[Protein digestibility and absorption of amino acids in various segments of the digestive tract of pigs. 2. Protein and amino acid balances at the end of the small intestine and of the whole digestive tract (apparent and true protein and amino acid digestibility)]

Black-Box Gastrointestinal Tract-Needs and Prospects of Gaining Insights of Fate of Fat, Protein, and Starch in Case of Exocrine Pancreatic Insufficiency by Using Fistulated Pigs

Exocrine pancreatic insufficiency (EPI) results in the maldigestion and malabsorption of nutrients. The digestive processes in humans and other monogastric species like rat and pig are characterized by a predominantly enzymatic digestion within the small intestine and microbial fermentation located in the hindgut. For protein, it is doctrine that only prececally absorbed amino acids can be transferred to the amino acid pool of the host, while postileal absorption of nitrogen-containing compounds occurs mainly in the form of ammonia, being a burden rather than a benefit for the organism. The pig is an established animal model for humans to study digestive processes. As digestion is markedly impaired in case of EPI the use of an appropriate animal model to study the effects of this disease and to optimize treatment and dietetic measures is of special interest. By using an animal model of experimentally-induced EPI allowing differentiating between digestive processes in the small as well as in the large intestine by use of ileo-cecal fistulated animals, marked effects of EPI on prececal digestion of starch and protein could be shown. The data indicatethat estimation of digestibility of nutrients over the entire digestive tract results in a distinct overestimation of enzymatic digestion of starch and protein. Therefore, this model clearly shows that protein and starch digestion are significantly reduced in case of EPI although this cannot be detected on a fecal level. As postileal fermentation of starch is associated not only with energy losses but also with intensive gas production, this is of special interest to minimize meteorism and improve wellbeing of patients.

Gaining insight into microbial physiology in the large intestine: a special role for stable isotopes

The importance of the human large intestine for nutrition, health, and disease, is becoming increasingly realized. There are numerous indications of a distinct role for the gut in such important issues as immune disorders and obesity-linked diseases. Research on this long-neglected organ, which is colonized by a myriad of bacteria, is a rapidly growing field that is currently providing fascinating new insights into the processes going on in the colon, and their relevance for the human host. This review aims to give an overview of studies dealing with the physiology of the intestinal microbiota as it functions within and in interaction with the host, with a special focus on approaches involving stable isotopes. We have included general aspects of gut microbial life as well as aspects specifically relating to genomic, proteomic, and metabolomic studies. A special emphasis is further laid on reviewing relevant methods and applications of stable isotope-aided metabolic flux analysis (MFA). We argue that linking MFA with the '-omics' technologies using innovative modeling approaches is the way to go to establish a truly integrative and interdisciplinary approach. Systems biology thus actualized will provide key insights into the metabolic regulations involved in microbe-host mutualism and their relevance for health and disease.

[Time course of amino acid absorption in growing rats after feeding of a 15N-labeled wheat/yeast ration]

The time course of AA digestion, AA balance (sV AS), and AA absorption (wV AS) was estimated on growing rats (Wistar rats, LW = 124 g) in different sections of the intestinal tract using the combination of 15N tracer and TiO2 marker techniques. The animals received once a diet of 15N labelled wheat and yeast as protein sources supplemented by TiO2 as a marker. Up to 6 h after feeding the amino acid composition the 15N excess and the TiO2 content in the digesta of stomach, small and large intestine were determinated in the relation of amino acids resp. of 15N labelled amino acids to the marker. In addition the content of amino acids and the 15N excess of these amino acids were estimated in plasma. From these data the disappearance rates and the relation of exogenous to endogenous amino acids as well as the sV and the wV values of the different amino acids were calculated for the different gut sections. The following results were obtained: The relative disappearance rate for N and TiO2 marker out of the stomach went approximately parallel but with a delay for TiO2 of about 30 minutes. The AA composition of the stomach content, the small and the large intestine content did not vary in dependence of the time. The AA composition of the stomach digesta was nearly identical to that of the diet, while that of the small intestine was between exogenous AA composition (feed) and endogenous AA composition (digesta on protein free feeding). AA composition of the large intestine digesta showed quite big differences (bacterial AA break down and AA synthesis). Considering a delay time (small intestine: 1 h, large intestine: 4 h) the exogenous portion of the different AA remained constant in both of these intestinal sections during the whole experimental time. The exogenous AA part varied for small intestine digesta between 31 and 69% (mean value: 41%), and for large intestine digesta between 13 and 39% (mean value: 22%). The sV AS values in the small intestine (AA balance resp. precaecal digestibility) differed from 61% (threonine) to 86% (proline) with an average of 73.4 +/- 7.4%, those for wV AS (AA absorption) from 81% (lysine) to 94% (proline) with an average of 88.1 +/- 4.1%. There were significant differences between AA, but they are negligible for practical purposes.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of virginiamycin on the digestive physiology in precaecal re-entrant cannulated pigs

The present experiment was set up to study the effect of Virginiamycin, a nutritional growth promoting antibiotic, on the digestive physiology using precaecal cannulated pigs. The semipurified diet used provided 21% protein and 60% of nitrogen free extract (NFE), 2/3 as starch and 1/3 as lactose. Due the older age of the pigs, the lactose induced some degree of malabsorption as precaecal flow rate of digesta was markedly higher (3.2 kg/d) compared with published data obtained with purified diets without lactose. This was also reflected in the rather low ileal digestibility of the nutrients (%): dry matter 68.6, protein 79.6, fat 78.4 and NFE 75.0. Virginiamycin markedly lowered flow rate (2.2 kg/d) and significantly improved apparent precaecal digestibilities (%): dry matter 74.0, protein 81.4, fat 81.9 and NFE 78.7. The faecal apparent digestibility was comparable with published data. There were no treatment differences indicating that precaecal digestibilities are much more sensitive then faecal ones. In order to explain the differences obtained the mean retention time in the upper intestine was measured. Although significant differences were noted (control: 5 h, Virginiamycin: 6 h) a direct cause-effect relationship was not evident. Also the activity of selected pancreatic enzymes in ileal contents was compared. There were no consistent differences between the two treatments, except for a lower lipase activity during Virginiamycin treatment.

[The effect of exogenous factors on pre-cecal nutrient and amino acid resorption determined in swine with ileo-rectal anastomoses. 2. The effect of the degree of grinding of plant protein-rich concentrates in rations]

In digestion trials using pigs fitted with ileo-rectal anastomoses and intact pigs, the influence of two different grinding finenesses (coarse, fine) of vegetable high-protein concentrates (soya bean meal, field bean, lupin) added to cereal diets was examined. It was found that neither the precaecal nor the total nutrient absorption and digestibility were practically injured, when in the concentrates the particle sizes bigger than 2 mm did not amount more than 20% and whole grains hardly occurred. The investigations concerned the crude putrients, watersoluble carbohydrates and starch as well as the indispensable and dispensable amino acids. The apparent and true precaecal absorption values and total digestibility data for soya bean meal (heat treated), field bean (variety 'Fribo' and yellow sweet lupin (variety 'Bornova'--calculated by the different method--are given and discussed.

[Effect of exogenous factors on prececal nutrient and amino acid reabsorption, ascertained in swine with ileorectal anastomoses. 1. Effect of the degree of grinding up of grain]

Pigs fitted with ileo-rectal anastomoses (IRA) and in parallel experiments intact (INT) pigs were used to estimate the influence of the different grinding fineness of barley and wheat (coarse, medium, fine) on the apparent and true precaecal and total digestibility resp. absorption of various N free and N containing nutrients, among them crude protein and the indispensable and dispensable amino acids. Coarse grinding (25 ... 50% of the particles greater than 2 mm) resulted in significantly lower digestibility values than medium and fine grinding--with more striking differences in barley than in wheat. Precaecally most nutrients and amino acids are distinctly less digestible than at the end of the total tract. The precaecal lysine absorption determined with IRA pigs is remarkably low. The results are discussed. In order to attain a good utilization of the protein contained in cereals grains should be ground in hammermills with maximal sieve meshes of 3 mm. It is proposed to tabulate crude protein and amino acids in future on the basis of a standardized true precaecal digestibility resp. absorption.

[The utilization of crude proteins from 15N-labeled straw by broiler hen breeds]

In an experiment with 10 colostomized broiler breeding hens the digestibility of wheat straw meal labelled with 15N and the incorporation of heavy nitrogen into individual body fractions were studied. The straw meal contained a 15N excess (15N') of 14.88 atom-%. Before the experiment part of the straw meal was treated with gamma-rays (2.0 MGy). 5 animals each received in addition to the basic ration 30 g untreated (group I) and irradiated 15N labelled straw meal (group II). The apparent 15N' digestibility amounted for untreated straw meal to 49% and for irradiated straw meal to 46% (p less than 0.05). The labelling of uric acid amounted to 0.25 atom-% 15N', urine with 0.30 atom-% 15N' was more highly labelled (p less than 0.05). On an average of both groups the same labelling of 0.18 atom-% could be detected in the follicles and the liver, whereas 0.17 were ascertained in the blood plasma and 0.16 atom-% 15N' in the oviduct. 18% of the digested 15N' were incorporated in the muscles. There were only insignificant differences between the two groups with regard to the incorporation of 15N'. In conclusion one can say that the apparent digestibility of straw protein is 47.5% and that the utilization of the absorbed N is about the same as that of wheat protein.

[Determination of endogenous nitrogen in feces using the isotope technic]

A ration consisting of wheat gluten and N-free components was supplemented with L-lysine and L-leucine and fed to two groups of growing Wistar rats. Group 1 received 15N Lys and unlabelled Leu, group 2 received unlabelled Lys and 15N Leu in order to study the influence of the utilization of the 15N marker on the labelling quota of faeces and urine as well as various fractions of the body. The good utilization of Lys in group 1 results in a higher 15N excess in faeces and a reduced 15N abundance in urine in comparison to group 2 with a lower utilization of 15N Leu. The results show that the 15N abundance in urine is unsuitable as an indicator of the 15N labelling quota of endogenous metabolic faecal nitrogen.

[Nitrogen and amino acid absorption in the small intestine of growing pigs. 2. Apparent and true crude protein digestibility and amino acid absorption to the end of the small intestine]

Studies of the apparent and true ileal digestibility of crude protein and the apparent and true amino acid (AA) absorption were carried out with 7 female pigs in the live weight range between 22 and 34 kg after ileorectostomy. Protein sources of varied quality with regard to the method of treatment (toasted) and untoasted soybean oilmeal) and to the AA composition (vital gluten or vital gluten + L-lysine X HCl) were used. Distinct differences regarding the apparent ileal digestibility of crude protein and the apparent absorption of amino acids were discovered between the protein sources, the cause of which is to be seen in the different amounts of endogenous N. The true ileal digestibility of crude protein and amino acid absorption were partly distinctly higher than the values of the apparent ileal digestibility of crude protein and AA absorption. On the whole one can say that the results of the investigation gained by means of ileorectostomy can be compared to the values gained from cannulated animals. Thus the experimental method used is suitable for studying the absorption process to the end of the small intestine of pigs.

An evaluation of total and digestible lysine as a predictor of lysine availability in protein concentrates for young pigs

Forty pigs between 23 and 51 d of age were given, ad lib., diets containing 7.9 g lysine/kg. The diets contained wheat and one of five protein concentrates: milk, peanut (Arachis hypogaea) meal, cotton-seed (Gossypium herbaceum) meal, meat meal or lupins (Lupinus augustifolius). Twenty of the pigs were given an indigestible marker, 103Ru-labelled Tris-(1,10-phenanthroline)-ruthenium(II) chloride, between 51 and 56 d of age and were killed at 56 d of age. A further forty pigs, between 23 and 51 d of age, were given the same diets supplemented with 3 g L-lysine hydrochloride/kg. The weight gains of the pigs given the diets containing 7.9 g lysine/kg (95-153 g/d) were significantly less (P less than 0.05) than those of the pigs given the diets containing 10.9 g lysine/kg (274-340 g/d). Weight gains of pigs given the diets containing meat meal were less than those of pigs given diets containing milk, peanut meal or lupins. Feed conversion ratios decreased and N balances increased with increasing lysine content of the diets. Apparent digestibilities of dry matter (DM) and nitrogen of the diets containing meat meal and cotton-seed meal were less than those of the other three diets, but there was no effect of lysine content of the diets on these indices. The major site of DM and N absorption for the diet containing milk was the duodenum while for the other four protein concentrates the jejunum and ileum were the major absorption sites. Apparent digestibility of lysine from the five diets ranged from 0.54 to 0.75. The retention of the apparently absorbed lysine in weight gain was 0.86-0.94, and there was no significant (P greater than 0.05) difference between diets which suggested that the apparent digestibility of lysine could be an indicator of its availability.

[Advances in possibilities for protein evaluation]

With protein evaluation the changing abilities of food proteins are characterized with regard to their covering the requirements of the organism for protein or amino acids, respectively. The biological value of proteins is influenced by several factors. Measuring the reaction of the whole organism (of man or animal) to the food protein the sum of all influencing factors is covered. Hence, these direct evaluation methods have priority. The general dose-reaction curve demonstrates the direct evaluation methods: The evaluation criteria protein efficiency or minimum protein requirement are presented and the different possibilities of interpretion are compared. Most direct evaluation methods are performed with suboptimal protein supply, therefore values for an optimum protein supply can be derived only with reservation. Improved values for protein evaluation can be obtained from investigations of the protein metabolism. With that the substrat-related evaluation can be more orientated to a organism-related one. Indirect biochemical evaluation methods are less important. That does not concern in-vitro evaluation by amino-acid analysis and/or in-vitro digestibility tests. Possibilities and limits of these methods are discussed.

[Relations between apparent fecal and apparent ileal crude protein digestibility in swine]

The crude protein and lysine digestibility values available in literature and ascertained in comparative investigations at the end of the small intestine (distal ileum) and in the complete digestive tract (faeces analysis method) of pigs were subjected to a correlation calculation in order to find out whether and to what degree there are relations between apparent 'ileal' and apparent 'faecal' digestibility. For both crude protein and lysine the relation between ileal and faecal digestibility is so close (r = 0.73 resp. 0.85 ... 0.98) so that for practical purposes it is not necessary to determine the apparent ileal digestibility for each feedstuff by means of the complicated cannula method. This can be calculated with great reliability from the experimentally ascertained apparent faecal digestibility. The differences between faecal and ileal digestibility are smaller for lysine (conversion factors 0.92 ... 0.99) than for crude protein (conversion factors 0.89 ... 0.93).

[Absorption and utilization of amino acids infused into the cecum of growing swine. 3. Studies with 15N- and 14C-labeled isoleucine]

In 3 experiments growing female pigs, (live weight 35-56 kg) received continuous infusions of 15N-labelled or 15N- and 14C-doubly labelled isoleucine by means of caecal cannulae. The whereabouts of the infused isoleucine were investigated. Between 8.9 and 12.3% of the infused 15N-excess (15N') was excreted in faeces mainly in the forms of bacteria protein, between 0.7 and 0.9% only of the infused amount unchanged as 15N-isoleucine. The highest quota is microbially decomposed in the colon and absorbed in the form of NH3 or amines. Between 45 and 70% of the infused 15N are excreted in urine, mainly as urea (85-95% of the 15N-amount in urine). Virtually no 15N from the infused isoleucine is incorporated in the organ and tissue proteins (exception: colon wall). These findings are corroborated by the 14C-activity measuring as no intact 14C labelled isoleucine could be detected in the tissue protein. These results show that intact isoleucine is not absorbed in the colon. The nitrogen originating from the absorbed NH3 is nearly completely excreted in urine and thus not available to the biosynthesis of body protein.

[Studies with 15N-labeled lysine in colostomized hens. 2. 15N excretion in feces]

Over a period of four days colostomised hens were given 15N-lysine, and the development of 15N-excretion both in the TCA-soluble and the TCA-precipitable fraction of the faeces was measured over eight days. In both fractions the total, lysine, histidine and arginine N and 15N-excess (15N') was determined. The average apparent digestibility of 14N was 81.2% +/- 1.1% and of 15N' 93.2% +/- 0.7%. Labelled N is already excreted in faeces 3 hours after its application. The TCA-precipitable N is less strongly labelled than the TCA-soluble N. During the application of 15N' the labelling in faecal lysine is nearly one power of ten higher than in total N. The atom-% 15N' of the lysine could also be distinctly detected in arginine and histidine. The quotas of the total 15N' in faeces were 3.5% for arginine-15N' and 0.8% for histidine 15N'; 15N' can mainly be detected in the soluble fraction.

[Absorption and utilization of amino acids infused into the cecum of growing pigs. 2. 15N-labeled lysine]

Over a period of 4 days 15N-labelled lysine was infused into two growing female pigs (live weight approximately 50 kg) through a caecal cannula. The feeding was restrictive (1,400 g dry matter/day) and, with regard to lysine, it didn't meet the requirement. In a 7-day experiment the N- and 15N-content was measured periodically in the excretions (feces and urine), in various fractions of the blood and in selected slaughtering samples. From the infused 15N 3-5% are excreted as lysine in feces, another 5% are in other amino acids of the bacteria protein. The disappearance rate of 15N' from the large intestine makes greater than or equal to 90%. The biggest part of this 15N (78-88%) is excreted with the urine in form of 15N-urea. Obviously the infused amino acid is decomposed to NH3 in the large intestine and then absorbed. The absorbed ammonia is changed into urea in the ornithine cycle and excreted in urine. The recovery rate of the 15N infused as 15N-lysine is 93 and 84% resp. Incorporation of 15N in to serum protein or other body protein could not be detected so that the remaining difference of 7-16% cannot necessarily be interpreted as incorporation rate of 15N into the body protein. Under practical conditions the maximal utilisation of lysine from the feed in the large intestine is 1.6% and should thus be without importance.

[Absorption and utilization of amino acids infused into the cecum of growing pigs. 1. Measurement of N-balance for utilization of lysine and isoleucine; isoleucine requirement for growing pigs]

In N-balance experiments with growing pigs (40-60 kg live weight) investigations were made whether lysine or isoleucine that is infused into the caecum can be absorbed there and to what extent these amino acids in that case can be utilised by the animal for protein synthesis. The pigs either received basic rations with insufficient lysine or isoleucine resp. (negative control group) or the amounts of lysine and isoleucine lacking to meet the requirement were supplemented with the feed (positive control group) or continuously infused into the caecum with the help of caecal infusion cannulae (test group). In the experiments with lysine the animals in the negative control group and in the test group showed considerably lower N-balances than the positive control group. There were no differences as regards the apparent digestibility of lysine between the positive control group and the test group. The urine of the test group contained distinctly more NH3. This shows clearly that lysine that is infused into the caecum cannot be utilised by the pigs, it is, on the contrary, microbially decomposed, the nitrogen is chiefly absorbed as NH3 and excreted in urine. As regards isoleucine, the deficit brought about with the basic ration was insufficient in order to achieve significant differences between the N-balance values of the groups so that unambiguous statements on the absorption and utilisation of isoleucine infused into the caecum cannot be made. Concerning apparent digestibility of isoleucine and the NH3 content of the urine, the results of the isoleucine experiments were similar to those in the lysine experiments. According to our N-balance experiments the isoleucine requirement of pigs indicated in relevant literature as 5.6 g/kg dry matter of the feed is by far too high. It should be limited to 3.5 or a maximum of 4.0 g isoleucine per kg dry matter of the feed.

[The protein digestibility and amino acid absorption in various segments of the digestive tract of pigs. 6. Results of the application of 15N-lysine]

From two fattening pigs (average live weight 63 kg) with re-entrance cannulae both in the duodenum and the ileocecal region, the intake, the excretion and the flow rates of nitrogen, 15N, lysine and 15N-lysine are measured after the oral application of 15N-lysine as supplement of a wheat-wheat gluten diet. A scheme of the lysine metabolism of pigs is drawn on the basis of the measured values. The absorption of synthetic and native lysine as well as the endogenous and exogenous lysine contents of the duodenal and ileum chyme are estimated.

[Protein digestibility and amino acid absorption in various segments of the digestive tract of pigs. 5. Results of the application of 35S-methionine]

The intake, excretion and the rate of flow of protein, methionine and 35S were measured at four pigs (live weight 63 kg) with re-entrant cannulae in the duodenum and the ileocecal region after the oral application of 35S-methionine and the feeding with a wheat + wheat gluten + lysine resp. a protein-free diet over a period of 7 days. From the measured values one pattern each for the N- and the methionine metabolism was laid down with the help of the compartment model, and the endogenous and exogenous levels of protein resp. methionine in the duodenum, the ileum and in feces were estimated.

[Protein digestibility and the absorption of amino acids in various segments of the digestive tract of pigs. 3. Results of the fractionation of ileum chyme after feeding various rations]

Growing female pigs provided with re-entrant ileum resp. ileocecal cannulae received 6 different rations (fattening feed I and II for pigs, rations with dried skim milk, wheat gluten + lysine resp. wheat + wheat gluten + lysine, N-free mixture). The ileum chyme was separated into the fractions supernatant 1 and sediment 1 and by a treatment of supernatant 1 with trichloracetic acid and subsequent centrifuging into supernatant 2 and sediment 2. In the complete chyme as well as in all fractions the crude protein and amino acid contents were determined. The distribution in per cent of the crude protein and the amino acids over the fractions was calculated as well. The influence of the rations, in particular rations of dried skim milk, on the amino acid pattern of the complete chyme and the chyme fractions could be established. An influence of the rations could not be recognised on sediment 2 only, which indicates a uniform amino acid pattern of these probably endogenous proteins. The percentage of crude protein and amino acids in the fractions was also influenced by the rations.

[Protein digestibility and the absorption of amino acids in various segments of the digestive tract of pigs. 4. Digestibility of crude protein and amino acids and rate of passage through the duodenum and ileum and the total digestive tract of growing pigs]

The crude protein digestibility and the amino acid absorption of six female pigs (average live weight 61 kg) with duodenal and ileocecal re-entrant cannulae, which were fed with a wheat + wheat gluten + lysine ration and an N-free ration, were determined in various segments of the intestines. Comparative experiments concerning the N-metabolism with pigs without and with cannulae showed that the animals renormalised their metabolism 14 days after narcosis and fistulation of the intestines. The extents of secretion and absorption of the various amino acids vary as it is shown from the values of the apparent and true digestibility resp. rate of passage through various segments of the intestines. While for methionine and glutamic acid absorption exceeds endogenous secretion already in the duodenum, the amino acids with a high endogenous quota (glycine, alanine, threonine, tryptophan) are, even at the terminal ileum, not as well absorbed as the others. Methionine is obviously synthesised on a large scale by the colon flora and excreted in feces. The fractionation of the duodenal and ileum chyme after feeding wheat + wheat gluten + lysine as well as N-free mixture, into the fractions "solid particles", "peptides-free amino acids" and "proteines precipitable by trichlor-acetic acid" supplies information on the degree of protein degradation in various segments of the intestines.