Effect of microbial phytase on ileal digestibility of phytate phosphorus, total phosphorus, and amino acids in a low-phosphorus diet for broilers

The study aimed to assess the effect of a commercially available microbial phytase added to a corn-soybean meal diet on phytate P and total P in terminal ileal digesta as well as on true ileal amino acid digestibility. Three low-P diets containing 0, 500, or 750 U/kg of microbial phytase were fed to 21-d-old broiler chickens. Titanium dioxide was used as an indigestible marker. Ileal contents were collected from euthanized birds and analyzed, along with the diets, for total P, phytate P, and amino acids. Endogenous P determined at the terminal ileum was 446 +/- 59 mg/kg food dry matter (mean +/- SE). Endogenous ileal amino acids ranged from 219 +/- 33 mg/kg food dry matter for tryptophan to 1,255 +/- 166 mg/kg food dry matter for glutamic acid. Supplementation with microbial phytase resulted in a significantly (P < or = 0.05) greater phytate P disappearance (11% greater disappearance vs. unsupplemented control) from the terminal ileum. Similarly, true ileal total P digestibility was (P < or = 0.05) higher (10 to 12%) when microbial phytase was added. True ileal amino acid digestibility was significantly (P < or = 0.05) greater in the presence of microbial phytase for all the amino acids examined with the exception of methionine, tyrosine, histidine, and tryptophan. The mean increase in true ileal amino acid digestibility was 3.4%. The effect of phytase on true ileal phytate P, total P, and amino acid digestibility was similar for the 2 phytase inclusion levels tested. Microbial phytase improved phytate P and total P digestibility, as well as true ileal amino acid digestibility, for a corn-soybean diet.

True amino acid availability in chinese high-oil corn varieties determined in two types of chickens

True amino acid availability (TAAA) was determined in conventional corn (CC) and in 2 Chinese high-oil corn varieties (CHOC1; CHOC2). The CC, CHOC1, and CHOC2 contained 3.7, 6.6, and 7.5% oil (ether extract) on a dry matter basis, respectively. The CP content (% dry matter) of the corn increased from 8.6 to 12.2% as oil increased from 3.7 to 7.5%. Birds (Hy-Line roosters or Arbor Acres broilers) were given 1 of the 3 corn varieties as the sole dietary ingredient in a conventional (intubation method) TAAA assay. There was a significant (P < 0.05) effect of bird type on gut metabolic (endogenous) amino acid excretion values with the broilers having higher excretions. For all amino acids, there was also a significant (P < 0.05) effect of bird type on TAAA with the Hy-Line roosters having higher TAAA values. The mean value for TAAA calculated over all of the amino acids showed a 9.8% unit higher digestibility for roosters compared with the broilers. Differences in TAAA between the corn varieties were statistically significant for alanine and valine only. Overall, the present results indicate that TAAA is equal to or superior to that in CC and that the TAAA content is higher in CHOC compared with CC. Bird type has an important effect on TAAA results and should be considered when developing TAAA assays and interpreting TAAA values.

Comparison of the enzyme-hydrolyzed casein, guanidination, and isotope dilution methods for determining ileal endogenous protein flow in the growing rat and pig1

The objectives of the two studies were to determine whether the guanidination and isotope dilution methods applied both by labeling the animal (15N-infusion method) and by diet (15N-dilution method) give similar estimates of ileal endogenous lysine (EL) and endogenous nitrogen (EN) flows, respectively, to that of the enzyme-hydrolyzed casein (EHC) method in the growing pig and to determine whether the guandination and 15N-dilution methods give similar estimates of EL and EN flows, respectively, to that of the EHC method in the rat. For the first study, the test diet contained guanidinated and enzymatically hydrolyzed casein (molecular weight < 5,000 Da), which was also labeled with 15N. Rats (n = 30; mean BW 178 g) and pigs (n = 6; mean BW 19.2 kg) received a preliminary EHC-based diet for 7 d. The test diet was then given to the rats and pigs on d 8. Digesta were sampled from the terminal 20 cm of ileum of killed animals. The EL flows determined using the guanidination method were lower than those determined using the EHC method (means of 298 vs. 382, and 214 vs. 287 microg/g of DMI, in the rat and pig, respectively; P < 0.05 for the rat and P < 0.01 for the pig). The EN flows determined with the 15N-dilution method were lower than those determined using the EHC method (means of 1,034 vs. 1,942 and 1,011 vs. 1,543 microg/g of DMI, in the rat and pig, respectively, P < 0.001 for the rat and P < 0.05 for the pig). In the second study, pigs (n = 6; mean BW 27 kg) were continuously infused via the jugular vein with 15N-leucine for 11 d. The pigs received an EHC-based diet (molecular weight < 5,000 Da) during this 11-d period, after which digesta were sampled at the terminal ileum under anesthesia. The EN flow determined using the 15N-infusion method (mean of 1,971 microg/g DMI) was higher (P < 0.01) than that determined using the EHC method (mean of 1,233 microg/g DMI). The guanidination method gave a lower estimate of EL flow than did the EHC method in both the pig and rat. The 15N-dilution method also gave a lower estimate of EN flow than the EHC method in the pig and rat, and the 15N-infusion method gave a higher estimate of EN flow than the EHC method in the pig.

The rat as a model animal for the growing pig in determining ileal amino acid digestibility in soya and milk proteins

The growing pig is an established model animal for humans to determine protein digestibility to the end of the small intestine. An ileal amino acid digestibility assay based on the laboratory rat offers an alternative. True ileal amino acid digestibility in high quality refined protein sources was determined and compared between the laboratory rat and the growing pig. Both species of animals were fed their daily ration in nine separate meals. Ileal digesta were collected at slaughter and chromic oxide was used as an indigestible marker. For several of the amino acids examined, there were no significant (p < 0.05) differences between the two species for true ileal amino acid digestibility, but for aspartic acid, serine, cysteine, methionine, tyrosine, phenylalanine and histidine, significant (p < 0.05) interspecies differences were found. The overall average amino acid digestibility, for all amino acids and all diets, was 95.8% for the pig and 96.1% for the rat. Cysteine digestibility was highly variable between individual animals fed the same diet. The extent of amino acid digestion and absorption appears to be broadly similar across the two species, but some important differences in digestibility were recorded.

Ileal amino acid digestibility assay for the growing meat chicken--comparison of ileal and excreta amino acid digestibility in the chicken

1. The apparent and true amino acid digestibilities in sorghum, wheat, soyabean meal, meat-and-bone meal, fish meal and blood meal for growing meat chickens were determined using an assay based on the collection of digesta from the terminal ileum and comparison was made with digestibility values determined using an excreta-based assay. 2. Five-week-old meat chickens were given maize-soyabean meal basal diet or mixtures of the basal diet and test diets containing the 6 ingredients as the sole source of dietary protein (50:50 on weight basis). Apparent amino acid digestibility values of assay diets at ileal and excreta levels were calculated using chromic oxide as the indigestible marker. True digestibility values were calculated using endogenous outputs determined by feeding a protein-free diet. Amino acid digestibilities of the ingredients were calculated by difference. 3. The site of measurement had no influence on endogenous amino acid output, the exceptions being aspartic acid and glutamic acid. The output of these two amino acids was higher in the excreta. 4. Significant differences were found between ileal and excreta-based digestibility of certain amino acids in some ingredients, with excreta values being usually higher than the ileal values, indicating a net catabolism of amino acids in the large intestine. The degree of net amino acid disappearance was found to be variable among amino acids and ingredients. In general, threonine had the lowest digestibility at the ileal level and, compared with other amino acids, the highest degredation during passage through the hindgut. 5. The results showed that digestibility determination based on excreta collection will overestimate the uptake for some amino acids in some feeds. The degree of overestimation was often considerable, ranging from 8.9% (apparent digestibility of threonine in soyabean meal) to 56% (apparent digestibility of aspartic acid in wheat). It is concluded that digestibility values measured at the terminal ileum provide a more reliable measure of amino acid availability than those measured in the excreta.

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.

Influence of dietary lysine and energy intakes on body protein deposition and lysine utilization in the growing pig

A serial slaughter study was conducted to determine the effects of true ileally digestible lysine (IDLys) intake and metabolizable energy intake (MEI) on whole-body protein deposition (PD) and dietary lysine utilization in pigs between 45 and 75 kg live weight (LW). Conventional N balances were determined at the start and end of the serial slaughter study. Semisynthetic diets based on casein and cornstarch provided protein-bound lysine to support protein depositions of approximately 70% (Lys70%, IDLys 11.1 g/d) or 90% (Lys90%, IDLys 13.2 g/d) of a determined maximum PD. During the serial slaughter study and at Lys70%, pigs were fed one of six levels of MEI ranging from 14.1 to 23.5 MJ/d; at Lys90%, pigs were fed one of seven levels of MEI ranging from 15.6 to 26.4 MJ/d. The serial slaughter study and N balances indicated that MEI and IDLys had independent effects on PD and lysine utilization. Lysine utilization (calculated as the fraction of absorbed available lysine, over and above maintenance lysine requirements, that was retained in body protein) and PD increased with increasing MEI until plateau values were reached. At the plateaus, PD was determined by lysine intake. When lysine intake determined PD, lysine utilization did not decline (P > 0.10) with increasing lysine intake. Based on the N balance study, there was no effect (P > 0.1) of LW on lysine utilization. The marginal efficiency of using absorbed available lysine for PD was 0.75 and was not affected by LW, MEI, or IDLys.

The effect of dietary peptide concentration on endogenous ileal amino acid loss in the growing pig

The aim of the present study was to determine whether dietary peptide concentration had an effect on endogenous ileal amino acid flow in the growing pig. Eight 33 kg live weight entire male pigs had post-valve T-caecum (PVTC) cannulas surgically implanted for the collection of ileal digesta. The pigs were fed twice daily at 100 g/kg metabolic body weight per d and were given diets containing enzyme-hydrolysed casein (EHC) at 0, 50, 100 and 200 g/kg in a Latin-square design. A basal casein-based diet was fed to the pigs for 6 d periods between receiving the experimental diets. The pigs received the experimental diets for 8 d periods, with continuous collection of digesta for 24 h on each of the fifth and eighth days. The endogenous ileal amino acid flows were determined with reference to recovery of the marker, Cr, directly for pigs receiving the protein-free diet or after centrifugation and ultrafiltration (10,000 Da molecular mass cut-off) for pigs on the EHC-based diets. Mean endogenous ileal N flows were 1753, 1948, 2851 and 5743 micrograms/g DM intake when the pigs received diets containing 0, 50, 100 and 200 g EHC/kg respectively. There was a significant (P < 0.05) effect of dietary peptide concentration on the endogenous ileal flows of N and all of the amino acids, with an increase in endogenous ileal amino flow with increasing dietary EHC concentration.

Relationship between plasma testosterone and urinary felinine in the growing kitten

Felinine, a unique amino acid the functions of which are not well understood, is found in large quantities in male cat urine. Our study ran for 13 calendar months and involved taking monthly samples of blood and urine from 10 male and 10 female kittens starting at 6 months of age and measuring urinary felinine and plasma testosterone concentrations. Felinine was detectable at 6 months of age in all cats (range, mean +/- SEM, nmol/mL, 13.8-801.1, 432.3+/-112.2, males and 34.3-393.0, 140.4+/-45.0 females). In entire males, felinine showed a biphasic pattern, peaking (2550 nmol/mL) between 11-13 months of age toward the end of the attainment of puberty then falling to a low (1048 nmol/mL) at 15 months of age then climbing to a peak (3661 nmol/mL) at 17 months of age. Natural plasma testosterone levels in entire males showed a similar biphasic pattern peaking (6.8 pmol/mL) at 12 months of age, falling (1.3 pmol/mL) at 15 months, and finally rising again (12.6 pmol/ml) at 16 months of age. Castration of half the male cats induced a parallel fall in both testosterone and felinine that was reversed following testosterone supplementation. Urinary felinine levels in entire females rose slowly throughout the study and reached 795 nmol/mL at 18 months of age compared to the level of 365 nmol/mL reached by the spayed females: these levels were not significantly different when expressed as felinine/creatinine ratios. We could not detect testosterone in either entire or spayed females and so concluded that felinine was unrelated to testosterone in these groups. There was strong evidence that plasma testosterone levels are positively correlated with urinary felinine levels in male cats. The control of felinine might be sex-linked and may be part of a pheromonal signaling process of the male cat.

Physiological approaches to determining gut endogenous amino acid flows in the mammal

Endogenous nitrogen and amino acid losses are associated with the digestion process. Different methods can be used to distinguish between gut endogenous and exogenous amino acid flows. These methods include feeding N-free diets, the regression approach, the use of enzyme hydrolysed proteins coupled with ultrafiltration and the use of markers (e.g., homoarginine, enzyme hydrolysed casein, 15N-labelled protein, 15N-leucine). All of the methods described have their limitations, but they have allowed major advances to be made in the measurement and understanding of endogenous amino acid secretion, reabsorption, flow and excretion.

The amino acid composition of human milk corrected for amino acid digestibility

Human milk was collected from women in their 10th-14th weeks of lactation, and was analysed for amino acids. Corrections were made for losses of amino acids which were presumed to occur during acid hydrolysis, using a non-linear mathematical model that describes the simultaneous processes of amino acid yield and decay. The mean amino acid composition of the human milk was found to be similar to previously reported estimates, although the cysteine content of the human milk in the present study was 20% higher than the average literature estimate. True (corrected for endogenous amino acid excretions) ileal amino acid digestibility of human milk was determined using the 3-week-old piglet as a model animal for the human infant. The piglets were given either human milk (n 6) or a protein-free diet (n 6) for a 6 d experimental period. Cr2O3 was added as an indigestible marker, to both the human milk and protein-free diet. At the end of the experimental period the piglets were anaesthetized and samples of digesta removed from the terminal ileum of each piglet. After sampling the piglets were killed. Endogenous ileal excretions of amino acids were determined in piglets fed on the protein-free diet. The true digestibilities of total N and amino acid N were 88% and 95% respectively. The true ileal digestibility of the non-amino acid N fraction in human milk, when calculated by difference was only 50%. The true digestibility of the amino acids in human milk ranged from 81-101% with threonine (86%) being the least digestible essential amino acid. When the true ileal digestibility values were used to correct the amino acid composition of human milk, the pattern of digestible amino acids in human milk was different compared with the currently recommended pattern of amino acid requirements for the infant.

The digestible amino acid composition of several milk proteins: application of a new bioassay

The aim of the present study was to determine the composition of amino acids that were truly digestible in the ileum. Several bovine milk products and two soy protein products were tested using the newly developed enzymatically hydrolyzed casein-ultrafiltration (UF) method. This method provides a novel approach for determining endogenous flows of amino acids at the terminal ileum, which are required for correcting apparent ileal digestibility values to true digestibility values. Digestibility was determined by sampling digesta of Sprague-Dawley male rats at the end of the small intestine (ileum). Chromic oxide was used as an indigestible marker. The traditional protein-free method for determining endogenous losses of amino acids was also used for comparison with the enzymatically hydrolyzed casein-UF method. Flows of endogenous amino acids at the terminal ileum of the rat following peptide alimentation were generally higher (1.8-fold) than those determined after a protein-free diet was fed. Compared with values for true amino acid digestibility, apparent values underestimated digestibility by 2 to 30%. True amino acid digestibility was high (79 to 102%) for all of the protein sources. The digestible amounts of methionine and lysine were 2 and 1.3 times higher, respectively, in dairy proteins than in soy proteins. The enzymatically hydrolyzed casein-UF method provides a physiological estimate of endogenous amino acid flow and appeared to be an appropriate method for correcting apparent digestibility values to true digestibility values. The data for true ileal digestibility of amino acids obtained using this technique demonstrated the high quality of bovine milk proteins.

Ileal amino acid digestibility assay for the growing meat chicken--effect of the imposition of a fasting period and the nature of the test diet

1. The objective of this study was to investigate the effects of cold-pelleting, the length of the fasting period before feeding of the test diet and the nature of the test diet on apparent ileal nitrogen (N) digestibility in the broiler chicken. 2. Four-week-old broiler chickens were given a pelleted or non-pelleted maize/soyabean meal (basal) diet. The birds were starved for 24 h, given a single test meal (25 g) by intubation and killed 4 h after the start of feeding by administration of a barbiturate, to allow sampling of ileal digesta (terminal 15 cm). Cold-pelleting did not affect apparent ileal N digestibility. 3. Four-week-old broiler chickens were fasted for 12 or 24 h and then received a test meal (1 h free access) of either a pelleted soyabean meal or a pelleted meat-and-bone meal diet or were continuously fed on one of the two diets. The imposition of a fast did not affect apparent ileal N digestibility. However, a 24 h fasting procedure was preferred, as the between animal variation for apparent ileal N digestibility was lower than for the 12 h fast or for continuous feeding. 4. Four-week-old broiler chickens were given either semi-synthetic starch-based diets containing maize, wheat bran, meat-and-bone meal or fish meal as the sole sources of protein or each of these diets in combination with the basal diet (50:50 on a dry matter basis). With the exception of the maize diet, the apparent ileal N digestibility values calculated by correcting for the digestibility of the basal dietary component were significantly lower than when digestibility was determined directly using a diet in which the respective proteins were the sole protein source. This implies that interactions between the dietary ingredients influence estimates of apparent ileal N digestibility.

Urinary excretion of endogenous nitrogen metabolites in adult domestic cats using a protein-free diet and the regression technique

The study was designed to determine urinary excretions of endogenous total, urea, ammonia and creatinine nitrogen in adult domestic cats. Endogenous urinary nitrogen metabolite excretions were determined by feeding adult cats a protein-free diet for 10 d or by regression to zero protein intake of the urinary nitrogen metabolite excretions of adult cats fed four levels of dietary protein. The mean (+/- SEM) endogenous total, urea and ammonia nitrogen excretions for the cats fed the protein-free diet were 360 (+/- 11.3), 243 (+/- 8.8) and 27.6 (+/- 1.06) mg x kg body weight(-0.75) x d(-1), respectively. Estimates of 316 (+/- 53.9), 232 (+/- 43.4) and 33.7 (+/- 5.68) mg x kg body weight(-0.75) x d(-1), respectively, were obtained using the regression technique. The differences in results between the two techniques were not statistically significant. Daily excretions of creatinine nitrogen were not significantly (P = 0.64) different between the protein-free and regression technique (mean +/- SEM, 14.4 +/- 0.49 and 15.9 +/- 1.05 mg/kg body weight(0.75), respectively). The endogenous urinary total and urea nitrogen excretion of adult domestic cats is higher than values for other mammals such as humans, dogs, rats and pigs.

Development of an ileal amino acid digestibility assay for the growing chicken--effects of time after feeding and site of sampling

1. The study aimed to establish the optimum time after ingestion and optimum sampling site for the development of an ileal amino acid digestibility assay for broiler chickens. 2. To establish the optimal sampling time, 4-week-old broiler chickens were given one of 6 protein sources (meat-and-bone, soyabean, cottonseed, fish, maize and wheat meals) as the sole source of protein in a test diet. The diets contained chromic oxide as an indigestible marker. The birds were starved for 24 h, fed and subsequently killed for sampling of ileal digesta (terminal 15 cm) at 2, 3, 4, 5 and 6 h after the start of feeding. 3. For the soyabean, fish, wheat and maize meal diets, sampling time had no significant effect on apparent ileal nitrogen digestibility, whereas for the meat-and-bone and cottonseed meal diets there was a significant quadratic effect of sampling time. The amount of digesta collected was maximised and the mean apparent ileal nitrogen digestibility had the lowest variation around the 4 h sampling time. 4. To establish the optimum sampling site, 4-week-old chickens were given either a meat-and-bone, a soyabean or a wheat bran meal-based diet. The birds were killed 4 h after the start of feeding, and digesta were sampled from 0-10, 0-15, 0-20 or 0-25 cm of terminal ileum. 5. There was no significant effect of sampling site on the apparent ileal digestibility of dietary nitrogen. The terminal 15 cm of ileum was considered a preferred site for sampling ileal digesta from broiler chickens.

The effect of condensed tannins from heated and unheated cottonseed on the ileal digestibility of amino acids for the growing rat and pig

The effect of condensed tannins (CT) from heated and unheated cottonseed on the apparent ileal digestibility of amino acids for the growing rat and pig was determined. In Expt 1, twenty-four rats were allocated to four semi-purified diets which contained cottonseed kernel and hulls as the only protein source. Two of the diets contained unheated solvent-extracted cottonseed kernel and hulls, while the remaining two diets contained similar material but which had been heat-treated by autoclaving at 110 degrees for 120 min. In Expt 2, twelve rats and twelve pigs were fed on four semi-purified diets containing commercial cottonseed meal (CSM) as the only protein source. Cr2O3 was added to all diets as an indigestible marker. For each pair of diets in both experiments, PEG was either included or excluded. The effect of CT was assessed by comparing control animals (-PEG; CT acting) with PEG-supplemented animals (+PEG; CT inactivated). Ileal contents from the terminal 150 and 450 mm of ileum were collected at slaughter, 7 h from the start of feeding, for the rats and pigs respectively. Apparent ileal amino acid digestibility for rats fed on the diet containing cottonseed kernel and hulls was significantly depressed by the heat treatment, particularly for lysine and threonine. On average, apparent ileal amino acid digestibility in the diets without PEG was decreased from 0.80 to 0.70 by heat treatment. Dietary cottonseed CT depressed apparent ileal protein digestibility in the pig and in the rat. The addition of PEG to the diets significantly increased the apparent ileal digestibility of N and some amino acids for the pigs and the rats. The mean increase in apparent ileal digestibility due to PEG addition for the fourteen amino acids was 2 percentage units in both species fed on the commercial CSM diets, and 2 or 4 percentage units in rats fed on the unheated or the heated cottonseed kernel and hull diets respectively. The effect of PEG was similar in the heated and unheated cottonseed kernel and hulls for most amino acids, but apparent ileal digestibilities of threonine, tyrosine and lysine were increased more by PEG in heated than in unheated CSM. Apparent ileal N digestibility was lower in the pig than in the rat. For several of the amino acids there were significant animal species differences in apparent ileal digestibility. Studies into the effects of cottonseed CT should be carried out in the target animal species. The commercial CSM had a low apparent ileal amino acid digestibility overall, particularly for the essential amino acids lysine and threonine. It was concluded that effects of heating did not eliminate the reversible reactivity of cottonseed CT on amino acid digestion in rats and pigs but rather appeared to increase it for threonine, tyrosine and lysine in Expt 1, causing large reductions in apparent ileal digestibility of these amino acids.

Correction for amino acid loss during acid hydrolysis of a purified protein

Hydrolyzing a protein in acid for a single hydrolysis interval, normally 24 h, will lead to inaccurate estimates of the amino acid composition of that protein due to an effect of the time of hydrolysis on peptide bond cleavage and amino acid degradation. The simultaneous yield and decay of amino acids during the hydrolysis of a protein can be described by a compartmental model with parameters for the hydrolysis and loss rates specific to each amino acid in a protein. The amino acid composition of the protein prior to hydrolysis can be determined by nonlinear regression of data derived from multiple hydrolysis intervals. In the present study egg-white lysozyme was hydrolyzed in 6 M HCl using 18 hydrolysis intervals (range, 2-141 h) using the conventional duplicate hydrolyses/interval system. Hydrolysis and loss rates were determined for each amino acid. Increasing the number of hydrolysis intervals prior to the maximum point on the hydrolysis curve, and including an hydrolysis interval greater than 100 h increased the accuracy with which the hydrolysis and loss rates were estimated. Most of the amino acids underwent some degree of loss during hydrolysis. Of particular note was the loss rate for cysteic acid, which was greater than that found for serine which is commonly regarded as an acid-labile amino acid. The determined amino acid composition of the protein, based on the nonlinear regression of the data from four different series of hydrolysis intervals, was compared with the known amino acid composition (sequencing). Using the routine duplicate sampling system, a nonlinear regression including 10 hydrolysis intervals (2, 6, 10, 14, 18, 22, 26, 30, 60, and 141 h) resulted in a mean amino acid recovery of 100% (range, 94-110%) and provided an acceptable compromise between accuracy and the cost of analysis.

The effect of cottonseed condensed tannins on the ileal digestibility of amino acids in casein and cottonseed kernel

The effect of adding cottonseed hulls to casein- and cottonseed-kernel-based diets on the apparent and true ileal digestibility of N and amino acids, and the proportion of this effect accounted for by condensed tannin (CT), were determined using the growing rat. Sixty rats were allocated randomly to ten semipurified diets, containing either casein (four diets) or purified unheated solvent-extracted cottonseed kernel (six diets) as the sole protein source, with Cr2O3 added as an indigestible marker. Two of the casein diets contained no hulls whilst the remaining two diets contained 70 g cottonseed hulls/kg. Two of the cottonseed-kernel-based diets contained no hulls, with two containing 23 g hulls/kg and the remaining two containing 46 g hulls/kg. For each pair of diets, PEG was either included or excluded. The effect of CT was quantified by comparing control rats (-PEG; CT acting) with PEG-supplemented rats (+PEG; CT inactivated) at each level of dietary hulls. The rats were given their respective experimental diets for 14 d. Each rat was given the food ad libitum for 10 min hourly from 08.00 to 18.00 hours. On day 14, samples of digesta were collected at death from the terminal 150 mm of ileum at 7 h from the first meal. Apparent and true ileal digestibilities were calculated for DM, N and the individual amino acids. The principal finding was that the inclusion of hulls depressed the apparent and true ileal digestibilities of N and amino acids, but with the response differing between diets. With the casein-based diet the mean apparent and true ileal amino acid digestibilities were significantly depressed from 0.89 and 0.96 to 0.85 and 0.92 respectively, by the inclusion of 70 g hulls/kg in the diet, and addition of PEG then restored these to 0.89 and 0.95. All of the depression could be explained by the CT content of the hulls. However, with the cottonseed-kernel-based diet the responses fell into three categories. The apparent and true ileal digestibilities of the essential amino acids cystine and methionine were not affected by hull addition, ileal digestibilities of leucine, isoleucine, lysine, threonine and valine were markedly depressed by hull addition with approximately 50% of the depression being explained by CT, whilst the ileal digestibilities of histidine, arginine and phenylalanine were depressed by hull addition but little or none of this effect could be explained by CT. Thus the effect of hulls on protein digestion clearly differed with source of protein. With the cottonseed-kernel-based diet it seems that components of the hulls other than CT also depressed the apparent and true ileal digestibilities of N and amino acids. The identity of these components is unknown.

Gut endogenous nitrogen and amino acid excretions in adult domestic cats fed a protein-free diet or an enzymatically hydrolyzed casein-based diet

Ileal and fecal gut endogenous nitrogen and amino acid excretions in adult domestic cats were determined. Ileal digesta were collected (10 cm of terminal ileum) from the cats fed either a protein-free diet or an enzymatically hydrolyzed casein-based diet (free amino acids and peptides < 10,000 Da) for 1 wk. Chromic oxide was included in each diet as an indigestible marker. The relative contribution of the hindgut to total endogenous gut excretion was investigated in a separate study by feeding cats a protein-free diet with or without added antibiotics for 10 d. Endogenous ileal nitrogen and amino acid nitrogen excretions of (mean +/- SEM 2.4 +/- 0.27 and 1.9 +/- 0.13 mg/g food dry matter intake, respectively, were found for the cats fed the protein-free diet, whereas higher excretions of 3.6 +/- 0.73 (P = 0.12) and 3.6 +/- 0.76 (P = 0.03) mg/g food dry matter intake were obtained in cats fed the enzymatically hydrolyzed casein. Significantly (P < 0.05) higher endogenous ileal amino acid excretions, for the enzymatically hydrolyzed casein-fed cats compared with those fed the protein-free diet, were found for methionine, aspartic acid, serine, glutamic acid, proline, valine and isoleucine, with the differences in excretions of glycine, alanine, leucine and histidine being significant at the 6% level. Most of the endogenous fecal amino acid excretions were unaffected by the inclusion of the antibiotics in the protein-free diet, although bacterial numbers were significantly lower (69%). Antibiotics addition led to significantly higher fecal endogenous excretions of nitrogen, taurine, threonine, serine and histidine but significantly lower excretions of methionine and lysine. Cats, like other simple-stomached mammals, excrete higher amounts of endogenous amino acids at the terminal ileum when the diet contains peptides.

Increased intestinal amino-acid retention from the addition of carbohydrates to a meal

Carbohydrates, added to a protein meal, are known to enhance the efficiency of dietary protein utilisation. However, the respective roles of the gut and liver in relation to this enhanced efficiency are not known. Therefore, we studied amino-acid, ammonia, urea, glucose and lactate fluxes for 6 h across the portal drained viscera and liver in conscious, multi-catheterised pigs of approximately 25 kg body weight after receiving a protein meal with added carbohydrates, a pure protein meal or a control meal. Additional carbohydrate caused a net glucose efflux in the portal drained viscera and increased arterial blood insulin levels. The appearance of amino-acids in the portal blood declined by some 30%, in spite of the dietary true amino-acid digestibility being approximately 95%. Liver uptake of most amino-acids was lower and there was a lower liver urea production. Finally, there was a smaller postprandial increase in the arterial blood concentration for most of the amino-acids. The results of this study suggest that inclusion of maltodextrin in the diet increases the net retention of meal-derived amino-acids in the portal drained viscera. The lower urea production and liver amino-acid uptake suggest a lower nitrogen loss. The gut could be an important site for nitrogen retention induced by the addition of carbohydrates to a protein meal.

Felinine: a urinary amino acid of Felidae

Felinine (2-amino-7-hydroxy-5,5-dimethyl-4-thiaheptanoic acid) has been identified in the urine of several members of the Felidae family including the cat (Felis catus). Rates of excretion of 95 mg/day have been recorded for entire male cats with entire female cats excreting around 19 mg/day. These high excretion rates in entire male cats may have a significant effect on the daily sulphur amino acid requirement. The isoamyl moiety of felinine seems to originate from the same isoprenoid pool as used for the synthesis of cholesterol in the cat. The sulphur in the felinine molecule appears to originate from cysteine, although some contradictory evidence exists. The site of synthesis and the method of transportation in the blood remain largely unknown. The biological significance of felinine to the animal is still a matter for speculation, but its function as a precursor to a pheromone seems likely. Recently, an accurate chemical assay for felinine has been developed that will allow investigation of felinine in different tissues and excretions and from a wider range of mammals.

The three-week-old piglet as a model animal for studying protein digestion in human infants

The piglet was evaluated as a model animal for studying the digestion of high-quality proteins in human infants. Three-week-old male piglets (n = 6) and 3-month-old male human infants (n = 6) were fed a bovine-milk-based formula over a 17-day experimental period comprising 7 days' adaptation followed by a 10-day fecal collection period. The piglets and infants were given 345-g liquid formula/kg body weight/day and 170-g liquid formula/kg body weight/day, respectively, which equated to similar dry matter intakes per unit stomach volume (0.923 g dry matter/cm3/day). Both the piglets and infants were individually bottle-fed the reconstituted milk formula (12.2% dry matter) at similar meal frequencies. Small but statistically significant differences (p < 0.01) were found for the apparent fecal digestibility (mean +/- overall SE) of dietary dry matter (98.8 versus 97.4% +/- 0.13%), organic matter (99.0 versus 97.7% +/- 0.12%), and total nitrogen (97.5 versus 94.5% +/- 0.36%) between the piglets and infants. The fecal digestibilities for most of the amino acids were not significantly different (p > 0.05) between the species. The digestion of protein appeared to be similar in the two species. The study provides support for using the piglet as a model animal for studying protein digestion in human infants.