1. The influence of temperature, moisture content and the presence of glucose on the level of available methionine and cysteine in casein was studied.

2. Differences between total and available methionine and cysteine contents of heated casein (90° for 24 h) were determined by an in vitro method. The maximum losses in total and available methionine content were 22 and 51% respectively. The losses in total and available cysteine content were 24 and 100% respectively.

3. The results indicated that for heated casein the release of amino acids by proteolytic enzymes was less complete than for native casein.

4. The results of rat growth assays suggested that diets containing oxidized casein are less well utilized by rats than those containing native casein. The decrease in body-weight of rats receiving the diets containing oxidized casein could be counteracted by the addition of methionine and 20 g unoxidized casein/kg diet.

5. There was a lower level of some available amino acids (determined after enzymic hydrolysis using pancreatopeptidase E (EC 3.4.4.7), leucine aminopeptidase (EC 3.4.1.1) and prolidase (EC 3.4.3.7)), including those essential for the rat, in oxidized casein as compared with native casein.

6. Cysteic acid, in oxidized casein, probably makes impossible the utilization of the amino acids in its neighbourhood.

7. From the differences in the available amino acid contents of the native, oxidized and heated casein it was concluded that the oxidation of casein causes the formation of complexes in the polypeptide chain, resistant to enzymic hydrolysis, but to a much lesser extent than does heating.

1. Rats were given diets containing different amounts of calcium, phosphorus and lead.

2. Pb retention was greatly increased when the diets contained less Ca or P than the minimum estimated requirement of the rat.

3. The release of Pb already incorporated into the skeleton was inhibited by diets low in Ca but was not affected by diets low in P.

4. The retention of Pb given intraperitoneally was not affected by dietary Ca or P.

5. It can be concluded that dietary Ca and P influence the absorption of Pb by the gut and dietary Ca influences the metabolism of Pb in the bone.

6. There were changes in the distribution of Pb among the tissues due to changes of dietary Ca.

7. At low body concentrations, Pb probably affected skeletal growth.

1. The available methionine and cysteine contents of proteins were determined by chemical methods after preliminary enzymic hydrolysis.

2. The values for the available methionine and cysteine contents of pure proteins (casein and bovine serum albumin) estimated by chemical methods were similar to those for the total content determined by the method of Moore, Spackman & Stein (1958).

3. Reductions of 15 and 11% respectively, when compared with unprocessed samples, were found in the available methionine contents of sweetened and unsweetened, condensed milks; of roller-dried milk and whey powders, and of mackerel sterilized at 126°, the reductions were 22, 14 and 19% respectively.

4. The available cysteine content of sweetened, condensed milk was reduced by about 32%, whereas for mackerel sterilized at 115 and 126° it was reduced by 64 and 75% respectively.

5. The contents of total sulphur amino acids for these food products did not differ from those for the unprocessed samples.

6. Values obtained for available S amino acid contents by rat bioassay confirmed the results of the in vitro estimations.

1. Hereford steers, housed in concreted yards and given demineralized water, were offered ad lib. a low-sodium (0.07 g Na and 4.5 g potassium/kg) basal diet of sorghum grain, urea and minerals, to which 0, 15 or 30 g K as KHCO3/kg diet had been added. Mean daily intakes of K were 26, 107 and 168 g/steer respectively.

2. The steers were given daily supplements of 0, 3.25 or 6.50 g Na as NaHCO3/steer, added to the food; mean daily intakes of Na (food plus supplemental NaHCO3 minus residues) were 0.41, 3.06 and 6.26 g/steer respectively.

3. Rate of gain of body-weight was positively related to the rate of Na supplementation and negatively related to the K content of the diet, but there was no interaction between Na and K contents of the diet.

4. The Na: K ratios for the parotid saliva from steers not given Na supplements was 0.3, whereas steers ingesting either 3.1 or 6.3 g Na/d had Na: K ratios of about 12. Increasing the amount of K in the diet had no consistent effect on the saliva Na: K ratio. The Na: K ratios for rumen fluid reflected changes in the saliva Na: K ratio in response to Na supplements and were inversely related to the amount of K in the diet.

5. The width of the adrenal zona glomerulosa from steers receiving the basal diet, without Na supplements, was significantly greater than that from steers given the Na supplements, but it was not affected by the amount of K in the diet.

6. Both Na supplements and the diet containing 30 g added K/kg significantly increased the Na: K ratio of the plasma.

7. The addition of 200 mg DL-α-tocopheryl acetate/steer per d to the diet had no significant effects on the growth rate of the steers.

8. It was concluded that the Na requirement of steers for growth was not significantly affected by the amount of K in the diet up to 168 g/d.

1. Three growth trials were done using male broiler chicks. In the first two trials, groundnut meal was used, with and without supplementary methionine and lysine. In the third trial, soya-bean meal was used with and without supplementary methionine. Protein levels ranged in the first trial from 120 to 420 g/kg diet and in the third trial from 120 to 300 g/kg diet. Thus the assumed minimal amino acid requirements of the chick were supplied by high levels of low-quality dietary protein.

2. Diets based on cereals and groundnut meal did not support maximum live-weight gain or maximum efficiency of food utilization at any level of dietary protein. When the principal deficiencies of lysine and methionine were corrected, this protein mixture was capable of supporting the same growth rate as a control diet of cereals and herring meal.

3. Diets based on maize and soya-bean meal did not support quite the same growth rate as similar diets supplemented with methionine, even though the protein level in the unsupplemented diets was sufficient to meet the assumed methionine requirements.

4. These results are interpreted as examples of amino acid imbalance in diets composed of familiar feeding-stuffs. It is concluded that one cannot assume that the poor quality of a protein source can always be offset by increasing the concentration of dietary protein.

1. The effect on body-weight of field work in Antarctica when travelling by mechanical transport has been studied.

2. A steady loss of weight (mean 6.2 kg) was found in the field, and there was a slow gain on return to less arduous conditions.

3. Changes in skinfold thickness and hip girth suggested that the loss of weight was due to an energy deficit, and the gain was due to an excess of energy.

4. However, although weight was being lost the energy balance was calculated to be positive. This was probably because the expenditure was underestimated as the result of a failure to take into account: (a) the weight and restriction of heavy clothing, (b) the high-protein diet, (c) the difficulty imposed by the terrain, (d) the intensity of the subjects' response to the cold.

5. Daily weight changes were significantly related to climatic conditions.

6. Daily weight changes were significantly related to fluid intakes, but it was not possible to assess with certainty the contribution made by dehydration to the recorded weight loss.

7. Daily fluctuations in weight were greater than those previously found under more standard conditions.

1. An experiment was done with rats (body-weight 160 g) to study the effects on fat metabolism and body composition of low (10 g/kg)- or high (140 g/kg)-fat diets fed as one meal for one 4 h period/d (meal-feeders) or as six spaced meals/d (nibblers). The daily energy intake/unit metabolic body-weight (body-weight0.73) was the same for all four groups, and this level of intake was about 80% of that consumed by rats allowed unrestricted access to the low-fat diet. The experimental period was 76 d.

2. Rats given the high-fat diet deposited more body fat/d and, as a result, grew faster and were energetically more efficient than rats given the low-fat diet. The high-fat diet depressed de novo lipogenesis from glucose in epididymal and perirenal fat pads, whose fatty acid composition resembled that of the diet.

3. For both diets meal-feeders had greater stomach plus small intestine weights than nibblers and had higher plasma free fatty acid levels, when they were killed 15 h after their last meal.

4. Meal-feeders given the low-fat diet had the greatest rate of lipogenesis for fat pads.

5. Meal-feeders given the high-fat diet deposited less of the main dietary fatty acids in their fat pads.

6. There was no evidence that meal-feeders eating a high-fat diet adapt their metabolism so completely that they become more efficient utilizers than those nibbling this diet. Meal-feeders eating the low-fat diet became no fatter than nibblers of this diet, possibly because they were eating less than their daily ad lib. intake.

1. Glucose in solution in saline, or saline alone, was administered to a group of twenty ewes during late pregnancy and again after lambing. Sequential blood samples were taken before and after the infusion and the concentration of plasma free amino acids was determined.

2. The effect of glucose was to reduce the concentrations of all amino acids except alanine. The reduction was greatest for tryptophan in the pregnant sheep, but this amino acid showed no significant change in the lactating animals.

3. An attempt to rank the amino acids on the basis of their response to glucose infusion indicated that, with the exception of tryptophan for the preparturient ewes, groups of essential amino acids could not be distinguished from each other. These groups were, for the preparturient sheep, valine, leucine, phenylalanine and isoleucine, and for the postparturient animals, isoleucine, lysine, methionine, valine and phenylalanine.

1. Seven groups of young turbot (Scophthalmus maximus) were given diets containing graded levels of thiamin (0.19–50 mg/kg) for 16 weeks and their growth rate was measured during this period.

2. Good growth was obtained on all these treatments except in the group given the lowest dietary thiamin level (0.19 mg/kg). These fish grew normally until the 12th week but thereafter their weight did not increase.

3. Measurements of erythrocyte transketolase (sedoheptulose-7-phosphate: D-glyceraldehyde-3-phosphate glycolaldehydetransferase; EC 2.2.1.1) activity at the end of the experiment and of percentage stimulation of erythrocyte transketolase by thiamin pyrophosphate indicated that the apoenzyme was saturated with coenzyme at a dietary thiamin level of 2.6 mg/kg, but not at 1.1 mg/kg.

4. An 8th group of turbot given the thiamin antagonist pyrithiamin (40 mg/kg diet) grew normally for 6 weeks. Thereafter mortalities began to occur and all fish died by the 10th week. No clear-cut signs of thiamin deficiency were observed.

5. The dietary thiamin requirement of turbot is much lower than published requirements of freshwater fish other than carp (Cyprinus carpio) and appears to be between 0.6 and 2.6 mg/kg diet.

1. Linseed oil was incorporated gradually into the diet of four sheep until the animals received 90 g additional fat/d. Attempts were made to measure changes in concentration of substances and rates of synthesis in the rumen directly, and by incubation of rumen contents in vitro (zero-time technique).

2. The high-fat diet increased the dilution rate and the volume of rumen contents and decreased the synthesis of diaminopimelic acid in the rumen. The number of protozoa decreased and the number of bacteria increased in the rumen of animals receiving the high-fat diet.

3. The concentration of volatile fatty acids (VFA) in the rumen decreased for sheep given the high-fat diet, but the capacity of rumen contents to produce VFA in vitro increased.

4. The incorporation of radioactivity from [14C]acetate into lipids during incubation of rumen contents in vitro increased with the amount of linseed oil in the diet. The greatest proportional increase was with the bacterial fraction of rumen contents.

5. In the group of four animals used, one animal showed consistent differences in the magnitude of the measured variables. This animal appeared to have a smaller rumen, a lower dilution rate and larger concentrations of some substances in the rumen. A higher proportion of fatty acids appeared to be synthesized by the micro-organisms from this animal.

1. A survey was done of 2333 men and women who claimed experience of slimming.

2. Their loss of weight was determined from their maximum stated weight and their present weight. The loss of weight was calculated as the percentage of the maximum weight and was related to the stated age of onset of obesity.

3. The results showed that those people in the survey who had been fat since childhood had lost just as much weight as those people who had become fat as adults.

4. These results suggest that the treatment of early-onset obesity may not be an unrealistic objective.

1. The effects of feeding with a purified magnesium-deficient diet (−Mg, 7–8 mg Mg/kg) on horse foal blood serum and tissue concentrations of Mg, calcium and phosphorus were studied, and the results compared with histopathological findings.

2. Serum concentrations of Ca and P were unaffected by feeding with the −Mg diet, whereas serum Mg concentrations decreased from a mean initial (day 0) concentration of 0.78 mmol/l to 0.53 mmol/l 7 d after foals were placed on the −Mg diet, and then continued to decrease at a slower rate.

3. Aorta concentrations of Ca and P, but not Mg, were positively correlated with the period of time foals were given the −Mg diet, verifying histopathological findings. Results for both aorta Ca and P analyses and histopathological studies indicated that mineralization of the aorta began approximately 30–35 d after foals were placed on the −Mg diet.

4. Feeding with the −Mg diet had no significant, analytically detectable effect on brain, liver, kidney, lung, spleen, skeletal or cardiac muscle concentrations of Ca, P or Mg, although microscopic evidence of mineralization was seen in some of these tissues from foals given the −Mg diet for 71–180 d.

5. A significant negative correlation was found between bone ash concentrations of Mg (rib, metacarpus and metatarsus) and the length of time foals were fed on the −Mg diet. Bone ash concentrations of Ca and P were, however, unchanged.

6. Low serum Mg values and negative correlations between the bone ash concentration of Mg and the period of time foals were fed on the −Mg diet supplemented with 390 mg Mg as MgO/kg were interpreted as suggesting that either this level of Mg supplementation is marginal for the growing foal, or that the Mg in MgO is not readily available to the growing foal.

1. The hydrolysis of glycyl-L-leucine, glycyl-L-tyrosine, tributyrin, sucrose, maltose, soluble starch and α- and β-glycerophosphates by everted segments of rat intestine was estimated separately or in combination.

2. A comparative study showed significant interaction between different substrates which affected their digestion.

3. Two types of interaction were identified: products of hydrolysis (1) affected the hydrolysis of homologous substances, e.g. methionine and alanine inhibited glycyl-L-leucine hydrolysis, maltose reduced glucoamylase (α-1, 4-glucan glucohydrolase; EC 3.2.1.3) activity (intracatenary interactions); (2) interfered with the hydrolysis of a different group of substances, e.g. tributyrin inhibited dipeptidase (glycyl-L-leucine hydrolase; EC 3.4.3.2) and alkaline phosphatase (EC 3.1.3.1), glycyl-L-leucine interfered with the activity of the latter enzyme (intercatenary interactions).

4. Mechanisms of interactions were suggested by the results of a comparison of the extent of inhibition or activation of two enzymes (glycyl-L-leucine hydrolase and alkaline phosphatase) in situ in everted intestinal segments or after solubilization with papain or Triton X-100, and different treatments known to affect allosteric sites of these enzymes.

5. Tributyrin and dipeptides were found to act on alkaline phosphatase as allosteric regulators. A discontinuity of the Arrhenius plot suggested the existence of different enzyme conformations which were re-arranged by tributyrin.

6. Substrate interactions in digestion were found in adult rat, cat, rabbit and hen. Substantial differences were found between classes (Aves and Mammalia), orders (rodents, lagomorphs and carnivores) and between age-groups within an animal strain (in this instance, for the rat).

7. These interactions are thought to be involved in the co-ordination of digestion with intestinal absorption and to regulate the time and site of subsequent hydrolysis.

1. Successive portions of boiled and mashed potatoes, roast pork, cooked, freeze-dried peas and ice-cream were taken in order to determine the total (sampling and experimental) error involved in the ‘duplicate analysis’ method of dietary survey.

2. These samples were analysed for water, nitrogen, fat, iron and energy.

3. The experimental error of the methods was also studied separately.

4. The sampling and experimental errors ranged from 0.3% for water in potatoes, to 23% for Fe in ice-cream. Sampling error was significantly greater than experimental error for all nutrients studied.

5. It is concluded that in reporting the results from dietary surveys, it is necessary to take account of the errors inherent even in the most precise methods.

1. Vitamin B12 metabolism was studied in bats of the species Rousettus aegyptiacus, which live on an all-fruit diet in the wild.

2. There was a wide range in values for the serum vitamin B12 concentration of newly captured bats, but bats captured in the early spring had significantly higher mean serum vitamin B12 levels than bats captured in the early autumn.

3. There was an exponential decrease in serum vitamin B12 concentration with time in captivity for bats fed on a vitamin B12-deficient, all-fruit diet; the biological half-life was 80 d in serum, 109 d in liver and 164 d in kidney.

4. The main storage organ for vitamin B12 in the bat was the liver, mean content 1067 ng vitamin B12. After 50 d, injected [57Co]cyanocobalamin had equilibrated with body vitamin B12 stores, and 17% of the retained radioactivity was present in the liver. From these results it was calculated that the total body vitamin B12 content of the bat was c. 6500 ng.

5. The biological half-life of injected [57Co]cyanocobalamin was 70–88 d and the calculated daily requirement was 50–60 ng (0.2 μg/kg body-weight per d).

6. As serum vitamin B12 levels decreased, serum folate levels increased. The erythrocyte folate concentration increased significantly after 130 d on the all-fruit diet and then decreased to the initial values after 190 d.

7. Vitamin B12 metabolism in the fruit bat is similar in many respects to that of man, but on a ‘weight-for-weight’ basis the bat has a 5- to 15-fold greater requirement for this vitamin.

8. Vitamin B12 deficiency may be induced fairly rapidly in fruit bats fed on an all-fruit diet.

1. In Expt 1, a pelleted grass-meal diet was supplemented with hydrochloric acid, added to the grass pellets before feeding, at five levels from 0 to 628 mmol/kg dry matter (DM). Each diet was offered ad lib. for 21 d to five sheep in a 5 × 5 Latin-square design.

2. Voluntary food intake decreased rectilinearly with increasing HCl supplementation (P < 0.001), to 42% of the control value for sheep on the high-HCl diet. The decrease in food intake was related both to dietary pH and to the extent of metabolic acidosis induced by the HCl treatment. Although the pH of rumen fluid decreased slightly with increasing HCl supplementation, effects of the HCl treatment on volatile fatty acid concentrations in rumen fluid were not significant (P > 0.05).

3. In Expt 2, palatability and metabolic effects of dietary HCl were studied by comparing its effect when mixed into the pelleted grass meal before feeding, with and without a supplement of an equivalent amount of sodium bicarbonate given intraruminally, or when HCl was given intraruminally while the sheep consumed pelleted grass meal alone. Each of the three treatments was given at two levels of HCl, 280 and 560 mmol/kg DM. At each level of dietary HCl supplementation, the three treatments and the control diet (pelleted grass meal alone) were each given to four sheep, in a Latin-square design, for 11 d.

4. At the low level of supplementation, HCl, when mixed into the pelleted grass meal, reduced food intake by 17%, this effect was not altered by NaHCO3 supplementation, but when HCl was given intraruminally food intake was not reduced. At the high level of HCl supplementation, food intake was reduced by about 40% by each method of HCl supplementation; and NaHCO3 supplementation did not appreciably alter the effect of HCl on food intake, but prevented metabolic acidosis associated with the HCl treatments. Food intakes for the low-HCl treatments were significantly higher than those for the high-HCl treatments (P < 0.01) and the level of dietary HCl×treatment interaction was also significant (P < 0.01). DM digestibility, and the pH and volatile fatty acid concentrations of rumen fluid were not significantly affected by the different treatments.

5. It is concluded that at a low level of HCl supplementation the adverse effects of dietary HCl on voluntary food intake of sheep is determined by palatability associated with low dietary pH, whereas at a high level of HCl supplementation the effect is determined by palatability and by a metabolic response.