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.     

Determination of endogenous amino acid flow at the terminal ileum of the rat

In a comparative study endogenous amino acid flow was determined in twenty-four 190-g male rats (protein-replete) given diets containing synthetic amino acids as the sole nitrogen source but devoid of specific amino acids, and six rats fed a protein-free diet. Endogenous flows were not significantly different (P > 0.05) for aspartic acid, glutamic acid, serine and lysine but were significantly higher (P < 0.05) under protein-free alimentation than amino acid alimentation for proline, glycine and alanine. This indicates that the protein-free method did not lead to lowered endogenous amino acid excretions owing to an altered amino acid metabolism in the protein-free state. The loss of some amino acids may be enhanced under protein-free alimentation. The high apparent digestibility of the synthetic amino acids not excluded from the diets (histidine, arginine, threonine, valine, isoleucine, leucine, tyrosine, phenylalanine) indicated that their ileal excretions were mainly of endogenous origin. There were no significant differences (P>0.05) between the latter excretions and those obtained by feeding the rats a protein-free diet.     

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.     

Effectiveness of an ultrafiltration device for use with the enzyme‐hydrolysed protein method for determining endogenous ileal nitrogen and amino acid excretion in the pig

The aim of the work was to perform an in vitro study to determine the effectiveness of Centriprep‐10 concentrator devices for use with the enzyme‐hydrolysed protein method for the determination of endogenous ileal nitrogen and amino acid flows. Different amounts of enzyme‐hydrolysed casein (EHC) were added to tubes containing digesta collected from pigs that had received a protein‐free diet for 5–8 days. The samples were centrifuged and then ultrafiltered using Centriprep‐10 concentrators. The precipitate from the centrifugation step was added to the retentate from the ultrafiltration, and this material was analysed for nitrogen and amino acids. The ultrafiltrates were also analysed for nitrogen. The amount of nitrogen that was deemed to have originated from the EHC and remained in the precipitate plus retentate fraction of digesta after processing, expressed as a percentage of the total amount of nitrogen added to the tubes as EHC, ranged from 1.0 to 5.0%. The overall mean amounts of amino acid in the precipitate plus retentate fractions originating from the EHC, expressed as a percentage of the amino acids added to the tubes as EHC, ranged from 2.4 to 5.8%. The results demonstrate that with Centriprep‐10 concentrators there is a less than complete separation of nitrogen and amino acids originating from EHC from endogenous material in digesta, but for most amino acids this is unlikely to be due to binding of the amino acids to digesta. The incomplete separation of EHC from the endogenous fraction of digesta by Centriprep‐10 concentrators may lead to a small overestimation (approximately 2%) of endogenous ileal nitrogen and amino acid flows. © 2001 Society of Chemical Industry     

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.     

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.     

Endogenous amino acid flow at the terminal ileum of adult humans determined following the ingestion of a single protein-free meal

The study sought to determine endogenous total nitrogen and amino acid flows at the terminal ileum of adult humans. Six adults (65 ± 10 kg bodyweight) with well-established ileostomics fasted for 14 h before consuming a single protein-free meal (240 g) containing Celite (acid-insoluble ash) as an indigestible marker. Ileal digesta were collected for 8 h after the meal and endogenous flows were determined by reference to the marker. The mean (±SE) total 8 h output of digesta dry matter was 9.1 (± 3.51) g. The mean ileal flow of total nitrogen was 4.38 (± 0.770). with the mean amino acid flows ranging from 0.17 (± 0.009) for methionine to 2.26 (± 0.258) for glutamic acid (mg g^?1 food dry matter intake).     

Perchloric and trichloroacetic acids as precipitants of protein in endogenous ileal digesta from the rat

The efficacy of perchloric and trichloroacetic acids as precipitants of protein from endogenous digesta collected from the distal ileum of the laboratory rat was evaluated. Twelve 190-g male rats were fed a protein-free diet and samples of ileal digesta were collected after slaughter. The digesta were pooled, and subsamples were treated with PCA or TCA or were left untreated. For both precipitants more than half of the total nitrogen (N) remained in solution post-precipitation, and for the PCA and TCA treatments respectively at least 35 and 69% of the supernatant N was in the form of soluble protein. The amino acids (after acid hydrolysis) having the highest concentrations in the supernate are known to be abundant in the mucoproteins. Around 6.4 and 9.8% of the supernatant N was in the form of non-amino N (creatinine N + urea N + ammonia N) for the PCA and TCA treatments respectively.     

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.     

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.     

Effect of the duration of feeding of a protein‐free diet on endogenous ileal nitrogen and amino acid loss in the growing pig

The aim of the study was to determine whether endogenous nitrogen and amino acid excretions at the terminal ileum change over time in the growing pig fed a protein‐free diet for 8 days. Seven entire male pigs with an overall mean live weight of 81.6 kg (SEM 3.3 kg) and surgically implanted post‐valve T caecum cannulas were fed a semi‐synthetic casein‐based diet for 8 days. Food was withheld from the pigs for 24 h, after which they were fed a protein‐free diet for a further 8 days at a rate of 10% of metabolic body weight per day. Chromic oxide was included in the protein‐free diet as an indigestible marker. Ileal digesta were collected continuously from 13:00 to 18:00 h on each day of the experimental period. Endogenous ileal nitrogen flows were determined for each pig each day the protein‐free diet was given, and endogenous ileal amino acid flows for the first and eighth days. There were no significant (P > 0.05) effects of the duration of feeding of the protein‐free diet on endogenous ileal total nitrogen or amino acid flows, except for the amino acids glycine and cysteine, the flows of which significantly decreased over the 8 day period (P < 0.01 and P < 0.05 for glycine and cysteine respectively), from (mean ± SEM) 1639 ± 217 to 892 ± 212 µg g⁻¹ dry matter intake (DMI) for glycine and from 173 ± 13 to 127 ± 19 µg g⁻¹ DMI for cysteine. The relative contributions (moles of each amino acid as a proportion of total moles of amino acids) of threonine, glycine and cysteine decreased significantly (P < 0.05) and that of proline increased significantly (P < 0.05) during the 8 days that the protein‐free diet was fed to the pigs. © 2000 Society of Chemical Industry     

The effect of digesta sampling time and dietary protein source on ileal nitrogen digestibility for the growing rat

The effect of time that digesta were collected on the quantity and representativeness of ileal digesta and on the determination of apparent and true ileal nitrogen (N) digestibility for growing rats was investigated. Semi‐synthetic diets containing chromic oxide as an indigestible marker were given to 200 g live weight rats for 8 days as a single daily meal. The experimental treatments comprised six diets (lactalbumin, soy protein isolate, wheat gluten, fish, protein‐free (PF), enzymically hydrolysed casein (EHC)) and four ileal digesta sampling times (3, 4, 5 and 6 h after the start of feeding). On the eighth day the rats were fed and slaughtered according to treatment, and digesta were sampled from the terminal ileum. Endogenous ileal nitrogen excretion was determined using both the protein‐free and peptide alimentation methods. There was a significant (P = 0.027) effect of experimental diet averaged across sampling times for chromium recovery (CrRec). The CrRec was higher for the rats fed the PF diet than for the other diets. Responses to sampling time varied significantly (P < 0.05) among diets for ileal digesta weight (IDW), nitrogen/chromium (N/Cr) ratio, ileal digesta weight relative to dry matter intake (IDW/DMI), CrRec, N flow, apparent N digestibility and true N digestibility (determined using the protein‐free method). The optimal digesta sampling times for each of the diets were 3 h for PF, EHC, lactalbumin and fish and 4 h for soy protein isolate and wheat gluten. Consequently, 3 or 4 h after the start of feeding is recommended as the optimum ileal digesta sampling time for most purified protein sources when fed to the growing rat as a single daily meal. © 2002 Society of Chemical Industry     

Endogenous amino acid flow at the terminal ileum of the rat determined under conditions of peptide alimentation

The study aimed to determine endogenous ileal amino acid excretion in the growing rat fed an enzymically hydrolysed casein (EHC) based diet with subsequent treatment of the digesta using ultrafiltration technology. Comparison was made with endogenous excretions obtained from rats fed an EHC-based or a protein-free diet and without any treatment of the ileal digesta. Preliminary investigations were made to determine the filtration efficiency of the ultrafiltration devices and to examine three alternative prefiltration treatments, trichloroacetic acid (TCA) and perchloric acid (PCA) precipitation, and centrifugation (SPIN). In the preliminary work, 15 purified protein, peptide and amino acid solutions were ultrafiltered using a molecular weight (MW) exclusion limit of 10000 Da, and the recovery of nitrogen indicated an effective filtration (generally >90% separation) on nominal molecular weight. Further, fresh rat ileal digesta samples were treated with either TCA, PCA or SPIN. The resulting supernates were ultrafiltered and the fractions were analysed for nitrogen and amino acids. The precipitates contained 23, 57 and 41% of the total nitrogenous material for the TCA, PCA and SPIN treatments, respectively, indicating that PCA was the most effective precipitant. In the main study, twelve 100-g male rats were fed either an EHC-based diet or a protein-free diet, and samples of ileal digesta were collected after slaughter. The digesta from the six EHC-fed rats were ultrafiltered after centrifugation, and the high molecular weight fraction was added to the precipitate. Endogenous ileal amino acid flows were determined for the total digesta and for the digesta following the centrifugation plus ultrafiltration treatment. The endogenous amino acid flows were generally higher for the total digesta than for the digesta following centrifugation plus ultrafiltration and significantly so (P<0.05) for lysine, glutamin acid and proline. The protein-free fed rats had significantly P<0·05) lower amino acid flows than those rats fed the EHC-based diedt (ultrafiltration treatment), the greatest differences occurring for isoleucine, serine, glutamic acid, valine, leucine, alanine and threonine.     

Quantitative and qualitative changes in endogenous nitrogen components along the small intestine of the calf

The aim of this study was to investigate the quantitative and qualitative changes in endogenous protein components along the calf's small intestine. A protein‐free diet and three milk substitutes based on skim milk powder and differing in their protein level (100, 200 and 280 g kg⁻¹ respectively) were prepared. Duodenal, jejunal and ileal digesta were collected through simple cannulae. The flow of non‐specific endogenous amino acids (AAs) determined with the protein‐free diet was 8, 13 and 12 g kg⁻¹ of dry matter intake in the duodenum, jejunum and ileum respectively. The flow of endogenous amino acids in digesta from calves fed diets containing protein was determined using multiple linear regression analysis. It was higher than the non‐specific flow at the duodenum and jejunum owing to additional specific endogenous components. At the ileum, milk proteins were completely digested and the flow of total AAs assayed was equal to the non‐specific flow. Seventy per cent of protein flowing at the jejunum was apparently reabsorbed before the terminal ileum. Endogenous protein at the duodenum resembled a theoretical mixture of proteins from saliva, gastric and pancreatic juices (140, 270 and 590 g kg⁻¹ respectively). Ileal protein losses corresponded to a mixture of proteins from the host and gut bacteria in a 50:50 ratio. By contrast, no theoretical mixture of reference proteins fitted the AA composition of jejunal endogenous protein. © 2000 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 diurnal pattern of ileal dry matter and endogenous ileal nitrogen flows in the growing pig

The aim was to examine the diurnal pattern of endogenous nitrogen flow at the terminal ileum of the pig. Seven entire male pigs with a mean body weight of 58 kg had post‐valve T‐caecum (PVTC) cannulae surgically implanted for the collection of ileal digesta. The pigs were fed equal‐sized meals (10% of metabolic body weight, W^0.75, per day) twice daily at 08:00 and 17:00. The semi‐synthetic diet included enzyme‐hydrolysed casein (<5000 Da, 100 g kg^?1 diet) as the sole source of nitrogen (N). The diet also contained chromic oxide (6 g kg^?1) as an indigestible marker. The pigs received the diet for an 8 day period, and digesta were continuously collected for 24 h periods (commencing at 08:00) on the fifth and eighth days. Digesta were analysed for dry matter (DM) and chromium (Cr), and endogenous N was determined in the precipitate + retentate fraction of the digesta following centrifugation and ultrafiltration (10 000 Da molecular weight cut‐off). The concentration of Cr expressed on a digesta DM basis and the ratio of endogenous N to Cr in the digesta were relatively constant over the 24 h digesta collection periods, with no statistically significant (P > 0.05) differences found for the latter measure in the digesta collected between 12:00 and 08:00. The endogenous N flow through the terminal ileum is the net effect of the secretion and reabsorption of endogenous N that occurs throughout the digestive tract. The net result of the latter two processes in the small intestine of the pig leads to a relatively constant endogenous N flow over time post‐feeding. © 2002 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     

Presence of indigestible peptide aggregates of soybean meal in pig ileal digesta residue

With the purpose of analysing the molecular size and composition, proteinaceous material was extracted from the insoluble components of a digesta sample obtained from pigs fed a feed consisting of only soybean meal. Gel permeation chromatography indicated that the alkali‐extractable fraction of the proteinaceous material from the residue was of relatively high apparent molecular weight. However, the combined results from gel electrophoresis, RPLC‐MS, and MALDI‐ToF MS showed that the extracted protein material was in fact, to a high extent, composed of aggregated peptides. To our knowledge this has not previously been described. Aggregates extracted by dilute alkali were fully degraded upon subsequent proteolytic treatment. N‐terminal sequencing of selected protein bands from SDS‐PAGE gels indicated the presence of partly degraded β‐conglycinin alpha subunits in the residue. Copyright © 2007 Society of Chemical Industry     

The nitrogen content of potato (Solanum tuberosum L.) tubers in relation to nitrogen application—the effect on amino acid composition and yields

The effect of nitrogen application on the nitrogen content and yield of amino acids from potato tubers was studied in one experiment in 1983 and two in 1984. Increasing fertiliser N over the range 0–250 kg ha^?1 raised tuber nitrogen concentrations from 0.68–0.81 to 1.27–1.49% DM. Applying half the fertiliser on the seedbed and half at tuber initiation did not increase tuber nitrogen concentrations compared with a single broadcast application at planting. Increasing tuber nitrogen concentrations had little effect upon the proportion recovered in amides or the different amino acids. Yields of some nutritionally essential amino acids were, therefore, substantially increased up to a maximum of 256 kg ha^?1 in 1982 and 308 and 384 kg ha^?1 in 1984 at the highest fertiliser level. These yields were significantly higher (P<0.01) than those found with the nitrogen application rate optimal for tuber dry matter production (213, 195 and 331 kg N ha^?1, respectively) in the same experiments. Methionine and cystine were the limiting essential amino acids. As the amount of each amino acid contained in a unit weight of fresh tuber increased with nitrogen supply, application of more nitrogen than is needed for maximal tuber dry matter production increased protein yields without decreasing the nutritional quality.     

Composition of Surimi-like Material from Beef or Pork

A surimi-like material was made from finely minced beef or pork by water washing followed by screening to remove connective tissue. Changes in component proteins, amino acid composition and vitamin, mineral and cholesterol content occurring during preparation were investigated. Total amino acid nitrogen contents of water-washed beef and pork were higher than those of the respective muscle by 7% and 6.5%. Among 16 amino acids measured, histidine and glycine decreased in both water-washed beef and pork, while others increased compared to original muscle. Thiamin content decreased after washing. Surimi-like beef and pork had less cytoplasmic minerals (K, Na, Mg) but more minerals associated with proteins or subcellular organelles (Ca, Cu, Zn, Fe). Fat content decreased, although cholesterol concentration was not changed by washing.