Ileal Endogenous Amino Acid Flow Research Articles

Effect of including purified jack bean lectin in casein or hydrolysed casein-based diets on apparent and true ileal amino acid digestibility in the growing pig

AbstractThe effect of including purified jack bean lectin (concanavalin A) in the diet of grower pigs on endogenous ileal nitrogen (N) and amino acid (AA) losses, and apparent and true ileal AA digestibility was investigated in a study with four growing pigs (average initial live weight (LW) 25 kg) fitted with simple T-cannulae at the terminal ileum. Both the homo-arginine (HA) method and peptide-alimentation method were used to estimate endogenous gut AA losses. The animals were offered four diets :(1) an enzymatically hydrolysed casein (EHC) containing diet, (2) an EHC containing diet supplemented with 266 mg/kg jack bean lectin, (3) a normal casein (NC) containing diet, and (4) a NC containing diet supplemented with 266 mg/kg lectin. For the estimation of ileal endogenous AA flows in pigs given NC diets, a subsample ofNC was guanidinated to convert lysine to HA. The experiment was conducted using a 4X4 Latin-square design. In each experimental period, pigs were adjusted to the experimental diets for 5 days. On day 6, ileal digesta was collected continuously for 24 hfor determination of apparent ileal digestibility. At 08:30 h of day 8 the HA NC diets were offered to pigs on NC treatments and ileal digesta were again collected for 24 h from all pigs. There were no interactive effects of casein type and added dietary lectin on apparent and true ileal AA digestibility and endogenous ileal AA flows (P > 0-05). The addition of lectin to the diet did not influence (P > 0-05) the apparent ileal digestibility of dry matter (DM), crude protein (CP) and AA. Casein type did not affect ileal DM digestibility (P > 0-05). Pigs given the NC-based diets had higher (P < 0-05) apparent ileal AA digestibility than pigs given the EHC-based diets. Addition of lectin to the diet did not influence (P > 0-05) endogenous ileal CP and AA flows. Endogenous ileal AA losses were generally higher (P < 0-05) in pigs given EHC diets than in pigs given NC diets. Neither casein type nor diet lectin level influenced (P > 0-05) the true ileal digestibility ofCP and AA; values ranged for most AA between 0-98 and 1-00. These data suggest that including purified jack bean lectin at the level of 266 mg/kg in a casein-based diet did not influence the ileal endogenous CP and AAflow, nor the apparent and the true ileal digestibility ofCP and AA, in growing pigs between 25 and 50 kg LW. Compared with the HA method, the peptide-alimentation method yielded higher estimates of ileal endogenous CP and AA acid losses in pigs given casein-based diets, although these two methods yielded similar estimates of true ileal AA and CP digestibility.

Effect of type of diet (casein-based or protein-free) and caecotrophy on ileal endogenous nitrogen and amino acid flow in rabbits

AbstractTwenty-eight New Zealand White X Californian doe rabbits weighing 3791±141 g were surgically fitted with a glass T-cannula at ileum level. Animals were given ad libitum access to either a casein-based diet (C) or a protein-free diet (PF). The only difference in the ingredient composition of the diets was the substitution of 160g/kg of maize starch by casein in the C diet. Animals were randomly allotted to each experimental diet. Seven rabbits per diet were not allowed to practice caecotrophy. The C diet resulted in higher food dry matter (DM) intake (DMI) (111-5 v. 51-5 g/day), food nitrogen intake (3-12 v. 0-20 g/day), ileal flow of DM (56-0 v. 23-8 g/day) and ileal flow of nitrogen (0-72 v. 0-24 g/day) but lower soft faeces DMI (21-7 v. 41-4 g/day) than the PF diet. A linear relationship between ileal endogenous nitrogen flow and total DMI was found for animals given the C but not for the PF diet. The ingestion ofC diet led to a higher (proportionately 0-41, on average), endogenous ileal amino acid flow than PF diet for all amino acids except for glycine. The ileal flow of glycine was proportionately 0-25 higher in animals given the PF diet than in animals given the C diet. The C diet resulted in higher content of nitrogen, threonine and proline in soft faeces than the PF diet. In contrast, the ingestion of the PF diet led to a higher content of lysine and methionine in soft faeces than the C diet. Within the C diet, animals practising caecotrophy showed higher ileal flow of DM (73-4 v. 56-0 g/day) and phenylalanine (0-834 v. 0-677 g/kg DMI) than animals not practising it. Caecotrophy led to a higher endogenous proportion of some of the most important limiting essential amino acids in rabbits, such as arginine, lysine, phenylalanine and threonine. In rabbits, the use of PF diets has limited practical application in the estimation of nitrogen endogenous losses as the low food DMI and the high soft faecesDMI leads to abnormal food: soft faeces intake ratio. Moreover, due to the important effect of caecotrophy on the amino acid composition of endogenous losses, it is important to correct the total amino acid content of the ileal chyme by the undigested amino acid residue coming from the soft faeces intake. This correction could be made, without the methodological complexity implied, by fitting animals with a wooden collar and thereby avoiding caecotrophy as in the present trial.

The enzyme hydrolysed protein method for the determination of endogenous ileal nitrogen and amino acid flows—a modification

The aim of the work was to examine the effect of using an ultrafiltration device with a molecular weight (MW) cut-off of 3000 Da on endogenous ileal amino acid flows determined using the enzyme hydrolysed protein method, as compared with those determined using a MW cut-off of 10,000 Da. Endogenous ileal nitrogen and amino acid flows determined using the enzyme hydrolysed protein method are normally determined using a MW cut-off of 10,000 Da for ultrafiltration. Digesta were sampled from the terminal ileum of male rats ( n=24) that had received a diet containing enzyme hydrolysed casein (EHC) at an inclusion level of 100 g/kg, for 8 days. The digesta samples were divided into six groups, each containing the digesta from four rats. Endogenous ileal nitrogen and amino acid flows were determined on each pool of digesta using the enzyme hydrolysed protein method with ultrafiltration using MW cut-offs of 10,000 and 3000 Da. The endogenous ileal nitrogen and amino acid flows determined using a MW cut-off of 3000 Da for ultrafiltration were greater than those determined using a MW cut-off of 10,000 Da. The percentage difference in endogenous flow between the results obtained following ultrafiltration at 10,000 Da and those at 3000 Da was 17% for nitrogen and ranged from 1.7% for arginine and phenylalanine to 26% for serine, with a mean difference of 12% for the amino acids. When determining endogenous ileal nitrogen and amino acid flows using the enzyme hydrolysed protein method, it is recommended that digesta be ultrafiltered using a MW cut-off of 3000 Da, but the MW cut-off for ultrafiltration must be related to the size of peptides present in the enzyme hydrolysed protein.

The effect of microbial phytase on ileal phosphorus and amino acid digestibility in the broiler chicken

1. The study aimed to assess the effect of a commercially available microbial phytase on phytate phosphorus and total phosphorus content at the terminal ileum as well as true ileal amino acid digestibility. 2. Five diets, each containing a different plant-based feedstuff, were supplemented with microbial phytase and fed, along with a non-supplemented corresponding diet, to 28-d-old broiler chickens, Chromic oxide was used as an indigestible marker. Ileal contents were collected and analysed, along with the diets, for total phosphorus, phytate phosphorus and amino acids. 3. Endogenous phosphorus determined at the terminal ileum was 272 ± 108 mg/kg food dry matter (mean ± SE). Endogenous ileal amino acid flows ranged from 58 ± 10 mg/kg food dry matter for methionine to 568 ± 47 mg/kg food dry matter for glutamic acid. 4. Supplementation with microbial phytase resulted in a significantly greater phytate P disappearance from the terminal ileum for rice bran (17% units), but not for soyabean meal, maize, wheat or rapeseed meal. Similarly total phosphorus digestibility was significantly ( P < 0.05) higher when microbial phytase was added to the rice-bran-based diet but not for any of the other feedstuffs. 5. Amino acid digestibility was significantly greater in the presence of microbial phytase for all the amino acids examined in wheat, for several of the amino acids each in maize and rapeseed meal and for one amino acid in rice bran and soyabean meal. The average increase in amino acid digestibility for those amino acids affected, was 13, 6, 10, 7 and 12% units for wheat, maize, rapeseed meal, rice bran and soyabean meal, respectively. 6. It appears that microbial phytase improves phosphorus digestibility and amino acid digestibility for certain plant-based feedstuffs.

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

AbstractThe 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 &lt; 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 &gt; 0.05). There were significant slopes (P &lt; 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

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 Current 15N-Leucine Infusion Technique Is Not Suitable for Quantitative Measurements of Ileal Endogenous Amino Acid Flows in Pigs

The current 15N-leucine infusion technique may overestimate the ileal endogenous nitrogen losses in pigs. To determine the reason, we infused four cannulated pigs intravenously, fed them a pea-based diet with 15N-leucine, and examined some methodological variables. Neither the blood sampling time nor the choice of precursor pool (total N or amino acid N of deproteinized plasma) or the method of estimation of the isotopic equilibrium level significantly affected the results. On the other hand, the 15N-enrichment of purified mucin, isolated from ileal digesta, was higher than that of the plasma amino acid pool (0.114 vs. 0.077 atom % excess). The endogenous proportion of the labeled amino acids (Ala, Gly, Ile, Leu and Val) in the ileal digesta ranged from 23 (Leu) to 74% (Ala), compared with 70% for total N. The low value of leucine was ascribed to the constant marker infusion condition. In pigs infused with 13C-leucine, a similar endogenous proportion was obtained for lumenal leucine with 13C-leucine and 15N-leucine infusion. However, the 13C-enrichment of the leucine bound to mucin was markedly lower than that of plasma leucine (38%). The endogenous amino acid flows were also estimated by combining the ileal N flow measured with 15N and the endogenous amino acid profile obtained by means of an N-free diet. They were different from those obtained with the 15N-amino acid dilution technique. We conclude that the precursor pool currently used (plasma total N or total α-amino acid N pools) is a poor indicator of the enrichment of the secretions and that the infusion of one labeled amino acid is not sufficient to extend the method at the amino acid level.

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

AbstractA 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 &gt; 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.

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

AbstractThe 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 &gt; 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.

True ileal digestibility of amino acids in meat and bone meal for the growing pig—application of a routine rat digestibility assay

Eight samples of meat and bone meal were evaluated for their nutrient compositions and true digestible amino acid contents using a routine rat ileal digestibility assay. The rat assay has been validated for application to the growing pig. Ileal endogenous amino acid excretion, used for the correction of apparent digestibility values to true estimates, was determined for rats given a protein-free diet, or an enzymically hydrolysed casein (EHC) based diet and after ultrafiltration of the ileal digesta. The meat and bone meals varied in their nutrient composition and in the true ileal digestibility of protein and amino acids. The gross contents (g per 100 g air-dry weight) for crude protein, ash, lysine and methionine + cystine ranged from 47.8 to 59.3, 19.1–31.1, 2.45–3.89 and 1.25–1.93, respectively. Mean ileal endogenous nitrogen (N) and amino acid flows were significantly higher with the EHC versus the protein-free method, except for histidine and glycine. The mean ileal endogenous N flows were 1843 μg and 1124 μg g −1 food dry matter intake for rats fed the EHC and protein-free diets, respectively. The true nitrogen and amino acid digestibility coefficients based on endogenous flows determined by the EHC method were markedly higher than those determined using the traditional protein-free method. The true ileal N and lysine digestibility coefficients based on the respective endogenous flows for rats fed the EHC diet ranged from 62.7 to 88.9% and 66.4–92.3%, respectively. Values determined with endogenous flows for rats fed the protein-free diet ranged from 59.0 to 85.2% for N, and 63.2–88.9% for lysine. The variable ileal digestible N and amino acid contents of meat and bone meal emphasise the limitation of tabulated compositional values and the need for a routine relatively inexpensive digestibility assay.

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

AbstractTwenty‐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 &lt; 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 &lt; 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.

The effects of feed intake and purified cellulose on the endogenous ileal amino acid flow in growing pigs.

The effects of level of feed intake (0.8, 1.2 and 1.6 kg/d) and body-weight of the pig (49 and 92 kg) in Expt 1, and dietary neutral-detergent fibre (NDF; 30, 60, 90, 120 and 150 g/kg) in Expt 2 on the endogenous ileal flow of amino acids (AA) and nitrogen were studied with protein-free diets into which purified wood cellulose was incorporated at the expense of maize starch. In Expt 1, one of the protein-free diets containing 90 g NDF/kg was used. Female pigs were fitted with a simple 'T' cannula at the terminal ileum. In Expt 1, the endogenous ileal AA and N flow, expressed as g/kg dry matter (DM) intake, decreased significantly (P < 0.05) with increasing DM intake, except for proline. By contrast, the values expressed as g/d remained constant. There was no significant difference in endogenous ileal flow (P > 0.05) between initial body-weights of 45 and 90 kg except for histidine, isoleucine, phenylalanine, threonine, valine and serine, in which the ileal flow determined at the higher body-weight was significantly higher (P < 0.05). In Expt 2, the effects of dietary cellulose levels on the endogenous ileal flow of AA and N were not significant (P > 0.05), although the values tended to increase as dietary cellulose levels increased for most AA and for N. It is concluded that the daily endogenous ileal flow of AA and N remains relatively similar at different DM intake and cellulose levels. Therefore, correction of apparent ileal digestibility of AA and N to the true ileal digestibility should be made with the endogenous ileal flow values expressed on a daily amount basis, not the values expressed on a DM intake basis.

Endogenous amino acid flow in the stomach and small intestine of the young growing pig

AbstractEndogenous ileal amino acid flows were determined in the young growing pig given an enzymically hydrolysed casein (EHC)‐based diet with subsequent treatment of the digesta by ultrafiltration. Comparison was made with endogenous excretions obtained from pigs fed an EHC‐based or a protein‐free diet but without treatment of the digesta. Ten entire male pigs of 15 kg liveweight were fed either an EHC‐based diet or a protein‐free diet, and samples of digesta were collected following euthanasia. The digesta from the EHC‐fed pigs were divided into two equal portions. One portion was untreated, and the second portion was ultrafiltered after centrifugation with the retentate (high‐molecular‐weight fraction) being added to the precipitate. Endogenous ileal amino acid flows were determined for the untreated digesta and for the digesta following the centrifugation plus ultrafiltration treatment. Except for arginine, glycine, leucine and phenylalanine, the endogenous amino acid flows were significantly (P &lt; 0.05) higher for the untreated digesta than for the digesta following the centrifugation plus ultrafiltration treatment. Except for arginine, glycine, leucine and phenylalanine, the endogenous amino acid flows were significantly (P &lt; 0.05) highter for the untreated digesta than for the digesta following the centrifugation plus ultrafiltration treatment. The pigs fed a protein‐free diet generally had lower amino acid flows than those fed the EHC‐based diet (ultrafiltration treatment). significantly (P &lt; 0.05) so for lysine, aspartic acid, threonine, serine, glutamic acid, glycine, valine, isoleucine and leucine. The endogenous flows in different segments of the upper digestive tract of the young growing pig were also determined in the animals fed the protein‐free diet. The endogenous amino acid flow was highest in the second third of the upper digestive tract. There was a significant (P &lt; 0.05) difference between the amino acid flows determined in the first and second thirds of the small intestine for most of the amino acids.

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

AbstractThe 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 &gt;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&lt;0.05) for lysine, glutamin acid and proline. The protein‐free fed rats had significantly P&lt;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.