The influence of gut micro-organisms on utilization of dietary protein

Amino acid ileal digestibility of some grain legume seeds in growing chickens

The apparent and true amino acid (AA) digestibility from soya-bean meal (SBM), vetch meal (VM), field pea meal (FPM) and bitter vetch meal (BVM) were determined in the lower ileum of growing chickens force-fed on semisynthetic diets (120 g crude protein and 13·1 MJ metabolizable energy per kg dry matter) based on each meal as the sole source of protein. The average apparent and true digestibility values were 0·82, 0·73, 0·76 and 0·60 and 0·90, 0·91, 0·87 and 0·74 for diets SBM, VM, FPM and BVM, respectively. Marked differences in AA digestibility among diets were found. The apparent digestibility of methionine, the most limiting essential AA in poultry diets, was significantly higher in diet SBM than in diets FPM and BVM (P < 0·05). It is concluded that the seeds of vetch and field pea may be suitable for inclusion in poultry diets as partial substitutes for soya bean. The use of bitter vetch is not recommended.

Digestibilities of nitrogen and amino acids in soya-bean, sunflower, meat and rapeseed meals measured with pigs and poultry

In order to determine the relative digestibilities of nitrogen and amino acids in foodstuffs for pigs and poultry, and the effects of manufacturing methods, equal quantities of soya-bean meal, sunflower meals [hulled (sunflower meal 1) and dehulled (sunflower meal 2)], meat meals [made with (meat meal 1), and without (meat meal 2), blood added at 250 g/kg meat tissue (wet weights)] and rapeseed meals [seeds heated at 80°C (rapeseed meal 1) or 100°C (rapeseed meal 2)] were mixed with protein-free ingredients. The diets were given to five growing pigs with ileo-rectal anastomoses, and, by crop-intubation, to 12 caecectomized and 12 intact cocks. Excreta were collected over 48-h periods. Endogenous excretion was estimated by giving protein-free diets.

In the order, soya-bean meal, sunflower meals 1, and 2, meat meals 1, and 2, rapeseed meals 1, and 2, true digestibilities were: with pigs, of nitrogen, 0·81, 0·80, 0·79, 0·64, 0·79, 0·73, 0·70 (s.e.d. 0·030), of lysine, 0·84, 0·83, 0·84, 0·65, 0·84, 0·76, 0·72 (s.e.d. 0·032); with caecectomized birds, of nitrogen, 0·92, 0·91, 0·91, 0·66, 0·78, 0·74, 0·75 (s.e.d. 0·018), of lysine 0·92, 0·91, 0·93, 0·62, 0·79, 0·70, 0·70 (s.e.d. 0·020); with intact birds, values were similar to those with caecectomized birds for soya-bean, and the sunflower meals, but lesser for meat meals 1 and 2; the solubilities of nitrogen in pepsin were 0·96, 0·92, 0·93, 0·80, 0·89, 0·87, 0·87.

Two hundred and eighty pigs (initial live weights 10 kg) were used to compare growth response to free lysine with that to lysine in soya-bean meal and sunflower meal 2. Lysine availabilities, assessed by analyses of regressions of live-weight gain against lysine intake were 0·82 (s.e. 0·12) for soya-bean meal, and 0·82 (s.e. 0·18) for sunflower meal 2.

Amino acid digestibilities of the sunflower meals were similar to those of soya-bean meal, and were not influenced by dehulling; values for the rapeseed meals were lower, and unaffected by differences in heating severity; values for the meat meal were reduced by blood addition. Values differed between pigs and poultry, but there was consistency in the extent to which each species discriminated between some foodstuffs. The pepsin test was insensitive. The large standard errors associated with availability values prevented meaningful comparisons with digestibility values.

NMR-based metabonomics analysis of mouse urine and fecal extracts following oral treatment with the broad-spectrum antibiotic enrofloxacin (Baytril)

The human gastrointestinal tract is home to hundreds of species of bacteria and the balance between beneficial and pathogenic bacteria plays a critical role in human health and disease. The human infant, however, is born with a sterile gut and the complex gastrointestinal host/bacterial ecosystem is only established after birth by rapid bacterial colonization. Composition of newborn gut flora depends on several factors including type of birth (Ceasarian or natural), manner of early feeding (breast milk or formula), and exposure to local, physical environment. Imbalance in normal, healthy gut flora contributes to several adult human diseases including inflammatory bowel (ulcerative colitis and Crohn's disease) and Clostridium difficile associated disease, and early childhood diseases such as necrotizing enterocolitis. As a first step towards characterization of the role of gut bacteria in human health and disease, we conducted an 850 MHz (1)H nuclear magnetic resonance spectroscopy study to monitor changes in metabolic profiles of urine and fecal extracts of 15 mice following gut sterilization by the broad-spectrum antibiotic enrofloxacin (also known as Baytril). Ten metabolites changed in urine following enrofloxacin treatment including decreased acetate due to loss of microbial catabolism of sugars and polysaccharides, decreased trimethylamine-N-oxide due to loss of microbial catabolism of choline, and increased creatine and creatinine due to loss of microbial enzyme degradation. Eight metabolites changed in fecal extracts of mice treated with enrofloxacin including depletion of amino acids produced by microbial proteases, reduction in metabolites generated by lactate-utilizing bacteria, and increased urea caused by loss of microbial ureases.

Effect of low protein and low energy diet on physiological status and digestibility of F344 rats

A long-term raising study was carried out on male F344/DuCrj rats with three low protein (Crude Protein (CP); 14.5, 11.5, 8.5%) and low energy (Digestible Energy (DE); 2.0 kcal/g) diets from 4 to 104 weeks of age. In rats fed the 8.5% CP diet, body weight and digestible crude protein (DCP) consumption at 10 weeks of age were lower (P < 0.05) but the body weight at 50 weeks of age was higher (P < 0.05) than in the other groups. In rats fed the 8.5% CP diet the crude fat digestibility was higher (P < 0.05), and the CP/nitrogen-corrected metabolizable energy (MEn) ratio was low. On the other hand, the mean survival time at 80 weeks of age was shorter in rats fed the 8.5% CP diet (P < 0.05).

Influence of caecal microflora and of two dietary protein levels on the adaptation of the exocrine pancreas: comparative study in germ-free and conventional rats

Dietary proteins are degraded by both endogenous enzymes and the caecal microflora. In conventional rats the enzyme content of the pancreas depends on the amount of dietary protein. The influence of the caecal microflora on this process is unknown. We report here the effect of the caecal microflora on pancreatic enzymes (proteases, amylase (EC 3.2.1.1), lipase (EC 3.1.1.3)) and on colonic metabolites (NH3, urea, short-chain fatty acids). Germ-free and conventional male Fischer rats were fed for 3 weeks with a diet containing 220 or 450 g protein/kg provided as a mixture of fish concentrate and soyabean isolate. The excretion of NH3 and the pH were specifically increased by the high-protein diet in the germ-free rats. The higher production of isobutyrate, valerate and isovalerate in conventional rats fed on the high-protein diet reflected a high bacterial proteolytic activity since these short-chain fatty acids are specific indicators of this activity. The microflora hydrolysed urea to NH3 and maintained the pH at neutrality whatever the amount of protein in the diet since there were changes in germ-free rats but not in conventional ones. In germ-free rats, amylase, trypsin (EC 3.4.21.4), elastase (EC 3.4.21.36) and carboxypeptidase A (EC 3.4.17.1) specific activities were significantly lower than in conventional rats. The adaptation of the pancreas to the 450 g protein/kg diet was not impaired by the bacterial status except for the specific activity of chymotrypsin (EC 3.4.21.1) which was more increased by this diet in germ-free than in conventional rats. Moreover, the specific activity of lipase increased only in conventional rats fed on the 450 g protein/kg diet. In conclusion, we observed a relationship between the enzyme content of the pancreas and the presence or absence of the caecal microflora suggesting that bacterial fermentation influences pancreatic function.

Splanchnic fluxes of amino acids after duodenal infusion of carbohydrate solutions containing free amino acids or oligopeptides in the non-anaesthetized pig

Seven non-anaesthetized pigs (mean body-weight 64.6 kg) were used to study the intestinal absorption and hepatic metabolism of glucose and amino acids (AA) using carbohydrate solutions (maltose dextrin; 440 g/2 I), containing 110 g of either an enzymic milk-protein hydrolysate (PEP) with a large percentage of small peptides (about 50% with less than five AA residues) and very few free AA (8%) or a mixture of free AA (AAL) with an identical pattern, infused intraduodenally. Each pig was previously fitted under anaesthesia with electromagnetic flow probes around the portal vein and the hepatic artery, and with permanent catheters in the portal vein, carotid artery, one hepatic vein and the duodenum. Each solution was infused for 1 h after a fasting period (18 h) and each pig received both solutions at 8 d intervals. The observation period lasted 8 h. For most AA (his, lys, phe, thr, arg, tyr, pro) the absorption rate after infusion of PEP was significantly higher than after that of AAL during the 1st hour, but the differences quickly disappeared. After 8 h, the only differences concerned his and tyr (PEP > AAL) and met, glu and asp (AAL > PEP). There was a large uptake of blood AA by gut-wall cells, higher after AAL infusion than after PEP infusion, particularly for branched-chain AA (BCAA). The absorption of ammonia-nitrogen after both infusions was equivalent to two-thirds of urea-N passing from blood to intestinal tissues and lumen. Glucose absorbed within 8 h represented only 76% (PEP) or 69% (AAL) of the infused amounts. The cumulative hepatic total AA (TAA) uptake increased from 13 to 27% of the infused amounts between the 1st and the 8th hour after PEP infusion, and from 8 to 31% after AAL infusion. Most essential AA were largely taken up by the liver, with the exception of met (PEP) and thr and of BCAA, which were poorly retained for both solutions; there was a high uptake of ala and gly, and a release of asp, glu, and gln. Urea-N released by the liver within 8 h was equivalent to 23-25% absorbed amino-N and to around 1.5 times ammonia-N taken up by the liver within 8 h. Glucose was highly taken up by the liver during the first hours then released, the total uptake within 8 h representing about half the absorbed amount.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of dietary calcium, phosphorus, and protein on the performance and nutrient utilization of broiler chickens

The effects of varying dietary Ca, available phosphorus (AP), and protein on 5- to 17-day performance (growth and feed efficiency), Ca and P contents of tibia and plasma, ME, and N utilization of broiler chickens were investigated in three experiments. In Experiment 1, high dietary Ca (24.3 versus 11.8 g/kg) reduced performance, N digestibility, and ME, whereas N retention was not affected. Reducing dietary protein (186 or 203 versus 217 g/kg) reduced performance and N retention but increased ME. In Experiment 2, high dietary Ca (25.3 versus 10.7 g/kg) reduced performance, tibia Ca, and plasma P and increased plasma total Ca; whereas the diet with both high Ca (25.3 g/kg) and high AP (9.8 versus 4.3 g/kg) reduced only performance. Reducing dietary protein from 206 to 166 g/kg diet reduced growth but improved feed efficiency and tibia P content. In Experiment 3, a diet containing 25.6 g of Ca and 4.9 or 10.7 g of AP compared with a diet containing 11.2 g of Ca and 4.9 g of AP/kg of diet reduced performance. Reducing dietary protein from 236 to 215 g/kg of diet decreased performance. It was concluded that high dietary Ca reduced growth performance and feed efficiency and that altering the dietary protein from 166 to 236 g/kg of diet did not overcome the growth depression effect of high Ca or of high Ca and AP diets.

Is increased ammonia liberation after bleeding in the digestive tract the consequence of complete absence of isoleucine in hemoglobin? A study in pigs

A variable protein-induced toxicity has been reported in liver disease. The aim of this study was to establish the cause of increased ammonia liberation in the gut after intraluminal bleeding. Therefore, blood was sampled from catheterized piglets [20 +/- 0.8 kg (means +/- S.E.); n = 10] to determine ammonia, urea and amino acid levels before and 1, 2, 3 and 6 hr after a standard pig meal (750 gm, 12% protein). After 1 week, this procedure was repeated after ingestion of an isonitrogenous amount of bovine whole blood (400 ml). In a second series of experiments, the same procedures were performed after ingestion of plasma, whole blood, erythrocytes and feed. Electromagnetically measured total intestinal, small and large bowel flow was not significantly influenced by the type of meal ingested. Portal ammonia release was significantly increased 2-fold after a blood meal, whereas intestinal glutamine utilization did not increase. Plasma urea levels were increased 200 to 300% after whole blood and erythrocytes, whereas after ingestion of plasma, urea levels were similar to values in controls. Glutamine utilization was not different among the various groups and occurred predominantly in the small bowel. In the fasted state, small bowel glutamine utilization paralleled ammonia production. In the fed state, this equimolar relationship could not be assessed because luminal glutamine utilization could not be determined. Isoleucine levels decreased to 25% of fasting levels. Analysis of blood constituents revealed a complete lack of isoleucine in the hemoglobin molecule. Net total alpha-amino-nitrogen absorption was doubled after a blood meal.(ABSTRACT TRUNCATED AT 250 WORDS)

[The energy preservation requirements of growing pigs of different sexes fed normal and high protein diets. 5. Comparison with the results obtained from castrated pigs, sows and boars]

In one experiment each with castrated pigs, sows and boars (hybrid pigs of line 150), two groups of six animals received rations containing 17 and 45% crude protein resp. over the complete test period from 35 to 130 kg (castrated pigs), 150 kg (sows), 170 kg live weight (boars) and passed alternatively through a total of 60 metabolism periods on growth and 48 on maintenance level. There were significant differences between the 3 categories of animals with regard to energy maintenance requirement in the relation of 100:105:110 for castrated pigs less than sows less than boars. In contrast to the estimated values derived from previous studies for energetic maintenance requirement of 650 kJ/kg LW0.62.d the measured values for all 3 animal categories are by approximately 50% higher. The protein content did not have an influence on the maintenance requirement of metabolizable energy of the animals. The utilization of metabolizable energy of the two rations for body energy retention corresponds to the expectations with regard to its dependence on nutrients. The requirement of metabolizable energy for protein and fat retention is 1.7:1.0. The energy content of the weight gain of boars was, on average, 85% of that of castrated pigs and sows. The studies of blood parameters did not show any deviations in the parameters tested.

Effect of dietary fibre and caecectomy on the excretion of endogenous amino acids from adult cockerels

1. Eight diets based on maize starch and sucrose were prepared, containing ground maize husks or semi-purified wood cellulose, with 30, 60, 90 or 120 g fibre source/kg diet dry matter (DM). 2. The diets were precision-fed to 12 caecectomised and 12 intact adult male domestic fowls. The quantities of amino acids and faecal N excreted over the 48 h following each feeding were measured. 3. Diet had no influence on the quantities of endogenous amino acids or endogenous faecal N excreted. 4. A proportion of the amino acids and N of the maize husks and of endogenous origin appeared to be degraded or retained in the caeca of intact birds.

Digestibilities of amino acids in soyabean, sunflower and groundnut meals, determined with intact and caecectomised cockerels

1. Three isonitrogenous diets were formulated in which soyabean (dehulled), sunflower (hulled) and groundnut (dehulled) meals were the sole protein sources. 2. 50 g of each diet was tube-fed to each of 24 intact and 24 caecectomised cockerels, which had been previously starved for 48 h. Excreta were collected, individually, for 48 h. The concentrations of amino acids in the diets and excreta were determined, and digestibility coefficients calculated. 3. Differences between intact and caecectomised birds for true digestibility evaluations reached significance for threonine, glycine and lysine only. Deamination of threonine and glycine, and synthesis of lysine, in the caeca was implied. 4. Neither the true digestibility of nitrogen, nor that of the sum of the amino acids differed between protein sources. 5. True digestibilities of most essential amino acids, considered individually, in sunflower and groundnut meals were similar to or greater than, those of soyabean meal. Exceptionally, lysine was more digestible in soyabean (0.879) than in sunflower (0.722) or groundnut (0.788) meals.

Gnotobiotes in nutritional studies

Studies with gnotobiotic animals have demonstrated extensive synthesis of vitamins, involvement in the metabolism of nitrogenous compounds and modification of lipids among the activities of the conventional microflora. The extent to which they affect the host depends on factors such as the structure of the gut, the position of the sites of bacterial proliferation and the host's nutritional status. Thus the findings in experimental animals may not always be applicable to man. Results so far indicate that in circumstances of dietary inadequacy bacterial activity may be detrimental or beneficial. However, these effects are small, and it seems reasonable to conclude that the influence of the indigenous microflora on the host's nutrition is of relatively minor importance compared with its role as a barrier against invasion by undesirable organisms.

[Nutrient dependence of energy preservation requirements in rats. 1. Dependence of energy requirements for preservation in fully-grown rats on the type of nutrient offered as the sole energy source]

In two experiments with fully-grown albino rats (Wistar strain) the energetic utilization of glucose, sunflower oil and casein in the maintenance metabolism was determined under thermoneutral conditions of keeping the animals. The relative requirement of metabolizable energy for maintenance was, with either glucose, sunflower oil or casein being the sole energy source of the feed, in experiment 1 100:105:133 and in experiment 2 100:102:135. The absolute values of the maintenance requirement of metabolizable energy were in experiment 1 347 +/- 26, 364 +/- 61 and 460 +/- 33 resp., and in experiment 2 330 +/- 11, 337 +/- 21 and 446 +/- 27 kJ/kg LW 0.75 resp. The results are discussed in connection with the efficiency of ATP synthesis (metabolizable energy/mol ATP gain) in the oxidative decomposition of nutrients.

Determination of digestible and available amino acids in meat meal using conventional and caecectomized cockerels or chick growth assays

1. The present study was designed to compare true digestible amino acid values for meat meal with available amino acid values. True digestible values were determined with a 48 h excreta collection assay using conventional (CONV) and caecectomized (CEC) cockerels. Available values for lysine, methionine and cystine were estimated by chick growth assays. 2. True digestibilities of all sixteen measured amino acids (expressed as a proportion of the total) were lower for CEC than for CONV cockerels, with the average difference being approximately 0.10. 3. Chick growth assays based on total weight gain indicated that the availabilities of amino acids expressed as a proportion of the total amino acids in meat meal were: 0.70 for lysine, 0.75 for methionine and 0.48 for cystine. Partitioning weight gains to reflect only growth attributable to supplemental crystalline amino acid or meat meal intake consistently yielded higher availability values than when total weight gains were used. 4. True digestibility values determined with CEC cockerels were in better agreement with chick available values than were true digestibility values determined with CONV cockerels. 5. The amounts of amino acids present in the caeca of meat meal-fed CONV cockerels at 48 h after feeding were small when compared with those levels voided in the excreta and those levels consumed in the feed. 6. Multiple regression analyses of excreta and caecal amino acid profiles at 12 and 48 h after feeding suggested that significant amounts of non-digested dietary amino acids flowed into the caeca and were subsequently metabolized by the caecal microflora.

Effect of the gut microflora on chick growth and utilisation of protein and energy at different concentrations of dietary protein

The effect of the gut flora on chick growth and protein and energy utilisation at a marginal dietary energy level (calculated metabolisable energy value 11.7 MJ/kg) was determined with diets containing 227 or 293 g protein/kg. Germ-free (GF) and conventional (CV) chicks were reared for 10 d on the diets, and excreta were collected during the last 4 d. The chicks were killed and carcases and droppings were analysed for N and fat. The GF chicks grew significantly faster than the CV controls on both diets. The growth of CV chicks given the high protein diet was similar to that of GF chicks given the adequate protein diet. Protein and energy utilisation were significantly less for CV than for GF chicks on both diets. It was concluded that the energy requirement of CV chicks was greater than that of their GF counterparts, and that their poorer growth was due to utilisation of some dietary protein as an energy source.

Protein and energy utilization in germ-free and conventional chicks given diets containing different levels of dietary protein

The present study was done to clarify the relationship between the amount of dietary protein given to, and the gut microflora of, the host. Day-old chicks were given diets containing three concentrations of dietary protein (50, 200 and 400 g/kg) for 14 d. Body-weight gain, food consumption, body consumption, and protein and energy utilization were measured. There was no difference in body-weight gain and food consumption between germ-free (GF) and conventional (CV) chicks, but food conversion efficiency (g body-weight gained/g food consumed) was significantly higher in GF than in CV chicks. Little difference was found in protein retention (g protein retained/14 d), but protein retention rate (g protein retained/g protein consumed) tended to be higher in GF chicks, particularly those given the diet with the lowest protein. The presence of micro-organisms improved metabolizable energy (ME) values of the diets, but not all of the digested energy in CV chicks was utilized for growth. Therefore there was little difference in energy retention (kJ energy retained/14 d) between environments, although energy retention rate (kJ energy retained/kJ ME consumed) was significantly lower in CV chicks. The amount of body fat in GF chicks was higher than that in CV chicks, especially in those fed on the low-protein diet. It is suggested that although the gut microflora may have beneficial effects on the digestion of dietary energy components, they may have detrimental effects on utilization of ME by their hosts, because chicks harbouring a gut microflora seem to have higher energy requirements for maintenance.

The influence of the gut microflora on protein synthesis in liver and jejunal mucosa in chicks

Protein synthesis in liver and jejunal mucosa was measured in 19-d-old germ-free (GF) and conventional (CV) chicks fed on a semi-purified casein-gelatin (SCG) diet using a massive-dose single injection of [U-14C]phenylalanine. The effect of subsequent feeding for 9 d either a nitrogen-free (NF) diet or an NF diet supplemented with L-methionine (5 g/kg) and L-arginine hydrochloride (2 g/kg) (MA diet) was investigated in both types of chick. In the liver, apart from the amount of DNA, the values for wet weight, protein, RNA, fractional synthesis rate (FSR) and the amount of protein synthesized were reduced after feeding the NF diet and, to a lesser extent, the MA diet. Except that the total amount of liver DNA was higher in the CV chicks than in their GF counterparts (P less than 0.01), no environmental effect was significant. When expressed on a unit body-weight basis, liver weight, protein, RNA and DNA were significantly higher in the CV than in the GF chicks. In the jejunal mucosa, the values for wet weight, protein and RNA tended to be reduced after the NF treatment but increased after the MA treatment. Mucosal DNA and the amount of protein synthesized (microgram/mm per d) were significantly reduced after the NF diet but were less affected after the MA diet. Mucosal protein FSR and the amount of protein synthesized per mg RNA were significantly reduced after both dietary treatments. No difference was found among dietary treatments in the amount of protein synthesized per mg DNA in jejunal mucosa. Mucosal DNA was significantly higher in the CV chicks and the reverse was true for mucosal protein: DNA. It was suggested that the increased protein synthesis in jejunal mucosa and possibly in liver on supplementation of an NF diet with methionine and arginine would partly, if not completely, account for the N-sparing effect of these amino acids. Although the protein: DNA value was smaller in CV chicks, the FSR and the amount of protein synthesized tended to be higher than in their GF counterparts irrespective of nutritional status. This might imply that protein degradation rate is greater in the CV state.

[Energy maintenance requirements and energy requirement for protein retention in growing rats and broilers. 1. Energy maintenance requirements of growing rats]

In 4 experiments with 3 times 3 male Wistar rats each, which received rations with different protein contents (10; 25 and 40% crude protein in the dry matter), in the growth range between approximately 65 and 180 g live weight and with an environmental temperature of 30 degrees C, a total of 226 measurings of the total metabolism were carried out on the energy level maintenance, partly also with the insertion of a fasting day. The most important results were: On the energy level maintenance with the simultaneous catabolisation of body fat there was considerable protein energy retention, which amounted to between 30 and 40% of the retention achieved in the growth periods. The energy maintenance requirement can be determined with good reproducibility (standard mean deviation: +/-6%). The average energy requirement directly measured at the feeding level maintenance of 437 kJ metabolizable energy (ME)/kg live weight 0,75.d (n=224) differs insignificantly from the average value obtained by means of multiple regression analysis from experiment periods with feeding for growth 423 kJ ME/kg live weight 0,75.d (n=437). Consequently it is not necessary to differentiate between energy requirement for maintenance and energy requirement connected correlatively with the live weight (metabolic weight of the body) under conditions of growth. Energy maintenance requirement proved to be insignificantly dependent on the amount of protein in the feed. The relative values of protein quotas of 10, 25 and 40% in the feed were 100, 101 and 103%; the expected values (derived from the efficiency of ATP synthesis in the oxidation of carbohydrates and protein) amount of 100, 104 and 109%. The problem of the thermogenous effect of protein, which is also of great importance to human nutrition urgently requires further experimental investigation. For growing rats the best adaptation of the energy maintenance over the investigated period of development is achieved if the 2/3 potence of the live weight is chosen as the expression of the metabolic body weight. With high probability this can also be transferred to the characterisation of protein metabolisation.

Dietary protein and cecal microbial metabolism in the rat

Adult rats were fed diets containing 0, 25, 50, 100, 200, or 400 g lactalbumin/kg diet for 10 days, and the activities of six cecal microbial enzymes were determined. Total activity per cecum of azoreductase, beta-glucosidase, and urease increased significantly with increasing dietary protein, whereas the activities of beta-glucuronidase and nitroreductase were not significantly affected. Nitrate reductase activity decreased significantly. Total numbers of cecal bacteria were not significantly altered by the treatment.

Energy and protein retention in holoxenic, axenic and gnotoxenic chickens monoassociated with Lactobacillus spp

1. Axenic, holoxenic and monoxenic chickens (strains LEM 220 or LEM 206 of lactobacilli isolated from the crop of the cockerel) were fed ad libitum on semi-purified diets containing 180 or 200 g protein and 30 g long (LCD) or short (SCD) chain dextrins/kg. Energy and protein retentions were determined from 0 to 3 weeks of age by carcass analysis. 2. Energy retained as a proportion of gross energy intake was only influenced by the microflora in birds receiving 180 g protein/kg and nitrogen retention followed a similar pattern, but differences were less marked: total flora always depressed retentions, but in monoxenic birds the action of the microflora varied with changes in the carbohydrate composition of the diet, the lowest retentions occurring when the diet contained carbohydrates (SCD) which allowed rapid lactate production in the crop.

[Utilization of 15N-labelled urea by laying hens. 1. Survey of the literature, 15N-excretion in feces and urine]

Three colostomated leghorn hybrids with an average laying performance of 75% received a ration with 17.7% crude protein and an energy content of 519 energetic feed units for hens per kg mixed feed over a period of 8 days. In the first six days of the experiment the 1%-supplement of urea to the ration was labelled. Its atom-% 15N excess (15N') amounted to 96.06%. During the last two days the urea supplement was not labelled. The total N, trichloracetic acid (TCA)-soluble N and the ammonia N were determined in the feces samples collected daily. In the urine samples collected daily the total N, urea N and ammonia N per hen were determined as well. In all samples the atom-% 15N excess (15N') was measured. The percentage of 14N in feces of the 14N dose was, on an average of the three hens, 21.3% and the analogous quota of 15N' 4.6%. The quota of ammonia 14N of the total 14N in feces had an average of 2.5%, the corresponding 15N' quota was 10.1%. The atom-% 15N' of the urea N in urine was considerably above that of the total urine N and had a maximum of more than 50%. The quota of urine 14N of the 14N taken in had an average of 44.4%, and the corresponding 15N' quota was 56.9%. On an average of the three hens, 61.6% of the 15N' were excreted in feces and urine during the 8-day test period.

[Some methodical problems in the determination of the true amino acid digestibility in swine]

Five castrated males bridge-fistulated at the end of the small intestine and fed a wheat-casein ration were used to study the influence of the microflora in the determination of the true amino acid digestibility applying the fecal analysis method. The experimental results allow to conclude that the influence of the microflora may be regarded as a very small one if certain parameters are taken into account in applying the fecal analysis methods.

[Secretion of endogenous amino acids in the gastrointestinal tract and amino acid resorption in the swine]

A trial was performed with 2 fistula pigs (each with 2 fistulas, one located about 30 cm below the pyloric orifice and the other at the end of the small intestine). Animal A received a casein diet containing 14% crude protein for a period of 2 weeks before the tracer amino acid was administered. Animal B received the same diet for a period of 10 days and was then fed a diet (at the same protein level) containing gluten as sole protein source. The two tracer amino acids, 14C-U-L-leucine and 3H-4,5-(N)-L-lysine, were injected intravenously. The passage rates for dry matter, organic matter and N measured at the beginning of the small intestine were higher than the rate of intake. The rate of passage of amino acids was also found to be increased relative to the rate of intake. In general, this increase involved the non-essential amino acids to a much larger extent. A considerable proportion of the amino acids passing into the large intestine is not excreted with the faeces but is probably converted in catabolic processes. It is for this reason that any values for the efficiency of amino acid absorption calculated on the basis of data on the faecal excretion of amino acids will not provide conclusive evidence for the availability of dietary amino acids in processes of the intermediate metabolism. The rate of secretion of 3H and 14C radioactivity into the digesta of the small intestine was found to increase rapidly within 1-2 hrs after administration of the tracer amino acids. The 14C radioactivity detected was found to be almost exclusively derived from 14C leucine while only about 60% of the 3H activity found in the digesta of fistula I were shown to be bound to lysine. Labelled lysine and leucine (of endogenic origin) are absorbed into the small intestine at a slower rate (i.e. endogenic proteins are less efficiently digested) than the non-radioactive amino acids (of exogenic origin) so that a process of concentration of endogenic amino acids is observed towards the end of the small intestine.

Further studies of the dynamics of nitrogen metabolism in sheep

1. A study of ammonia and urea metabolism in sheep was made using isotope dilution techniques with (15NH4)2SO4,[15N]urea and [14C]urea in order to determine quantitatively the movements of urea-N and NH3-N throughout the body of normal, feeding sheep. 2. Single injections of 15N-labelled compounds were made into the rumen fluid NH3, caecal fluid NH3 and the blood urea pools, in order to estimate the rates of flux through, and the transfer of N between, these and other nitrogenous pools in the body. 51CrEDTA was injected into the rumen and caecum with (15NH4)2SO4 to allow estimation of fluid volumes and to provide an indication of mixing, and of times of transit of isotopes between different sampling sites in the digestive tract. 3. The sheep ate approximately 22 g lucerne chaff/h and the mean dietary N intake was 16-3 g/d. 4. The rate of flux of NH3 through the rumen NH3 pool was 15-0 g/d (i.e. 90% of the dietary N ingested; however, this amount also included N from plasma urea (1-1 g/d) and other endogenous sources including NH3 derived from caecal NH3 (0-4 g/d). 5. Only 40% of the N in isolated rumen bacteria was derived from NH3, indicating that a considerable proportion of their N requirements were obtained from compounds other than NH3 (e.g. peptides and amino acids). 6. There was evidence of recycling of N between nitrogenous pools in the rumen, probably through rumen NH3 leads to microbial N leads to NH3. 7. It was estimated that 5-3 g blood urea-N/d entered the digestive tract; 20% of this urea was degraded in the rumen, 25% in the caecum and the remainder was apparently degraded elsewhere; there was evidence of urea degradation in the large intestine posterior to the caecum and it is suggested that urea degradation and absorption of the resultant NH3 may occur in the ileum. 8. Of the 4-8 g N/d entering the caecal NH3 pool, 4-2 g N/d left and did not return and the difference (0-6 g N/d) was recycled, possibly through caecal NH3 leads to microbial N leads to NH3. 9. A large proportion of the NH3 entering the caecal NH3 pool (70% or 3-2 g N/d) was apparently derived from degradation of nitrogenous products, other than urea, including rumen microbial N (1-0 g N/d) passing undigested from the small intestine. 10. Less than half the NH3-N of caecal origin entering the rumen passed through the blood urea pool; the remainder was apparently transported as other nitrogenous compounds in the blood or body fluids. 11. The results of the three experiments were combined in a general three-pool, open-compartment model which formally recognizes an unlimited number of other unspecified, interconnected pools together comprising the whole-animal system. Rates of flux through, and transfer of N between these and other nitrogenous pools in the body were calculated by solving this model and the information derived has been applied to whole-animal models with a view to subsequently using these models in computer simulation studies.

The influence of the gut microflora on the digestion of dietary and endogenous proteins: studies of the amino acid composition of the excreta of germ-free and conventional chicks

1. To assess the part played by the microflora in the digestion of proteins, the amino acid composition of the excreta and the apparent and true digestibilities of individual amino acids were measured in germ-free (GF) and conventional (CV) chicks.

2. Three diets were used: diet 1, nitrogen-free; diet 2,280 g protein/kg as (g/kg): casein 80, gelatin 100 and freeze-dried egg albumen 100 and diet 3,280 g protein/kg as diet 2 but with heat-damaged instead of freeze-dried egg albumen. Half of the GF and half of the CV chicks received the N-free diet in the first 7 d of test and the other half of each group received either diet 2 or diet 3. In the second 7 d test period those chicks which had been given the N-free diet received either diet 2 or diet 3 while those which had been given protein diets received the N-free diet. Total amino acids were measured in hydrolysates of the soluble and insoluble fractions of the excreta collected in the last 3 d of each test period.

3. The amino acid composition of the soluble fraction of the excreta of chicks given either diet 2 or diet 3 differed markedly from that of chicks given the N-free diet. The amino acid composition of the insoluble fraction of the excreta of chicks given diet 2 was similar to that of chicks given the N-free diet, whereas that of chicks given diet 3 was markedly different and resembled egg albumen in composition.

4. In the soluble fraction of excreta from CV chicks given diets 1 and 2 the proportions of threonine, serine and glucosamine were lower and those of methionine, leucine, isoleucine and phenylalanine were higher than in those from GF chicks, particularly on diet 1. In the insoluble fraction of excreta from CV chicks given these two diets, compared with GF chicks, there were lower proportions of serine and proline and higher proportions of cysteic acid and lysine, the latter particularly with diet 1.

5. Lower proportions of threonine, serine and glucosamine were also observed in the soluble fractions of excreta from the CV chicks given diets 1 and 3, compared with GF chicks, whereas the proportion of glutamic acid was higher. With these two diets the insoluble fraction from CV chicks contained a higher proportion of alanine. In each instance the environmental effect was greater with diet 1.

6. No effect of environment on either apparent or true digestibility of individual dietary protein amino acids was demonstrated, with the exception of threonine in diet 2, the true digestibility of which was higher in GF than in CV chicks.

7. It was concluded that the gut microflora of the chick had little influence on the digestion of the proteins in the diets tested, but may serve an important role in the degradation of endogenous proteins and the recycling of N.

The utilization of protein and excretion of uric acid in germ-free and conventional chicks

1. The influence of the gut microflora on protein utilization has been investigated with a series of good- and poor-quality protein diets in germ-free (GF) and conventional (CV) chicks by the measurement of net protein utilization (NPU) and uric acid excretion.

2. The diets used were: 280 g protein per kg diet containing unheated or heat-damaged albumen (100 g/kg), casein (80 g/kg) and gelatin (100 g/kg); sesame protein (220 g/kg); sesame protein (220 g/kg) supplemented with lysine (5 g/kg); freeze-dried cod muscle (160 g/kg); heat-damaged cod muscle (160 g/kg); mildly-steamed egg albumen (100g/kg); heat-damaged egg albumen (100 g/kg).

3. No significant differences in NPU values for the proteins measured in GF and CV chicks were found, with the exception of unsupplemented sesame protein, for which the NPU value was slightly higher in GF chicks.

4. The replacement of unheated egg albumen by heat-damaged egg albumen in the 280 g protein/kg diet resulted in a decrease in uric acid excretion. With the cod-muscle diets, heat-damaging the protein caused an increase in uric acid excretion. Supplementing the sesame protein with lysine resulted in a decrease in uric acid excretion.

5. Excretion of uric acid tended to be higher in CV chicks than in GF chicks with all proteins except sesame protein, with which uric acid excretion was a little higher in GF chicks.

6. Endogenous nitrogen excretion was higher in GF than in CV chicks.

7. It is concluded that the gut microflora has little influence on the utilization of dietary protein by chicks, although it may modify the route of excretion of the N which survives digestion and reaches the lower gut.