Comparison of three markers for the determination of bacterial protein in terminal ileal digesta in the growing pig.

The aim of the study was to compare three methods commonly used to determine the concentrations of bacterial protein in digesta collected from the terminal ileum of growing pigs that had been fed a casein-based diet. The amounts of bacterial protein in terminal ileal digesta were determined using three different markers: 2.6-diaminopimelic acid (DAPA) and the d-amino acids, d-aspartic acid (d-Asp) and d-glutamic acid (d-Glu). The effectiveness of each marker was compared against a control based on physical fractionation by centrifugation. The total bacterial protein concentrations derived from the markers d-Asp and d-Glu were significantly different (p = 0.05) to those calculated from DAPA and the control, but there was no difference between DAPA and the control. The percentage of bacterial nitrogen ranged from 40% to 52% dependent on the marker used. Bacterial protein expressed as a percentage of the total protein, ranged from 48% to 62%, a substantial proportion of which (12-28%) was derived from lysed bacterial cells. Statistical correlations between the estimation methods were low. Such poor correlation between the markers may be the result of random errors such as variance in the epimerization of the two d-amino acids during protein hydrolysis. DAPA was accepted as a reliable marker for determining microbial protein in ileal digesta.

Amino acid losses in ileostomy fluid on a protein-free diet.

The contribution of losses via the gastrointestinal tract to maintenance amino acid requirements was assessed by collecting the ileostomy fluid of volunteers given a protein-free diet for 5 d. The subjects were eight adult men and women with terminal ileum ileostomies after ulcerative colitis. Four consecutive 24-h collections of both digesta and urine were made. On the last 2 d an antibiotic was given that suppressed microbial activity in the digesta and slightly reduced ileostomy outflow. Mean daily amino acid excretion in ileostomy fluid ranged from 32 mg/d for methionine to approximately 330 mg/d for aspartate and glutamate. These losses were compared with current international estimates of amino acid requirements. For most essential amino acids gastrointestinal losses accounted for 14-33% of daily maintenance requirements but for threonine the contribution was 61%.

Validation of the in vivo measurement of adipose tissue by magnetic resonance imaging of lean and obese pigs.

In vivo quantification of adipose tissue with magnetic resonance imaging (MRI) was validated with pigs. Thirteen transaxial MRI sections were collected, at intervals proportional to body length, from each pig, which was then killed, frozen, and sliced at the locations of the MRI sections. Adipose-tissue quantities were determined by dissecting each slice, and lipid contents of the dissected slices and of the tissue segments between slices were measured. Compared with dissection, MRI underestimated abdominal percent adipose tissue and overestimated cervical percent adipose tissue by less than 6%. When all 13 sections were used, MRI closely predicted percent lipid and dissected percent adipose tissue with small residual SDs (RSD = 1.9 and 2.1, respectively), which increased only slightly if two sections (4, upper thorax and 8, upper abdomen) were used (RSD = 2.3 and 2.6, respectively). In conclusion MRI accurately quantifies adipose tissue in vivo, matching values produced by dissection and chemical analysis.

Total and subcutaneous adipose tissue in women: the measurement of distribution and accurate prediction of quantity by using magnetic resonance imaging.

Total and subcutaneous adipose tissue in seven lean and seven obese women were quantified using magnetic resonance imaging (MRI). The distributions of adipose tissues along the body were closely correlated: subcutaneous with total, both within and between lean and obese groups. Lean women had proportionally less adipose tissue in the lower thorax and upper abdomen than did obese women. Reducing the number of MRI scans from 17 to 4 did not increase the residual SD of predicted body adipose tissue (2.9 percent) when body density was used as the reference measure. MRI gave an estimate of total-body adipose tissue significantly closer to the value for fat percent produced when the results from five other techniques (skinfold thickness, underwater weighing, 40K whole-body counting, isotopic water dilution, and tetrapolar bioelectrical impedance) were averaged than when any other technique was used alone. MRI-determined percent body adipose tissue in women is close to, and proportional to, estimates derived by underwater weighing.

Incorporation of urea and ammonia nitrogen into ileal and fecal microbial proteins and plasma free amino acids in normal men and ileostomates.

BACKGROUND: The importance of urea nitrogen reutilization in the amino acid economy of the host remains to be clarified. OBJECTIVE: The objective was to explore the transfer of (15)N from orally administered [(15)N(2)]urea or (15)NH(4)Cl to plasma free and intestinal microbial amino acids. DESIGN: Six men received an L-amino acid diet (167 mg N*kg(-)(1)*d(-)(1); 186 kJ*kg(-)(1)*d(-)(1)) for 11 d each on 2 different occasions. For the last 6 d they ingested [(15)N(2)]urea or, in random order, (15)NH(4)Cl (3.45 mg (15)N*kg(-)(1)*d(-)(1)). On day 10, a 24-h tracer protocol (12 h fasted/12 h fed) was conducted with subjects receiving the (15)N tracer hourly. In a similar experiment, (15)NH(4)Cl (3.9 mg (15)N*kg(-)(1)*d(-)(1)) was given to 7 ileostomates. (15)N Enrichments of urinary urea and plasma free and fecal or ileal microbial protein amino acids were analyzed. RESULTS: (15)N Retention was significantly higher with (15)NH(4)Cl (47.7%; P < 0.01) than with [(15)N(2)]urea (29.6%). Plasma dispensable amino acids after the (15)NH(4)Cl tracer were enriched up to 20 times (0. 2-0.6 (15)N atom% excess) that achieved with [(15)N(2)]urea. The (15)N-labeling pattern of plasma, ileal, and fecal microbial amino acids (0.05-0.45 (15)N atom% excess) was similar. Appearance of microbial threonine in plasma was similar for normal subjects (0.14) and ileostomates (0.17). CONCLUSION: The fate of (15)N from urea and NH(4)Cl differs in terms of endogenous amino acid metabolism, but is similar in relation to microbial protein metabolism. Microbial threonine of normal and ileostomy subjects appears in the blood plasma but the net contribution to the body threonine economy cannot be estimated reliably from the present data.

Effects of naloxone, metaclopramide and domperidone on plasma levels of prolactin and LH following suckling in the female rabbit.

Saline, naloxone, domperidone or metaclopramide was injected into lactating rabbits immediately before suckling. Blood samples were taken prior to injection (0 minutes) and then at 15, 30, 45 and 60 minutes after the start of suckling, after which the samples were assayed for plasma prolactin and LH concentrations. In all the does there was a significant increase in prolactin concentration, which was highest 15 minutes after the start of suckling, and which declined exponentially thereafter to levels significantly higher than before suckling. The increase in prolactin concentration was similar in does given saline and naloxone, but it was significantly enhanced in does given metaclopramide; with domperidone the increase was intermediate and not significantly different from that following treatment with saline. In does given saline, domperidone, and metaclopramide plasma LH concentrations declined slowly during the hour after suckling but the concentration was increased significantly in does given naloxone. The inverse correlations between prolactin and LH were low weak and were not significant.

Fertility of the early postpartum, lactating domestic rabbit.

Sixty-four crossbred primiparous lactating does each suckling six pups were allocated at random into four groups and were mated on either Day 1, 2, 3, or 4 post partum (where Day 0 = the day of parturition). They were subsequently killed on Day 10 post coitum (where Day 0 = the day of mating) to assess fertility. There were no significant differences between treatment groups in their mating response (97% overall), ovulation response (77% overall), implantation response (83% overall), implantation rate (8.7 overall), or preimplantation mortality rate (24% overall). Ovulation rate was significantly increased in does mated on Days 3 and 4 (13.3 and 13.1, respectively), compared with those mated on Day 1 (10.2, P<0.05) and Day 2 (9.6, P<0.01) post partum. From these results we conclude that fertility is high throughout the early postpartum period in the lactating rabbit.

A molecular biological approach to reducing dietary amino acid needs.

Rapid developments in transgenic animal technology make it possible to consider introducing new metabolic capabilities into animals, using genes from other species. Lysine and threonine are both essential amino acids in mammals, and are commonly the first and second limiting amino acids, respectively, for protein accretion in pigs and poultry fed cereal based diets. Here we consider the potential for transgenic animals with microbial biosynthetic pathways for these amino acids.

Endogenous proteins in the ileal digesta of adult humans given casein-, enzyme-hydrolyzed casein- or crystalline amino-acid-based diets in an acute feeding study.

BACKGROUND/OBJECTIVES: To ascertain if the form of dietary nitrogen (free amino acids (AA), small peptides, or intact protein) affects the endogenous nitrogen containing substances lost from the upper digestive tract of humans. SUBJECTS/METHODS: Digesta were collected via a naso-ileal tube from the terminal ileum of 16 adult humans in a single parallel study following an acute feeding regimen. Subjects were given an iso-nitrogenous and isocaloric test meal containing 150 g of casein (CAS) (n=6), enzyme-hydrolyzed casein (HCAS) (n=5) or crystalline AA (n=5) dissolved in 550 ml of water, as the sole sources of nitrogen. RESULTS: The mean concentrations and flows of total nitrogen, protein nitrogen, and soluble protein nitrogen passing the terminal ileum were significantly higher (P <0.01) for the CAS and HCAS test-meal groups compared to the AA meal group. Dietary CAS and HCAS had a considerable influence on digesta mucin concentrations and flows compared to free AA (+41%). Only 3-4% of the total nitrogen remained unidentified. CONCLUSIONS: The form of dietary nitrogen (protein, small peptides or free AA) had an acute effect upon the secretion or reabsorption of endogenous proteins in the small intestine of healthy humans, as evident from significant differences in both the quantity and composition of the proteins found in digesta at the end of the ileum.

Lower gut nitrogen supply does not affect apparent ileal digestibility of nitrogen or amino acids in growing pigs.

An implicit assumption in measures of ileal digestibility (ID) to estimate bioavailability of AA and N is that ID is not influenced by lower gut N metabolism. The absorption of nitrogenous compounds from the lower gut, derived from fermentative AA catabolism, may have an impact on N metabolism and microbial AA synthesis in the upper gut as a result of CO(NH(2))(2) recycling. The objective of this trial was to determine the apparent ID of N and AA in growing pigs fed a corn (Zea mays) starch and soybean (Glycine max) meal-based diet and receiving an infusion of N into the caecum at 40% of N intake. Eight pigs (initial BW of 23.3 ± 0.55 kg) were fitted with simple T-cannulas in the ileum and cecum and randomly assigned to 1 of 3 continuous cecal infusion treatments [saline, sodium caseinate, or CO(NH(2))(2)] according to a crossover design with 3 periods. Digesta samples were collected and pooled per pig for each 2-d period, freeze-dried, ground, and analyzed for DM, OM, total N, and AA. Lower gut N supply did not affect apparent ID of DM, OM, total N (85.4, 83.4, and 82.7 ± 1.74%; P = 0.31), or any AA (e.g., 90.1, 89.0, and 89.9 ± 1.08% for Lys; P = 0.70) for saline, casein, and CO(NH(2))(2) treatments, respectively. Apparent ID may be an insufficiently sensitive measure to determine effects of lower gut N metabolism on N absorption from the lower gut and subsequent recycling into the upper gut.

The impact of lower gut nitrogen supply on nitrogen balance and urea kinetics in growing pigs fed a valine-limiting diet.

An N-balance and isotope dilution study was performed to determine the effect of lower gut N supply on N retention and CO(NH(2))(2) kinetics in growing pigs. Nine cecally cannulated and jugular-catheterized barrows (initial BW 22.4 ± 1.2 kg) were randomly assigned to 1 of 3 cecal N infusion treatments: saline, casein, or CO(NH(2))(2); the latter 2 treatments were infused at a rate of 40% of daily N intake. All pigs were fed a Val-limiting corn (Zea mays) starch and soybean (Glycine max) meal-based diet. Cecal N infusions did not affect apparent total tract digestibility of N (P > 0.05). The efficiency of using N [% of apparent ileal digestible intake; 72.9 ± 1.9, 84.9 ± 1.9, and 85.6 ± 2.3% (P = 0.01) for saline, casein, and CO(NH(2))(2), respectively] and Val (76.9 ± 1.9, 86.5 ± 1.9, and 86.5 ± 2.4; P = 0.02) for whole body protein and Val retention increased for casein and CO(NH(2))(2). Urea flux and urinary N excretion increased (P < 0.05) similarly for both N infusions, but this increase did not fully account for lower gut N disappearance. Lower gut N disappearance is in the form of NPN, which can be used for microbial AA production in the upper gut and should be considered when determining N and AA supply and requirements.

Invited review: Amino acid bioavailability and digestibility in pig feed ingredients: terminology and application.

In this review, the terminology that is used to describe the bioavailability and ileal digestibility of AA in pig feed ingredients is defined. Aspects of the methodology to establish bioavailability and ileal digestibility values also are discussed, and recommendations about the use of these values are provided. Two main factors can contribute to differences between bioavailability and ileal digestibility of AA. First, some AA, such as Lys, may be absorbed in chemical complexes that preclude their use for metabolism. Second, fermentation in the upper gut may result in a net loss or gain of AA to the animal. In addition, dietary effects on the efficiency of using bioavailable AA intake for tissue growth or milk production should be considered and may be attributed to endogenous AA losses in the hindgut and the metabolic costs associated with endogenous gut protein synthesis and losses. Ileal digestibility values may be expressed as apparent ileal digestibility (AID), standardized ileal digestibility (SID), or true ileal digestibility (TID). These terms are used to specify how ileal endogenous AA losses are reflected in digestibility values. Ileal endogenous AA losses may be separated into basal losses, which are not influenced by feed ingredient composition, and specific losses, which are induced by feed ingredient characteristics such as levels and types of fiber and antinutritional factors. Values for AID are established when total ileal outflow of AA (i.e., the sum of endogenous losses and nondigested dietary AA) is related to dietary AA intake. A concern with the use of AID values is that these are not additive in mixtures of feed ingredients. This concern may be overcome by correcting AID values for defined basal endogenous losses of AA, which yields SID values. Furthermore, if the AID values are corrected for basal and specific endogenous losses, then values for TID are calculated. However, reliable procedures to routinely measure specific endogenous losses are not yet available. It is recommended that basal ileal endogenous losses of AA should be measured in digestibility experiments using a defined protein-free diet and that these losses are reported with observed AID and SID values. It is suggested that SID values should be used for feed formulation, at least until more information on TID values becomes available.

Energy and nitrogen balances in young pigs maintained at constant weight with diets of differing protein content.

Pigs of 7 kg were fed diets containing 25% (diet 25), 8% (diet 8) or 2.5% (diet 2) protein per kilogram in quantities sufficient to maintain constant body weight for 42 days. Another group was fed diet 25, but these animals were pair-fed to animals fed diet 2. The average daily metabolizable energy required for weight stasis by the pigs fed diet 2 was nearly twice as great as that taken by pigs fed diet 25. The lipid content of the pigs was approximately 107 g/kg at the start and at the end of 42 days was 195 g/kg in pigs fed diet 2, 75 g/kg in pigs fed diet 8 and only 11 g/kg in pigs fed diet 25. The gains or losses of body energy computed from the changes in body N and lipid agreed well with those estimated directly by bomb calorimetry of carcass samples. Taken as a whole, the results do not support the suggestion that diets extremely low in protein elicit an increase in heat production greatly in excess of that expected from the results of calorimetric studies with animals fed conventional diets.

The protein-sparing effect of carbohydrate. 1. Nitrogen retention of growing pigs in relation to diet.

1. Measurements were made of the losses of nitrogen in the faeces and urine of sixty pigs of approximately 33 kg, given dietary regimens comprising twenty-nine combinations of fish flour (0-800 g/d) and maize starch (0-1200 g/d). 2. The results were used to develop a generalized equation describing N retention as a joint function of N intake and starch intake. 3. The protein-sparing effect of starch was exerted in all circumstances. It was greatest when protein intake exceeded 220 g/d but some effect persisted with protein-free diets. With a high protein supply, the increase in N retention per unit increase in dietary starch decreased from 36 mg/g with the first increment to 3 mg/g with the highest attainable starch intake. 4. From the generalized equation the relationships between net protein utilization and protein concentration and food intake could be described as continuous functions. The equations may be of use in comparing the protein values of diets measured under non-standardized conditions.

Nitrogen cycling in the gut.

This review examines the involvement of the gastrointestinal tract in the utilization of nitrogen, the identities of the nitrogenous substances entering and leaving the gut, and the significance of this recycling in the overall nitrogen economy of the body. It is concerned with nonruminant mammals, including man.

The form of response of body protein accretion to dietary amino acid supply.

The mean response of body protein accretion in growing animals to their amino acid intake is sometimes described by a rectilinear ("broken-line") model and sometimes by a curvilinear model. The response of a population may be curvilinear as a result of averaging individual rectilinear responses or because individual responses are themselves curvilinear. This experiment was undertaken to distinguish these possibilities by examining the responses of individual animals. Eighteen pigs with a mean initial weight of 35 kg and a mean final weight of 73 kg were each fed, in a different sequence, six diets providing a daily nitrogen intake of 0.5, 1.5, 1.83, 2.17, 2.5 or 3.5 g/kg body wt0.75. Each diet was given for 10 d, with complete collections of feces over the last 6 d and of urine over the last 4 d. Rates of nitrogen retention (expressed per kg0.75 per day) were related to rates of nitrogen intake (in the same units) using a rectilinear (broken line), an exponential or a saturation kinetics model. Mean square errors were significantly larger for the rectilinear model than for either of the curvilinear models and were slightly but not significantly less for the saturation kinetics model than for the exponential model.

Nutrient intake and protein metabolism: responses to feeding.

Lean tissue growth occurs when the rate of protein synthesis exceeds the rate of protein breakdown. Although absolute rates of protein synthesis and breakdown rise during growth from birth to maturity fractional rates fall. Both these processes are sensitive to nutrient intake but responses to feeding vary greatly amongst different tissues. Protein, carbohydrate and fat can all stimulate body protein accretion in immature animals and in children but the mechanisms by which they do so, and the energy expenditures involved, seem to be different.

The effects of excessive amounts of protein on lysine utilization in growing pigs.

Two experiments were conducted to investigate whether the utilization of lysine in growing pigs is affected by the level of excess protein in the diet. Nine lysine-deficient diets containing 100, 200 or 300 g crude protein/kg and between 1.2 and 6.8 g ileal digestible lysine/kg were prepared. In the first experiment the apparent ileal digestibility of lysine in three of the nine diets was determined using pigs with simple T-cannulas and Cr2O3 as an indigestible marker. Ileal digestibility of lysine in the other diets was calculated by interpolation. In the second experiment N retention, as a measure of lysine utilization, was determined in all nine diets using growing pigs over the weight range 30-50 kg. The effect of excess protein on lysine utilization was assessed by comparing the regression of N retention v. lysine (ileal digestible) intake at the three levels of protein. Increasing ileal digestible lysine in the diets resulted in a linear increase in N retention with all three protein levels and there was no significant difference amongst the three regressions, indicating that lysine utilization was not affected by the level of protein. Therefore, all data were pooled together to calculate a single regression for all treatments. An increase of 1.0 g ileal digestible lysine led to an increase of 1.43 g N or 8.96 g protein (N x 6.25) retained. Assuming a lysine concentration in the retained body protein of 65-72 mg/g, lysine was utilized with an efficiency of 0.58-0.65.