous evidence that this ratio is fixed at birth.

3. Energy deficiency during the first 21 d of life resulted mainly in fewer kidney cells, whereas protein-energy deficiency between 21 and 36 d resulted mainly in a smaller cellular content of RNA and protein.

4. In response to metabolic acidosis, both groups of malnourished rats increased urinary excretion of ammonia and there was enhanced gluconeogenesis in vitro; the basal rate of gluconeogenesis was lower in the protein-energy-deficient rats than in the controls.

5. Protein-energy-deficient rats did not exhibit the renal hypertrophy shown by the control rats in response to acidosis.

1. The changes in the concentration of some enzymes and their metabolites were studied in the first stages of vitamin A deficiency in chicks.

2. Kidney arginase (EC 3.5.3.1) and liver xanthine dehydrogenase activities had increased even before complete disappearance of vitamin A from the plasma. Similarly, an increase was found in plasma uric acid, and plasma urea also increased but to a lesser extent. Liver proteolytic activity also was slightly increased by vitamin A deficiency.

3. Kidney D-amino acid oxidase (EC 1.4.3.3) activity and plasma concentrations of total protein and free amino acids were not affected, at least in the first stages of the deficiency.

4. Oral dosing of deficient chicks with retinyl palmitate to provide 300 μg retinol, 24 h before killing, brought about a decrease in the activities of both enzymes and of plasma uric acid, and an increase in plasma urea.

5. Dietary levels of vitamin A were reflected not only in the liver concentrations of the vitamin but also in the plasma concentrations.

1. The duodenal flow of digesta and the concurrent pancreatic secretion were compared when six Ayrshire calves, with duodenal re-entrant and pancreatic sac cannulas, were fed on three reconstituted milks. The diets were: reconstituted, ‘mildly’ preheated, spray-dried skim-milk powder (SK); the same skim milk containing 20 g fat/l (SKF); and reconstituted, ‘severely’ preheated skim-milk powder containing 20 g fat/l (HSKF). The calves were fed ad lib. from teats twice daily from 9 to 21 d of age, each diet being offered for 4 d. Collections of duodenal digesta and pancreatic secretions were made for 12 h after the fourth and eighth meals on each diet.

2. The calves tended to have the highest liquid intakes when diet SK was given. After adjustment for differences in intake, diet SK resulted in the appearance of more hydrogen, chloride and potassium ions but less undigested protein nitrogen in the duodenal digesta than with either diet SKF or HSKF.

3. Compared with diets SK and SKF, the whey fluids from diet HSKF took significantly longer to leave the abomasum, less H+ passed through the duodenum during the first 6 h after feeding and less Cl− during the whole postprandial period. More undigested protein N and fat from diet HSKF passed through the duodenum during the first 6 h after feeding, although this difference was significant only for protein N during the 1st hour after feeding.

4. Over the 12 h postprandial period, the duodenal digesta contained almost exactly the same quantities of polyethylene glycol (PEG), N and fat as those in the meal. The total volume of digesta was 2.25 l greater than the quantity of milk ingested. When the hourly duodenal flows of PEG and fluid were expressed as the square root of the hourly quantities recovered, the pattern of abomasal emptying was rectilinear. The flows of N and fat were curvilinear, when expressed on the same basis.

5. The concentration of ‘sodium-free’chloride in the duodenal digesta, in excess of that ingested in the milk, was used as an indicator of the quantity of acid secreted by the abomasum. The relative quantity of acid secreted was greatest with diet SK and least with diet HSKF.

6. The pancreatic secretion of fluid was highest during the period 5–9 h after feeding but the secretion of enzyme activity was highest during the first 2 h after feeding.

7. Considerable variability in the secretion of enzyme activity was observed and the rate of secretion did not appear to be related to any component of the duodenal digesta.

8. Diet SKF was associated with a greater volume of pancreatic secretion and more pancreatic protease secretion than either diet SK or HSKF, but most amylase activity was secreted when diet HSKF was given. Evidence is presented which suggests that pancreatic enzyme activity adaptation occurred when diet HSKF was offered in succession to diet SK or SKF. The secretion of trypsin activity did not differ between diets.

1. A protein-free diet, to which an odour had been added, was offered to rats immediately after giving a gastric load of an histidine-free, but otherwise balanced, amino acid mixture. The same diet with a different odour was offered to the rats on another day, after administration of a control load of saline or a balanced amino acid mixture. After access to stock diet for 6 h of 1 d, the rats were offered two samples of protein-free diet, each with one of the two odours.

2. The rate of consumption of odorized protein-free diet was depressed 2–4 h after administration of the histidine-free load. In the later preference test, the dietary sample with odour which had been offered after the deficient load was rejected in favour of the sample with the odour which had been offered after the control load.

3. Rejection of the deficiency-paired odour in the final preference test did not occur when the histidine-free load had been given 2 h before the rats were first offered odorized diet. Also, there was in these instances no depression of rate of food consumption 2–4 h after loading. This indicated that aversive reactions to the odour were established by association of the odour with some effect of the histidine-free load which had occurred within 2 h of its administration, and that the early depression of intake and the much later rejection during choice were both expressions of these acquired reactions.

4. This rapid conditioning of selective rejection did not depend on previous prolonged protein deprivation or on the use of immature rats but did depend upon an intermittent supply of amino acids during 3 d before conditioning. Subcutaneous injection of deficient amino acid mixture did not establish rejection, suggesting that conditioning depended on rapid delivery of the deficient mixture into the circulation.

5. It is concluded that the critical biochemical events which lead to the rejection of diets that are imbalanced or deficient in essential amino acids occur soon after ingestion of the diet, and may have been effective in producing a conditioned aversion before any suppression of food intake appears. It is suggested that the depression of food consumption, which is the normal response to an imbalanced diet, is in this instance the result of conditioned response to sensory qualities of the diet rather than to the direct effect of biochemical stimuli.

1. The rate of flow of digesta along the intestinal tract, and particularly the changes occurring in proteins during their passage through the intestine were determined in six rams; each animal was fistulated with three cannulas which involved six different sites of the intestine. Cr2O3 was used as a marker substance to measure the rate of flow of the digesta.

2. In the sections of the intestine from 1 to 15 m posterior to the pylorus the amounts of water, dry matter and total nitrogen decreased gradually as a result of their absorption through the intestinal wall. The region of the intestine situated at a distance of 7–15 m from the pylorus was more active with respect to the absorption of N, whereas water and dry matter were adsorbed to a greater extent in the region from 1 to 7 m from the pylorus.

3. The only part of the intestine in which substantial increases of water, dry matter and total N were found was the section immediately distal to the pylorus, and these increases were caused by the inflow of bile, and pancreatic and duodenal juices. The net increase found beyond the entry of the common bile duct was 2.7 g protein N and 2.0 g non-protein N (NPN)/24 h.

4. The activities of trypsin, chymotrypsin and carboxypeptidase A and the ratio α-NH2 NPN: protein N increased from the pylorus up to a distance of 7 m and decreased again from this point to a distance of 15 m from the pylorus.

5. In the sections of the intestine between 1 and 3 and between 3 and 7 m distant from the pylorus the extent of proteolysis exceeded considerably that of absorption of amino acids through the intestinal wall. This was concluded from the decrease in the rate of flow of protein amino acids (by 31% between 1 and 3 m distant from the pylorus and by 34% between 3 and 7 m) and the simultaneous increase in non-protein amino acids (by 20% in the region between 1 and 3 m) or no change in non-protein amino acids (between 3 and 7 m).

6. The relatively greater decrease in non-protein amino acids (by 57%) compared with that of protein amino acids (by 41%) occurring in the section 7 to 15 m distant from the pylorus showed that this is an area of most intensive absorption of amino acids.

7. In the lower section of the intestine, from 15 to 25 m distant from the pylorus, the total amount of amino acids showed almost no change; probably a net effect of loss and gain of amino acids mainly due to microbial activities. Increases in the dehydrogenase activity suggested enhancement of bacterial activity in this lower region of the intestine.

8. The supply of essential amino acids to the tissues of sheep is improved, compared with the amino acid composition of the diet, as the result of ruminal biosynthesis of essential amino acids and ruminal degradation of non-essential amino acids and preferential absorption of essential amino acids through the intestinal wall, particularly in the section of most intensive absorption, 7–15 m distant from the pylorus.

1. Five proteins, freeze-dried cod muscle, a white fish meal, a yeast-protein concentrate, a soya protein and a fish-protein concentrate (a solvent-extracted fish meal) were given separately, as single sources of protein in diets containing 500g crude protein/kg, to small plaice (Pleuronectes platessa) of mean initial weight 12–15g. Weight gain and net protein utilization (NPU) were examined.

2. Even at these high protein intakes, significant differences in growth rate between fish given the different proteins were evident. These findings were reflected in different NPU values between the proteins. This position contrasts with that in the rat where proteins which differ markedly in NPU at low protein intakes have similar NPU values when given at high dietary levels.

3. Coefficients of apparent digestibility measured on larger plaice (150–200g) were high for all the proteins used except soya-bean meal, which had a digestibility coefficient of 0.68.

4. At high protein intakes there was no clear relationship between NPU values and essential amino acid content (as measured chemically) of the proteins tested.

5. The preparation of protein concentrates from fatty fish by the use of detergents is described. One of the preparations obtained gave weight gains and NPU values similar to those obtained with commercially available feedstuff proteins.

1. Sheep, cows and calves fitted with rumen cannulas were given diets mostly containing 10–16 g nitrogen/kg dry matter and consisting of roughage and cereals. Mixed bacteria were separated from samples of their rumen contents.

2. Bacteria taken 4–6 h after a feed from calves which were kept in an experimental calf-house with no contact with adult animals (environment A) contained more α-dextran, less total N and higher nucleic acid:total N ratios than similar bacteria from calves reared in contact with adult sheep (environment C) but otherwise treated in an identical way.

3. Mixed bacteria taken 4–6 h after a feed from sheep and cows were similar in composition, with respect to nitrogenous components, to those from the ‘environment C’ calves. This composition did not vary significantly when diets containing differing proportions of roughage were given.

4. The ‘environment A’ calves were free of ciliate protozoa. When they were placed in contact with, and were inoculated with rumen contents from, adult cattle (environment B), they rapidly developed a normal protozoal population and the chemical composition of their rumen bacteria became like that of the bacteria from the ‘environment C’ calves.

5. Mixed bacteria taken just before a feed, from either cows or ‘environment A’ calves, showed significantly lower RNA-N:total N ratios and slightly (but not usually significantly) higher DNA-N:total N ratios than bacteria taken 4–6 h after feeding. Total N contents of the bacteria did not change consistently with time after feeding.

6. The possible significance of these differences in relation to the nutrition of the host animal is discussed.

1. Test diets were given to chicks from 1 to 28 d of age. The basal diet contained soyabean meal as the sole source of protein and contained no vitamin B12.

2. The basal diet supported poorer growth and feed conversion efficiency than did the same diet supplemented with 0.01, 0.03 or 0.3 mg cyanocobalamin/kg.

3. Each of the four diets was also offered with a supplement of 20 g propionic acid/kg. This caused a significant growth depression at all but the highest level of cyanocobalamin addition.

4. Methylmalonic acid was detected in the excreta of chicks that received the supplements of 0 and 0.01 mg cyanocobalamin/kg diet, and in those of chicks receiving 0.03 mg only for the chicks that were also receiving propionic acid.

5. The results suggest that giving the odd-carbon, propionic acid to chicks may increase their requirement for vitamin B12.

1. Protein concentrates were prepared from freshly cut lucerne by the Pirie process and freeze-dried. When supplemented with methionine or cystine and given to rats as the sole source of protein at 120 g protein/kg diet, the adjusted mean protein efficiency ratio was 2.89 (casein standard at 2.50). As a supplement to protein from barley meal the lucerne leaf-protein concentrate (LPC) was similar to casein.

2. To investigate nutritional safety, lucerne LPC supplemented with methionine was given to rats at high levels for 6 months; exposure of these rats to diffuse daylight was avoided to prevent a severe disfiguring photosensitivity reaction. At a dietary protein concentration of 100 g/kg, rats grew equally well with lucerne LPC or casein. When the supplement was given at protein concentrations of 200 or 300 g/kg the rates of body-weight gain of male and female rats were less than those of control rats given casein. However, after 5 months on the diets, body-weights of male rats had nearly reached those of the controls.

3. Apparent protein digestibility ratio was about 0.80 with all three levels of lucerne LPC.

4. Reproduction was normal in seventeen of the eighteen female rats given the lucerne LPC at the three levels; lactation was also normal and litters were successfully raised to weaning.

5. Organ weights, liver histology and blood haemoglobin were normal in male rats given the lucerne LPC for 6 months.

6. Total body lipid of male rats given lucerne LPC was about half that of the control rats given casein. Body protein was slightly increased, and moisture content was higher in rats given lucerne LPC.

7. The ‘whey’ remaining after precipitation of the protein from lucerne juice strongly inhibited the initial growth of mice given a complete control diet. The mice soon accommodated to the depressive effect of ‘whey’, and body-weight gains were normal during the 3rd week.

1. Rates of protein synthesis and catabolism were measured in longissimus dorsi and hind-limb muscles of suckling piglets.

2. Half-lives for synthesis and catabolism for mixed sarcoplasmic proteins were 4.8 and 9.4 d respectively. The corresponding values for mixed myofibrillar proteins were 5.7 and 16.4 d.

3. The half-lives for synthesis of sarcoplasmic proteins were significantly different from those of myofibrillar proteins and were not confounded by contamination of the sarcoplasmic protein fraction with plasma proteins of higher specific activity.

4. Individual myofibrillar proteins were synthesized and catabolized at rates which were not statistically significantly different. Intramuscular connective tissue also appeared to turnover rapidly, the half-life for synthesis being 8 d and that for catabolism 20 d.

5. Values obtained for the specific radioactivities of aspartate + glutamate in mixed plasma proteins support the view that, in so far as the young of animals larger in mature body size than rats or mice are concerned, muscle assumes a more important role relative to liver in regulating whole body amino acid metabolism.

1. The influence of the gut microflora on protein utilization has been investigated with a series of good- and poor-quality protein diets in germ-free (GF) and conventional (CV) chicks by the measurement of net protein utilization (NPU) and uric acid excretion.

2. The diets used were: 280 g protein per kg diet containing unheated or heat-damaged albumen (100 g/kg), casein (80 g/kg) and gelatin (100 g/kg); sesame protein (220 g/kg); sesame protein (220 g/kg) supplemented with lysine (5 g/kg); freeze-dried cod muscle (160 g/kg); heat-damaged cod muscle (160 g/kg); mildly-steamed egg albumen (100g/kg); heat-damaged egg albumen (100 g/kg).

3. No significant differences in NPU values for the proteins measured in GF and CV chicks were found, with the exception of unsupplemented sesame protein, for which the NPU value was slightly higher in GF chicks.

4. The replacement of unheated egg albumen by heat-damaged egg albumen in the 280 g protein/kg diet resulted in a decrease in uric acid excretion. With the cod-muscle diets, heat-damaging the protein caused an increase in uric acid excretion. Supplementing the sesame protein with lysine resulted in a decrease in uric acid excretion.

5. Excretion of uric acid tended to be higher in CV chicks than in GF chicks with all proteins except sesame protein, with which uric acid excretion was a little higher in GF chicks.

6. Endogenous nitrogen excretion was higher in GF than in CV chicks.

7. It is concluded that the gut microflora has little influence on the utilization of dietary protein by chicks, although it may modify the route of excretion of the N which survives digestion and reaches the lower gut.

1. The photosensitizing effect of leaf-protein concentrate (LPC) prepared from lucerne (Medicago sativa) was demonstrated when it was included in the diet of albino rats at concentrations between 40 and 480 g/kg diet.

2. Skin lesions of varying severity up to the sloughing of ears and tails occurred when such rats were illuminated with natural daylight through window-glass or with simulated daylight from a bank of lamps having emission maxima at 410, 437 and 660 nm and with approximately 4% of the energy of summer sunlight.

3. Protein concentrates prepared from ryegrass (Lolium multiforum) and a crude chlorophyll extract of spinach (Spinacea oleracea) did not cause these effects.

4. Extracts from blood plasma and livers of rats given lucerne LPC contained pheophorbide-a and two other unidentified green pigments, but no detectable phylloerythrin or chlorophyll. Extracts from the blood of rats given ryegrass LPC had no detectable pheophorbide or other chlorophyll-derived pigments.

5. The lucerne LPC given to the rats contained relatively large amounts of pheophorbide-a among a variety of pigments. The ryegrass LPC and the spinach extracts had only small amounts of this pigment relative to the other chlorophyll-type pigments.

6. These findings indicate that pheophorbide-a and related pigments are the agents responsible for the photosensitization of the rats. Possible explanations of their presence in lucerne LPC are discussed.

1. Adult rats were fed on diets free of either lysine, methionine, threonine or protein. The threonine- and protein-deficient animals lost weight at approximately the same rate, about 100 g in 14 weeks, at which time several were moribund. In contrast, lysine-deficient animals lost only about 30 g in 14 weeks and had lost only 46 g after 22 weeks, when they were killed. Methionine-deficient animals showed an intermediate response. Losses in weight of several tissues – kidney, heart and two muscles – were related to, but not necessarily proportional to, the loss of body-weight. Liver weights relative to body-weights were large in lysine- and threonine-deficient animals and smallest in methionine-deficient animals.

2. Adult rats were fed on diets containing zero, a moderate amount (about twice the estimated minimal requirement) or an excess (about four times the estimated requirement) of lysine or threonine in all combinations (3 × 3 design). Analysis of variance of the body-weights, tissue weights and tissue nitrogen contents indicated, in general, a significant effect of each amino acid, as expected, but also, in most instances, a significant interaction. Plasma concentrations of lysine and threonine were affected by the intakes of the respective amino acids, but plasma lysine concentrations were also affected by the threonine intake.

3. Liver histology also suggested significant interactions between the two amino acids. Animals given no lysine but moderate amounts of threonine developed severely fatty livers; next most severely affected were animals receiving excess of both amino acids. Threonine deficiency, in the presence or absence of lysine, produced moderately fatty livers similar to those seen in protein-deficient animals.

4. Since animals have varying ability to conserve body nitrogen when they are fed on diets limiting in different essential amino acids, measurements of biological value (BV) and net protein utilization by conventional methods, over a short period of time, over-estimate nutritive value relative to amino acid score and probably over-estimate the true nutritive value of poor-quality proteins, particularly those limiting in lysine. If so, this is a serious error, since it leads to underestimates of the protein requirements if BV is used. The fact that certain tissues, particularly the liver, do not necessarily lose nitrogen in proportion to total body nitrogen and may show specific pathological effects depending on the limiting amino acid or the proportions of amino acids in the diet also indicates that general measures of nitrogen economy may not be sufficiently discriminating tests of the nutritive value of proteins.

1. The effect of changes of dietary calcium concentration on Ca metabolism in eight adult wethers has been studied by the use of balance and radioactive techniques.

2. Animals receiving an adequate Ca intake absorbed sufficient Ca to supply their maintenance requirements only; a change in intake resulted in a corresponding change in the rate of absorption and disturbed this Ca balance. The new rate of absorption appeared to be determinded by the Ca concentration of the new diet and the efficiency of absorption of Ca from the previous diet.

3. Provided the new diet contained sufficient available Ca, animals quickly altered their efficiency of absorption of Ca until they were again absorbing enough for maintenance only.

4. When a lack of available Ca in the diet made it impossible for them to meet their maintenance requirements, they slowly reduced faecal endogenous excretion of Ca.

5. Ca-deficient animals absorbed Ca at a very high rate when given a diet plentiful in Ca, and absorption decreased only when all the previous losses had been restored.

6. Ca-deficient animals also mobilized Ca reserves more readily in response to a severe loss of blood Ca than did animals which were not deficient.

7. Retention of Ca was directly related to the rate of absorption of Ca and inversely related to the rate of resorption of Ca from bone.

8. The results indicate that resorption of Ca from bone is the major process involved in Ca homoeostasis and that Ca absorption is responsible for the long-term control of Ca metabolism and in particular for maintaining body Ca reserves.

1. Electroencephalographic and nerve-conduction studies were undertaken in children who had been treated in hospital for kwashiorkor 6–8 years previously; the results were compared with those for age-matched controls of similar cultural and socio-economic backgrounds.

2. The electroencephalograms were normal in all.

3. In three survivors of kwashiorkor, the amplitude of the sural nerve potential was less than that of the lower limit of the normal range.

4. The findings are discussed in the context of the present knowledge of protein-energy (protein-calorie) malnutrition.

1. Weanling rats 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. Torula yeast (50 g/kg diet) and dried brewers' yeast (50 g/kg) significantly improved the rats' growth rate. Part of this activity was attributed to the minerals present in the yeasts, zinc, iodine, iron, copper and manganese all being implicated.

3. Marmite (20 g/kg) and a basic fraction (6.6 g/kg) obtained from it by cation-exchange chromatography significantly improved growth. The ash component of the basic fraction was inactive.

4. Growth was increased by an extra supplement of vitamins and by treating the rats with neomycin sulphate and tetracycline. The growth stimulus due to Marmite was additive with that due to the antibiotics, but not with that due to the vitamin supplement.

5. The growth rate with torula yeast (50 g/kg) was maintained at about 30% greater than on the basal diet during a test lasting 80 d. At the end of that period six control and five supplemented male rats sired normal litters. Post-mortem examination, including histology, of others showed no abnormalities due to factor G deficiency.

6. Fresh ox liver (100 g/kg diet) significantly improved the growth rate, but this improvement could be attributed to the effects of the water and minerals contained in the liver.

7. These results confirm the discovery by Schwarz, Smith & Oda (1966) that yeasts contain an organic growth-promoting factor (factor G) for rats receiving amino acid diets. Factor G is not likely to be one of the vitamin B group.