1. Glucose, and acetic, propionic and butyric acids, the major energy sources available to ruminants, have been comparatively evaluated as energy sources for growth in lambs. The energy sources were administered intravenously at 2·092 and 2·510 MJ metabolizable energy per 24 h for periods of 9–12 d. Nitrogen was given in excess of requirement so that growth rate was limited by energy, as indicated by the increased N retention after intravenous administration of energy.

2. The N-balance results from the trials showed that propionic acid promoted a significantly (P < 0·01) higher N retention than acetic acid. In some of the experiments there were no significant differences between propionic and butyric acids, and in others, no significant differences between acetic and butyric acids. Compared with isoenergetic glucose infusion, all volatile fatty acids were less efficiently utilized than glucose. The mean values for N balance (g/d) were 2·31 during control infusion, 6·53, 5·71, 5·48 and 4·59 during glucose, propionate, butyrate and acetate infusions, respectively.

3. All energy sources reduced the faecal N excretion significantly. The greatest reduction was observed during butyrate treatment. The mean values for faecal N excretion (g/d) were 4·24 for control, 4·00 for acetate, 3·89 for propionate, 3·83 for glucose, and 3·76 for butyrate infusion. The reduced faecal N excretion after butyrate infusion partly accounts for the increased N retention with that treatment.

1. Three cows were given 3, 5 or 7 kg hay once daily in a Latin-square design, and samples of digesta from four sites in the rumen and one site in the reticulum were taken at six times within the 24 h period after the feed. Dry-matter content and distribution of particle size and of particle density were measured for each sample. The changes in these measurements with time were studied. The incidence of rumination was also recorded.

2. Dry-matter contents of samples ranged from 15 to 3%. Values for samples from the dorsal sacs of the rumen were considerably higher than those for samples from the ventral sites; they also changed more with time after feeding and with level of feeding.

3. Particles were fractionated by sieving into six size groups with mean dimensions (mm) of 9·3 × 0·8, 4·4 × 0·6, 2·6 × 0·3, 1·6 × 0·25, 0·5 × 0·1 and smaller than 0·5 × 0·1. Coarse particles occurred at highest concentrations in the dorsal sacs of the rumen and responded to effects of time and level of feeding; smaller particles showed less response.

4. Particle densities ranged from 800 g/l to 1500 g/l. The proportions of low-density particles were higher in samples from the dorsal sacs of the rumen than in samples from ventral sites; the latter samples had higher proportions of high-density particles than of low-density particles. The changes which occurred are discussed.

5. The density of coarse particles tended to be low and that of fine particles tended to be high.

6. Rumination started at the time of maximum concentration of particles of low density and minimum concentration of particles of high density. Conversely, rumination ended when the concentration of the low-density particles was a minimum and that of the dense particles a maximum.

7. The results are discussed in relation to the possible movement of particles within the reticulo-rumen and the kinetics of particle breakdown.

1. Digestibility of maize stalk from Troyer Reid (Tr) maize and its isogenic mutant (bm1) was studied by suspending nylon bags containing ground tissue in the rumen of a fistulated steer. The animal was given a grass hay–concentrate (5:3) diet or a maize silage–grass hay–concentrate (4:1:3) diet.

2. The digestibility of the organic matter of the mutant maize stalk was greater than that of the normal maize stalk.

3. Adaptation of the rumen to maize silage increased the organic-matter digestibility of the maize stalk.

4. Lignin content was determined by two methods, namely organic matter insoluble in 72% sulphuric acid (method of the Association of Official Agricultural Chemists, 1960) (AOAC-lignin) and the organic matter lost from the ligno-cellulose complex (represented by acid-detergent fibre) by oxidation with potassium permanganate. The AOAC-lignin concentration was twice the permanganate-lignin concentration, but the amount of lignin estimated by both methods showed a significant negative relation to organic-matter digestibility. The AOAC-lignin concentration was greater in Tr than in bm1 maize but the permanganate-lignin concentration in Tr was slightly lower than in bm1.

5. There was an irregular relationship between the amount of lignin extractable with dimethylformamide (DMF) and digestibility of organic matter due to the solution of some of the DMF-lignin during digestion. The loss of lignin was greater from the mutant maize stalk tissue than from the parent maize stalk tissue.

6. The chemical composition of DMF-lignin determined by analysis showed a significant correlation between the syringealdehyde, p-hydroxybenzaldehyde and vanillin concentrations, and digestibility of organic matter.

7. Higher concentrations of both phenolic aldehydes and acids were found in the less digestible Tr material than in the bm1 stalk tissue.

1. Sheep given 400 and 1200 g lucerne chaff/d in equal hourly meals were infused continuously with the complex 51Cr EDTA into the rumen for 5 d and then slaughtered. The retention times of 51Cr EDTA along the small intestine and the apparent quantities of water absorbed in the small and large intestines were calculated.

2. The apparent quantities of water absorbed for the 400 and 1200 g food intakes were 5844 and 13110 ml/d in the small intestine and 2101 and 8520 ml/d in the large intestine respectively.

3. The mean total retention times of 51Cr EDTA in the small intestine were 136 and 91 min for the sheep given 400 and 1200 g/d respectively. The marker was retained up to seventeen times longer in the ileal than in the duodenal or proximal jejunal segments.

1. In pregnancy, severe hypoproteinaemia, cirrhosis and anaemia, plasma free α-amino nitrogen (FαAN) was found to be lowered. The non-essential:essential amino acid ratios, determined by paper chromatography, were increased in hypoproteinaemia and anaemia.

2. The erythrocytic FαAN content increased in early hypoproteinaemia and values lower than normal were found in severe hypoproteinaemia. There was also a rise in anaemia, which was due to increased cellular non-essential amino acids.

3. The leucocytic FαAN was reduced in all hypoproteinaemic states. The increased FαAN values in patients with thyrotoxicosis demonstrated that, in catabolism, leucocytic uptake of amino acids is increased. The non-essential:essential amino acid ratios were decreased in cirrhosis, possibly due to poor biosynthesis of non-essential amino acids by the liver.

1. Glycine absorption rate from a 300 mm jejunal segment was determined in vivo in four Zambian African subjects with acute, and four with chronic, respiratory infections. Glycine solutions (100, 150 and 250 mmol/l) were perfused, by means of a double-lumen tube technique. The results were compared with those for four relatively normal Zambian African subjects (‘reference’ group) previously studied. The group with acute-infections had a significantly higher mean absorption rate than the reference or chronic-infection group.

2. Glycine absorption results from a 100 mmol/l glycine solution in an additional twenty-four Zambian African subjects have also been analysed. When results for the thirty-six subjects were combined, those with acute bacterial infections had a significantly higher mean absorption rate than the normal subjects or those with chronic infections. For the twenty-one normal subjects there was a significant positive correlation between the individual absorption rates and serum total globulin and γ-globulin concentrations.

3. It seems likely that the rapid catabolism of protein associated with infection is counteracted by an increase in amino acid absorption rate. In subjects on a low-protein diet that mechanism would be limited. The deterioration in nutritional status during infections in developing countries could therefore be partly explained by the present observation.

1. Metabolic alterations related to protein catabolism were studied in rats in transitional states induced by changing from a low-protein (LP) (50 g casein/kg) diet to a high-protein (HP) (250 g casein/kg) diet.

2. Twenty-four hours after the diet was changed, the rats showed a more rapid increase in live-weight gain than controls that had been fed on the HP diet throughout. On the 5th day after the diet change, their increase in body-weight had returned almost to the control rate. Food and therefore nitrogen intakes on the 1st and 5th days after the change in diet were the same as those of the controls. It seems likely therefore that the initial high rate of live-weight gain is an indication of a metabolic adaptation which occurred on the LP diet and which did not fully return to normal until the 5th day after the change of diet.

3. N balance was higher 24 h after the change in diet than in the controls, owing to a reduction in total urinary N and in urea excretion, but when measured on the 5th day it was similar in both groups.

4. Carcass N determination showed that, after 7 d on the LP diet total-, trichloroacetic acid (TCA)-soluble- and TCA-insoluble-N contents (in terms of mg/g rat) were all slightly lower than control values but they had almost returned to normal 5 d after the diet change. There was a significant increase in the TCA-soluble-N content after 24 h on the HP diet to a value greater than the control value.

5. Proteolysis was measured in vitro by incubation of liver slices and diaphragms under anaerobic conditions. With liver slices it was significantly lower 24 h after the diet change than in control rats. On the 5th day it was significantly higher than 24 h after the diet change but had not quite reached the control level. In the diaphragm, proteolysis was also lower 1 d after the diet change, and had not increased at all by the 5th day.

6. Ureogenesis in the liver was reduced significantly 24 h after the diet change and it had almost returned to the control level on the 5th day. On the other hand, arginase (L-arginine amidinohydrolase; EC 3·5·3·1) activity was significantly lower 24 h after the diet change and did return completely to the control level on the 5th day.

7. These results show that the initial increased N balance and reduced N excretion were due to enzymic adaptation to the LP diet, the reduced N excretion being attributable to reduction in hepatic urea production.

1. Effect of glucose infusions on the rate of gluconeogenesis, as indicated by changes in the irreversible loss of plasma glucose, synthesis of glucose from ruminal propionate or fixation of blood bicarbonate into glucose, has been examined in sheep.

Sheep, feeding at hourly intervals, received intravenous infusions of [U-14C]glucose, NaH14CO3, or [6-3H]glucose, infused simultaneously with an intraruminal infusion of [2-14C]propionate. Glucose (4–144 mg/min) was infused intravenously at a single rate or at two different successive rates of equal duration. The glucose infusions were over a 6 h period and followed estimates of pre-infusion kinetic measurements.

2. The infusion of glucose suppressed endogenous glucose production in direct proportion to that infused for sheep given diets of lucrene or wheat. The maximum rate of suppression recorded was equivalent to about 50–60% of the endogenous production rate of glucose.

Transfer rates of carbon-14 from blood bicarbonate or ruminal propionate to plasma glucose were reduced during glucose loadings. The results indicate that administration of glucose was more effective in suppressing the synthesis of glucose from substrates other than ruminal propionate.

3. The percentage of glucose carbon derived from blood bicarbonate was lower in sheep given wheat than in sheep given lucerne. It was suggested that this difference may have been due to absorption of glucose from the alimentary canal of sheep on the former ration. Approximately 8% of the wheat starch may have escaped fermentation and been absorbed as glucose in these animals.

1. Two surgical techniques were developed in the calf to study the role of pancreatic secretion in digestion. The secretion was collected through a cannula placed in a small sac of duodenum into which the pancreatic duct drained. The continuity of the duodenum was re-established in the first technique by duodenal re-entrant cannulas, and in the second technique by end-to-end anastomosis of the duodenum with a cannula placed cranial to the anastomosis to return the pancreatic secretion. The accessory pancreatic duct was ligated.

2. The flows of digesta through the duodenum of milk-fed calves were 5505, 6369 and 7709 ml/12 h at 7, 24 and 63 d of age respectively, similar to values reported previously in the literature. In a 12 h collection period 297, 441 and 602 ml pancreatic fluid were secreted by calves of 7, 24 and 63 d of age respectively. The secretion from the mucosa of the duodenal sac was 40 ml/12 h in two other calves.

3. The rate of secretion from the pancreas varied markedly in milk-fed calves, being lowest 2–3 h and highest 6–10 h after feeding. Changes in the concentration of chloride and bicarbonate with pancreatic secretion rate were indicative of a secretin stimulus to secretion.

4. The rates of inactivation of pancreatic enzymes collected from the duodenal sac were measured at 4°, 20° and 39°.

1. A new product of the bacterial degradation of riboflavin has been isolated from fermentations in vitro of mixtures of either rumen bacteria or caecal bacteria with excess of the vitamin.

2. This product has been identified as 7,8-dimethyl-10-carboxymethylisoalloxazine and has also been shown to occur in the urine of ruminants and man.

3. The bacterial formation of this compound is compared with the bacterial formation of other isoalloxazines previously identified in similar incubation mixtures, and is discussed in relation to the factors influencing the mode of degradation of riboflavin.

1. Short-term effects of infusions of propionate, amino acids and butyrate on gluconeogenesis, as indicated by changes in the irreversible loss of plasma glucose, synthesis of glucose from ruminal propionate or fixation of blood bicarbonate into glucose have been examined in sheep given their daily ration in twenty-four equal portions at hourly intervals.

Sheep received intravenous infusions of [6-3H]glucose usually, in combination with [U-14C]glucose or NaH14CO3 or with intraruminal infusions of [2-14C]propionate. Substrates were infused over a 3–7 h period and followed estimates of pre-infusion kinetic measurements.

2. It was demonstrated that intraruminal and intramesenteric vein infusions of sodium propionate and intra-abomasal infusions of casein hydrolysate stimulated gluconeogenesis. Glucose synthesis showed a linear response to the infusion of these substrates, which varied from 0·35–6·35 mmol propionate/min and 50–160 mg casein/min.

3. The increment in the measured production rate of propionate in the rumen was consistently less than the rate of addition of propionate to the rumen.

4. Intramesenteric vein infusions of sodium butyrate at successive rates of 0·25 and 0·50 mmol/min produced only an initial transient increase in plasma glucose production. Since the rate of glucose synthesis from ruminal propionate was not altered, it was suggested that butyrate initiated glycogen mobilization.

1. During the initial stages of the development of hypoalbuminaemia, with concentrations between 25 and 30 g/l, fasting serum cortisol and growth hormone values remained normal. Corresponding fasting serum insulin concentrations were, however, significantly above normal. During the same period, called phase B, valine concentrations were moderately low but alanine concentrations were raised.

2. In more severe hypoalbuminaemia, culminating in kwashiorkor, a marked switch in hormonal balance occurred. Insulin concentrations fell to subnormal levels whereas cortisol became raised. Eventually growth hormone concentrations also increased rapidly to values similar to those found in acromegaly. By this time, phase C, alanine concentrations as well as those of valine were falling to very low levels.

3. The possible causes of these changes in hormonal balance, their role in the development of the distorted fasting serum amino acid pattern and their consequent effect on serum albumin synthesis and the appearance of clinical kwashiorkor are discussed.

4. Information is also presented on the differences between these components in kwashiorkor and marasmus. Attempts have been made to rationalize apparent inconsistencies in the literature.

1. Four feeding trials were made to investigate relations between diet and protozoal population in the rumen.

2. When a ration containing no concentrate was used, the number of entodiniomorphs decreased rapidly. The number of entodiniomorphs increased with the amount of concentrate. Rice straw, which was used as a sole source of roughage, was not always necessary for protozoa to survive in the rumen.

3. The type of diet affected the holotrich population to a much smaller extent than the entodiniomorph population.

1. Germ-free and conventional chicks were given diets containing raw or heated navy (haricot) (Phaseolus vulgaris L.) bean meal, or the heated meal supplemented with one of two fractions from raw navy beans: F3 was a preparation of navy bean trypsin inhibitor; F4 was a toxic factor known to depress the growth of rats. After 2 weeks, body-weights and pancreas weights were determined and proteolytic and amylolytic enzymes in the pancreas were assayed. The contents of the small intestine were collected and analysed for nitrogenous compounds.

2. In germ-free chicks final body-weights were not affected by F3 and only slightly depressed by F4. A significant depression of 12% occurred when raw meal was given. In conventional chicks depressions in final body-weights of 13·5, 26·5 and 48% were recorded with F3, F4, and raw meal respectively.

3. In birds given either raw meal of F3, there was an increase in size of the pancreas and in its concentration of trypsin, but a reduction in concentrations of chymotrypsin and amylase. The concentration of nitrogen in the insoluble fraction of the intestinal contents was increased by raw meal and F3 in both environments.

4. It was concluded that the presence of the gut microflora aggravated the growth-depressing effect on chicks of raw navy-bean meal. In the absence of the gut flora neither factor had any effect on growth. Possible explanations are discussed.