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. 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. 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. 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. 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. 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 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. 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. 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. 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. Measurements were made of portal blood flow, heat production and oxygen consumption in the digestive tract of sheep either fasted or given the following diets: chopped, dried grass; pelleted, dried grass; chopped, dried lucerne; pelleted, dried lucerne; or a pelleted baley diet.

2. For sheep that had been fasted for 48 h, portal blood flow was 1.84 1/min, total visceral heat production was 62.3 kJ/kg body-weight0.75 per 24 h and aerobic heat production, estimated from oxygen consumption, was 62.1 kJ/kg body-weight0.75 per 24 h.

3. Portal blood flow was markedly influenced by food intake, increasing from 1.8 1/min for starved sheep to 2.4 and 4 1/min for sheep fed at maintenance and 2.5 × maintenance levels of intake respectively. Variations in the quality and physical form of the diets had no apparent effect on portal blood flow.

4. There was a curvilinear relationship between total heat production in the gut and metabolizable energy (ME) intake. The increase obtained for levels of intake below maintenance was greatest with lucerne diets, and least with pelleted, dried grass or pelleted barley diets. Above maintenance levels of intake the rate of increase in heat production, with all diets, was about 150 kJ/MJ ME intake.

5. The heat of fermentation, estimated from the difference between total visceral metabolism and the aerobic metabolism of the tissues of the gut wall, was 76, 60 and 22 kJ/MJ digestible energy intake for the dried grass, lucerne and barley diets respectively.

6. The contribution of fermentation heat and the aerobic metabolism of the gut to the total heat increment of feeding in sheep was assessed. It was concluded that about half the heat increment must be derived from tissues outside the digestive tract.

1. The feasibility of improving iron nutrition by fortifying cane sugar with Fe and ascorbic acid was studied.

2. It was found to be possible to add a number of Fe salts together with ascorbic acid to sugar without affecting its appearance or storage properties.

3. The absorption of Fe from fortified sugar eaten with maize-meal porridge or made into jam or biscuits was measured in ninety-four volunteer multiparous Indian women using the 59Fe erythrocyte utilization method.

4. The absorption of Fe from sugar fortified with ascorbic acid and ferrous sulphate and eaten with maize-meal porridge was increased about twofold if the ratio, ascorbic acid: Fe was 10:1 by weight. If the ratio was increased to 20:1, Fe absorption was increased a further threefold.

5. Sugar fortified with soluble Fe salts, including FeSO4. 7H2O, discoloured both tea and coffee; sugar fortified with ferric orthophosphate did not have this effect.

6. Fe from FePO4. H2O was poorly absorbed when added with sugar to maize-meal porridge, and also when added with adequate quantities of ascorbic acid. This form of Fe was absorbed much less well than was the intrinsic Fe present in the maize.

7. When sugar fortified with FePO4.H2O and ascorbic acid was added to maize-meal porridge before cooking or was made into jam there was a several-fold increase in the amount of Fe absorbed.

1. Twenty-two samples of high-protein feeding-stuffs, sixteen of them fish meals, were used in a collaborative study of the precision and the limits of discrimination of the Streptococcus zymogenes assay procedure, as applied to the estimation of available methionine, tryptophan and isoleucine contents.

2. All the participating laboratories ranked the test samples in much the same sequence with respect to content for all three amino acids. There were apparently systematic differences between laboratories which impaired the precision of some of the estimates, and these were greatly reduced by including a common reference sample in the tests as an auxiliary standard.

3. Values for available methionine content for eleven test samples were highly correlated (r 0.86) and quantitatively similar to those obtained for chick growth assays, but those for available tryptophan content were markedly lower and were probably in error.