1. The effect of different protein sources in milk-substitute diets on abomasal acidity and proteolytic activity was studied in Friesian calves, aged 20–58 d (Expt 1). The diets contained ‘mildly’ preheated, spray-dried skim-milk powder (MHM), ‘severely’ preheated, spray-dried skim-milk powder (SHM), fish-protein concentrate (FPC) or solvent-extracted soya-bean flour (SF) as the main protein source.

2. Gastric juice was collected from abomasal pouches before feeding and at 15 min intervals for 8 h after the morning feed. Samples of digesta were obtained from the abomasum at 1 h intervals during the same period.

3. Digesta pH was lower and titratable acidity higher 0-3 h after giving the diet containing MHM than when any of the other three diets was given.

4. Acid secretion from the pouches for the different diets was in the order: FPC > MHM > SHM ≥ SF.

5. Protease secretion from the pouches, assayed at pH 2.1, was in the order: MHM > SHM = FPC > SF.

6. The effect of dry matter (dm) intake and concentration on abomasal acidity was also studied in calves given diets which contained MHM (Expt 2). This diet was reconstituted at either 100 or 149 g dm/kg liquid diet and fed at either 32.5 or 49.0 g DM/kg live weight 0.75 per d. Samples of abomasal digesta were collected as in Expt 1.

7. A high intake of dm at a low dm concentration resulted in low acidity of the digesta in the first 3 h after feeding, which suggested a dilution effect. Comparison of two diets of different dm concentration, which were fed in the same volume of liquid, indicated that the greater the dm intake, the greater was the amount of acid secreted.

8. It is concluded that the protein sources varied in their ability to stimulate abomasal acid and protease secretion and it is suggested that this may relate to calf performance.

1. An isotope tracer method for estimating methane production in sheep is described.

2. The technique was used to estimate methane produced in both the upper and lower digestive tract and to determine the routes by which it was excreted.

3. Four Merino ewes given lucerne chaff (33 g every hour) were used.

4. Total methane production rate was 21±1.1 (se) ml/min; production in the rumen accounted for 87±1.2% of the total production; 95±1.4% of the methane produced in the rumen was excreted by eructation.

5. Of the methane produced in the lower digestive tract, 89±2.3% was excreted through the lungs and 11% through the anus.

1. The B-vitamin status of fifty-nine patients, mainly from the lower socio-economic classes in Bombay, with a history of chronic malnutrition, and of alcoholism of 1·5–20 years’ duration, was studied before and during treatment, and in relation to their clinical, especially neurological, condition. These patients were divided into two neurological categories: (1) those with peripheral neuropathy (mainly sensory and distal) alone, (2) those with mental changes (mainly confusion and disorientation) also. Both categories frequently showed pellagrous pigmentation and mucocutaneous signs of B-vitamin deficiency.

2. Thiamin and erythrocyte transketolase (EC 2.2.1.1) activity, riboflavin, nicotinic acid, pantothenic acid, total and pyridoxal fraction of vitamin B6, folate and total vitamin B12 were estimated in the blood and the cerebrospinal fluid (CSF) of these patients, and also in the blood of sixty-nine control subjects and in the CSF of some of them. The concentrations of all the vitamins, except vitamin B12, were highly significantly lower in the blood of patients of category 1 compared to the controls, and erythrocyte transketolase activity and pyridoxal concentration in patients of category 2 were significantly lower than those of category 1 patients. Blood pantothenic acid and folate concentrations were reduced less consistently.

3. Serum vitamin B12 concentration was significantly increased (though within normal range) in the patients compared to the control group, probably because of the moderate hepatic insufficiency (as assessed by liver function tests) in the former.

4. The concentrations of thiamin, riboflavin, nicotinic acid and total vitamin B6 were also highly significantly lower in the CSF in patients of category 1 compared with controls. Furthermore, thiamin, nicotinic acid and total vitamin B6 concentrations were significantly lower in patients of category 2 than those of category 1 patients, indicating that CSF levels reflect better the neurological status of these patients.

5. There was a moderate increase in the blood concentration of all the vitamins tested, after a relatively poor hospital diet alone. There was a concurrent increase in the blood levels of thiamin, riboflavin, nicotinic acid and pantothenic acid after parenteral treatment with either thiamin or nicotinic acid. The administration of pyridoxine resulted in a significant increase in the blood levels of riboflavin and the pyridoxal fraction of vitamin B6.

1. The excretion of urinary and faecal nitrogen by young Nigerian men of a low income group was found to vary significantly between subjects, but was not significantly different in the same subject, when they were given a mixed diet composed of rice, vegetables and fish on two separate occasions. At the levels of energy and protein supplied by this diet the men gained or lost small amounts of weight, mean values indicating N equilibrium, the variation around the mean being high.

2. The correlation between the urinary and faecal N of these men was significantly negative at and below the level of N equilibrium, becoming positive 2–3 weeks after they had consumed the above diet supplemented by 400 g of lean beef per day, and had already established considerable rates of gain in body-weight and N retention. The diets were made isoenergetic by adding the beef at the expense of cassava flour and red palm oil.

3. The physiological processes involved in the adaptation, by young Nigerian men of low income, to a highly efficient use of low-protein diets are discussed in relation to the biological value and true digestibility of those diets, and to the ‘safe level of protein intake’ and protein-energy ratios proposed by FAO/WHO (1973, 1975).

4. It is concluded that the protein requirements of apparently healthy men can only be established in the context of their ecological, socio-economic and nutritional backgrounds.

1. Kinetic experiments were done with pepsin (EC 3.4.4.1) using haemoglobin as a substrate in the presence of different metal cations.

2. The activation of peptic hydrolysis with higher concentrations of cupric ions added to the reaction mixture was determined from turnover-rate curves in experiments with constant substrate concentration. With a Cu2+ concentration greater than 1.67 × 10-4M activation was obtained

3. Nickel ions at a concentration of 8.33 × 10-4 M and at higher concentrations also increased pepsin activity. Additions of ferrous ions and zinc ions had no effect.

4. Experiments were done using variable substrate concentrations in the presence of different Cu2+ concentrations. The concentrations of haemoglobin ([S]) at half maximum velocity were determined. The double-reciprocal plots of [S] v. reaction velocity (v) (i.e. I/[S] v. I/v) had no common intersection point. Therefore the kinetics did not correspond to any of the known kinetics. The activation brought about by Cu2+ cannot easily be explained by the study of the kinetics. Certain simple explanations of the phenomenon can be eliminated.

1. Cataract formation in streptozotocin-induced diabetes in rats was reduced by approximately 85% when a diet rich in maize oil (300 g/kg diet) (fat diet) was given, thus confirming results of earlier studies. However, the concentration of sorbitol in the lens of diabetic animals remained high, the values for diabetic rats given the standard diet and the fat diet being 65 and 40 μmol/g protein respectively.

2. With the standard diet, the fatty acid profile of the triglycerides of the epididymal fat pads was characterized by a greater relative proportion of saturated fatty acids for the diabetic animals compared to that for the normal animals. The fat diet moderated the tendency towards saturation in the diabetic animals.

3. The fat diet had other effects on the diabetic animals; these included a reduced mortality rate, increased body-weight, a decrease in the daily water intake, and in the daily urinary excretion of glucose and urea.

4. In the diabetic animals the fat diet had no effect on the specific activities in the liver of hexokinase (EC 2.7.1.1), glucokinase (EC 2.7.1.2), phosphofructokinase (EC 2.7.1.11) and pyruvate kinase (EC 2.7.1.40). However, the specific activity of glucose-6-phosphatase (EC 3.1.3.9) was reduced, while that of malate dehydrogenase (decarboxylating) (NADP) (EC 1.1.1.40) was increased. The NAD+: NADH ratio, as calculated from liver pyruvate and lactate concentrations, tended to increase.

5. The results suggested that the fat diet moderated the long-term metabolic effects of diabetes.

1. The diets and living conditions of nine Asian boys with biochemical, and in most instances also radiological, signs of rickets were compared with those of nine other boys who appeared to be normal. The groups were matched according to age, religion, place of father's origin and boy's own place of birth.

2. There were no outstanding differences between the diets of the boys with, and of those without signs of rickets. All had adequate to high calcium intakes. Most of the boys had low intakes of vitamin D, and those with signs of rickets generally had lower intakes than the normal boys. The food tables used for making the calculations of vitamin D intakes report the amount of the vitamin in the lipid fraction of milk. If it proves to be true that most of the vitamin D activity of milk is in the aqueous fraction, the boys would have been getting considerably more vitamin D than the results suggested, and their average intake may have been about 3.5 μg/d.

3. It was not possible to make any quantitative measure of the exposure of the boys to sunlight. All Asian boys studied appeared to have their bodies more completely covered than British or West Indian boys.

4. The problem of why nine boys had signs of rickets and nine had none has not been solved. It is suggested that those with signs of rickets may have had higher requirements for vitamin D than the others. When the intake of vitamin D is low and exposure to sunlight is minimal, those with high requirements will be the ones to develop signs of rickets.

1. Plasma urea entry rate, urinary urea excretion and, by difference, urea recycling in the body, together with the flow of non-ammonia N through the abomasum and digestion of dry matter (dm) before the abomasum were determined in both wethers and lambs receiving cereal-starch diets supplemented with urea to give 60–120 g crude protein (N × 6.25)/kg dm.

2. Lambs excreted less urea in urine than wethers given the same diet.

3. Relationships between plasma urea entry rate or urine urea excretion rate and plasma urea concentration were different for lambs compared to wethers suggesting greater conser vation of body N by renal control in lambs.

4. Recycling of urea was not related to plasma urea concentration in wethers but was related exponentially in lambs, suggesting recycling is controlled rather than the result of simple diffusion from the blood to the gastro-intestinal tract.

5. Abomasal non-ammonia-N flow was similar for wethers and lambs and increased linearly with urea supplementation.

6. dm digestion prior to the abomasum was not significantly altered, although there was a tendency for decreased digestion of the basal diet given to lambs.

7. Maximum microbial N flow to the abomasum was estimated as 30 g N/kg organic matter (OM) fermented in the rumen.

8. This work and the literature reviewed suggested maximum net microbial production can be obtained when the diet supplies an amount of fermentable N equal to the microbial N output. It is calculated the diet should supply approximately 26 g fermentable N/kg digestible OM or 1.8 g fermentable N/MJ metabolizable energy. This corresponds to a fermentable crude protein supply varying from 65 to 130 g/kg DM as digestible OM content increases from 400 to 800 g/kg DM.

1. Pangola grass (Digitaria decumbens) grown with and without calcium fertilizer was cut at three stages of regrowth to measure voluntary intake of dry matter (DM) and digestibility of various components of the dried-grass diet by sheep kept in metabolism crates. To determine the extent of a simple Ca deficiency half the sheep on each diet were supplemented with 1·4g Ca/d. Retention times of the various dietary components in the reticulo-rumen were also determined.

2. Feeding a Ca supplement had no effect on voluntary intake or digestibility.

3. Ca fertilizer increased the Ca content of the grass from 2·2 to 3·8 g/kg DM and DM digestibility from 0·455 to 0·476 (P < 0·01) due to an increase in the digestibility of the hemicellulose.

4. Voluntary intake was increased from 38·8 to 43·2 g/kg body-weight0·75 per d by Ca fertilizer due to an 18% reduction in the period of time the DM was retained in the reticulo-rumen.

5. Regressions relating voluntary intake to DM digestibility for the Ca-fertilized and control grass were significantly different (P < 0·01). When compared at the same DM digestibility the voluntary intake of the Ca-fertilized grass was 2·6 g/kg body-weight0·75 per d higher than that of the control.

6. It was concluded that Ca fertilizer increased both DM digestibility and voluntary intake as a result of changes in the structural composition of the grass and not by a simple increase in the Ca content of the diet.

1. A low-magnesium diet was fed to four sheep, each of which had been surgically prepared with a rumen fistula, a tube into the cranial one-third of the omasum, a tube to the cranial one-third of the abomasum and a re-entrant duodenal cannula. Mg, as gluconate or acetate, was continuously infused for 12–14 d in turn into (1) the caudal duodenal cannuia, (2) the abo-masum, (3) the omasum, (4) the rumen. A continuous infusion of the chromium-ethylene- diaminetetraacetic acid complex (CrEDTA) was maintained to the rumen. The abomasal effluent which flowed through the cranial duodenal cannula was continually sampled and the flow of Mg calculated from the concentrations of Mg and CrEDTA. Blood and rumen fluid samples were taken and urine and faeces collected during each period of Mg infusion.

2. The Mg infused to either the abomasum or omasum was completely recovered at the duodenum, indicating a lack of net absorption of Mg from these stomach compartments. In contrast, 13.7–18.7 mmol (36–61 %) of the Mg infused to the rumen was not recovered at the duodenum which suggested that a substantial net absorption of the infused Mg occurred from the reticulo-rumen. Absorption of Mg caudal to the pylorus was not related to the site of Mg infusion and averaged 3.28 ±0.56 (sem) mmol/d.

3. Compared with the intraruminal infusion, the post-ruminal infusion of Mg was associated with decreased plasma and rumen fluid Mg concentrations, decreased urinary Mg excretion, decreased Mg balance and increased faecal Mg excretion.

4. It is concluded that no significant absorption of Mg occurs from either the omasum or abomasum in sheep and that the reticulo-rumen is the principal site of Mg absorption before the pylorus. Absorption of Mg post-ruminally is insufficient to maintain normal Mg status in the animal.

1. Supplementing a lysine-deficient diet (5 g lysine/kg) with five increments of lysine, each of 2 g/kg, resulted in increases in growth rate of Yorkshire piglets, aged between 3 and 7 weeks, up to the highest level of lysine (15 g/kg).

2. The free lysine concentration of plasma tended to increase as the dietary lysine level increased from 13 to 15 g/kg, and plasma threonine concentration decreased significantly as the lysine content of the diet was increased from 11 to 15 g/kg indicating that threonine was the second limiting amino acid in the diet.

3. Oxygen consumption and carbon dioxide production of the piglets were not influenced by supplementing the diets with lysine. The heat production was 0.313 kJ/min per kg body-weight in the 6 h experimental period.

4. Supplementation of the diet with lysine had no consistent effect on the recovery of 14C as 14CO2 from a single dose of l-[U-14C]lysine.

5. Adjustment of the determined recoveries of the tracer dose of lysine for the differences in the plasma concentrations of free lysine for the pigs receiving the graded levels of dietary lysine simplified the relationship between recovery and dietary lysine level: it was linear for the first four increments in dietary lysine and then increased sharply for the fifth increment. This indicated that a marked change in the rate of lysine catabolism occurred as the level of dietary lysine was increased from 13 to 15 g/kg.

6. The results of this experiment indicate that the piglets' requirement for lysine is between 13 and 15 g lysine/kg in a diet which contained 181 g crude protein (nitrogen × 6.25)/kg.

1. In a number of separate experiments, yeast RNA, mixtures of its constituent nucleosides, its constituent bases and ribose were administered orally to rats. In each instance, the resultant changes in the composition of body fluids were monitored using sensitive methods.

2. Ingestion of RNA (100g/kg diet) caused detectable increases in intestinal ribose, inorganic phosphate, uridine, pseudouridine, uracil, inosine, uric acid and probably other purine bases. Their accumulation did not detectably affect the rate of passage of food along the digestive tract, even though some nucleosides are known to affect gut motility.

3. Although plasma levels of uric acid and uridine were higher when RNA was administered in the diet, these changes were very slight compared with those in plasma uracil, which in some experiments were increased more than 20-fold compared with control levels (300μmol/l). Analysis of erythrocytes indicated that the internal environment of at least some cells of the body are similarly altered.

4. Analyses indicated that all dietary RNA-phosphate passed into the urine from the gut but most of the RNA-ribose was probably metabolized. Uracil and uric acid levels in the urine reflected plasma composition.

5. The effect of orally administered mixed nucleosides on blood and urine composition was similar to that of RNA, but the response to an equivalent mixture of free bases differed in several respects; cytosine, adenine and hypoxanthine appeared in urine only under these circumstances.

1. The influence of a 24 h fast on the concentrations of free amino acids in the plasma, and upon the oxidation rates of methionine, isoleucine and threonine was studied (using early weaned, 4-week-old piglets which were receiving a semi-purified diet.

2. There was no change in the total concentration of the essential amino acids as a result of the 24 h fast: the concentration of the branched-chain amino acids increased, but the effect of this was offset by decreases in the concentrations of arginine, histidine, lysine, methionine and phenylalanine. There was a reduction in the concentration of the non-essential amino acids.

3. The piglets received infusions of L-[1-14C]methionine, L-[U-14C]isoleucine and L-[U-14C]threonine, and the recovery of the label in carbon dioxide was determined. Less than 5% of the activity from methionine was recovered in the CO2 from the fed piglets, whereas 12% was recovered from the fasted piglets. The corresponding values with threonine were 11 and 19% but there was no effect of fasting on the recovery of the label from isoleucine in CO2.

4. The initial dilution of a single dose of a labelled amino acid infused into the bloodstream depends on the plasma concentration of the amino acid. Nutritional regimens may effect the free amino acid concentration in the plasma. Thus comparisons based upon direct determination of activity recovered in CO2 from the labelled dose of an amino acid with animals on different nutritional regimens could be misleading, unless the differences in the concentrations of the amino acid in the plasma are considered.

1. Experiments were done using 8-d-old kids to determine the metabolic effect of feeding a carbohydrate-free diet, and the effects of supplementation of this diet with a small amount of glycerol, sodium propionate or glucose.

2. The experimental (carbohydrate-deficient) diets permitted growth nearly equal to that with the control diet (cow's milk). The kids given the experimental diets generally had lower levels of blood glucose than those given the control diet.

3. With all experimental diets there were increases in the concentrations of plasma lipid and total liver lipid and a decrease in the concentration of liver glycogen; supplementation of the carbohydrate-free diet with glycerol, sodium propionate or glucose had no additional effect on these values.

4. The ingestion of cow's milk produced hyperglycaemia 2 h after feeding, while in kids given the carbohydrate-free diet there was no increase in blood glucose level. The concentration of plasma free fatty acids in the kids given the carbohydrate-free diet was higher than that in control animals 24 h after feeding, suggesting that the kids given the experimental diet preferentially utilize free fatty acids as an energy source.

1. Calves were given a basal diet of straw and flaked maize (12 g nitrogen/kg dry matter (DM)) or diets with some flaked maize replaced by untreated (UT) casein or formaldehyde-treated (FT) casein to give 19, 26 or 34 g N/kg DM.

2. At all intakes rumen ammonia concentrations were lower and amounts of total-N, non-ammonia-N and amino acid-N entering the duodenum were higher when FT-rather than UT-casein supplements were given.

3. Direct measurement of casein entering the duodenum indicated that giving FT rather than UT casein led to much greater amounts of dietary casein escaping degradation in the rumen (70–90% compared to 10–20%). Calculated values for fermentable N indicated that with this low degradability diets containing FT-casein would have provided inadequate N for maximum microbial synthesis in the rumen, and this probably accounted for the marked reduction in amounts of non-casein-N entering the duodenum when FT rather than UT casein was given.

4. Amino acid patterns in duodenal digesta samples after giving the basal diet or diets containing UT-casein were similar. Giving diets containing FT-casein led to changes in this pattern which could sometimes, although not always, be accounted for by estimated differences in proportions of dietary and microbial proteins.

5. At the highest level of N intake FT-casein-supplemented diets led to significantly higher concentrations of most essential amino acids and lower concentrations of most non-essential amino acids in plasma than did UT-casein-supplemented diets. Plasma urea concentrations increased with increasing N intake but were not significantly different for UT- and FT-casein-supplemented diets.

1. Twenty-four pigs (mean body-weight 44 kg) were used to determine the digestibilities of energy, nitrogen and amino acids in dried microbial cells (DMC) grown on methanol and in white fish meal (WFM). N utilization and the excretion of various nitrogenous compounds were also studied.

2. Semi-purified diets containing DMC, WFM or no protein source were offered at the rate of 1 kg fresh food/d. Daily N intakes were 26.5, 24.7 and 0.65 g respectively.

3. Mean metabolic faecal N determined with the protein-free diet was 1.11 g/d (1.26 g/kg dry matter (dm) eaten) for the two experiments. The corresponding endogenous urinary N value was 2.91 g/d.

4. Daily urinary N output of pigs given the diet with WFM was significantly greater than that of pigs given the diet with DMC, with the result that N retention, net protein utilization and biological value were higher for pigs given DMC.

5. Apparent and true digestibility of amino acids were higher for the diet with DMC than for the diet with WFM.

6. N excretion in the form of ammonia, urea, uric acid and allantoin accounted for 81, 91 and 99% of the total N excreted by the groups given the protein-free diet, DMC and WFM respectively. Pigs given DMC excreted greater quantities of allantoin-N and less urea-N than pigs given WFM.