Showing papers in "British Journal of Nutrition in 1971"

Proposal to use time spent chewing as an index of the extent to which diets for ruminants possess the physical property of fibrousness characteristic of roughages.

Abstract: 1. Previous publications by the author and his colleagues have provided extensive records, and additional ruminating behaviour of cows receiving a wide range of diets. These recoreds, and additional unpublished records, have been used to justify a proposed index of the physical property of fibrousness, or roughage, in diets for ruminants.2. It is proposed that the total time spent by ruminants in chewing their food, during eating and during ruminating, should be the basis of the basis of the roughage index3. Experssion of the roughage index as total time spent chewing per kg dietary dry matter largely eliminates differences resulting from variation in the amount of food consumed, and differences resulting from the time of access to the food.4. Examples of the proposed roughasge index are given. The values range from 145 to 191 min/Kg dry matter for oat straw ot under 20 min/kg dry matter for diets of concentrates or of finely ground herbages; hays and silages tend to fall in the region of 90–110 min/kg dry matter. Values for the indx increase with dietary proportaions of hay or straw.

Nitrogen metabolism in sheep.

Abstract: 1. 15 NH 4 Cl was continuously infused for periods of 120–216 h into the rumens of sheep which were allowed to feed 2 out of every 10min. These treatments achieved steady metabolic states and allowed the assessment of nitrogen conversions by means of tracer methodology. The sheep were given either a barley diet or one of three hay diets. In two trials, the flow of abomasal material was determined using lignin and polyethylene glycol as markers. The amounts of dry matter (DM), gross energy, total N, soluble N, microbial N and microbial DM in abomasal digesta, and the concentration of ammonia in the rumen liquor were measured. The concentrations of 15 N in the N of urine, faeces, rumen and abomasal bacteria and protozoa, rumen and abomasal bacterial and protozoal protein, abomasal particulate matter and in rumen ammonia were determined. 2. Comparisons of the steady-state concentrations of 15 Nin the microbes with that in rumen ammonia indicated that from 50 to 65% of the bacterial N and from 31 to 55% of the protozoal N were derived from rumen ammonia in vivo. 3. An amount of N equivalent to 60–92% of the daily intake was transformed into ammonia N in the runen. 4. Some 17–54% of the ammonia was absorbed from the rumen, but this was not readily converted into urea. 5. Microbial growth in the rumen resulted in the assimilation of 1.7–2.6 g N/100 g DM fermented. 6. The generation-time of bacterial protein in the rumen was calculated from the rate of in- crease of 15 N concentration in this fraction, and values of 38 and 42 h were obtained for sheep given barley and hay diets respectively. 7. The combined results allowed quantitative estimates to be made of the complete metabolism of rumen N, and from these the possibility of fixation of N gas in the rumen was suggested.

Measurement of the bacterial nitrogen entering the duodenum of the ruminant using diaminopimelic acid as a marker.

Abstract: 1. A technique for the separation and colorimetric estimation of 2, 4-diaminopimelic acid (DAP) using automated ion-exchange chromatography coupled with an acid ninhydrin detection system is described.2. Only traces of DAP were found in rumen protozoa and no DAP was detected in rumen fluid prepared by ultracentrifugation or dialysis.3. The concentration of DAP in rumen bacteria from sheep on a constant feeding regimen, and the ratio of nitrogen to DAP for these bacteria were found to be constant over a 3-month period.4. The method has proved suitable for the estimation of bacterial N in the duodenal digesta of ruminants.5. The contribution of bacterial N to the total N leaving the abomasum of a lactating cow fitted with a permanent re-entrant cannula in the duodenum was found to be 50%.

Digestion of concentrates in sheep. 4. The effects of urea on digestion, nitrogen retention and growth in young lambs.

Abstract: 1. The effects of adding increasing supplements of urea to mainly barley diets for early-weaned lambs were investigated in two experiments. In the first experiment the passage of nutrients along the alimentary tract was studied by taking samples of abomasal, ileal and rectal contents and using a marker technique. In the second experiment, feed consumption and rate of gain were recorded over the growth period up to 40 kg live weight, and nitrogen balances were carried out. In the second experiment a barley-fish meal diet was also included.2. The fermentation of organic matter in the rumen increased with the amount of urea in the diet and levelled off when the diet contained about 12% crude protein.3. Urea supplementation had significant effects in increasing N retention and rate of live-weight gain and in decreasing feed conversion ratio, but supplementation beyond about 12% crude protein in dry matter had no further effect on these measurements. In each instance results with the barley–fish meal diet were better than the results with any of the barley-urea diets.4. From the concentrations of diaminopimelic acid (DAPA) in abomasal fluid it was estimated that microbial protein was produced in the rumen at a rate of 15.6% g/100 g organic matter fermented. This ratio did not appear to alter significantly with urea supplementation, but the comparison depends on the assumption that the concentration of DAPA in the bacterial protein did not itself change with urea supplementation.5. Using results from both experiments, it was calculated that the retained N on the urea-supplemented barley diets was approximately 47% of the amount of protein N absorbed in the small intestine.6. It is suggested that barley diets for early-weaned lambs can with advantage be supplemented with non-protein N to increase the crude protein in the dry matter up to about 12%. When barley diets are given with a protein supplement the addition of non-protein N is unlikely to be beneficial unless the protein supplement is given in such a way that it is not subject to degradation to yield ammonia in the rumen.

The effect of the absence of rumen ciliate protozoa on growing lambs fed on a roughage-concentrate diet.

Abstract: 1. Lambs were removed form their dams at 2 d of age, and at 5 weeks of age eitht of one group were incoulated with a mixed rumen ciliate and seven in a second group were maintained ciliate-free throughout the 61 weeks of the experiment. Performance of the groups was compared when given a 2:1 roughage:concentrate diet as a set ration and with ad lib. roughage.2. Mixed ciliate populations developed in all faunated lambs and average-sized populations were maintained. Large numbers of flagellate protozoa developed in the ciliate-free animals after flagellates had been introduced into the building with the ciliate-free animals after flagellates had been introduced into the building with the ciliate inoculum.3. Higher numbers of rumen bacteria were found in the ciliate-free group.4. Only between the 14th and 21st weeks was there a significant different between groups in weight gain and this was infavour of the faunated group. The only significant different in body measurements was greater girth in the ciliate-free lambs.5. Only minor differences were found between the groups in calorimetric trials, digestibility and nitrogen balanes. There were no differences between groups in concentration of total protein N and soluble sugar in the rumen. The ammonis concentration was significantly higher in the faunated group.6. The concentrations of total rumen volatile fatty acids (VFA) were higher in the faunated group. Differences, between groups, in proportions of VFA were attributed to the activity of the rumen bacteria rather than the ciliates per se.7. No differences between groups were found in the concentrations of blood sugar and haemoglobin.8. It was concluded that the changes due to the presence of rumen ciliates were not great enough to be reflected in animal performance under the conditions of this experiment.

An assessment of the nutritive value of a maize-soya mixture 'Soy-Ogi' as a weaning food in Nigeria.

Abstract: 1. Sour maize pap fortified with soya (Soy-Ogi), developed at the Federal Institute of Industrial Research, Oshodi, Nigeria has been evaluated chemically for its nutrient composition, biologically for protein quality and toxicity, and therapeutically on patients with kwashiorkor. 2. The indications are that it is a complete protein food suitable for feeding to children after weaning, and it compares favourably and economically with milk foods. 3. It was successfully used to restore normal health to children suffering from kwashiorkor.

The retention of ascorbic acid by guinea-pig tissues

Abstract: 1. Male and female guinea-pigs with high tissue concentrations of L-xyloascorbic acid (ascorbic acid, AA) and male guinea-pigs with high tissue concentrations of D-araboascorbic acid (isoascorbic acid, isoAA) were given a scorbutogenic diet and the rates of depletino from various tissues were measured fro both isomers.2. The loss of AA from the brain and eye lens was considerably less rapid than the loss from the adrenal glands, spleen and aqueous humour. After 14nd on the AA-free diet the AA concentrations in the brain and eye lens were 24 and 27% respectively of the initial concentrations; the corresponding values for the aqueous humour, adrenal glands and spleen were 3,4 and 5%. There was no apparent sex difference in the rate of loss of AA.3. The loss of isoAA was much more rapid than that of AA in the spleen, adrenal glands and aqueous humour; in the brain and eye lens the depletion patterns of the two isomers were similar.

Nutritive value of the winged bean (Psophocarpus palustris Desv.).

Abstract: 1. The winged bean (Psophocarpus palustris Desv.) has been grown successfully for several seasons, on an experimental basis, in the forest belt of Ghana, where earlier attempts to grow the soya bean had proved unsatisfactory.2. Although botanically different, the composition of the dry seeds was found to be very similar to that of the soya bean, containing 37·3% protein, 18·1% fat, 13·9 ppm thiamin and 1·8 ppm riboflavin. The oil of the seeds contained 125·9 mg tocopherol (γ + β) per 100 g. The amino acid composition of the protein was very similar to that of the soya bean, with methionine as the first-limiting amino acid. The content of unsaturated fatty acids and that of poly-unsaturated essential fatty acids were satisfactory.Active trypsin inhibitor found in the raw seeds could be destroyed satisfactorily by moist heat. No urease activity was detected.The protein efficiency ratio (PER) and net protein utilization (NPU) of the beans determined with rats, were superior to those of groundnuts. The supplementary value of the protein was shown by mixing two parts of the winged bean and three parts of maize flour. When adjusted to either 10% or 16% protein, the PER values of these mixtures were similar to those of skim milk. At the 16% protein level, addition of skim milk or 0·3% DL-methionine to this mixture produced only an insignificant improvement in PER value.The pleasant, sweet taste even when in the raw state is one of the advantages of the winged bean. Although, it is a climber, and should be staked, its cultivation on a small scale in selected areas of Ghana is recommended.

Determination of the energy expenditure of penned and grazing sheep from estimates of carbon dioxide entry rate

Abstract: 1. NaH14CO3, was infused at a constant rate either subcutaneously or intraperitoneally into sheep kept in a uniform environment and consuming a standard amount of food each hour. After 3 h of infusion the specific radioactivity (SR) of COe obtained by acidification of samples of blood taken from the right atrium showed no significant change with time until after 22 h when the infusions were stopped.2. Entry rates of COa (I/h) in sheep were estimated from the ratio of rate of infusion of 14CO2, as NaH14C08 (µCi/h) to the SR of CO2 (µCi/l) in samples of jugular venous blood, urine and exhaled gas taken after infusions had been in progress for at least 3 h. Concurrently, rates of energy expenditure were calculated from the gaseous exchanges over periods of 60–90 min which were determined for grazing sheep by use of re-entrant tracheal cannulation and meter-ing and analysis of exhaled gas, or for housed sheep by measurement in respiration chambers.3. Significant positive relationships were found between entry rate, the independent variable, and the contemporary energy expenditure. Equations obtained for grazing sheep were not significantly different from those obtained for other, housed, sheep when both groups were infused subcutaneously and COz for assay of radioactivity was obtained in all instances from blood, or in all instances from urine.4. With subcutaneous infusion the equation relating energy expenditure to entry rate estimated from the SR of urinary COa differed significantly from that where entry rate was derived from radioactivity assays of blood or exhaled CO2. There was also a significant differ-ence between two equations where entry rates were determined from the SR of blood CO2 but route of infusion was in the one instance intravenous and in the other was sub-cutaneous. Reasons for the differences between equations are discussed.5. Changes in the rates of energy expenditure of sheep effected by intermittent exercise on a treadmill were reflected in changes in CO2 entry rates. Values for the energy cost of hori-zontal locomotion by the sheep were derived from the entry rates and were similar in magni-tude to those reported by other workers.6. I t is suggested that the method of determining energy expenditure from COz entry rate may be adapted for use on many species of animal in a variety of environments.

The effect of age and level of dietary calcium intake on calcium metabolism in sheep.

Abstract: 1. A combination of balance and isotope techniques has been used to study the effects of age and dietary calcium content on Ca metabolism in forty-two wether sheep. 2. The amount of Ca absorbed by young growing animals varied significantly with intake. The percentage of the dietary Ca absorbed, however, remained unchanged. In older animals the amount of Ca absorbed was not altered by changes in intake, but decreased slightly with age. 3. Retention of Ca was directly related to the amount of Ca absorbed and was independent of age or breed. Furthermore, nearly all the Ca absorbed above the minimum mean amount required for maintenance was retained. 4. Faecal endogenous loss of Ca also was related to the amount of Ca absorbed. Values for faecal endogenous Ca were much lower than those used in the calculation of dietary require-ments by the Agricultural Research Council (1965). 5. Urinary Ca excretion was variable, and was not related to age or changes in dietary Ca intake. 6. Increased absorption of Ca in young growing animals was accompanied by a decreased rate of bone resorption, but the rate of bone accretion remained unchanged. Changes in dietary Ca in older animals had no effect on either of these two processes. Results indicate that bone resorption is the main pathway governing Ca homoeostasis. Both the rates of Ca accretion into bone and resorption from bone decreased with age. 7. Neither the rapidly exchangeable Ca pool (P) nor the slowly exchangeable bone pool (E) was altered by changes in dietary intake in young or mature animals. Both, however, decreased in size with age. 8. The size of the slowly exchangeable pool (E) was directly related to the rate of Ca accretion into bone. 9. The results were used to calculate dietary Ca requirements of sheep gaining weight at different rates, and these values have been compared with values recommended by the Agricultural Research Council (1965).

The effects of vitamin E and training on physiological function and athletic performance in adolescent swimmers.

Abstract: 1. Two experimental groups, each of thirteen boarding schoolboys, were given either 400 mg α-tocopheryl acetate or placeboes daily in addition to their normal diet during training in swimming and various athletic activities over a period of 6 weeks. Evaluation of the experimental treatments was made from tests of anthropometric status, cardiorespiratory efficiency and motor fitness and performance, which were administered at the beginning and end of the experimental period.2. Whereas training significantly improved physiological function and performance in both groups (P < 0·05), vitamin E did not.

The effect of drying and ensiling grass on its digestion in sheep. Sites of energy and carbohydrate digestion.

Abstract: 1. The effect of drying and ensiling ryegrass on the site of digestion of the energy andcarbohydrate fractions was studied in sheep fitted with rumen cannulas and re-entrant can-nulas in the proximal duodenum and terminal ileum.2. The sheep were given fresh (frozen) grass, dried grass, wilted and unwilted silage pre-pared from herbage harvested from the same sward. The grass diets were offered twice dailyto each animal and paper impregnated with chromium sesquioxide was administered twicedaily into the rumen. Twenty-four hour collections of duodenal and ileal digesta, adjusted togive 100 yo recovery of Cr2O3, were analysed to determine the extent of digestion in the fore-stomachs, the small intestine and the caecum and colon.3. Total digestibility of the gross energy was similar for the fresh grass, dried grass andwilted silage diets (67·4,68·1 and67·5 %)but higher for the unwilted silage (72·0 %, P < 0·01).There was an increased flow of energy into the small intestine when the sheep were given driedgrass and unwilted silage. The proportion of the apparently digested energy lost within thesmall intestine was greater when the dried grass was given (302 yo) than when the fresh grasswas given (23·6 yo).4. Drying or ensiling of wilted material affected digestion neither in the entire alimentarytract nor in the different sections of the tract, of some carbohydrate fractions. About 97 yo ofthe digested water-soluble carbohydrate, over 90 yo of the digested cellulose and over 70 yo ofthe digested hemicellulose were digested before reaching the small intestine. The increasedamount of energy entering the duodenum of the sheep given the dried grass was notaccounted for by changes in the fate of these carbohydrate fractions in the digestive tract. Withunwilted silage, digestibilities of the cellulose and hemicellulose fractions were higher, andlower proportions of the digested carbohydrates were lost before the small intestine.

Nucleic acid metabolism in the ruminant. 3. Amounts of nucleic acids and total and ammonia nitrogen in digesta from the rumen, duodenum and ileum of calves.

Abstract: 1 Concentrations of nucleic acid nitrogen and other nitrogenous constituents were estimated in digesta taken from the proximal duodenum of calves which were given, either, one of a number of stall diets or pasture These concentrations were compared, using polyethylene glycol (PEG) as a non-absorbed marker, with corresponding concentrations in rumen fluid and ileal contents2 There was little net change in amounts of RNA or DNA between rumen and duodenum relative to PEG, but there was a marked increase in amounts of total-N In duodenal digesta, for any one animal given most diets, nucleic acid-N formed a fairly constant percentage (8–11 for different animals) of the total non-ammonia-N This value was lower (by about 3) than the corresponding percentage in rumen fluid Comparison of nucleic acid-N: total-N ratios in duodenal contents and bacteria suggested that, for these diets, about 40–55% of the non-ammonia-N in duodenal contents was of microbial origin3 During passage of digesta between the duodenum and ileum the mean percentage disappearances of total-N, RNA and DNA were estimated to be about 67, 85 and 75 respectively There was evidence that these values varied with the amounts of the constituents entering the duodenum4 Ammonia was absorbed in the omasum-abomasum only when concentrations in rumen fluid were high (40 mM), but even moderate concentrations of ammonia entering the duodenum (3 mM) were efficiently absorbed (about 90%) in the small intestine

The influence of the microflora of the alimentary tract on protein digestion in the chick.

Abstract: 1. The course of digestion of freeze-dried and heat-damaged egg albumen labelled with 14C in all its constituent amino acids was compared in germ-free and conventional chicks. The albumen was given at a level of 10% in a test meal containing 28% protein. Samples of digesta were taken 5 h later and analysed for 14C and nitrogenous constituents.2. After administration of unheated albumen, 11% of the 14C remained in the germ-free gut, compared with 23% in the conventional gut. The poorer digestibility of the heat-damaged albumen was shown by recovery of 42 and 47% of the 14C from the gut of germ-free and conventional birds respectively.3. With both diets there was a higher 14C: nitrogen ratio in the contents of the lower gut of conventional birds. Most of the N remaining in the gut was composed of protein or the hydrolysis products of protein, the amounts of which tended to be higher in the germ-free environment; urea and uric acid formed only a small proportion of the total N. There was less urea and more uric acid in the lower gut and excreta of conventional chicks.4. It was concluded that microbial activity did little to increase the availability of protein to the chick. However, its effect on the nitrogenous material in the lower part of the alimentary tract might result in low recovery of N in the faeces and thus lead to erroneously high estimates of protein quality in tests with conventional chicks.

Nitrogen balance studies with the milk-fed lamb. 7. Effect of age of the lamb.

Abstract: I. Eighteen male cross-bred lambs, aged between z and 5 d, were allotted to two equal groups and given artificial milk diets of either low protein (diet A) or high protein (diet B) content for an experimental period of 6 weeks. Live-weight gain, diet digestibility, wool growth and the utilization of nitrogen and sulphur were measured. 2. There was a significant decrease with age in wool growth and in the apparent digestibility of dry matter, energy and N by lambs given diet A. There was no significant effect of age on the apparent digestibility of the nutrients in diet B. Live-weight gain and N balance were unaffected by age when expressed in relation to metabolic body size (kgo*7a).

Digestion of concentrates in sheep. 2. The effect of urea or fish-meal supplementation of barley diets on the apparent digestion of protein, fat, starch and ash in the rumen, the small intestine and the large intestine, and calculation of volatile fatty acid production.

Abstract: 1. Diets of rolled barley supplemented with urea or fish meal at four different levels were given in a change-over experiment to four sheep with cannulas in the abomasum and in the terminal ileum.2. Estimates were made of the disappearance of protein, ether extractives, starch, and ash in the various segments of the alimentary canal, and of the production of volatile fatty acids when the urea supplements were given.3. The disappearance (Y, g/d) of non-ammonia crude protein from the small intestine increased with increasing protein intake (X, g/d) on the fish-meal diets according to the equation Y = 0.37X+44. There was no increase in the disappearance with the urea supplements.4. In agreement with earlier work, it was shown that faecal nitrogen excretion was influenced to a much greater extent by fermentation in the large intestine than by that in the rumen. There was an apparent synthesis of ether-extractable lipid in the rumen at rates of 21and 18 g/d with the urea and the fish-meal diets respectively.5. The energy of the volatile fatty acids produced when the urea diets were given was estimated to be 59% of the digestible energy consumed.

Metabolism of heat-damaged proteins in the rat. influence of heat damage on the excretion of amino acids and peptides in the urine.

Abstract: 1. Freeze-dried cod muscle and casein were subjected to various conditions of heat treat-ment. Diets containing the different products, or the unheated materials, were given to a group of four adult male rats during successive 48 h periods, and urine was collected during the second 24 h of each 48 h period. A further collection of urine was made from the rats after they had been given protein isolated from heated skim-milk powder. The content and amino acid composition of the ‘peptide’ and ‘free amino acids’ in the urines were determined.2. Heat damage to the cod-fillet protein increased the total urinary excretion of peptide-bound amino acids, from 18·6 to 48·8 µmol/rat.d. The composition of the peptide also changed, and in particular there was a marked increase in lysine, from 2·98 to 20·30 µmol %. Three amino acids - lysine, aspartic acid and glutamic acid - together comprised nearly 70 % of the total amino acid residues. There was a corresponding increase in urinary excretion of free amino acids, from 53·7 to I 14·4 µmol/rat.d. The combined losses of lysine in urinary peptide and free amino acids were 1·5 % of the total lysine ingested, as against 0·3 % for the unheated cod fillet.3. The effects of similar heat treatment of casein on the composition of the urinary peptide and free amino acids were less marked. There was no increase in total urinary peptide excretion and there was a smaller increase in the lysine content of the peptide.4. In urine of rats given protein isolated from heated skim-milk powder, the peptide hydro-lysate was rich in lysine and in furosine, which together comprised 41 mol % of the total amino acid composition. These compounds were presumably formed, together with a smaller quantity of pyridosine, from lysine-carbohydrate complex in the urine. It is probable that, as compared with free lysine, the lysine-carbohydrate complex was absorbed relatively in-efficiently from the rat intestine.5. The findings are discussed in relation to the wider question of the metabolism of the ‚unavailable peptide’ that is released in the course of digestion of heat-damaged protein.

The effects of environmental temperature on the growth and metabolism of pigs given different amounts of food. 1. Nitrogen metabolism, growth and body composition.

Abstract: 1. Twelve castrated male pigs were kept at each of three temperatures and given food at one of three levels of intake. The temperatures and daily food intakes (expressed as g/kg 0.73 ) were 23° (80, 100, 120), 13° (100, 120, 140), 3–5° (120, 140, 160). Growth and nitrogen metabolism were measured during growth from 20 kglive weight until slaughter at gokg live weight, when the body contents of N and fat were estimated. 2. Growth rate increased with each unit of daily food intake (I g/kg 0.73 live weight) by 7.73 ± 0.74 g/d. This value did not vary significantly with temperature. Daily growth rate was depressed by 17.8 ± 2.3 g for each I° fall of temperature. 3. Daily N retention estimated by the balance method exceeded by 2.59 g/d that estimated by the comparative slaughter technique. Both results led to the same conclusion, which echoed that found with growth rate, that there was no significant effect of temperature on the response of N retention to increasing food intake. Taking the mean of the two estimates, N retention at a constant food intake fell by 0.38±0.055 g/d for each I° fall of temperature. 4. The N content of the ingesta-free carcass at slaughter fell with each increase in daily food intake by 0.007±0.002%, and the fat content rose correspondingly by 0.116±0.027%. These regressions did not vary significantly with temperature. When considered at a constant food intake, body composition did not alter significantly with temperature.

Relative palatability to sheep of straw, hay and dried grass.

Abstract: 1. In the first of two experiments four sheep were fed on dried grass and oat straw in the following combination: (1)straw eaten to appetite and an equal quantity given via a rumen fistula, (2)straw eaten and grass by fistula, (3)grass eaten and straw by fistula, (4)grass eaten and grass by fistula. Mean daily dry-matter intakes (g/kg metabolic live weight, W0·75) for the four treatments respectively were: 13·3, 23·2, 47·8 and 59·4. Dry-matter digestibility coefficients (%) were 37·2, 53·1, 53·3 and 71·3. Changing the digestibility of the diet without changing the component eaten (1 v.2; 3v.4) had a large effect on intake, but changing the component eaten without changing digestibility (2v. 3) caused a twofold change in intake. The latter result implied a difference in palatability between the feeds.2. The quantities of digesta in the rumen, determined by removal before and after feeding, were generally twice as great for treatments 3 and 4 as for 1 and 2. There were corresponding differences between treatments in the rates of passage of stained particles of feed and of chromic oxide.3. In the second experiment the treatments were the same except that meadow hay replaced oat straw. Mean daily dry-matter intakes (g/kg W0·75) were 41·7, 55·1, 59·9 and 68·7 for treatment 1 to 4 respectively, and digestibility coefficient were 54·0, 61·3, 62·3 and 72·0. In this experiment there appeared to be only a small difference in the palatability of the feed.

Nutritional aspects of amino acid metabolism. 1. A rat liver perfusion method for the study of amino acid metabolism.

Abstract: 1. Experiments were done to find whether the rat liver can be maintained in a satisfactory condition when perfused with oxygenated Krebs-Ringer bicarbonate buffer without added protein or red cells.2. The condition and preformance of the liver in this system were assessed from measurements made to ascertain its general condition or viability, its basal characteristics and its response to added substrates.3. It was found that the rapid flow-rate of the medium through the livers and the efficient oxygenation of the medium ensured that enough oxygen was available for the livers to deal with large quantities of added lactate.4. The potassium concentrations in the livers and the rates of alanine aminotransferase (EC 2.6.1.6) from the cells during perfusion, and the water content after perfusion showed that the livers were not grossly damaged and that they did not deteriorate measurably for up to 3 h of perfusion.5. Liver oxygen consumption, ATP concentrations, lactate and pyruvate concentrations and ratios, and rates of urea and glucose synthesis and bile secretion, all in perfusions without added substrate, were either similar to measurements by other workers from livers perfused withmedia containingred cells and protein or were reasonable extrapolations from availabledata.6. The rates of glucose production from lactate, and urea and glucose output from amino acids indicated that the liver responds adequately to added substrates.7. Measurements of amino acid concentrations in perfusate indicated that the livers of rats starved for 18–20 h regulated the amino acids to characteristic levels, by overall output or uptake, except for valine, leucine and isoleucine which were continuously given out into the medium. The results suggest that in vivo there is a general flow of most of the amino acids from extrahepatic tissues to the liver during fasting, while valine, leucine and isoleucine flow from liver to extrahepatic tissues.8. When pentobarbitone sodium (Nembutal) was used as the anaesthetic for removal of the liver from the donor rat, the rates of urea and glucose output in perfusions without added substrates were lower than when halothane (Fluothane) was used, indicating that pentobarbitone has an inhibitory effect on these measures of liver function during the subsequent perfusion.

The course of digestion of different food proteins in the rat: 2*. The effect of feeding carbohydrate with proteins

Abstract: 1. Single meals of protein (24.3 mg nitrogen/100 g body-weight) were fed with and without carbohydrate (167 mg/100 g body-weight) to groups of rats kept in anticoprophagy cages after an 18 h fast. The contents of the gastro-intestinal tract were collected and analysed and the rises in plasma amino acid concentrations were also determined.2. After ingestion of different proteins with sucrose, the passage of protein from the stomach was delayed compared with that when the meal was of protein alone: the initial stomach emptying was little affected by the nature of the protein in the diet, but subsequently the relative rates of evacuation of different proteins were similar to those when the proteins were given alone.3. When proteins were given with different carbohydrates the subsequent digestion and absorption of the meal was modified in a way which could be explained by the observed properties of the carbohydrates given alone, particularly with regard to solubilization in the stomach.4. The rises in concentration of plasma free amino acid were lower after ingestion of proteins with carbohydrate than when the proteins were eaten alone, and different carbohydrates affected these rises to different degrees.

Digestion of concentrates in sheep. 3. Effects of rumen fermentation of barley and maize diets on protein digestion.

Abstract: 1. The effect of the extent of ruminal fermentation of starch on the postruminal digestion of starch and protein was investigated in sheep, differences in rumen fermentation being obtained by giving diets based on barley, maize, or maize plus sodium chloride. The mean percentages of starch (α-linked glucose polymers) fermented in the rumen wert 91, 79 and 78 respectively with these diets, but there was considerable variability, particularly with the maize diets.2. When large amounts of starch escaped fermentation in the rumen, substantial quantities passed the terminal ileum and were mostly fermented in the large intestine; the greatest amount of starch found in the faeces was 2 % of intake.3. A decrease in the extent of rumen fermentation of starch was associated with a decrease in the concentration of crude protein and of diaminopimelic acid (DAPA) in the abomasal fluid, but there was no difference in quantity of crude protein disappearing from the small intestine. The concentration of DAPA was greater with the barley diet than with the maize diet, indicating that more dietary protein, originating from maize than from barley, escaped the rumen un-degraded. This conclusion was supported by a greater similarity between the amino acid composition of the abomasal fluid and the diet when maize was given.

A theoretical consideration of the effect of preventing rumen fermentation on the efficiency of utilization of dietary energy and protein in lambs.

Abstract: I. The effect of preventing rumen fermentation of feed on the utilization of energy and protein by growing lambs has been studied by theoretical means. 2. Initially, the differences in feed utilization resulting from microbial fermentation compared with digestion by host enzymes were estimated. It was assumed that a diet containing 85 yo of unspecified carbohydrate and I 5 yo casein was placed directly into the rumen (ruminant lamb) or abomasum (non-ruminant lamb) of animals weighing 20 kg, and that in both instances the diet was completely digested. In the non-ruminant lamb from 39 to 45 yo more net energy was available for maintenance, and from 22 to 61 yo more net energywas available for production, than in the ruminant lamb. The smaller differences applied to concentrate diets and the larger differences to highly fibrous diets. When dietary protein was completely degraded by microbes approximately 50 Yo less protein was absorbed from the small intestine in the ruminant lamb than in the non-ruminant lamb. It is suggested that this may significantly reduce tissue synthesis and growth in early-weaned lambs weighing less than 30 kg, but it may not limit growth in heavier animals. 3. Because part of the food of ruminants generally escapes fermentation and is digested by enzymes in the small intestine, and because part of the food of non-ruminants is fermented in the hind-gut, the estimates were adjusted accordingly. In this situation the utilization of digested energy in the non-ruminant lamb was from 30 to 45 % more efficient for maintenance and from 10 to 60 % more efficient for production than in the ruminant lamb. Some dietary proteins are so resistant to microbial degradation that a lower efficiency of utilization in the ruminant lamb when these proteins are given could only result from a limit in availability of energy. 4. Since ruminants digest crude fibre more efficiently than non-ruminants, it was calculated that the level of dietary crude fibre must exceed at least 22 yo, and in some instances 35 Yo, of the dry matter before the ruminant digestive system results in a better utilization of dietary energy in lambs. Thus, many common feeding-stuffs would be more efficiently used by lambs if they by-passed the rumen. The possible limitations to the adoption of this procedure are discussed. 5. The present techniques available for reducing the degradation of food within the rumen are outlined. It is suggested that an improvement in food utilization in ruminants could be achieved by feeding fats or formaldehyde-treated fat-casein complexes in solid diets, or alternatively, by feeding liquid diets which activate the reticular groove. The efficiency of feed utilization in ruminants is influenced by the activity of rumen micro-organisms. When low-protein diets are consumed, the nitrogen content of digesta increases as it passes through the rumen, with the result that more protein is absorbed from the intestine than was eaten (Hogan & Weston, 1968). Alternatively, when large quantities of soluble proteins are given there is often a substantial loss of N from the rumen and a reduction in protein absorption (Hogan & Weston, 1967 b). Furthermore, microbial digestion of food invariably reduces the efficiency of utilization of digested energy by animals because of the energy losses associated with methane production, heat of fermentation and poor utilization of absorbed volatile fatty acids (Blaxter, 1962). Hence production from ruminants is often improved when 3-2

Chemical composition of growth in nestling blackbirds and thrushes

Abstract: 1. The bodies of twenty-three nestling blackbirds and twenty-one nestling thrushes were analysed at different ages for water, fat, nitrogen, calcium, phosphorus, sodium, potassium and magnesium. These birds grow from a weight of 5 g at hatching to 70 and 50 g respectively when they leave the nest 12–13 d later.2. The concentration of N in the bodies doubled, while Ca increased seven to eight times during this period, so that the total amount of Ca in the body increased by about 100 times.3. The femurs of the newly hatched birds were very immature and contained little Ca or collagen but in the fledgelings the femurs were as well calcified as those of 17-d-old chicks.4. The gastro-intestinal tracts of the birds contained large amounts of Ca. Their food consists of caterpillars, adult insects and earthworms, none of which have much Ca in their tissues but their gut contents may contain much Ca. It is suggested that it is the gut contents of these invertebrates that provide nestling birds with Ca.

Studies of the food intake of sheep at a single meal.

Abstract: 1. Experiments are described in which the food intake and the water intake of sheep at a single meal were measured. The sheep were offered lucerne chaff ad lib. for 2 h only each day.2. Following the peritoneal infusion of physiological saline the food intake increased, while the injection of a diuretic before feeding caused the food intake to be decreased.3. In eight experiments the osmolality of the ruminal liquor was increased by the addition to the rumen of NaCl, KCl or the salts of volatile fatty acids in 250 ml water. The decrease in food intake was related to the osmolality, but not to the energy content, of the added electrolyte solution. In a further experiment, sheep receiving a highly digestible lucerne chaff, containing 1% (w/w) NaCl, increased their food intake when water was added to the rumen. Other workers have concluded that gastric osmolality is an important variable in the control of food intake in monogastric animals. The results of the eight experiments now described suggest that ruminal osmolality is of similar importance in ruminants.4. It is suggested that all these observations are consistent with the theory, which has been proposed for non-ruminant animals, that the food intake at a single meal may be related to the degree of tissue hydration at the beginning of the meal.

Ammonia in the large intestine of herbivores.

Abstract: 1. The object was toinvestigate the importance of urea a source of ammonia in the large intestine of herbivores. Urea was present in small intestinal contents of slaughtered horses in concentrations similar to those in blood but, in the small intestine of salughtered sheep, the urea was less than in blooc.2. There was little ammonia in small intestinal contents of slaughtered horses but consider-able ammonia was present in small intestinal contents of slaughtered sheep. The ammonia in small intestinal contents of the slaughtered sheep was probably formed from urea, as ileal con-tents taken from a sheep with an ileal cannula contained considerable urea and little ammonia.3. The ammonia concentration in caecal contents of sheep was related to the concentration of urea in blood except when ileal contents were prevented from entering the caecum.4. Ileal digesta of sheep contained more free amino nitrogen than did caecal digesta.5. Ammonia was absorbed more rapidly than water from the caecum of sheep. The rate of absorption was related to the concentration of ammonia in the caecum.

The degradation of lignin and quantitative aspects of ruminant digestion.

Abstract: 1. The technique for the quantitative estimation of lignin by digestion with 72% H2S04 has been investigated. Two methods of pretreatment designed to eliminate interference products of carbohydrates and proteins were compared, namely (a) acid and pepsin and (b) acid detergent. The latter technique gave low lignin yields owing to the colloidal dispersion of lignin in the acid detergent treatment. Erroneous results arise from an inadequate digestion in 72% H2SO4. It was found preferable to filter the product lignin without prior dilution of the acid since white particles of material, assumed to be cellulose, flocculated from solution on dilution. Also there is some loss due to colloidal dispersion of lignin during refluxing in dilute acid.2. Analysis of soda lignin and sulphuric acid lignin preparations from hay, duodenal contents and faeces of sheep with exteriorized flow through a re-entrant duodenal fistula provided evidence for the degradation of lignin by digestive processes. Demethoxylation of lignin occurred mainly in the stomach, suggesting that this was the main site of breakdown.3. A new displacement method of measuring duodenal flow is described. Quantitative results obtained also indicate that lignin is degraded mainly in the stomach to the extent of about 10%.4. These results suggest that faecal lignin is an adequate marker for the estimation of duodenal flow, and hence of the extent of changes in the stomach and intestines respectively.

The effect of siderosis and ascorbic acid depletion on bone metabolism, with special reference to osteoporosis in the Bantu

Abstract: 1. There is an association between iron overload, ascorbic acid deficiency and osteoporosis in middle-aged South African Bantu males. The iron overload contributes to the ascorbic acid deficiency by accelerating its oxidative catabolism. The object of the present investigation was to explore the possibility that the osteoporosis results from chronic ascorbic acid deficiency.2. On quantitative microradiography, percentage bone-formation surface was normal but percentage bone-resorption surface was significantly increased in ten osteoporotic subjects compared with seven control subjects.3. There was a significant inverse correlation between bone mineral density and liver storage iron concentration in thirty-five Bantu subjects. In thirteen individuals aged 39 years or less, liver storage iron concentration was significantly correlated with percentage bone-resorption surface.4. Guinea-pigs deprived of ascorbic acid for 21 d exhibited both significantly diminished percentage bone-formation surface and increased percentage bone-resorption surface.5. Guinea-pigs overloaded with iron by injections of iron dextran developed significantly reduced hepatic ascorbic acid concentrations and bone mineral densities; percentage bone-formation surface was significantly diminished and percentage bone-resorption surface significantly increased. Ascorbic acid injection largely prevented the bone changes.

Metabolism of nitrogenous compounds in the large intestine of sheep.

Abstract: 1. The deamination, ureolytic and proteolytic activities and rates of cellulolysis and gas production in large intestinal contents have been compared with those activities and rates in rumen contents of sheep. 2. Large intestinal contents produced ammonia. The rate of ammonia production was greater in caecal contents than in faeces. Incubation of caecal contents under toluene resulted in decreased production of ammonia and volatile fatty acids and an increase in the concentration of αamino nitrogen. 3. Proteolytic activity of large intestinal contents was much greater than that of rumen contents. There was little difference in proteolytic activity between caecal or faecal contents and their liquors whereas the activity in rumen whole contents was greater than in rumen liquor. Some proteolytic activity was present in caecal and faecal cell-free liquors but none was present in rumen cell-free liquor. 4. Deaminase activity was greater in rumen than in caecal contents or faeces. The activity in rumen liquor was less than half that in rumen whole contents. 5. Urease activity of caecal contents was less than that of faeces or of rumen contents. 6. The rate of gas production in rumen contents was less than that in caecal contents. The rate in faeces was low. Less gas was produced in rumen liquor than in rumen contents, whereas there was little difference between rates in caecal liquor and whole contents. 7. Rates of breakdown of cellulose in vivo were similar in the rumen and the caecum.