[Further studies on the multi-compartmental model of protein metabolism]

Estimation of inevitable macro mineral losses in amazons (Amazona spp.) as basis for the calculation of maintenance requirement

To determine the endogenous losses of macro minerals via excrements, adult amazons (Amazona spp., n=5) were fed a purified diet supplemented with vitamins, trace elements and amino acids according to recommendations for poultry, but almost free of calcium, phosphorus, magnesium, sodium and potassium. The diet was offered ad libitum for nine days and was compared to mineral excretion when fed a commercial seed mixture. Daily dry matter (DM) intake was 22.2 g DM/bird (16.3 MJ ME/kg DM) compared to 8.18 g DM/bird when offered a commercial seed mixture (20.0 MJ ME/kg DM). Daily amounts of excreta corresponded to the physiological amounts of this species (5.2 g DM/bird). The digestibility of organic matter was similar for the purified diet and seeds (75% and 77%, respectively). Inevitable losses of major elements reached a basal level latest after five days and amounted to 10.6 mg calcium, 2.9 mg phosphorus, 1.3 mg magnesium, 1.7 mg sodium and 10.8 mg potassium (values per kg BW(0.75)). Feeding a diet almost free of major elements resulted in a decrease in blood content for magnesium (24.4%), potassium (21.8%) and sodium (4.5%), whereas the calcium and phosphorus content in plasma stayed constant or did not show unidirectional changes in all animals.

Effects of graded levels of soya-bean protein on endogenous ileal lysine loss and amino acid digestibility in growing pigs

This experiment investigated the effects of feeding graded levels of a soya-bean protein product (HP300, Hamlet Protein A/S Company, Denmark) on endogenous ileal lysine loss, apparent ileal amino acid digestibility, standardized true ileal amino acid digestibility determined using the protein-free (PF) method, and real ileal amino acid digestibility determined using the homoarginine (HA) method. The soya-bean protein product was obtained by purifying and defattening soya bean via a proprietary microbial process that decreased the level of trypsin inhibitors and other anti-nutritional factors in soya bean. Six barrows, with an initial body weight of 37·4 ± 1·3 kg, were surgically fitted with simple T-cannulae at the distal ileum and offered six maize-starch-based diets according to a 6 × 6 Latin-square design. The six diets were formulated to provide 0, 50, 100, 150, 200, or 250 g crude protein (CP) per kg by dietary inclusion of 0, 90, 182, 274, 367 or 460 g/kg of soya-bean protein. Five kg of soya-bean protein product was guanidinated in order to estimate endogenous amino acid flow and real ileal amino acid digestibility. Chromium III oxide (5 g/kg) was included in the non-guanidinated diets while dysprosium chloride (0·1 g/kg) was included in the guanidinated diets as an indigestible marker. The experimental periods lasted 8 days. On day 6 of each period, ileal digesta was collected for 24 h to determine apparent and standardized true ileal amino acid digestibility of the non-guanidinated diets. At 08:00 h on day 8, the pigs were given a single meal of the diets containing guanidinated protein and their ileal digesta was collected for 24 h in order to determine the total HA flow and the real ileal digestibility of lysine. Endogenous ileal lysine flow appeared to follow a sigmoid curve starting at about 370 mg/kg dry matter (DM) intake for pigs given the PF diet and continuing asymptotically to about 750 mg/kg DM intake when the inclusion level of the soya-bean protein product was increased to 182 g/kg (100 g/kg of CP). The endogenous ileal lysine flow for pigs given the PF diet was similar (P > 0·05) to that of pigs given 90 g/kg soya-bean protein (50 g/kg of CP) and it increased sharply (P < 0·05) as the level of soya-bean protein increased from 90 to 182 g/kg (50 to 100 g/kg of CP). Thereafter, it was relatively constant (P > 0·05). With an increase in soya-bean protein, there was a quadratic increase (P < 0·01) in the apparent ileal digestibilities for all amino acids except valine and phenylalanine. Standardized true ileal amino acid digestibility decreased (P < 0·05) with an increase in soya-bean protein level. However, real ileal amino acid digestibilities were not influenced (P > 0·05) by soya-bean protein in the diet at levels between 90 and 367 g/kg (50 and 200 g/kg of CP). In conclusion, endogenous ileal lysine flow was not constant and was significantly affected by soya-bean protein level. The results of this study suggest that standardized true ileal amino acid digestibility should be measured between 100 and 200 g/kg of CP (182 and 367 g/kg soya-bean protein) while real ileal amino acid digestibility is unaffected by protein levels between 50 and 200 g/kg of CP (90 and 367 g/kg soya-bean protein).

[Determination of the protein quality of food and animal feed]

The estimated value of true digestibility of food and feed proteins is in dependence from the excretion of metabolic faecal nitrogen (MFN). Results of many authors showed that a high fibre content of the diet increase the MFN-excretion and lower the true digestibility of the diet protein. The exact estimation of MFN is only possible with isotopic methods. The labelling of feed proteins with isotopic nitrogen (15N) is possible in experiments with small animals. In big animals (pigs) the utilization of recycled 15N is too high following the long transit time of non digested 15N-labelled feed protein and the parallel 15N-labelling of MFN. The best method for the estimation of true digestibility of proteins is the method with 15N-labelled animals and the differentiation between nonlabelled undigested feed protein and the 15N-labelled MFN in faeces. The estimation of digestibility of essential amino acids at the end of the ileum as a measure for protein quality is not in advantage because the bacterial breakdown and synthesis of amino acids in the small intestine is unknown. The estimation of the biological value (BV) of proteins with the classical method is useful when the exact MFN was determined. The classic formula of BV [formula: see text] is only applicable in experiments with growing animals with nitrogen retention. This result of BV value is in agreement with the method only valid for growing animals with N-retention and not for animals or human beings in maintenance. The measurement of a BV of proteins with animals in maintenance is possible when the animals are labelled with 15N. The 15N-loss of the animal after the feeding of different protein sources is the smallest when the amino acid pattern of the protein is adapted to the need of amino acids for the maintenance metabolism of the animal. It was found that proteins with a high content of glutamic and aspartic acid (proteins of grains) are better proteins for the maintenance metabolism as animal proteins. Measurements with the method of the oxydation rate of essential amino acids showed that the amino acid pattern of wheat protein is in agreement with the need of amino acids for maintenance of the adult men. The evaluation of protein quality in animal nutrition for growing or lactating monogastric animals is in the present time the balance of essential amino acids in the feed protein and the need of this amino acids of the animals.

[Determination of a prececal N-absorption from natural feed by 15N-labeled laboratory rats using the isotope dilution method]

60 Wistar rats (5 animals/group) received 12 different feedstuffs over a period of 7 days and were simultaneously labelled with 15N (orally by means of 15NH4Cl in the feed). In the subsequent 5 days faeces were collected in order to determine the apparent and true digestibility of crude protein. On the 13th experimental day the animals were killed 3 hours after the intake of half the daily ration and the atom-% 15N excess (15N') was determined in the TCA-soluble and TCA-precipitable fractions of the blood plasma and the digesta of the 2nd and 3rd thirds of the small intestine. Precaecal N-absorption was calculated with the help of the quotient [formula: see text] the blood plasma and the digesta The following values (in %) were registered in comparison to true N-digestibility (in the following in brackets): casein = 95.8 (99.2), whole egg = 92.1 (97.5), fish meal = 85.8 (93.4), dried skimmed milk = 98.4 (96.1), soybean meal = 79.6 (90.6), assay protein = 94.2 (98.9), wheat = 92.9 (90.7), barley = 84.3 (84.8), yeast, grown on molasses = 85.6 (87.2), yeast, grown on whey = 86.1 (88.5), biomass of liquid manure = 43.6 (68.9), activated sludge = 54.4 (64.1). One can conclude that the isotope dilution technique demonstrated here as an evaluation method is very well suited for the characterization of the N-digestibility of a feedstuff in the small intestine.

Bioavailability of amino acids in plant feedstuffs determined by in vitro digestion, chick growth assay, and true amino acid availability methods

An in vitro, pepsin-pancreatin digestibility method was used to estimate the bioavailabilities of amino acids in plant feedstuffs, including two cultivars of four cereal grains and three high-protein feedstuffs. As a technique for separating hydrolytic products from substrate, trichloroacetic acid (TCA) was compared with three ultrafiltration techniques. Solutions were filtered continuously by a membrane of 500-Dalton pore size (cUF) and terminally by membranes of 500 Dalton (tUF) and 10,000 Dalton (CX). Additionally, bioavailability of amino acids was determined in vivo by the true amino acid availability (TAAA) method and utilization of lysine was determined by chick growth assay (CGA). Correlations of in vitro and in vivo estimates of availabilities were ranked CX = cUF greater than tUF greater than TCA for total amino acids and were ranked similarly for most individual amino acids. When determined using the superior technique, correlation between in vitro digestibilities of amino acids and TAAA were moderately high for the combined cereal grains (r = .92), were lower when data included wheat middlings (r = .90), but were unreliable when data included soybean meal and corn gluten meal (r = .29). Prediction of CGA values from in vitro digestibility was less reliable (r = .42) than that using TAAA values. There was agreement between values for lysine availability when determined for six grain samples by CGA and TAAA (r = .79). Evaluation from the correlations of the in vitro with the in vivo estimates of availabilities indicated that terminal filtration by a membrane of medium pore size (10,000 Dalton) or continuous filtration by a membrane of very low pore size (500 Dalton) made separations superior to those of terminal filtration (500 Dalton) and TCA precipitation.

Estimation of the endogenous N proportions in ileal digesta and faeces in 15N-labelled pigs

Four 40 kg castrated male pigs fitted with simple 'T' cannulas in the terminal ileum were given 15N-labelled ammonium salts, added to a low protein diet, for 6 days. Excretion of 15N in urine and faeces was monitored daily throughout the labelling and subsequent experimental periods. During the experimental period the pigs were given a diet based on wheat and fish meal, supplemented with varying levels of partially hydrolysed straw meal to give crude fibre contents ranging from 40 to 132 g/kg. After adaptation to the particular levels of straw meal, faeces and ileal digesta were collected during successive 24 h periods. N digestibility values were determined by the chromic oxide ratio method. The retention of 15N labelled non-specific N was 0.46 of the dose given. The validity of using urine values as a measure of 15N abundance in endogenous N was demonstrated by the similarity of 15N abundance in urine immediately before slaughter at the end of the experiment and in the digestive secretory organs thereafter. The average amount of endogenous N passing the terminal ileum was 3.4 g/day or 0.30-0.50 of total ileal N flow. This was not affected by dietary fibre level. The proportion of faecal N which was of endogenous origin was similar to that in ileal digesta, suggesting similar utilization of endogenous and residual dietary N by hindgut bacteria. Half the endogenous N entering the large intestine was reabsorbed there. Increasing dietary crude fibre from 40 to 132 g/kg increased faecal endogenous N excretion from 1.3 to 2.0 g/animal and day.

[The effect of straw meal on the crude protein and amino acid metabolism and digestibility of crude nutrients in broiler hen breeds. 1. Problems, experimental review and N-excretion in the urine]

The metabolization of the straw N and the influence of the straw on N excretion in urine were studied in 2 experiments with colostomized broiler hens and with 15N labelled wheat straw as well as 15N labelled wheat. In experiment 1 the test animals divided up into 4 groups received 0 g, 20 g, 30 g and 40 g straw meal per animal and day in addition to 120 g mixed feed. The daily 15N-excess (15N') intake from the straw was 18.4 mg, 27.5 mg and 36.7 mg. The amount of 15N' daily consumed with the labelled wheat in experiment 2 was 119.7 mg. 40 g straw meal resulted in a significantly increased amount of urine (p less than 0.05). The amounts of urine N and uric acid N were only increased as a tendency. On average the productive N decreased as a consequence of the straw meal supplement from 1070 mg/animal and day (control) to 764 mg/animal and day after 40 g straw meal supplement. The productive 15N' of the labelled wheat was not influenced by the straw meal supplement. The productive 15N' of the straw increased from 3.8 mg/animal and day (20 g straw) to 13.4 mg/animal and day (40 g straw). In contrast to 15N wheat, straw as a 15N source resulted in a lower labelling of uric acid N in comparison with urine N. It can be assumed that the changed metabolization of the straw N is influenced by microbial processes in the intestines.

[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.

[Dependence of intestinal excretion of amino acids on the amino acid content of animal feed. 2. Intestinal excretion of amino acids feeding soybean oil meal]

In an experiment with 20 15N-labelled growing rats the excretion of amino acids and the excretion of metabolic faecal amino acids were investigated after the feeding of soybean oil meal as sole protein source. A low, yet statistically significant increase of the excretion of amino acids and metabolic faecal amino acids was ascertained in accordance with a growing quota of soybean oil meal in the ration. The true digestibility of amino acids ascertained according to conventional methods is above 90% and, under consideration of the increase of metabolic faecal amino acids, on average increases by 3.5 digestibility units (1.4 to 6.2).

[Dependence of metabolic fecal amino acids on the amino acid content of the feed. 1. Metabolic fecal amino acids of rats fed with maize]

The amount of metabolic fecal amino acids (MFAA) in dependence on the amino acid intake was determined for graded maize rations with 15N-labelled rats and the quota of labelled endogenous amino acids in faeces was calculated according to the isotope dilution method. The excretion of amino acids and MFAA in faeces are described as functions of the amino acid intake for 17 amino acids and regressively calculated. For all 17 amino acids investigated, there was a more or less steep increase of MFAA according to an increasing amino acid intake. In contrast to MFAA in N-free feeding, MFAA in feeding with pure maize (16.5% crude protein) increase to the 2- to 4.5-fold value. The thesis of the constancy of the excretion of MFAA can consequently be no longer maintained. The true digestibility according to the conventional method is, on an average of all amino acids, 7.3 units below the one ascertained according to the 15N-isotope method. For the limiting amino acids lysine and threonine the difference is biggest (23 resp. 17 units). Tryptophane as first limiting amino acid could not be determined. The true digestibility of nearly all amino acids ascertained for maize according to the isotope method is above 90%. For the limiting amino acids the expenditure resp. the loss of endogenous amino acids is biggest.

[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.

[Investigations of the connection between the quality of protein, the protein level and endogenous N-excretion]

The influence of various protein qualities as well as of different levels of protein on the amount of endogenous N-excretion, metabolic fecal nitrogen (MFN) and endogenous urinary N (EUN) was determined at growing albino rats. The test rations were labelled with admixtures of 15N-DL-methionine resp. 15N-DL-lysine or contained feed protein enriched with 15N. EUN and MFN and their sum (the N maintenance requirement) showed the influence of the respective protein source and its dependence on the protein level. The endogenous N-excretions showed an opposite tendency to the N-balance; for high-quality protein feedstuffs with a high N-balance (e.g. dried eggs) they are lower than for protein source of inferior quality, with a low N-balance only (e.g. wheat gluten). Presumably this interaction of retention and maintenance is due to the complementary effect of exogenous and endogenous amino acids in the N-resp. amino acid-pool. Provided that the N-dose and the liver weight of the animals are comparable, the N-balance appears to be more suitable as parameter for the description of the protein quality and the calculation of the protein utilisation than N-retention, as the sum of N-balance and the values of MFN and EUN (depending on the feedstuffs and the N-level).

[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 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)]

Growing pigs with ileum and ileocecal re-entrant canulae were given 5 different rations (pig fattening feed 1 and 2, rations with dried skim milk, wheat gluten + lysine and wheat + wheat gluten + lysine). The crude protein and amino acid excretion was quantitatively determined with ileum chyme and feces. The calculation of the amino acid balances (apparent and true digestibility) at the end of the small intestine, at the end of the wholedigestive tract and the isolated colon showed characteristic differences for the individual amino acids. On ileum level the amino acids with relatively high endogenous quotas, threonine, tryptophane, alanine, aspartic acid and glycine showed a distinctly lower, the amino acids arginine, methionine, phenylalanine, glutamic acid, proline and tyrosine a distinctly higher digestibilityhan crude protein. In comparison of the values on the feces level, including the true digestibility, these differences are largely balanced out. At the end of the small intestine the absorption of the amino acids is in the main completed. The disappearance rate of amino acids from the colon shows large differences with reference to the different rations as well as the individual amino acids. They were particularly high for various rations as far as proline, tryptophane, glycine and cystine are concerned. If wheat gluten + lysine rations were given, a net synthesis of methionine in the colon could be proved.

[New method of checking the quality of food proteins required for maintenance. 2. 15N excretion in feces of test rats labelled with 15N after feeding with different protein sources]

For 7 days 37 test rats received a casein diet with an extra of 6.6 mg 15N-excess in the form of ammonium acetate. From the eighth test day onwards 4 resp. 5 rats each received various protein sources under maintenance conditions (115 kcal/kg body mass0,75). The atom-% 15N-excess was determined in feces, blood liver and muscles (urine cf. 1st information). The endogenous quota of N in the feces was calculated as follows: (formula: see text). The numerical value of the TCA-soluble fraction of N in the total blood was corrected by the decrease of the atom-%15N' in the last 12 hours (time for the passage of the fecel matter from small intestines to excretion). Since the endogenously excreted N-amount varied greatly according to different feed, a scale is proposed as biologic value of food proteins, which exclusively refers to the metabolic fecal nitrogen (MFN) under conditions of maintenance (abbr. MFN-BV). A proposal for its definition is: (formula: see text). Above that, a total BV is suggested which also refers to maintenance metabolism. The total BV is calculated as follows: (formula: see text). The following values were ascertained for MFN-BV and total BV: casein = 80 and 82; complete egg=68 and 67; fish meal=61 and 86; Torula yeast=31 and 46; peas=41 and 43; soya (assay protein)=73 and 61; wheat=47 and 71; gelatin=64 and 42. Finally, the recommendation is given to include in feed tables real digestibility values for food proteins ascertained with the 15N method. In the above mentioned order the following values of the real digestibility of proteins were ascertained with the 15N method and classical methods: casein=98.2 and 97.2; complete egg=100.0 and 98.7; fish meal=96.9 and 93.4; Torula yeast=83.0 and 67.6; peas=97.1 and 85.6; soya (assay protein)=98.3 and 96.4; wheat=95.7 and 87.3; gelatin=99.1 and 96.0. *cf. 1st information Bergner et al. (1978)

[Tracer studies in rats with 15N labeled wheat for the determination of endogenous and exogenous fecal nitrogen]

In an experiment with growing Wistar rats of 100 g live weight the N-values and the 15N-frequency of the nitrogen in feces, urine and the experimental carcasses were determined after feeding 15N-labelled wheat. Proceeding from CZARNETZKI's multicompartment model (1969) for N-metabolism in monogastric animals, the measured data were used to calculate the endogenous and exogenous fecal N-proportion of total nitrogen. In agreement with earlier studies the intestinal nitrogen loss was found to rise as the protein intake increased. In this experiment, the intestinal nitrogen loss went up from 8.2 mg N/animal and day (N-free diet) to 33.9 mg N/animal and day at a daily nitrogen intake of 240 mg/animal and day. The true digestibility of the wheat protein (determined by taking into account the rise of fecal N loss) was 97.2% this value being 8.4 units higher than the true digestibility calculated by the conventional regressive method of fecal analysis with a constant value being taken for fecal N loss. In connection with earlier findings, this experiment allows to draw the conclusion that the true digestibility determined conventionally by regression analysis does not reflect the actual digestibility of the protein.