Endogenous lysine in ileal digesta in the growing rat determined using different methods

BACKGROUND: Endogenous lysine in ileal digesta has been determined directly using highly digestible proteins and hydrolysates and assuming a complete absorption of dietary amino acids. In this study, the endogenous lysine in the ileal digesta of rats fed casein was determined using the guanidination method (baseline) and directly (assuming complete digestion and absorption) for casein and a highly hydrolysed casein. The peptide alimentation/ultrafiltration technique was also used to determine the endogenous ileal lysine for the casein hydrolysate (Peptopro®). RESULTS: Mean endogenous ileal lysine for rats given the unguanidinated casein and determined directly assuming complete digestion and absorption (644 mg kg^?1 dry matter intake (DMI)) or for a highly hydrolysed casein with the same assumption (596 mg kg^?1 DMI) was significantly (P < 0.05) higher than the endogenous ileal lysine for casein determined using the guanidination method (274 mg kg^?1 DMI). The endogenous lysine in ileal digesta for a casein hydrolysate determined using the alimentation/ultrafiltration method (302 mg kg^?1 DMI) was not significantly (P < 0.05) different from that based on the guanidination method but was significantly (P < 0.05) lower than the equivalent endogenous lysine determined directly. CONCLUSION: Dietary amino acids are not completely absorbed from casein or its hydrolysate and determining endogenous amino acids in ileal digesta directly, assuming complete absorption, overestimates the amount of endogenous ileal amino acids. Copyright © 2009 Society of Chemical Industry     

Endogenous lysine and other amino acid flows at the terminal ileum of the growing pig (20 kg bodyweight): The effect of protein-free,synthetic amino acid,peptide and protein alimentation

Twenty-four crossbred pigs of 15 kg initial bodyweight were fed four semi-synthetic diets for 10 days according to a completely randomised design. The study aimed to determine the effects of state of body nitrogen balance and the presence of dietary peptides and protein in the digestive tract on the excretion of endogenous amino acids from the ileum of the pig. Endogenous lysine excretion was determined for pigs given a protein-free (PF) diet, an enzymically hydrolysed casein- (EHC), a zein- (ZN) or a synthetic amino acid- (SAA) based diet. Digesta from the EHC-fed animals were centrifuged and ultrafiltered after collection and the precipitate plus retentate fraction was used to determine the endogenous flows. Such processing excludes unabsorbed dietary amino acids from the measure of endogenous loss. ZN is naturally deficient in lysine and tryptophan and these two amino acids were omitted from the synthetic amino acid-based diet to allow direct measurement of endogenous lysine flow. Pigs given the ZN and SAA diets received free lysine and tryptophan orally throughout the study except for the final 2 days of the study, when these amino acids were infused intravenously. Endogenous flows for amino acids other than lysine were determined for pigs given the PF and EHC diets. On the final day of the study the pigs were given their daily dietary allowance hourly and killed 10 h after the start of feeding. Digesta were collected from the terminal ileum (20 cm anterior to the ileo-caecal junction) and endogenous flows were determined by reference to the marker chromic oxide. The mean endogenous ileal lysine flows for the ZN- and EHC-fed pigs were not significantly different (overall mean, 419 mg kg^?1 dry matter intake), but were higher (P < 0.05) than those for the PF- and SAA-fed pigs (overall mean, 268 mg kg^?1 dry matter intake) whose mean flows were not significantly different from each other. The mean endogenous ileal flows for amino acids other than lysine were higher (P < 0.05) for the EHC-fed pigs compared to the animals on the PF diet, except for proline, glycine and arginine. The similar endogenous ileal lysine excretion for pigs receiving a SAA-based diet and in positive body nitrogen balance, and PF-fed pigs in negative body nitrogen balance, indicates that negative body nitrogen balance per se does not lead to a lowered endogenous ileal excretion. It would appear, however, that the presence of dietary peptides or protein in the gut increases amino acid excretion at the terminal ileum above that found with PF or SAA alimentation. Consequently, endogenous ileal amino acid flow in the pig may be underestimated when determined by the traditional PF method.     

An effect of dietary protein content on endogenous ileal lysine flow in the growing rat

The aim of this study was to determine whether dietary protein content influences endogenous ileal lysine flow in the growing rats. Male rats (n = 72; mean body weight 170 g) were given free access to experimental diets for 10 min each hour for 8 h each day. The rats received diets containing 50, 100, 150 or 200 g kg^?1 zein for 8 days. Zein is virtually devoid of lysine and this allows a direct determination of gut endogenous lysine losses. The diets were supplemented with synthetic lysine and tryptophan for the first 6 days. Over the final 2 days of the 8‐day period, synthetic lysine and tryptophan were given to the rats via intraperitoneal injections. The rats were euthanized on day 8 and digesta were sampled from the terminal ileum. Digesta were pooled to give a total of six digesta samples for each experimental diet and the flows of endogenous lysine at the terminal ileum were determined by reference to the marker, chromic oxide. Increasing the amount of zein in the diet led to a significant (P < 0.001) increase in the mean flow of endogenous lysine through the terminal ileum from 391 to 558 µg g^?1 dry matter intake (overall SEM = 33.3) when the rats received diets containing 50 and 200 g kg^?1 zein, respectively. Copyright © 2006 Society of Chemical Industry     

Determination of True Ileal Amino Acid Digestibility in Feedstuffs for Pigs with the Linear Relationships between Distal Ileal Outputs and Dietary Inputs of Amino Acids

This study was carried out to investigate the methodological aspects of extrapolating the ileal losses of endogenous amino acids (AA) with linear relationships between the distal ileal outputs and dietary inputs of AA. Six barrows, average initial body weight 35 kg, were fitted with a simple T-cannula at the distal ileum and fed six diets according to a 6×6 Latin square design. Six maize starch-based diets containing six levels of crude protein (CP) and AA from soya bean meal (4, 8, 12, 16, 20 and 24% CP, respectively) were formulated. Chromic oxide (4 g kg^-1 diet) was included as the digestibility marker. Each experimental period consisted of 8 days. Ileal digesta were collected, at 2 h intervals, for a total of 24 h during days 7 and 8. There were strong linear relationships (P<0·01) between the ileal outputs and dietary inputs of AA. Differences in ranges of graded dietary levels of AA affected the linearity and caused large differences in the extrapolated levels of ileal endogenous AA. Therefore, the design of a suitable range of graded dietary levels of AA is the most important methodological consideration for the determination of endogenous AA losses and the true ileal digestibility values of AA with the linear relationship. For CP and the essential AA, the true ileal digestibility values (%) in soya bean meal and the ileal endogenous losses (g kg^-1 dry matter intake, in parentheses) were as follows: CP, 89·4 (16·4); arginine, 96·1 (0·68); histidine, 92·4 (0·24); isoleucine, 91·7 (0·45); leucine, 90·7 (0·69); lysine, 90·5 (0·48); methionine, 93·6 (0·13); phenyl-alanine, 92·5 (0·38); threonine, 86·5 (0·71) and valine, 90·3 (0·56). Furthermore, the levels of endogenous AA extrapolated with the linear relationships between the ileal outputs and dietary inputs of AA were very close to the values estimated with the linear relationships between the dietary contents of apparent ileal digestible and total AA, suggesting that both models of linear relationships can be used as the regression analysis technique for determination of ileal losses of endogenous AA and true ileal digestibility values of AA in feedstuffs for pigs. © 1997 SCI.     

Comparison of methods to determine the endogenous amino acid flow at the terminal ileum of the growing rat

The aim was to compare a recently developed peptide alimentation method and the protein-free and regression methods for determining endogenous ileal nitrogen (N) and amino acid excretion in the rat, and to apply the endogenous loss estimates to determine the true ileal digestibility of a meat and bone meal (MBM). Preliminary investigations determined the effect of the time of sampling of digesta after a meal (slaughter method) for rats given a protein-free or an enzymically hydrolysed casein (EHC) based diet, on ileal digesta and endogenous N excretion. There was a significant (P < 0.05) effect of the time of sampling on the amount of digesta collected and the endogenous N excretion for both the EHC and protein-free fed rats. The amount of digesta collected from the terminal 20 cm of ileum and the endogenous N excretion for both the EHC and protein-free fed rats were greatest and least variable at 3 h post-feeding. In the main study, endogenous ileal amino acid excretions were determined in the growing rat fed an EHC-based diet (n = 6) and with subsequent treatment of the digesta using ultrafiltration or in six rats given a protein-free diet or by extrapolation from data for 30 animals given five diets which contained graded levels of MBM as the sole protein source. For the EHC treatment, the ileal digesta precipitate plus retentate was used to determine the endogenous flows. The ultrafiltration step excludes unabsorbed dietary amino acids from the measure of endogenous loss. Chromic oxide was the reference marker in all diets. The endogenous N flows determined by the protein-free and regression methods were similar but both significantly (P < 0.01) lower than those for rats fed the EHC-based diet. The mean endogenous ileal N flows determined by the peptide alimentation method, the protein-free and regression approaches were 1866, 1103 and 1019 μg g^?1 freeze dry matter intake, respectively. The endogenous amino acid flows at the terminal ileum were lower when determined using the traditional protein-free or regression methods. The true ileal digestibility coefficients for MBM were considerably higher based on the EHC versus protein-free endogenous flows.     

Effect of condensed tannin in cottonseed hulls on endogenous ileal amino acid loss in the growing rat

The effect of condensed tannin (CT) in cottonseed hulls (CSH) on endogenous ileal amino acid flow in the growing rat was evaluated. CSH contain around 900 g kg^?1 fibre and 52 g kg^?1 total CT. Twenty-four rats were allocated to four semi-synthetic diets, which contained enzymically hydrolysed casein (EHC) as the sole source of dietary nitrogen and chromic oxide as an indigestible marker. Two of the diets contained no CSH while the remaining two contained 50 g kg^?1 CSH. At each level of hull inclusion (0 and 50 g kg^?1), polyethylene glycol (PEG: MW 3500) was added (6 g kg^?1) to one of the diets. The effect of CT was assessed by determining endogenous ileal amino acid loss in the presence or absence of PEG, which binds and inactivates CT. The rats were given their respective experimental diets ad libitum for 14 days. Samples of digesta were collected at slaughter from the terminal 15 cm of ileum. The digesta samples were centrifuged and the supernate ultrafiltered. The precipitate plus retentate (MW > 10000) fraction affords an estimate of endogenous loss. Inclusion of CSH in the EHC based diet increased ileal flow of total nitrogen (1387 versus 1623 μgg^?1 dry matter intake; P ≤ 0.05), increased ileal flow of total amino acids (23%; P ≤ 0.01), and significantly increased ileal flow of several individual amino acids. There was no significant effect of PEG and no PEG × diet interaction; showing that the CSH effects could not be explained by action of CT. The presence of hulls in commercial cottonseed meal would appear to contribute to the reported low apparent ileal amino acid digestibility coefficients for cottonseed meal by increasing endogenous ileal amino acid flow, but this effect is not due to the CT component of the hulls.     

Ileal digestibility of defatted soybean,lupin and chickpea seed meals in cannulated Iberian pigs: I. Proteins

Five castrated male Iberian pigs (100 ± 2 kg body weight) fitted with T‐shaped cannulas at the terminal ileum were used to determine ileal digestibility of legume seed meals. The diets were based on defatted soybean, lupin or chickpea seed meals and contained similar levels of digestible energy (14.2–15.1 kJ g^?1) and protein (107 g kg^?1). Protein‐free and a hydrolysed casein diets were used to study endogenous ileal amino acid flows. Chromium oxide (10 g kg^?1 diet) was added to the diets as an indigestible marker. Ileal flows in pigs fed the hydrolysed casein diet were different (p < 0.05) in amino acid contents and composition from those on the protein‐free diet. Ileal sialic acid flows in pigs fed lupin‐ or chickpea‐based diets were higher (p < 0.05) than those of animals fed soybean or casein diets. Among essential amino acids, only the apparent ileal digestibilities of phenylalanine and valine in lupin meal were lower (p < 0.05) than those in soybean. Apparent ileal digestibilities of lupin aspartate and proline, together with chickpea aspartate, were also lower (p < 0.05) than those of soybean. True ileal digestibility of nitrogen in pigs fed lupin or chickpea meals, calculated according to values from animals fed the protein‐free diet, was lower (p < 0.05) than that for soybean or casein. Among individual essential amino acids, only the true ileal digestibility of phenylalanine in lupin was lower (p < 0.05) than that in soybean. True ileal digestibility of nitrogen calculated according to values obtained with pigs fed a hydrolysed casein diet was not different among soybean, lupin or chickpea meals. Among essential amino acids, only the true ileal digestibilities of isoleucine and lysine in chickpea were lower (p < 0.05) than those of soybean. It is concluded that true ileal nitrogen and amino acid digestibilities of lupin and chickpea meals are comparable to those of defatted soybean in Iberian pigs. The results with protein‐free diets tended to underestimate endogenous protein secretion in pigs fed on diets containing protein. Copyright © 2005 Society of Chemical Industry     

Estimates of basal ileal endogenous losses of amino acids by regression analysis and determination of standardised ileal amino acid digestibilities from casein in newly weaned pigs

BACKGROUND: This study was carried out to estimate basal ileal endogenous crude protein (CP) and amino acid (AA) losses (IAAL_B) in newly weaned pigs by regression analysis from apparent ileal digestible and the corresponding total dietary contents of CP and AA in order to obtain standardised ileal digestibilities (SID) of CP and AA originating from casein. A total of fourteen 3‐week‐old barrows were fitted with simple T cannulas at the distal ileum and were fed six diets with two pigs per diet in 4 weekly repeated measurements. Corn starch‐based diets containing six graded levels of CP from casein with 90, 155, 220, 285, 350 and 415 g kg^?1 CP (as‐fed basis) were formulated. RESULTS: Linear relationships (P < 0.001) between apparent ileal digestible and total dietary contents of CP and AA (g kg^?1 dry matter intake (DMI)) exist for CP and all AA in the range of 90–220 g kg^?1 CP content in the diet. The IAAL_B extrapolated from the range of 90–220 g kg^?1 CP content are different from zero (P < 0.001 to P = 0.019) except for tryptophan (P = 0.220). Based on regression analysis in the range of 90–220 g kg^?1 CP, estimates of IAAL_B, expressed as g kg^?1 DMI, and SID of CP and AA in casein (in parentheses, %) were as follows: CP 9.3 (98.0); arginine 0.4 (98.9); histidine 0.2 (98.5); isoleucine 0.2 (98.1); leucine 0.5 (99.2); lysine 0.4 (99.0); methionine 0.1 (99.1); phenylalanine 0.4 (99.9); threonine 0.6 (97.8); tryptophan 0.1 (96.2); valine 0.4 (98.5). CONCLUSION: The IAAL_B and SID of CP and AA originating from casein in newly weaned pigs are in close agreement with values obtained in grower finisher pigs. Copyright © 2007 Society of Chemical Industry     

The effect of food dry matter intake on endogenous ileal amino acid excretion determined under peptide alimentation in the 50 kg liveweight pig

The daily ileal excretion of amino acids was measured at different food dry matter intakes for the 50 kg liveweight pig under conditions of peptide alimentation. The experiment comprised two cross-over design trials each involving four pairs of entire male pigs fitted with simple T-cannulae at the terminal ileum and fed a hydrolysed casein semi-synthetic diet. Each pair of pigs received one of four sequences of food dry matter intake arranged in a Latin square design, namely 0.06, 0.08, 0.10 and 0.12 (Trial 1) and 0.05, 0.07, 0.09 and 0.11 (Trial 2) of metabolic body weight (W^0.75) day^?1. Each pig received the diet at its described level of intake for 8 days, with continuous 24 h collection of ileal digesta on the fifth and eighth days. Chromic oxide was included in the diet to permit correction of ileal flows to complete digesta collection. Pooled digesta from each pig at each level of dry matter intake were centrifuged and ultrafiltered and the high-molecular-weight fraction was analysed for amino acid and nitrogen contents. There were significant (P < 0.05) linear relationships between endogenous ileal amino acid, nitrogen and dry matter excretion (mg day^?1) and food dry matter intake (g day^?1) except for lysine, glutamic acid and phenylalanine which increased in a curvilinear manner (P < 0.05). The results indicate that dietary dry matter intake influences endogenous excretion from the ileum. The relationships, determined under physiological conditions, provide preliminary data on the magnitude of small intestinal amino acid loss in the young growing pig.     

The effect of amino acid and peptide alimentation on the determination of endogenous amino acid flow at the terminal ileum of the rat

Endogenous ileal amino acid (free + bound) flow was determined in four 190-g male rats given a diet whose sole nitrogen source was enzyme hydrolysed casein and compared with that of six rats whose diet contained synthetic amino acids as the only nitrogen source but excluding alanine, glutamic acid and serine, and six rats fed a protein-free diet. The enzyme hydrolysed casein, a mixture of free amino acids and oligopeptides, was assumed to be completely absorbed in the small intestine of the rat. A further seven rats were given an enzyme hydrolysed casein-based diet and their ileal digesta were treated, post-collection, with perchloric acid to precipitate soluble proteins. The latter procedure removed the need to assume complete absorption of the casein nitrogen. The endogenous flow of amino acids for enzyme hydrolysed casein-fed rats was higher than that for the protein-free diet (P < 0.05) which did not differ from the synthetic amino acid diet for the flows of alanine, glutamic acid and serine. The high apparent digestibility of the synthetic amino acids not excluded from the diet indicated that their ileal excretions were mainly of endogenous origin. It would appear, therefore, that the protein deplete state per se does not influence endogenous amino acid flow at the terminal ileum of the growing rat, but there is a direct effect of small peptides on the net loss of endogenous amino acids from the small intestine. The estimates of endogenous amino acid flow obtained following the perchloric acid treatment of digesta were unrealistically low and thus inconclusive, but raised doubt as to the eficiency of perchloric acid in precipitating protein from rat ileal digesta.     

Digestible reactive lysine in selected milk-based products

Reactive lysine contents, true ileal reactive lysine digestibility, and true ileal digestible reactive lysine contents were determined in a wide range of processed milk products. A previously validated assay based on determining reactive lysine in both food and ileal digesta, after reaction of these materials with O-methylisourea, was applied. Semisynthetic diets containing milk products as the sole sources of protein and including chromic oxide as an indigestible marker were fed to growing rats. Digesta from the terminal ileum were collected posteuthanasia and, with samples of the diets, analyzed for reactive lysine (homoarginine) contents. True reactive lysine digestibility was determined after correcting for endogenous lysine loss at the terminal ileum of rats fed an enzyme hydrolyzed casein-based diet, followed by ultrafiltration (5000 Da) of the digesta. Digestible total lysine (determined using conventional methods) was also determined. The true ileal reactive lysine digestibility was high (>91%) in all the milk products tested, but was highest in the UHT milk (100%) and lowest in the infant formulas (91 to 93%). Total lysine digestibility (conventional measurement) significantly underestimated reactive lysine digestibility for all the products tested. The mean underestimation ranged from 1.3 to 7.1% units. The mean digestible total lysine content was significantly different from the available lysine content for most of the products examined. In some cases this difference was small (<3%), but for a number of the products (evaporated milk, whole milk protein, lactose hydrolyzed milk powder, and a sports formula) the difference was greater (6.5 to 14%). This would suggest firstly that total lysine and total lysine digestibility determined using conventional methods were inaccurate when applied to some milk-based foods, and secondly that some of the milk products have undergone lysine modification. In general, milk proteins are a highly digestible source of amino acids and lysine.     

The effect of food dry matter intake on the flow of amino acids at the terminal ileum for rats fed an enzyme‐hydrolysed casein‐based diet

The aim of the study was to determine whether food dry matter intake had an effect on endogenous ileal amino acid flows in the rat when the flows were expressed in units of mg g^?1 dry matter. Eighty 200 g body weight rats were trained for 7 days to consume a casein‐based diet over a daily 3 h feeding period, and then an enzyme‐hydrolysed casein (MW < 5000 Da)‐based diet, with chromic oxide as an indigestible marker, was fed for a further 8 days. The mean ratio of food intake to metabolic body weight over all 80 rats was determined on days 11 and 12. On day 15, food was offered to groups of 10 rats at each of eight intake levels. The intake levels were calculated from the mean food intake value and individual metabolic body weights and scaled in increments of 0.1 by factors ranging from 0.3 to 1.0. Digesta were collected from the terminal ileum 3 h after the start of the meal, and endogenous ileal amino acid flows were determined after amino acid and Cr analyses of the diet and endogenous ileal digesta fractions prepared by centrifugation and ultrafiltration (10 000 Da molecular weight cut‐off). The linear regression relationships between ileal amino acid flows, expressed as mg g^?1 dry matter, and dry matter intakes demonstrated that all slopes were negative but that the slopes for nine of these amino acids were not significantly different from zero (P > 0.05). There were significant slopes (P < 0.05) for the other eight amino acids, although the magnitudes of the effect were small. When the data were re‐examined after removing the lowest feeding level, the slopes for most of these amino acids were no longer statistically significant. The results showed that the measures of amino acid flow (mg g^?1 dry matter), except for isoleucine and cystine, over a wide range of food intakes were not materially affected by food intake. From the perspective of bioassay logistics the results indicate that expressing ileal amino acid flows proportional to dry matter intake is justified over the range of intakes found in practice for determining true ileal amino acid digestibility by the enzyme‐hydrolysed casein method. © 2002 Society of Chemical Industry     

The 15N-isotope dilution method for determining ileal endogenous nitrogen excretion in the young (10 kg liveweight) pig

A study was conducted with four crossbred 5-week-old castrated male pigs at an average body weight of 10 kg to determine the endogenous amino acid and nitrogen flows at the terminal ileum using the peptide alimentation and ¹⁵N-isotope dilution methods. The pigs were fitted with a post-valvular T caecal cannula and two indwelling blood catheters. They were fed a cornstarch-based semisyn'hetic diet formulated to contain enzymically hydrolysed casein (EHC) as the sole source of nitrogen at twice their maintenance requirement for energy. Digesta were centrifuged and ultrafiltrated after collection and the precipitate plus retentate fraction (mol wt > 10000) was used to determine the endogenous amino acid and nitrogen flows. To estimate the endogenous N flow at the terminal ileum of these EHC-fed pigs using the ¹⁵N-isotope dilution method a constant 10 day ¹⁵N-leucine infusion was performed at a daily rate of 5-04 mg of ¹⁵N-leucine (95% ¹⁵N enrichment) kg^?1 body weight. The mean ¹⁵N-enrichments above background for the trichloroacetic acid soluble blood plasma and ileal digesta nitrogen pools were 0.0249 and 0.0178, respectively. There were no statistically significant differences for ¹⁵N-enrichment excess between the days of ileal digesta collection. The results demonstrated that glutamic acid, aspartic acid, proline and serine formed about 50% of the total ileal endogenous amino acid flow. The total daily amount of endogenous amino acid flow at the terminal ileum was 6.2 g day^?1. The endogenous ileal N flows determined with the peptide alimentation and the ¹⁵N-isotope dilution methods were similar (P = 0.40) at 1.37 and 1.17 g day^?1, respectively. Endogenous N as a proportion of total N flow passing the terminal ileum was 83% and 72% for the peptide alimentation and the ¹⁵N-isotope dilution method, respectively. The study provides some support for application of the ¹⁵N-isotope dilution method with pigs.     

Evaluation of the isotope dilution technique for determining ileal endogenous nitrogen excretion in the rat

Three body amino acid pools (plasma free, plasma bound and small intestinal tissue) were evaluated as precursors to allow measurement using the isotope dilution technique of endogenous excretion at the terminal ileum of animals. Eighteen 150-g bodyweight rats were given either a protein-free, an enzyme-hydrolysed casein based or a synthetic amino acid based diet, and digesta were collected from the terminal ileum. The animals had been subjected to a constant 8-day infusion of tritiated leucine via subcutaneously implanted osmotic mini pumps. Specific activities (dpm nM^?1 leucine) of the ileal digesta and the plasma free, plasma bound and small intestinal tissue pools were determined and the specific activity for the ileal digesta was expressed as a proportion of the respective precursor pool value to give dilution factors for each dietary treatment. For the protein-free diet, where the ileal nitrogenous flow is endogenous by definition, the dilution factor for an appropriate precursor pool would be unity. For the hydrolysed casein and synthetic amino acid diets, in which the peptides and amino acids are expected to be virtually completely absorbed anterior to the ileum, high dilution factors (close to unity) would be expected. The mean dilution factors based on the plasma free amino acid pool were untenably low (0-2 to 0-3). For the plasma bound amino acid pool mean dilution factors of 1-3 were found for animals given the protein-free and synthetic amino acid diets, while a lower value (0-7) was obtained for the hydrolysed casein treatment. Untenably high factors (1-5) were found with the small intestinal tissue for the protein-free and synthetic amino acid treatments, while the corresponding value for the hydrolysed caseinfed rats was unity. The dilution factor data within treatments were highly variable, and none of the pools examined gave consistently reliable results and could thus be accepted as a valid precursor pool for the endogenous proteins.     

The availabilities of lysine,methionine and tryptophan in Pruteen by chick growth assay

The concentrations of available lysine, methionine and tryptophan in the single-cell protein, Pruteen^a (ICI), have been determined by growth assay with young chicks. Symmetrical, six-point, parallel-line assays were used with weight gain and gain: food ratio as responses. All diets were balanced as far as possible, especially with respect to essential amino acid composition. Concurrently with the determination of each amino acid in Pruteen, its contents in typical fish and soya bean meals were determined. The assays were acceptable by the statistical criteria used. They yielded estimates of potencies that were realistic in relation to the total contents of lysine, methionine and tryptophan in Pruteen, fish and soya bean meals. The variances of potency estimates were typical of such assays. The values obtained for Pruteen considering both weight gain and gain:food ratio as responses, were about 40 g lysine, 18 g methionine and 8.7 g tryptophan kg^?1 air-dry matter. For lysine and methionine these represent high availabilities of total amino acids. The availability of tryptophan is less clear because of uncertainty about the total content of tryptophan in Pruteen.     

Stoichiometric dye-binding procedure for the determination of the reactive lysine content of soya bean protein

A new analytical method has been developed for the determination of the reactive lysine content of soya bean protein. The method is based on the reaction of the free basic groups of the protein with 1-phenylazo-2 naphthol-6,8 disulphonic acid. With regard to the stoichiometry of the procedure, it has been proved, contrary to earlier reports, that the basic amino acids, histidine, arginine and lysine, each combine with one mole of the dye. After acylation with propionic anhydride lysine alone loses its dye reactivity. The usefulness of the proposed method has been demonstrated by the determination of the reactive lysine content of several untreated, heat-treated and acid-treated soya bean samples. The results show that heat damage of about 5% in reactive lysine content can be measured in 1·5 h with good reproducibility.     

Prediction of apparent heal protein digestibility in pigs with a two-step in-vitro method

The use of a two-step in-vitro method to predict the in-vivo ileal digestibility of proteins in pigs was investigated. It proved not possible to predict accurately the ileal protein digestibility with the in-vitro method. By dividing the samples into groups of closely related products, a good relationship (r² = 0.93) between in-vivo and in-vitro data was only obtained for wheat products, where only five samples were analysed. For beans, peas, rapeseed products and soya bean products it was still not possible to predict the in-vivo protein digestibility (r² = 0.03-0.60). The in vivo-in vitro relationship was mainly determined by the properties of the proteins and the presence of antinutritional factors, such as lectins and trypsin inhibitors. The first influences both the in-vitro and in-vivo protein degradability and the latter only reduces the in-vivo degradability by stimulating the secretion of endogenous protein. It is suggested that, with the in-vitro method, real ileal digestibility of proteins is predicted. The apparent ileal protein digestibility can only be predicted with the in-vitro method after making corrections for the influence of these antinutritional factors on the secretion of endogenous protein. Possibly corrections are also needed for microbial protein, and protein which is solubilised in the small intestine but not absorbed because of the physical state of the chyme.     

Influence of dietary protein level and origin on the flow of mucin along the small intestine of the preruminant calf

The objective of this study was to investigate the effect of the dietary crude protein (CP) content and origin on the flow of mucin protein along the small intestine of the preruminant calf. Diets contained 1, 10, 20 and 28% of CP supplied by skim milk powder (SMP) in experiment 1. Diets differed by the nature of protein [soybean protein concentrate (SPC), partially hydrolyzed soybean protein isolate (HSPI) or potato protein concentrate (PPC)] in experiment 2. Duodenal, jejunal, and ileal digesta were collected from calves fitted with simple cannulae and continuously infused the milk replacers into the abomasum. In experiment 1, the basal flow of mucin protein was 1.1, 1.8, and 4.0 g/kg of dry matter intake at the duodenum, jejunum, and ileum, respectively. Mucin protein contributed to 19 and 40% of ileal loss of CP and lysine, respectively. When dietary CP rose from 1 to 28%, the flow of mucin protein increased at the duodenum (+300%). In experiment 2, the flow of mucin protein increased by 70% at the duodenum and at the jejunum when SMP was partially replaced by SPC and HSPI. With PPC, this flow increased at the duodenum (+24%) and ileum (+52%). These data demonstrate the importance of mucin as a source of endogenous nitrogen and the impact of dietary protein content and origin on this flow.     

Effects of methionine addition in soya bean or casein diets supplemented with carrageenan on weight gain and blood lipids in rats

Seven groups of 12 Wistar rats were fed during two experimental periods. During the first period of 4 weeks, rats were fed diets containing 100 g kg^?1 of casein or soya-protein. In the case of casein, diets contained casein, casein + 3.5 g kg^?1 of sodium carrageenan and casein + 3.5 g kg^?1 of sodium carrageenan + 1 g kg^?1 of DL-methionine. In the case of soya protein, diets contained soya protein, soya protein + 6.2 g kg^?1 of sodium carrageenan, soya protein + 6.2 g kg^?1 of sodium carrageenan + 1 g kg^?1 of DL-methionine and soya protein + 1 g kg^?1 of DL-methionine. During the second period of 8 weeks, all rats were fed laboratory pellets containing 170 g kg^?1 of standard protein mixture. Methionine supplementation of heated soya bean meal containing carrageenan prevented the decrease of growth observed with unsupplemented diet. Methionine supplementation of casein improved protein efficiency ratio and had no effect on long-term growth of rats because carrageenan did not cause growth retardation. At the end of second period, carrageenan ingested during the first period had no effect on plasma cholesterol. When carrageenans added to casein were ingested during the first period, plasma triglycerides were significantly lower after the second period. It would seem that carrageenans induce protein malnutrition by a lack of methionine when they are present in low protein diets with low methionine content, and that a sufficient content of methionine in diets prevents the carrageenan effect.     

Effects of dietary rumen‐protected lysine on milk yield and composition in lactating cows fed diets containing double‐low rapeseed meal

This study investigated the effects of dietary rumen‐protected lysine (RPLys) on milk yield and composition in lactating cows fed diets containing double‐low rapeseed meal. Twenty‐four cows were divided into three groups and fed one of three dietary treatments: 10% soya bean meal (SBM) diet (control), 15% double‐low rapeseed meal (DLRSM) diet and 15% DLRSM + 32 g/d RPLys (DLRSML) diet. The results showed that no differences (P > 0.05) were observed in milk yield, 4% fat correction milk (FCM), energy correction milk (ECM), protein yield, milk fat yield, milk fat, lactose yield and lactose between control and DLRSM. Supplementation with DLRSML increased (P < 0.05) milk yield, 4% FCM, ECM, and protein yield compared with the SBM. The results indicated that DLRSM and DLRSML might be used to substitute for SBM as a protein source in lactating cows, and the latter might be more beneficial to improve the performance.