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. 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. 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. 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. 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.

1. The ovulation rate of forty-eight Scottish half-bred ewes was increased by using pregnant mare's serum gonadotrophin thus inducing litters of one to four foetuses.

2. The effects of increased litter size upon the foetal growth rate and upon the rate of transfer of calcium and phosphorus across the placenta were studied at 108–112, 122–126 and 136–140 d gestation.

3. The number of foetuses had little effect upon foetal weight at 112 d, the mean weights of a singleton, twin, triplet or quadruplet being similar. However, by 140 d mean foetal weight decreased markedly as litter size increased.

4. Failure of individual quadruplets to grow as fast as a singleton was associated with a limitation in the capacity of the placenta for transferring minerals. The maximum rates of transfer of Ca and P, whatever the number of foetuses, were approximately 2·8 and 1·4 g/d respectively. These rates were attained by 112 d when quadruplets were being carried, by 126 d for triplets, and by 140 d for twins.

1. The butterfat in a whole-milk diet was replaced by either beef tallow, coconut oil or soya-bean oil. The diets contained 280 g fat and 720 g dried skim milk per kg and were supplemented with vitamins A, D, E and K.

2. These diets were offered as a milk, containing 200 g solids/Kg, to pigs weaned at 2 d of age during a 26 d experiment. The pigs were fed at hourly intervals to a scale based on live weight (scale E).

3. The performance of the pigs and the apparent digestibility of the dietary fats indicated that soya-bean oil was equal to butterfat. Butterfat was slightly superior to coconut oil and markedly superior to beef tallow.

4. The amount and composition of the fatty acids were studied in the proximal, mid and distal portions of the small intestine. When the beef tallow diet was given there was an increased amount of total fatty acids in the digesta of the small intestine, mainly in the distal portion. The digesta contained the smallest quantity of fatty acids when the soya-bean oil diet was given. The fatty acid composition of the digesta indicated that the short- and medium chain fatty acids from all the diets were well utilized, but an increasing proportion of stearic acid occurred in the distal portion of the small intestine. The interpretation of changes in fatty acid composition in the digesta in relation to absorption is discussed.

1. Two experiments were conducted to compare the effect on nitrogen retention of three dietary levels of N given either as groundnut or as urea to growing heifers. Additions of maize starch or dextrose were made to the diets to equalize the inputs of digestible energy within and between experiments.

2. In the first experiment, in which the maximum level of N supplementation was 69·0 g/d, the response to additional N was linear, and was identical for both sources of N. Differences in faecal N between treatments were small; differences in urinary N were large and were entirely attributable to level of N intake.

3. In the second experiment, the maximum level of N supplementation was raised to 103·3 g/d. The response to additional N was again linear and identical for both sources of N; however, for a given level of N input, the amount of N retained was 4·6 g less than in Expt 1. This reduction in N retention may have been due to the change in the proportion of digestible energy derived from the fibrous components of the ration.

4. Live-weight changes calculated from the observed N retentions have been compared with published responses to the inputs of N and energy used in these experiments.

1. Purine or pyrimidine bases, nucleosides or nucleotides were incubated, in vitro, with whole rumen contents, or with a cell-free filtrate prepared from rumen contents of calves fed on diets of flaked maize and hay.

2. During incubations with whole rumen contents, all derivatives bearing a side amino group were deaminated to varying extents.

3. All nucleotides and nucleosides were rapidly degraded to the parent base or its desamino counterpart.

4. Evidence suggests that guanosine was degraded to guanine before deamination occurred whereas deamination preceded ribosidic cleavage for adenosine.

5. Xanthine, uracil, hypoxanthine and thymine resisted further degradation to varying degrees.

6. Little or no breakdown was observed when any derivative was incubated, in vitro, with cell-free preparations.