1. Standard zinc solutions for the atomic absorption analysis of rat plasma were prepared to contain 14% (w/v) of sucrose. In this way the problems of sample nebulization were overcome with a minimum of manipulation before assay.

2. Plasma Zn concentrations in rats were found to fall by approximately 40% (from 1.2 to 0.7 μg/ml) after 1 d on a Zn-deficient (< 0.25 ppm) diet. Thereafter, the fall became less marked and after 5 d the concentrations usually varied between 0.4 and 0.6 μg/ml.

3. A single oral dose (20–200 μg) of Zn was reflected in high plasma Zn concentrations in the depleted rats 1.75 h after dosing, but to a much lesser extent in animals receiving 10–60 ppm Zn in their diet before dosing.

4. It is suggested that the plasma Zn response to a single oral dose of zinc sulphate may provide a useful method for the detection of a subnormal Zn status in individual farm animals without the necessity of determining breed norms.

1. Groups of newborn calves were fed on liquid diets which had fat contents ranging from 0.2 to 17% (dry- weight basis) and which provided linoleic acid in amounts ranging from 0.01 to 0.7% of the calorie intake. Two commercial milk replacers, high in fat (17–18%) and linoleic acid (3.4 and 5.0% of calories) were also given. All diets were given for at least 65 d.

2. Except for reduced feed utilization associated with the two diets lowest in fat (0.2 and 0.4%), the calves developed normally, without signs of essential fatty acid deficiency.

3. The polyunsaturated fatty acid content of erthrocytes and plasma phospholipids and cholesteryl esters rose rapidly during the first few days on all diets. At 65 d, these concentrations were higher than at birth and appeared generally to be related to the linoleic acid intake. However, in the low dietary linoleic acid range, the fat content of the diet also seemed to exert some influnce. In no instance was there any indication of the appearance of 20:3ω9, which is observed in other species under conditions of essential fatty acid deficiency.

4. Some of the experimental diets were given to weanling rats. There was a rapid fall in the polyunsaturated fatty acid content of erythrocyte lipids and plasma phospholipids and cholesteryl esters, accompanied by the appearance of 20:3ω9.

5. These results suggest that calves on liquid diets have apparently a very low requirement for essential fatty acids.

1. Propane-1:2-diol (loog/d) was infused through a cannula into the rumen of sheep receiving a ration of hay and dried grass. The concentration of volatile fatty acids, propanediol, lactic acid and of added polyethylene glycol, and the pH of the rumen contents were measured. The energy metabolism of the sheep was also determined.

2. Most of the propanediol disappeared from the rumen within 4 h of its infusion. The infusion of propanediol resulted in a 10% decrease in the concentration of total volatile acids; the concentration of acetic acid decreased by about 30%, that of propionic acid increased by up to 60% and there was no change in the concentration of butyric acid.

3. The methane production of the sheep decreased by about 9% after the infusion of propanediol and there were increases in the oxgyen consumption, carbon dioxide production and heat production of the animals; each of these increases was equivalent to about 40% of the theoretical value for the complete metabolism of 100 g propanediol.

4. It is concluded that, when propanediol is introduced into the rumen, a proportion is metabolized in the rumen and a large proportion is absorbed directly. Our thanks are due to Dr J. H. Moore for helpful discussions, to Mr D. R. Paterson, Mr J. R. McDill and Mr C. E. Park for looking after the animals and to Miss K. M. Graham, Miss A. T. McKay and Mrs C. E. Ramage for performing the analyses.

1. Energy expenditure determinations have been made on thirty-two soldiers newly arrived in the warm humid climate of southern Malaya. Ergometer cycling was investigated as well as everyday activities such as lying, sitting, riding in a trunck, abultions, buildings a jungle camp and walking with loads over four different routes.

2. The inter-individual variation in the gross energy expenditure (kcal/min and kJ/min) of each activity has been compared with the variation in energy expenditure standardized for body-weight, surface area and lean body mass. Standardization for body size did not consistently or effectively reduce the coefficients of variation of energy expenditure.

3. The gross energy expenditure of most activities was significantly correlated with bodyweight, surface area or lean body mass but the correlation coefficients were not of a high order, suggesting that less than 41% of the inter-individual variation in energy expenditure was accounted for by variation in body size.

4. The energy expenditure of walking at various speeds over both firm and uneven terrain was related to the square of the walking speed and the total weight of the man and his equipment (correlation coefficients 0.89–0.92, P < 0.001).

1. The effect of zinc deficiency on the activities of rat duodenal alkaline phosphatase and inorganic pyrophosphatase has been investigated.

2. Zn deficiency adversely affected the activity of these enzymes before growth rate and food intake were reduced.

3. The level of food intake was without effect on the activity of alkaline phosphatase but markedly influenced that of inorganic pyrophosphatase.

4. The relevance of changes in the activities of Zn-dependent intestinal enzymes to the food intake of Zn-deficient rats is discussed.

1. The effects of intraduodenal infusions of sterculic acid, a naturally occurring inhibitor of desaturase activity, on the yield and composition of milk were examined in a lactating goat.

2. Sterculic acid administration increased the percentage of stearic acid in milk fat, reflecting inhibition of mammary desaturase activity. Milk yield was not affected, but milk fat output decreased. Possible explanations are discussed.

3. No evidence was obtained for an alternative pathway of oleic acid synthesis from acetate.

Experiments with a small-scale artificial rumen have shown that of forty-two compounds tested the majority were fermented, as judged by the production of volatile fatty acids, but methane production was associated only with the fermentation of formate, certain hydroxy-acids, pyruvic acid, primary alcohols (methanol, ethanol, propanol and butanol), glycerol and methyl compounds. With primary alcohols there was a stoichiometric relationship between methane production and the oxidation of the alcohols to the corresponding acids.

The fermentation of rhamnose and 1,2-propanediol was studied in detail. With both compounds there was a temporary accumulation of lactic acid and a continuous net production of propionic acid. The initial rate of acetate production was rapid with rhamnose but decreased subsequently, whereas propionate continued to increase. With propanediol the net rate of production of acetate was slow at first and then increased. There was no increase in the production of butyric acid with either rhamnose or propanediol, and the endogenous methane production was inhibited by 20–40%. There was evidence for the formation of an unidentified compound during fermentation of rhamnose and propanediol.

1. Serum β-lipoprotein and cholesterol have been measured in children ‘at risk’ to severe protein-calorie malnutrition and in others with kwashiorkor or marasmus. β-Lipoprotein was estimated by an immunological technique. In children recovering from kwashiorkor, serum triglyceride estimations and lipoprotein electrophoretic separations were also carried out.

2. β-Lipoprotein concentrations did not fall significantly until serum albumin concentration was less than 2.5 g/100 ml; cholesterol concentration fell before β-lipoprotein.

3. In frank kwashiorkor, serum β-lipoprotein concentration was reduced by about 30%, whereas cholesterol and triglyceride concentrations were reduced by about 50% in comparison with apparently normal children. Electrophoretic evidence showed that serum α-lipoprotein concentration was also reduced or absent altogether. Marasmic children had normal serum concentrations of β-lipoprotein and the other lipid components measured.

4. The metabolic significance of this degree of reduction in serum β-lipoprotein concentration in the pathogenesis of the fatty liver of kwashiorkor has been discussed. It was concluded that, in Ugandan children with serum albumin concentrations below 2.50 g/100 ml, the β-lipoprotein concentration was probably insufficient for normal mobilization of fat from the liver and the children could therefore be considered susceptible to the development of a fatty liver.

5. The recovery from kwashiorkor was marked by a rapid rise in serum β-lipoprotein concentration and hypertriglyceridaemia but a slower rise in cholesterol concentration. This confirmed the results of previous investigations.

1. The production and metabolism of volatile fatty acids were studied in sheep offered a cobalt-deficient diet.

2. The molar proportions of acetic (60%), propionic (26%) and butyric (14%) acids in the rumen fluids of sheep given the Co-deficient diet, but whose stores of vitamin B12 were adequate, were similar before and after administration of an oral supplement of Co.

3. In pair-fed sheep, one member of which was vitamin B12-deficient and the other (control) treated with vitamin B12 parenterally, the concentrations after feeding of both total and individual volatile fatty acids in the blood tended to be higher in deficient than in control sheep.

4. Following injection of the respective salts of individual volatile fatty acids into the blood-stream, formate clearance was apparently not affected, whereas that of acetate was slightly, and that of propionate very significantly, delayed in vitamin B12-deficient sheep compared with pair-fed control animals.

5. Acetate metabolism was retarded in the presence of propionate; the effect was greater in deficient than in pair-fed control sheep.

6. The hypothesis is advanced that it is the failure to metabolize propionate at the normal rate that leads to the progressive loss of appetite in vitamin B12-deficient sheep.

1. Fasting serum cholesterol and triglyceride, and post prandial insulin secretion and lipaemia were measured in human subjects in a metabolic ward, who were given an ordinary diet (diet 1) in which the sucrose was isocalorically replaced by starch (diet 2) or vice versa. The subjects were nine healthy normolipaemic adult males. In eight of these subjects the effect of sucrose calorie reduction (diet 3) on fasting serum lipids was also studied.

2. When starch replaced sucrose, there were no singnificant differences in fasting serum lipid concentrations or immunoreactive insulin or in the insulin response and alimentary lipaemia after a standard mixed breakfast.

3. Serum triglyceride concentration fell and cholesterol concentration rose during the period of sucrose (and calorie) restriction.

4. After lunch and supper on the first two diets (when different carbohydrates were given) the lipaemic response was larger and the insulin response smaller after meals containing sucrose.

5. Thus, there was no difference between concentrations of fasting serum lipids when starch replaced sucrose at 23% total calories, but the concentrations of serum triglycerides were higher after individual mixed meals containing sucrose.

6. There were no significant differences in the fatty acid patterns of serum lipids on the different diets.

1. A study was made on the folate content of goat's milk in relation to stage of lactation, and on the interrelationship between blood and milk folate concentrations in the dam and in the kid.

2. In seven goats the folate concentration in the colostrum at parturition ranged from 136 to 300 ng/ml, and averaged 205 ng/ml. The concentration fell sharply during the early days of lactation and by day 14 it averaged only 9.5 ng/ml. This pattern of rapid decline in milk folate concentration with advancing lactation was little affected by daily provision of folic acid parenterally in relatively large amounts.

3. The colostrum and milk contained a minor whey protein that combined strongly with folate, and presumably acts as a trapping mechanism to accumulate the vitamin from the plasma into the milk. The milk folate concentration determined by the rate of milk secretion in relation to the availability of free folate in the blood plasma.

4. At parturition the plasma folate concentration in the kids was very low – about 1 ng/ml – but by day 2 it had increased to about 28 ng/ml. This folate was protein-bound and accompanied by an excess of free binder protein. It appeared that the folate-protein complex from the colostrums was transmitted intact into the kids' blood circulation.

5. The possible importance of the folate-binding protein in regulation of folate metabolism is discussed.

1. In malnourished, compared with recovered children, fasting blood glucose concentrations were low and there was impaired peripheral glycolysis as shown by a failure of blood lactate to rise after glucose was injected intravenously.

2. Homogenates of muscle biopsies from malnourished and recovered children produced equal amounts of lactate when incubated anaerobically with various substrates, but when compared with homogenates of biopsies from normal children the pattern suggested an impairment of glycolysis.

3. The rate of glucose disappearance after intravenous glucose was slow in the malnourished child and there was possibly diminished sensitivity to exogenous insulin.

4. Isocaloric diets relatively high or low in fat were fed to children who had recovered from malnutrition. Glucose tolerance, insulin sensitivity, fasting plasma insulin and insulin response to intravenous glucose were all the same in children on either diet.

1. Pre- and post-prandial metabolic rates were measured in twelve malnourished Jamaican infants.

2. On admission to hospital, minimal increase in postprandial metabolic rate were found, whereas during the recovery phase when growth was rapid, inreases in postprandial metabolic rate of up to 38% occurred.

3. After recovery only the five children who were still gaining weight at a rate of more than 4 g/kg body-weigh. d continued to show a substantial increase in postprandial metabolism.

4. A highly significant correlation was found between growth rate and the increase in postprandial metabolic rate.

5. Marked differences existed in the respiratory quotient measured 4 h after the last meal, the values being low on admission and high during the phase of rapid growth.

6. After a test meal, the respiratory quotient rose sharply both innewly admitted and in recovered children, but fell slightly when the children were studied during the phase of rapid growth.

1. The absorption rates of L-methionine and L-methionyl-L-methionine (dimethionine) from the upper jejunum and lower ileum of the rat were studied in vivo after different dietary treatments. Rates were expressed per unit gut length and per unit gut weight; the former was considered to be the more satisfactory under the different dietary conditions.

2. The dietary treatments were either short-term (10 d) or long-term (40–84 d).

3. The rate of absorption of methionine increased in the jejunum after a restricted dietary intake, a high-protein diet or a high-methionine diet, but decreased after long-term protein deprivation. Short-term dietary restriction had a similar effect on methionine absorption in jejunum and ileum, though less pronounced in the latter. The rate of absorption of dimethionine was less influenced by dietary changes than that of methionine.

4. Under all conditions studied, the absorption rate of methionine was greater when presented as the dipeptide than when presented as the equivalent amount of free amino acid. This confirms that dimethionine is taken up intact from the intestinal lumen, and it seems likely that there are different mechanisms of mucosal uptake for methionine and its dipeptide.

1. Radioactive calcium has been used to study the placental transfer of Ca in ewes at three stages of gestation.

2. At each stage virtually all the radioactive Ca injected into a foetus was still present 5–6 h later and little or none was found in the mother or in a twin foetus if present.

3. It was concluded that there is neither exchange of Ca between foetal and maternal pools nor transfer from foetus to mother. Passage of Ca across the placenta of the ewe is therefore a one-way process.

4. The rapidly exchangeable Ca pool of the foetus tended to increase in size with the stage of gestation and was found to contain only about half of the total Ca of the foetal soft tissues.

5. Two methods for calculating the rate of accretion of Ca into the foetal skeleton have been applied. The results obtained from these calculations suggested that rates of foetal bone accretion also increased with the stage of gestation. Accretion per unit foetal weight, however, remained fairly constant irrespective of age or number of foetuses present.

6. Bone accretion rates calculated from the results of the present work were very similar to the rates obtained previously for transfer of Ca across the sheep placenta, indicating that resorption of Ca from bone is negligible in the foetus.

1. Four hundred and fifty patients who were treated for megaloblastic anaemias in northern Finland were grouped according to the month of diagnosis.

2. Only slight seasonal variation was detectable in the occurrence of megaloblastic anaemia.

3. During the first half of the twentieth century the seasonal variation in occurrence of megaloblastic anaemia was pronounced. The decrease in the variation is most likely related to the more even distribution throughout the year of the supply of foods containing folate and vitamin B12.

1. Pigs from 20 to 60 kg live weight were fed on cereal diets, supplemented only with vitamins and minerals, with and without supplementary lysine.

2. Growth rate, feed:gain ratio and carcass quality of pigs given a high-barley diet (75% barley meal, 23% wheat offal) were inferior to those of pigs given a high-wheat offal diet (75% wheat offal, 23% barley meal).

3. On both diets, but particularly on the high-barley diet, performance was improved by the addition of L-lysine (to give a total lysine content of 5.2 g/16 g nitrogen, approximating to that present in a standard barley meal–wheat offal diet supplemented with 7% white fish meal).

4. Percentage N retention was improved on both diets by supplementation with lysine.

5. Results for carcass composition showed that the carcasses of pigs fed on the unsupplemented high-wheat offal diet contained more lean tissue than those of pigs given the unsupplemented high-barley diet. Lysine supplementation resulted in an increased content of lean tissue on both diets, the percentage increase due to lysine being greater (but not significantly so) on the high-barley diet. The increased lean content was reflected in the carcass measurements but not in the total N retention values, which did not differ significantly between treatments.

6. The results are discussed in relation to the shortage and high cost of animal protein concentrates and the possible replacement of these concentrates with synthetic amino acids.

1. To obtain a quantitative model for nitrogen pathways in sheep, a study of ammonia and urea metabolism was made by using isotope dilution techniques with [15N]ammonium sulphate and [15N]urea and [14C]urea.

2. Single injection and continuous infusion techniques of isotope dilution were used for measuring ammonia and urea entry rates.

3. Sheep were given 33 g of chaffed lucerne hay every hour; the mean dietary N intake was 23.4 g/d.

4. It was estimated that 59% of the dietary N was digested in the reticulo-rumen; 29% of the digested N was utilized as amino acids by the micro-organisms, and 71% was degraded to ammonia.

5. Of the 14.2 g N/d entering the ruminal ammonia pool, 9.9 g N/d left and did not return to the pool, the difference of 4.3 g N/d represented recycling, largely within the rumen itself (through the pathways: ruminal ammonia → microbial protein → amino acids → ammonia).

6. Urea was synthesized in the body at a rate of 18.4 g N/d from 2.0 g N/d of ammonia absorbed through the rumen wall and 16.4 g N/d apparently arising from deamination of amino acids and ammonia absorbed from the lower digestive tract.

7. In the 24 h after intraruminal injection of [15N]ammonium salt, 40–50% of the N entering the plasma urea pool arose from ruminal ammonia; 26% of the 15N injected was excreted in urinary N.

8. Although 5.1g N/d as urea was degraded apparently in the digestive tract, only 1.2g N/d appeared in ruminal ammonia; it is suggested that the remainder may have been degraded in the lower digestive tract.

9. A large proportion of the urea N entering the digestive tract is apparently degraded and absorbed and the ammonia incorporated in the pools of nitrogenous compounds that turn over only slowly. This may be a mechanism for the continuous supply to the liver of ammonia for these syntheses.

10. There was incorporation of 15N into bacterial fractions isolated from rumen contents after intraruminal and intravenous administration of [15N]ammonium salts and [15N]urea respectively.

11. A model for N pathways in sheep is proposed and, for this diet, many of the pool sizes and turn-over rates have been either deduced or estimated directly.

1. Two pairs of Friesian steers were changed from ad lib. to restricted intake of a pelleted barley diet and were maintained on this latter intake for periods of 18 or 25 weeks. The restricted level of intake was 70 g/kg0.73 and was adjusted weekly according to individual live weights. The daily allowance was given in three equal feeds during day-time.

2. After an initial period of 9 weeks on the restricted diet, during which all four animals were kept free of rumen ciliate protozoa, one member of each pair was given an inoculum of rumen ciliates. Eight weeks later, the ciliate-free member of the younger pair of steers was similarly inoculated. Observations were made on the rumen bacterial and protozoal populations and on changes in rumen pH and volatile fatty acids (VFA) throughout each treatment period. The concentrations of urea and haemoglobin in blood and of glucose and amino acids in plasma were examined on one occasion in each animal.

3. In the absence of ciliates, restriction of intake resulted in rumen pH values and molar proportions of VFA similar to those normally encountered on an ad lib. intake of a barley diet. A decrease in bacterial numbers and certain minor changes in bacterial types were observed on changing from ad lib. to restricted intake but the resultant population under ciliate-free conditions was basically the same as that found later in the faunated animals. In culture, organisms of the genus Bacteroides were predominant.

4. Large populations of rumen ciliates were established in each animal inoculated. Relative to the ciliate-free periods, the presence of ciliates resulted in an increase in rumen pH, a reduction in total VFA concentration and a decrease in the ratio of propionic to butyric acid in rumen fluid. It is concluded that these changes are a direct effect of ciliate activity.

5. Conditions within the rumen remained more stable from day to day when large ciliate populations were present than when ciliates were absent. In one animal, spontaneous fluctuations in ciliate number were accompanied by corresponding changes in rumen pH and VFA proportions.

6. Significant differences were observed between faunated and ciliate-free animals in the concentration urea in blood and of glucose in plasma; only minor differences were noted in blood haemoglobin and plasma amino acid concentrations.

1. The equation used for calculating heat production of ruminant animals is expressed in a new form, convenient for application to open-circuit calorimetry.

2. It is shown that in open-circuit calorimetry the possible error involved in making the assumption that respiratory quotient is equal to unity is small compared with the possible error involved in neglecting methane production.

3. In open-circuit calorimetry heat production can be predicted with accuracy to within ± 2% solely from the measurement of oxygen concentration and ventilation rate.