1. [24-14C]cholic acid was given to conventional and germ-free rats and the faecal isotope excretion studied for 8 days. The turnover, pool size and daily excretion of cholic acid and its metabolites were calculated for rats on three different diets, i.e. a commercial type diet (pellets), a semi-synthetic diet without (D7) and with 20% cellulose (D7+cellulose). The transit time of the intestinal contents was evaluated by following the excretion of an orally administered dose of carmine.

2. The amount of bile acids excreted was two to three times higher in both conventional and germ-free rats receiving pellets than in those receiving diet D7. This difference in bile acid excretion between animals receiving different diets cannot, therefore, be caused by an influence of the diet on the gastro-intestinal microflora. This effect of the commercial diet could not be due to a high fibre content, since an increase in the fibre content of the semi-synthetic diet D7 by the addition of 20% cellulose did not reproduce the effect obtained with the commercial diet.

3. The difference observed in bile acid excretion between germ-free and conventional rats on diet D7 was mainly ascribed to the much longer transit time of intestinal contents in germ-free as compared with conventional rats.

1. In an experiment of 3 x 3 latin square design, four lactating Holstein cows were given a basal ration designed to induce low percentages of milk fat. The treatments were (I) basal ration, a pelleted mixture of lucerne hay (20%) and concentrates (80%), with 40 l. of water infused intraruminally, (2) basal ration with acetic acid substituted for 15.4% of the metabolizable energy (ME) and (3) propionic acid substituted for 15.4% of the ME. In the last 3 weeks of the 6-week experimental period respiration trials were carried out in an open-circuit indirect calorimeter. The levels of feeding offered in the three periods were 325, 275 and 225 kcal ME/kg body-weight 0.75 in periods 1, 2 and 3 respectively.

2. No differences were detected in the utilization of the energy of acetic and propionic acids, but there were differences in the partition of energy into milk or body tissues; with acetic acid infusion more energy was secreted as milk and with propionic acid infusion more was deposited in body tissue.

3. There was an increase in milk fat percentage with acetic acid infusion, but not complete recovery to normal. The milk fat percentages were 1.96, 2.58 and 1.92 for treatments 1, 2 and 3 respectively. Acetic acid infusion caused increases in the C12, C14 and C16 fatty acids of milk fat and decreased the proportion of C18:1 fatty acids.

4. It is suggested that the low percentages of milk fat found when cows are given concen- trates could result from a decreased extent of fermentation in the rumen, allowing a greater proportion of the starch consumed to be absorbed as glucose in the small intestine.

1. In four feeding experiments with sheep the utilization of proteins contained in lucerne hay and of those in toasted soya-bean meal (SBM), representing a roughage and concentrate feed respectively, were examined. The ration of one group of animals contained lucerne hay as sole source of digestible protein and that of the other SBM.

2. Measurements of the nitrogen balance showed clearly the superiority of lucerne hay as protein source compared with soya-bean meal; this arose from the greater N retention found with the lucerne hay ration.

3. The influence of both rations on the metabolic pathways of the proteins was examined by following the changes of concentration of various metabolites in the rumen contents and of blood urea at different intervals after feeding.

4. Concentrations of urea found in the blood of the sheep given lucerne hay were lower than those of the other group, a finding which is in agreement with the results of the balance experiments.

5. The concentrations of NH2-N and of aminoacids in the rumen liquor were higher in sheep given lucerne hay than in those given SBM. These concentrations appeared to be related to the differences between the soluble non-protein N contents of the two feeds.

6. The results agree with the finding from in vitro experiments that rumen liquor from sheep receiving lucerne hay promoted greater synthesis of protein than rumen liquor from sheep receiving SBM.

7. Total bacterial activity as measured by the reduction of triphenyltetrazolium chloride (dehydrogenase activity) was much higher in the rumen liquor of sheep given lucerne hay than when SBM was given.

8. The concentrations of volatile fatty acids (C2-C6) were much higher in the rumen liquor in sheep on the lucerne hay diet than in those on the SBM diet. After meals of the lucerne hay diet, the concentrations of acids higher than C2, particularly those of valeric acid, exceeded those present in the rumen liquor of the animals kept on the SBM diet.

9. Proline and alanine appeared in relatively higher concentrations in the rumen liquor than the other amino acids determined, and these two acids together with valine disappeared very rapidly. The possible conversion of these amino acids into valeric acid is considered. It is suggested that valeric acid found in relatively high concentrations in rumen liquor of sheep given lucerne hay may be due in part to the deamination of proline, which likewise disappeared very rapidly together with alanine and valine.

1. Male and female chickens were reared from hatching on vitamin A-free diets, either unsupplemented or containing retinoic acid (vitamin A acid), methyl retinoate or retinyl acetate (vitamin A acetate). The birds given retinyl acetate grew well and had a normal appearance, but those given the unsupplemented diet died before 4 weeks of age after developing typical signs of avitaminosis A. The birds given retinoic acid or methyl retinoate did not show overt signs of vitamin A deficiency or other abnormalities except for a progressive failure of vision. Minimal histological changes were found in their retinas, and their vision was rapidly restored after feeding with retinyl acetate.

2. The cocks maintained with retinoic acid or methyl retinoate had normal testes and the hens laid eggs at a normal rate, but although their eggs could be obtained fertile the development of the embryo became abnormal after 2 days incubation and it always died. The development of the embryos could be stimulated and sometimes restored to normal by injection of various forms of vitamin A into the eggs before incubation, or by previous administration of retinyl acetate to the hens.

3. It is concluded that feeding retinoic acid as the sole source of vitamin A enables the hen to produce eggs that lack vitamin A but are otherwise normal, thus permitting the demonstration of a hitherto undescribed requirement of the early chick embryo for vitamin A.

4. The toxicity of vitamin A derivatives to chick embryos was investigated; injected retinoic acid was found to be extremely toxic.

1. A new method has been devised for the nutritional evaluation of food protein quality. The method is analogous to the classical determination of net protein utilization (NPU). The suggested new criterion, the protein utilization by the liver (LPU), expresses the amount of food nitrogen ‘retained’ in the liver as a percentage of the food nitrogen intake.

2. Five different foods, casein, soya-bean protein isolate, maize gluten, wheat gluten, cottonseed meal alone or with supplements of amino acids, a total of thirteen samples, were tested for LPU and NPU in groups of six rats. The correlation coefficient between values for LPU and NPU for all seventy-eight rats was +0.85 and was highly significant.

1. Adult rats were maintained on a protein-deficient diet for 6 weeks following which laparotomy was performed and peritoneal wounds of standard size were constructed,

2. The diet resulted in a progressive weight loss and a fall in plasma protein. Tissue protein, expressed as percentage protein in dried voluntary muscle, did not fall significantly.

3. Following laparotomy the rats were killed in groups on successive days and the peritoneal wounds were removed for measurement of area and for histological examination.

4. There was no apparent difference between control and protein-deficient animals in the rate or extent of peritoneal wound contraction although there was histological evidence of delay of collagen formation in the protein-deficient animals. This supports the theory that collagen formation is not a function of wound contraction.

1. The effect of saccharin and cyclamate on growth of young rats fed on a poor rice diet or a balanced diet was investigated.

2. Saccharin and cyclamate retarded the growth of rats on the multi-deficient diet but not of those on the well-balanced diet during an 8-week feeding period.

3. The sweeteners did not produce any macroscopic or microscopic changes in the liver, kidneys, intestines, spleen or lungs of the animals receiving the poor rice diet other than the changes resulting from the nutritional deficiency of the diet.

4. The sweeteners did not inhibit the liver xanthine oxidase activity of rats receiving the poor rice diet to an extent greater than the inhibition brought about by the deficiency of protein in the diet.

5. When given by intubation to healthy rats, the sweeteners inhibited the induction of liver tryptophan oxygenase; given in vitro, they inhibited the succinate dehydrogenase activity of rat liver mitochondria.

1. Changing cows from a diet with low hay and high flaked maize content, which depressed milk fat secretion, to a high-roughage diet resulted in increased milk fat secretion and in changes in the pattern of rumen fermentation and in the composition of the blood plasma.

2. During the 1st week following the change in diet the proportions of propionic and valeric acids in the rumen decreased and the proportion of acetic acid increased. These changes in rumen volatile fatty acids were associated with decreases in the concentration of lactic acid, increases in pH and increases in the rate of breakdown of cotton threads in the ventral sac of the rumen. After 1 week, only minor fluctuations in the proportions of volatile fatty acids occurred from day to day.

3. The percentage of fat in the milk increased over a period of 3 weeks following the change in diet and, with the exception of linoleic acid which decreased, the yields of all fatty acids in milk progressively increased over this period. The increase in yield of oleic acid was relatively much smaller than the increases in yield of saturated acids.

4. The concentrations in blood plasma of acetic acid and β-hydroxybutyric acid increased in two cows and, in all cows, saturated triglyceride fatty acids increased, whereas the concentrations of the unsaturated triglyceride fatty acids decreased, during the 1st week after change to the high-roughage diet. The recovery in milk fat secretion is discussed in relation to the observed changes in rumen fermentation and blood composition.

1. Eight groups of ten weanling rats were maintained for 60 days on diets containing calcium and phosphorus in the ratio 10:1 at four different levels of mineral, namely 0.8, 1.19, 2.29 and 3.33% Ca.

2. At the two lower levels of mineral intake the provision of vitamin D reduced final body-weight. Increasing the mineral intake increased final body-weight except at the highest level.

3. Increasing the dietary mineral content had no effect on serum Ca, but serum P was higher in the groups receiving the two higher levels of dietary mineral. Vitamin D raised the serum Ca level in the rats receiving the two lower levels of mineral, and serum P was raised by the vitamin at all levels of mineral intake.

4. Provision of vitamin D at the two lower levels of mineral intake decreased the fresh weight, dry weight and volume of the humerus but had no significant effect on the absolute amount of mineral ash in the bone. Consequentially there was an increase in percentage of ash, overall density and the ratio of weight of ash to organic matter in dry fat-free bone (A:R value). With increasing mineral intake there was an increase in all the bone measurements except volume.

5. The presence of vitamin D had no effect on tooth mass or ash content. Increasing the mineral intake caused an increase in tooth mass and ash except at the highest level of intake.

6. The ratio of tooth ash to bone ash was very much greater at the lower levels of mineral intake than at the higher levels.

7. In the animals on the two lower levels of mineral intake the bones were frankly rachitic, and the presence of vitamin D ameliorated the condition. With increase in mineral intake histological signs of rickets were reduced, but even at the highest level of dietary mineral the epiphyseal discs appeared slightly wider than normal.

8. The incisor teeth of animals on the two lower levels of dietary mineral had wide predentine, and the presence of vitamin D reduced the amount of predentine. At the two higher levels of mineral intake the dentine appeared normal when vitamin D was present in the diet.

9. Quantitatively, the bones were much more affected than the teeth by a low intake of mineral at a Ca to P ratio of 10:1.

1. Several in vitro methods were compared with in vivo methods for estimating the nutritive value of leaf-protein concentrates (LPC), using a freeze-dried preparation from wheat (A) fresh, (B) after heating moist, (C) after heating moist and then extraction with chloroform, and (D) after extraction with an acidified solvent.

2. The treatments had little effect on the biological value (BV) of the samples for rats.

3. Heating moist decreased true digestibility (TD), net protein utilization (NPU) and protein efficiency ratio (PER), but the original values were almost restored by lipid extraction. Acidified solvent extraction decreased TD, NPU and PER of LPC perhaps by making it brittle and difficult to wet.

4. Papain solubility and TD were well correlated. Pepsin-pancreatin solubility and TD were less well correlated.

5. Microbiological estimations of available amino acids, involving predigestion with pepsin, correlated poorly with TD determinations.

6. Unsaturated fatty acids, particularly linolenic, formed complexes during heating of LPC. The effect of this on enzyme solubilization procedures and on digestion in vivo is discussed.

7. Some comparisons are made between the effect of heat and of extraction with solvents on LPC and on fish meal.

1. The plasma levels of individual amino acids were studied in dairy cows under different conditions of production and energy nutrition.

2. A preliminary experiment was conducted which established that there was no regular change in amino acid levels with time of sampling in animals offered food twice daily at milking.

3. For animals in the 8th month of pregnancy plasma concentrations of lysine, valine, serine and isoleucine were higher, and of threonine lower, in Jersey than in Friesian cows. Lactation was accompanied in most cows by a fall in the plasma concentrations of lysine, arginine, threonine, histidine, glutamic acid, leucine and alanine and a rise in the level of glycine.

4. In lactating cows an improvement in the plane of energy nutrition was associated on average with an increase in the plasma concentrations of ‘non-essential’ amino acids and a decrease in the concentrations of ‘essential’ amino acids.

5. Intraruminal infusion of propionic acid in the lactating cow increased the concentrations of certain ‘non-essential’ amino acids, glutamic acid in particular, and decreased those of most other ‘essential’ and ‘non-essential’ amino acids.

6. These observations are discussed in terms of the possibility that an increased output of amino acids in milk proteins results in a depression in the concentrations of the ‘essential’ and certain of the ‘non-essential’ animo acids in the plasma. The hypothesis is put forward that the plasma supply of the other ‘non-essential’ amino acids, glutamic acid and proline in particular, may limit synthesis of milk proteins.

1. It was shown that when polyethylene glycol (PEG) was added to suspensions of food particles in aqueous buffer solutions, its distribution in the total water of the food mass was not uniform. The marker was excluded from a large proportion of the water contained in the swollen food particles. This effect was independent of temperature, pH, and, within limits, the time of contact.

2. It was shown that the theoretical concentration (C0), assuming a uniform distribution of marker, could be calculated from the observed concentration (C), weight of food in suspension (W) and the total volume of water (V), using the equation C = C0(I + b[W/V]) where b is constant for any given food. The addition of PEG solution to dry food particles gave a smaller effect.

3. The distribution of PEG was usually, but not invariably, more uniform in a suspension of roughages than in a suspension of concentrates.

4. Possible implications of these findings with respect to marker experiments with PEG are discussed.

1. Studies were made of the fermentation of D-glucose, D-fructose, D-galactose, D-xylose, L-arabinose and sucrose by rumen contents from two cows fed 1 kg hay and 4 or 5 kg flaked maize once daily. The proportions of volatile fatty acids (VFA) in the rumen before addition of carbohydrates varied widely but on average acetic acid constituted about 52%, propionic acid about 29% and n-butyric acid about 13% of the total.

2. In in vitro experiments, 896 mg of the monosaccharides and 851 mg sucrose were added to 150 g mixed rumen contents incubated for 2 h; the carbohydrates were added at 10 min intervals throughout the incubation on three occasions with each cow. Mean proportions of the carbohydrates fermented ranged from about 60% of the pentoses to about 85% of sucrose and glucose. Of the VFA produced from galactose and the pentoses, acetic acid constituted about 40%, propionic acid 45–55% and n-butyric acid 1–7%; very little n-valeric acid was produced. With the other carbohydrates results from the two cows differed, owing mainly to the production of appreciable amounts of n-valeric acid with one cow only. Acetic acid constituted about 40% of the VFA produced from fructose and sucrose, propionic acid 20–40%, n-butyric acid 14–22% and n-valeric acid up to 12%. The proportions of VFA produced from glucose were intermediate between the other two groups.

3. Net recovery of carbon from fermented carbohydrate in VFA was about 35–45%. A further 1–6%, of fermented glucose, fructose and sucrose was recovered in lactic acid.

4. In in vivo experiments, the monosaccharides only were infused into the rumen for 8 h at the rate of 200 g/h. Changes in the concentrations of substrates and products varied widely, owing to the variable basal fermentation, but changes in the proportions of VFA in the rumen were similar to those found in vitro.

5. The results of the in vitro experiments were compared with those obtained in earlier experiments in which the same cows were given a diet containing 70% hay. Significant regressions (P < 0.05) were found between the molar proportions of acetic, propionic and n-valeric acids produced from the substrates and the proportions of these acids present in the rumen contents at the start of the incubations, but the relationships differed markedly among the different carbohydrates. Most of the significant regressions were positive but negative regressions for propionic acid production from fructose and sucrose with one cow suggested the existence of more complex interrelationships among two or more VFA.

1. Four wether sheep, each fitted with re-entrant duodenal cannulas and a rumen cannula, were used to determine the relative quantitative importance of digestion in the stomach compared with that in the intestines when diets of low (HM1) and high starch (CM1) content were fed at 0.9 times maintenance and when the high-starch diet was fed at 1.7 (CM2) and 2.3 (CM3) times maintenance. Paper, impregnated with chromic oxide, and polyethylene glycol (PEG) were administered.

2. An apparatus is described which allowed one operator to collect, record, sample and return the duodenal digesta from two sheep simultaneously.

3. Total digestion was determined by faeces collections over 7–10 day periods, and digestion in the stomach by measuring the total flow of digesta from the abomasum to the duodenum over two 24 h periods with two or three sheep on each ration. Flow values were adjusted to give 100% recovery of chromic oxide.

4. The recoveries of chromic oxide and PEG were similar and it was concluded that either marker was satisfactory for adjusting 24 h flow values. Disadvantages of using PEG are discussed.

5. There was relatively little difference between rations HM1 and CM1 in the proportion of digestible organic matter and energy digested in the stomach. Only 57.1% of the total dry-matter digestion occurred in the stomach for ration HM1 compared with 65.0% for ration CM1 reflecting a smaller net gain in ash for ration CM1. Doubling the level of intake (ration CM2) resulted in a decrease in the proportion of digestible dry matter, organic matter and energy digested in the stomach. When the level was increased still further with ration CM3, the proportion continued to decrease with one sheep but increased with the other.

6. All but 5–11% of the digestible starch (measured as α-linked glucose polymer) was fermented in the stomach, the lowest proportion being with ration HM1.

7. The amount of nitrogen reaching the duodenum was approximately equal to the amount ingested with rations HM1 and CM1 but considerably greater with the other two rations. All rations contained approximately 2% nitrogen.

8. Calculation of the estimated loss of energy as methane and heat of fermentation suggested that 50–54% of the digestible energy was absorbed as volatile fatty acids.

1. One hundred and seven fine-wool Merino wethers and non-pregnant ewes varying in age from newly born to 110 months and in live weight from 1.7 to 55.1 kg were slaughtered and minced.

2. The nitrogen, fat, ash, calcium, phosphorus, sodium and potassium contents of the mince were determined. Energy content was estimated from the contents of fat and fat-free organic matter.

3. Weighted regression relationships were calculated between the energy, N, Ca, P, Na and K contents of the sheep, and age, live weight and (age x live weight). The relationships were differentiated with respect to age and live weight, and the rates of nutrient deposition at different rates of live-weight gain, and for sheep differing in age and live weight were calculated.

4. The rates of nutrient deposition were compared with those estimated by the Agricultural Research Council (1965) and by Mitchell (1962). and were in general lower in energy content and higher in ash constituents per unit live-weight gain.

1. Groups of rabbits were given diets containing different proportions of butterfat and maize oil. After the animals had been given the experimental diets for 40 weeks the plasma phospho- lipids were fractionated and the fatty acid composition of each fraction was determined.

2. Phosphatidyl choline and lysophosphatidyl choline accounted for about 75 and 12% respectively of the total plasma phospholipids: phosphatidyl ethanolamine, sphingomyelin and phosphatidyl serine accounted for only about 5.3, 5.0 and 2.6% respectively. Changes in the linoleic acid content of the diet had little effect on the relative proportions of the individual plasma phospholipids, but there was an over-all decrease in the concentration of total phospholipids in the plasma as the linoleic acid content of the diet was increased from 0.25 to 10.6%.

3. When the diet contained 0.25 % linoleic acid, the linoleic acid:oleic acid ratio in the phosphatidyl choline (1.3) was similar to that in the phosphatidyl ethanolamine (1.2), but as the linoleic acid content of the diet was increased to 10.6% the linoleic acid:oleic acid ratio in the phosphatidyl choline increased to 48, whereas that in the phosphatidyl ethanolamine increased only to 2.2. Increases in the linoleic acid content of the diet resulted also in increases in the linoleic acid:oleic acid ratios in the phosphatidyl serine, lysophosphatidyl choline and sp hingomyelin.

4. When the linoleic acid content of the diet was increased, the stearic acid:palmitic acid ratio in the phosphatidyl choline increased, whereas it decreased in the phosphatidyl ethanol- amine and remained relatively unaltered in the phosphatidyl serine. The stearic acid contents of the lysophosphatidyl choline and sphingomyelin were unaltered by dietary treatments, but the palmitic acid content of these two phospholipids decreased as the linoleic acid content of the diet increased.

5. The results are discussed in terms of the metabolic relationships that exist between the various phospholipids.

1. Hooded rats were fed from weaning on a basal retinol-deficient diet containing retinoic acid. Such a diet maintains growth and general health but does not prevent the appearance of lesions associated with vitamin A deficiency in the retina and testis. Some animals were also given supplements of retinol averaging 0.1, 0.25, 1 or 5 μg retinyl acetate per day. Rats were killed at intervals up to 28 weeks after weaning. The weights of the testes and the histological appearance of the testes and epididymides indicated that 5 μg retinyl acetate per day had maintained spermatogenesis throughout the experimental period. Doses averaging 1 μg retinyl acetate per day were only partially effective and the two smaller doses had little beneficial effect.

2. In a second similar experiment rats were given doses of retinyl acetate averaging 0.25, 0.5, 1, 2 or 100 μg per day. Measurements of the electroretinogram thresholds of the rats indicated that a dose of 1 μg retinyl acetate per day maintained mainly normal vision until the end of the experiment 29 weeks after weaning. Additional histological observations made 21 weeks after weaning showed that this dose level had not maintained spermatogenesis but that doses of 2 μg retinyl acetate per day had been effective.

3. The experiments show that the differing functions of vitamin A in spermatogenesis and vision are reflected in the hooded rat in differences in the dietary retinol levels needed to maintain these processes.

1. [24-14C]cholic acid was given orally to rats receiving three different diets, a semi-synthetic diet (D7) with and without 20% cellulose, and a commercial, pelleted diet. The labelled metabolites excreted in the faeces in the 8 days following administration of the labelled cholic acid were chromatographically separated, and tentatively identified by means of thin-layer chromatography.

2. In all three dietary groups the faecal bile acids mainly consisted of unconjugated and 7α-dehydroxylated metabolites. In rats receiving pellets or diet D7 with cellulcse, there was a higher percentage of monohydroxy-monoketo-cholanoic acids than in those receiving diet D7 alone. Dihydroxy-cholanoic acids, present in approximately the same ratio as were the 3α- and 3β-hydroxy isomers, were excreted by all the rats in the three dietary groups.

1. The effects of dietary antibiotics (penicillin, neomycin or terramycin) on the absorption of D-glucose, D-galactose, L-arginine or L-histidine by the mouse were investigated by using sacs of entire everted ileum.

2. Compared with the controls, there was generally an increased absorption of all these solutes. Tissue uptake of the solutes remained unaltered. The inward movement of water into the sacs was increased but was generally independent of solute transport.

3. The body-weight decreased slightly and caecal weight increased with penicillin only. The weight of the small intestine decreased with the different antibiotics, and the gut wall became thinner. Faecal fat increased slightly, but not significantly, with neomycin only. Water intake decreased with the different antibiotics.