1. Energy exchanges and other physiological functions associated with eating and rumination were determined in four experiments. Sheep were given chopped, dried grass (DGC), pelleted, dried grass (DGP) or fresh grass (FGC).

2. In Expt 1 a preliminary study was made using all three diets. The dry matter (DM) of DGP was eaten significantly faster than that of chopped diets. Sheep salivated most during eating and ruminated longest when given DGC. Rates of contraction for the reticulo-rumen did not differ significantly between diets during idling and rumination, but were significantly faster during eating with DGP. The apparent energy costs of eating were 17, 109 and 176 kJ/kg DM eaten for DGP, DGC and FGC respectively, but these probably underestimated the true energy cost.

3. Expt 2 compared DGP and DGC at two levels of intake. The mean energy costs of eating DGP and DGC were 23.5 and 267 kJ/kg DM respectively. There was no consistent relationship between the energy cost of eating and the duration of the meal. The proportion of time the sheep spent ruminating DGC was about 23% but less than 1% for DGP. There was no significant relationship between heat production and the time spent ruminating.

4. In Expt 3 four sheep were offered fresh grass and, later, an equivalent DM intake after the material had been dried. The sheep ate the dried meal significantly faster. The mean energy costs of eating were 208 and 346 kJ/kg DM for DGC and FGC respectively. In this experiment the sheep ruminated significantly longer when given FGC, and the energy cost of rumination was 0.11 kJ/min.

5. Increases in heat production during and after fistula-feeding were only 2–8% of those obtained during eating, indicating that nearly all the increase in heat production during eating could be attributed to the energy cost of eating per se.

6. The contribution of the energy costs of eating and rumination to the heat increment of feeding and the energy requirement for maintenance of sheep are discussed.

1. Sheep fitted with a rumen fistula and either a re-entrant cannula at the proximal duodenum or a re-entrant cannula at the terminal ileum were given twice daily 480–520 g dry matter as fresh perennial ryegrass, or white or red clover. Flows of digesta were corrected to 100% recovery of chromic oxide.

2. The quantities (g/24 h) of zinc and cobalt leaving the stomach were significantly greater than those in the food. No significant change was found in the quantities of copper and manganese. Significantly smaller quantities of Co (all three diets) and Zn (all diets except red clover) left the small intestine than those which entered this region. No significant differences in the quantities of Cu and Mn entering and leaving the small intestine were found. Significantly smaller quantities of Zn, Co, Cu and Mn were excreted in the faeces than entered the large intestine.

3. From the flow results it was determined that there was a significant net secretion of Zn and Co in the stomach, and a significant net absorption of Zn (except with the red-clover diet) and Co from the small intestine, and of Zn, Co, Cu and Mn from the large intestine.

1. Five experimental diets were offered ad lib. for 21 d to five sheep in a 5 × 5 Latin-square design experiment as follows: pelleted grass meal alone (control); pelleted grass meal plus hydrochloric acid (470 mmol/kg dry matter (DM)); pelleted grass meal plus 470 mmol HCl/kg DM and either an equivalent amount of calcined magnesite (MgO) (235 mmol/kg DM) or twice the amount (470 mmol MgO/kg DM); pelleted grass meal plus 470 mmol MgO/kg DM.

2. MgO supplementation partly prevented the reduction in food intake caused by HCl, being more effective at the low than at the high level. When fed alone, the high level of MgO had a slight adverse effect on food intake.

3. There was no significant treatment effect on either the pH or volatile fatty acid concentrations of rumen fluid. MgO supplementation was only slightly effective in preventing the metabolic acidosis caused by HCl supplementation, as indicated by blood and urine acid–base measurements.

4. With the MgO-supplemented diets, values for the faecal and urinary excretion of magnesium were approximately 70 and 10% respectively of Mg intake and were not significantly affected by HCl supplementation. For rumen fluid, the water-soluble Mg concentration as a percentage of the total Mg concentration was similar for each treatment, approximately 90%. For faeces, the corresponding value was also similar for each treatment, approximately 30%.

5. MgO supplementation altered the effect of dietary HCl on faecal calcium excretion and on the balance of Ca, but did not alter its effect on urinary Ca excretion.

6. It is concluded that the beneficial effect of MgO supplementation on the intake of the HCl-treated diet was related more to its influence on dietary pH than on conditions in the rumen or the acid–base balance of the sheep.

1. The ability of organic and inorganic sulphur to influence the copper and molybdenum metabolism of sheep was compared in a series of three 2 × 2 factorial design experiments. In each experiment, four groups of five to seven hypocupraemic ewes were repleted with a basal diet supplemented with 6 mg Cu/kg and containing S and Mo at one of two concentrations, 1 or 4 g S and 0.5 or 4.5 mg Mo/kg respectively. Sodium sulphate (Expt 1), methionine (Expt 2) or cysteine (Expt 3) were used as the S sources. Cu and Mo concentrations in plasma were estimated in each experiment and in Expt 3 the concentrations of Cu in liver and Mo in urine were also estimated.

2. The effects of the three S sources on Cu and Mo metabolism were similar. Repletion of the plasma Cu pool was unaffected by Mo alone, reduced by S alone and totally inhibited by Mo + S. Plasma Mo was greatly increased by Mo supplements, slightly decreased by S supplements and unaffected by Mo and S supplements given together.

3. In Expt 3 the treatments were found to affect urinary Mo and plasma Mo in a similar manner; S prevented dietary Mo from increasing Mo excretion. The only group to show a significant repletion of the liver Cu pool was that given Mo alone.

4. Supplementation of the diet with organic S significantly reduced the within-treatment variation in plasma Cu and Mo, liver Cu and urinary Mo.

5. It is suggested that variations in dietary S and Mo within the normal range for herbage affect the Cu and Mo metabolism of the grazing animal, and that total S rather than inorganic S is the more useful measurement in the context of the Cu–Mo–S interrelationship.

1. Measurements have been made of the size and number of muscle fibres and number of nuclei in a small indicator muscle (m. flexor digiti V brevis) in the fore-foot of the pig. Wellnourished, 10-d-old and 1-year-old animals were studied, as well as 1- and 2-year-old animals that were severely energy-deficient and protein-deficient.

2. The normal 1-year-old animals had much larger muscle fibres, with more nuclei, than the pigs in any of the other groups.

3. There were no significant differences between the numbers of fibres in the muscles of pigs in any of the four groups.

4. There was a significant difference between the number of fibres in the muscles of pigs coming from different litters, irrespective of their dietary history after birth. This suggests that the number of fibres is determined genetically before birth, and all that can take place after birth is an alteration in size.

1. Studies were done of the possible development of a biotin deficiency in domestic fowl of various ages as a result of feeding with diets composed mainly of wheat, and meat-and-bone meal. The degree of deficiency was estimated from physical symptoms, liver and kidney composition and hepatic enzyme activities.

2. Only a mild biotin deficiency developed in 3-week-old chickens and no adverse metabolic effects were found for chickens reared to 7 or 15 weeks of age or maintained for 9 months in lay on these diets, which were suspected of producing fatty liver and kidney disease in young chickens. At 3 weeks of age the deficiency was more severe the heavier the strain of chicken and the greater the rate of body-weight gain.

3. The present results question the supposition that biotin deficiency is the sole factor responsible for the development of fatty liver and kidney syndrome in young chickens.

1. The inclusion of phytate (10 g/kg) in a purified diet containing zinc (15 mg/kg) fed to young male rats significantly reduced growth rate and food intake, and promoted a cyclic pattern of food intake characteristic of an uncomplicated Zn deficiency. The decreased growth rate could be accounted for by the reduced food consumption.

2. Rats maintained on a Zn-deficient diet (0.5 mg Zn/kg) were found to have a cyclic pattern of food intake and a very slight weight gain. The addition of phytate (10 g/kg) to the Zn-deficient diet promoted a net loss of mean body-weight.

3. Rats maintained on the Zn-supplemented diet containing phytate excreted significantly more Zn in their faeces than either pair-fed or ad lib.-fed control rats. Rats given the Zn-deficient diet supplemented with phytate excreted more Zn in their faeces than Zn-deficient control rats.

4. Dietary phytate significantly reduced the average daily accumulation (μg/d) and wholebody retention (relative to dietary intake) of iron, copper, manganese and Zn, whether or not the diet was supplemented with Zn.

5. The addition of phytate to the lumen fluid of ligated loops of rat duodenum maintained in situ significantly inhibited 65Zn absorption, compared with the control systems without added phytate.

6. Other studies using ligated duodenal and ileal loops indicated that Zn is secreted into the gut lumen and approximately one-third of this is normally reabsorbed. Recycling of endogenous Zn may be a significant process in the over-all body economy of this trace element.

7. The absorption of 65Zn added to the diet was significantly reduced by dietary phytate. Dietary phytate also reduced the biological half-life of body 65Zn from 91 to 211 h post-administration, possibly by inhibiting reabsorption of endogenous 65Zn and thus promoting a more rapid loss from the body.

1. The contribution of school milk to the nutrition of 396 Kent primary schoolchildren aged 8–11 years was assessed using information collected in a survey which included a weighed-diet record, a socio-economic questionnaire and a medical examination.

2. Over half the children (59% for boys, 54% for girls) drank school milk every school day of the diet-record week.

3. Children who drank school milk every school day, when compared with those not drinking it, had a significantly higher mean daily intake of liquid milk, a higher total daily intake of several important nutrients including animal protein, calcium, thiamin and riboflavin, and a diet richer in Ca and riboflavin (boys) and animal protein and Ca (girls). They were also less likely to have intakes of Ca and riboflavin below the recommended daily intakes for these nutrients (Department of Health and Social Security, 1969).

4. The increased nutritional intake associated with school milk consumption was not related to any differences in height, weight, arm circumference or skinfold thickness.

5. There was no evidence that school milk consumption was associated with obesity (as assessed clinically).

1. A procedure is described for assaying in vitro the activity of various inhibitors of methane production by rumen micro-organisms.

2. Methods of preparation of various inhibitors are described together with attempts to characterize these compounds by determining their physical properties (physical state, density, chromatographic behaviour), their hydrolysis by rumen contents and their relative potency as inhibitors.

3. The results of preliminary studies with trichloroethanol and its ester with pivalic acid are given.

4. The inhibitory activities of several groups of related compounds are reported. These include the polyhalogenated alcohols and their esters with pivalic acid, the esters of trihalogenated alcohols and monobasic fatty acids from C2 to C16 and the trihalogenated alcohol esters of dibasic acids. The results of experiments with esters of alcohols and polyhalogenated carboxylic and sulphonic acids are also given.

5. It is concluded that the mechanism of action of the inhibitors might be similar to that of known polyhalogenated methane analogues (e.g. chloroform). The relative activity of various compounds might be partly governed by the ease of their absorption into the microbial cells and by the extent to which the esters can be hydrolysed by rumen contents.

6. The results show that some substances are very poor inhibitors, unless they are esterified (e.g. trichloroacetic acid) but on the whole the esters in which the polyhalogen grouping is on the alcohol portion of the molecule are better inhibitors than those in which it is on the acid portion of the molecule.

1. Plasma amino acid levels have been estimated at 0, 15, 30 and 45 min after ingestion of doses of (1) an amino acid mixture simulating casein and (2) a tryptic hydrolysate of casein consisting mainly of oligopeptides. Both doses contained the same amount of nitrogen.

2. After ingestion of both preparations, there was a prompt increase in plasma amino acid levels, followed by a decrease. No such change occurred in fasting subjects. There were no significant differences between increments in plasma amino acid levels after ingestion of the amino acid mixture and the corresponding increments after ingestion of the tryptic hydrolysate.

3. Correlations were found between the areas under the curves for individual amino acid concentrations, after ingestion of the two preparations, and the amino acid composition of casein. The results do not suggest that increases in plasma amino acid levels following small doses of protein digestion products are the result of circadian changes, or that such increases are ‘swamped’ by absorption of amino acids from endogenous protein in the lumen of the small intestine.

1. Male rats were maintained from weaning to between 4 and 16 weeks of age on a semisynthetic diet which was deficient in copper.

2. Methyl esters of fatty acids from adipose tissue of the rats were analysed by gas-liquid chromatography and the desaturase activity of liver microsomes, with [1-14C]stearic acid as the substrate, was determined. Liver and plasma Cu concentration, cytochrome c oxidase (EC 1.9.3.1) activity and caeruloplasmin activity were determined as indices of Cu status.

3. Cu deficiency was associated with decreased mono-unsaturated: saturated ratios for C16 and C18 fatty acids from subcutaneous adipose tissue and decreased desaturase activity for liver microsomes. When Cu-deficient rats were given free access to the Cu-adequate diet or were injected intraperitoneally with an aqueous solution of CuSO4, that is, when the animals were repleted with Cu, the indices of Cu status, and desaturase activity for liver microsomes returned to values found in control animals.

4. When Cu or a Cu-chelator (Neocuproine) was added to microsomes, there was no effect on the activity of the desaturase enzyme system; the stability of the desaturase was not affected by Cu.

5. These results are indicative of an involvement of Cu in the desaturase reaction. It is suggested that the site of this involvement could be the terminal component of the microsomal electron transport chain.

1. Two inhibitors of rumen methane production were given to sheep and their effects were measured using an in vitro technique.

2. The substances used were trichloroethyl pivalate (TCE-P) and trichloroethyl adipate (TCE-A). In one experiment with two sheep TCE-P was injected into the rumen and in another experiment with two sheep the same inhibitor was mixed with the food just before feeding. In another experiment, TCE-A was given to two sheep at two dose levels, and in an experiment with four sheep two levels of inhibitor and two levels of diet were used.

3. In general the inhibition of methane production was greater with samples of rumen contents taken after feeding than with those taken before feeding. When sheep were given 120–300 mg TCE-P/d the inhibition of methane production ranged from 21 to 81%. When sheep given maintenance rations were given 125–300 mg TCE-A/d there was 28–90% inhibition of methane production. When sheep were given twice maintenance rations 150 mg TCE-A/d gave no inhibition and 300 mg TCE-A/d gave very low inhibition of methane production (about 16%).

4. In most experiments there was a significant increase in the propionic acid:acetic acid concentration ratio in the rumen when methane production was inhibited.

5. The possible practical use of inhibitors is discussed.

1. Flow rate of digesta and its components in the upper jejunum, and the absorption of L-histidine and glucose from the jejunum segment were measured in pigs fitted with three simple cannulas. The pigs were fed once daily at 08.30 hours.

2. A maximum flow of digesta was obtained in the period 10.00–10.30 hours; the flow rate decreased with time after feeding, reaching a minimum in the period 22.00–22.30 hours.

3. The absorption rate for L-histidine and glucose increased in a hyperbolic manner with increasing concentrations of infused test material, which ranged from 2.5 to 20 g/l for each material.

4. L-histidine and glucose were absorbed nearly independently when perfused in combination. The absorption rates for glucose were significantly (P < 0.01) greater than the corresponding rates for L-histidine at each concentration of infusate.

5. The absorption of both L-histidine and glucose expressed as a percentage of the amounts in the perfusate decreased with increasing flow rate of perfusate, from 400 to 800 ml/h. The increase in flow rate from 400 to 800 ml/h was associated with a 20% increase in L-histidine absorption rate; there was a 30% increase in glucose absorption rate when the flow rate was increased to 600 ml/h, but no further increase at 800 ml/h.

6. The absorption of both L-histidine and glucose decreased with time after feeding; the absorption rates for L-histidine and glucose measured for the period 10.00–10.30 hours were 126 and 133%, respectively, of those measured for the period 22.00–22.30 hours.

1. The heat loss for individual growing pigs, whose initial body-weight was 25–40 kg, was measured continuously for periods of 14 or 21 d when they were maintained at an environmental temperature of either 20 or 30°. For each temperature the feeding level before and after a period of fasting was held at either 39 or 45 g/kg body-weight per d. Four pigs were given each treatment; food was withheld from three animals for a 4 d period in each experiment, and the fourth pig (control) was fed for the whole experimental period.

2. After the withdrawal of food, the heat loss decreased rapidly and minimum values were recorded during the third and fourth days of fasting. Fasting heat loss was higher at 20° than at 30° and was not significantly dependent on the preceding level of feeding. The mean values obtained at 20 and 30° were 457 and 380 kJ/kg0.75 per d respectively.

3. The heat loss during the periods of feeding was significantly higher (P < 0.05) at 30° than at 20°, and was also higher at the higher level of feeding.

4. The apparent efficiency of utilization of metabolizable energy for maintenance was calculated as 0.80.

5. It was concluded that the critical temperature for a fasting pig weighing 25–40 kg is approximately 25°.

1. Male chickens, 1 week old, were fed alternately for 6 or 12 h periods with diets complementary in their amino acid composition. The isonitrogenous, isoenergetic diets were based on fish meal or sunflower meal as the sole source of protein, or fish meal–sunflower meal (40:60, w/w); each diet contained 120 g crude protein/kg. Other groups of chickens were given these diets ad lib.

Net protein utilization (NPU) values obtained after a 1-week experimental period indicated that sequential feeding for both 6 and 12 h resulted in significantly improved responses compared with chickens given the same diets ad lib. These results suggested that the two protein sources, although provided at separate times, could complement each other.

2. In certain treatments there was a 6 or 12 h fasting period between feeding periods to reduce the effect of nutrients from the previous period.

3. For alternate feeding and fasting periods of 6 h with the combined diet, food intake and gain in body-weight were both significantly reduced compared with the corresponding values for the combined diet fed ad lib. The NPU value was virtually the same for both treatments. For 12 h periods of alternate feeding and fasting the gain in body-weight was only just significantly lower than that for the control group (combined diet fed ad lib.), but the NPU value was highly significantly better than that for the control group.

4. For the treatments which included 6 and 12 h fasting periods between the two singleprotein diets, the food intake and gain in body-weight were significantly lower compared with the treatment groups given alternate feeding and fasting periods of either 6 or 12 h with the combined diet. The NPU values for the two groups given 12 h alternate feeding and fasting periods differed significantly, whereas the NPU values for the two groups given 6 h feeding and fasting periods were the same.

1. Serum colloidal osmotic pressure was measured in children ‘at risk’ to kwashiorkor, in others with frank signs of the disease and during recovery. Simultaneous estimations of serum albumin and globulin concentrations and assessments of the extent of oedema were also made.

2. During the development of kwashiorkor, serum colloidal osmotic pressure did not decrease significantly until albumin concentration was 25.1–27.5 g/l. Above 30.0 g/l, colloidal osmotic pressure was maintained at normal levels during which time a significant reciprocal relationship existed between albumin and globulin concentrations. These findings provide support for suggestions that there may be an oncotic regulation of albumin synthesis.

3. Low albumin concentrations were mainly responsible for the low colloidal osmotic pressures found in children with kwashiorkor and in agreement with previous findings the threshold for the formation of oncotic oedema was found to be about 2.35–2.65 kN/m2.

4. Values for colloidal osmotic pressure calculated from serum albumin and gobulin concentrations using empirical formulas did not agree well with measured values and no constant correction factor suitable over the whole range of albumin concentrations found in rural Ugandan children could be devised. In many hypoalbuminaemic children only direct measurement of serum colloidal osmotic pressure will indicate the true extent of risk to an episode of oedema.

1. A study was made of the metabolism of ɛ-(γ-L-glutamyl)-L[4, 5-3H]lysine (GL) in the rat.

2. The compound was largely absorbed from the intestine and metabolized. Labelled lysine was incorporated into blood proteins.

3. In an in vitro experiment with everted sacs of rat small intestine, GL passed through the intestinal wall unchanged.

4. The results of comparative tests using homogenates of different body tissues indicated that the kidneys were particularly active in hydrolysing GL. Their activity was nine times greater than that of the liver and eighteen times greater than that of the small intestine.

1. A study was made of the absorption of [58Co]cyanocobalamin in suckling piglets. Cyanocobalamin given at birth and at 7 d of age was efficiently absorbed from the intestine and retained within the body, mostly in the liver. A 10 μg test dose was absorbed no less efficiently than 0.5 μg, despite the virtual absence of intrinsic factor in the gut. In piglets given a 10 μg test dose at different ages between 0.5 and 56 d, there was a marked decrease in the efficiency of retention between about 7 and 21 d of age.

2. Vitamin B12-binding capacity in the gastric mucosa increased with age, from 40 ng at birth to about 2000 ng at 14 d and 7000 ng at 35 d. This binder-protein was largely endogenous, whereas much of the unsaturated binder-protein in intestinal mucosa was apparently derived from milk.

3. The chyme in the stomach and small intestine contained unsaturated binder-protein, partly endogenous and partly deriving from milk, which prevented uptake of added [G-3H]-cyanocobalamin into the ‘solids’ phase of the intestinal contents. The intestinal chyme contained large numbers (log10 7.0–9.1/ml) of bacteria, some of which were isolated and shown to take up cyanocobalamin or folic acid or both.

4. The findings are discussed in relation to the concept that for some days or weeks after the cessation of transport of intact protein across the neonatal gut epithelium (‘closure’), protein-bound vitamins may continue to be taken up into the epithelial cells and there released for transport into the circulation. It is concluded that unsaturated vitamin-binders may strongly influence the ecology of the intestinal microflora.

1. Two groups of adult rats were placed in a metal-free environment and pair-fed with selenium-supplemented and Se-deficient diets.

2. After 5 months the animals were killed and skeletal muscle concentrations of creatine, creatine phosphate, ATP, protein and Se were determined.

3. Se deficiency was indicated by the low Se content of the skeletal muscle from the deficient animals, but no changes were found in the amounts of the other components.

4. These results suggest that Se may not be involved in creatine metabolism and that Se deficiency may not be concerned independently in the development of nutritional dystrophy, where changes are found in the levels of protein, creatine, creatine phosphate and ATP.

1. Enzymes that may contribute to liquefaction of the cornea in retinol-deficient animals and in man have been studied using rat cornea. The established technique of culturing tissue fragments and determining the activity of collagenase (EC 3.4.24.3) and other enzymes in the medium after different periods of culture was used.

2. A collagenolytic system was detected in the media from cultures of rat corneas. This system probably consists of at least two enzymes, a collagenase and a neutral proteinase.

3. Both proteolytic and specific collagenolytic activity were greater in media from retinol-deficient rat corneas. The hydroxyproline level increased in parallel with the increase in enzyme activity.

4. In the final stages of retinol deficiency the cornea is invaded by granulocytes and other cells of the blood and we suggest that destruction of cornea collagen may be due largely to the activity of the enzymes from these cells.