Methodology was developed for measuring the gastrointestinal endogenous phosphorus (P) outputs and true P digestibility values in studies with piglets. Four barrows, average initial body weight 6.8 kg, were fitted with a simple T-cannula at the distal ileum and fed four diets according to a 4 × 4 Latin square design. Four cornstarch-based diets containing four levels of P (1.1, 2.1, 3.2 and 4.3 g/kg diet) on a dry matter (DM) basis were formulated from soybean meal (SBM). Each experimental period comprised 8 d with a 4-d adaptation and 4-d collection of ileal digesta and feces. The apparent ileal and fecal P digestibility values in SBM were affected (P < 0.05) by P levels in the assay diets. The ileal and fecal P digestibility values increased from −24.8 to 37.1% and from 18.8 to 42.5%, respectively, as P contents increased from 1.1 to 4.3 g/kg DM diet. Linear relationships (P < 0.05), expressed as g/kg DM diet intake, between ileal and fecal outputs and dietary inputs of P, suggested that the endogenous P outputs can be determined by linear regression analysis. The endogenous P output was higher (P < 0.05) in ileal digesta than in feces (0.86 ± 0.09 vs. 0.31 ± 0.06 g/kg DM diet intake). There was no difference (P > 0.05) between the true ileal (50.7 ± 7.1%) and fecal (48.5 ± 5.4%) P digestibility values in SBM. These results suggest that differences in P contents between assay diets are primarily responsible for the large variability in apparent P digestibility values reported within the same ingredient. Apparent digestibility values underestimate the true digestive utilization of P by ∼25%. True rather than apparent P digestibility values should be determined and used in diet formulation for pigs. In addition, this study shows that the gastrointestinal endogenous P output is important in whole-body P requirement and homeostasis.

Our objective was to examine the distribution of enterocyte digestive enzyme activity along the crypt-villus and longitudinal axes of the small intestine in formula-fed neonatal pigs between the ages of 14 and 18 d. The distended intestinal sac method was used to isolate 12 sequential fractions (F1 through F12) of epithelial cells. Enterocyte migration rate was measured in the proximal and distal intestine using in vivo bromodeoxyuridine labeling. Specific activities of representative villus cell marker enzymes of alkaline phosphatase, aminopeptidase N, sucrase, and lactase increased 6- to 17-fold from F12 (crypt cells) to F1 (villus cells), whereas the crypt cell marker [³H]thymidine incorporation increased 8- to 18-fold from F1 (villus cells) to F12 (crypt cells). Enterocyte migration rate was similar (3.2 vs 3.0 μm/h), whereas the villus height (547.4 vs 908.5 μm) and enterocyte life span (4.7 vs 10.2 d) were markedly lower (P < 0.05) in the proximal than in the distal segments, respectively. In general, the specific activities of all enzymes were lowest in the crypt fractions (F9 through F12) but increased markedly (ranging from 8- to 17-fold) from F12 to F1. The activity of aminopeptidase N was higher and that of sucrase was lower in the distal than in the proximal segment. The activities of the remaining enzymes were similar in the proximal and the distal segments. Our results suggest that the enterocyte life span in the distal small intestine is approximately twice as long as in the proximal small intestine. However, despite the difference in life span, the patterns of enzyme activities along the crypt-villus axis were generally similar in the proximal and the distal regions.

Expression of the small intestinal alkaline phosphatase (IAP) is enterocyte differentiation dependent and plays essential roles in the detoxification

Enteral l-glutamate is extensively utilized as an oxidative fuel by the gut mucosa in the neonate. To identify major uptake pathways and to understand uptake regulation, we examined transport kinetics and molecular identities of apical membrane l-glutamate transporters in epithelial cells sequentially isolated along the small intestinal crypt-villus axis from milk protein-fed, 16-day-old pigs. The distended intestinal sac method was used to isolate 12 sequential cell fractions from the tip villus to the bottom crypt. Initial rates and kinetics of l-glutamate uptake were measured with l-[G-³H]glutamate by fast filtration in apical membrane vesicles prepared by Mg²⁺precipitation and differential centrifugation, with membrane potential clamped by SCN⁻. Initial l-glutamate uptake results suggested the presence of B^oand X_AG⁻transport systems, but the X_AG⁻system was predominant for uptake across the apical membrane. Kinetic data suggested that l-glutamate uptake through the X_AG⁻system was associated with higher maximal transport activity but lower transporter affinity in crypt than in villus cells. Molecular identity of the X_AG⁻glutamate transporter, based on immunoblot and RT-PCR analysis, was primarily the defined excitatory amino acid carrier (EAAC)-1. EAAC-1 expression was increased with cell differentiation and regulated at transcription and translation levels from crypt to upper villus cells. In conclusion, efficiency and capacity of luminal l-glutamate uptake across the apical membrane are regulated by changing expression of the X_AG⁻system transporter gene EAAC-1 at transcription and translation levels as well as maximal uptake activity and transporter affinity along the intestinal crypt-villus axis in the neonate.

The objectives of this study were to determine true phosphorus (P) digestibility and the endogenous P output associated with corn for growing pigs using the regression analysis technique. Four barrows, average initial body weight of 25 kg, were fitted with a T-cannula and fed four diets according to a 4 × 4 Latin square design. Four cornstarch-based diets, containing four levels of P at 0.7, 1.5, 2.2 and 2.8 g/kg dry matter intake (DMI), were formulated from corn. Each experimental period comprised 8 d with 4-d adaptation and 4-d collection of ileal digesta and fecal samples. The apparent ileal and fecal P digestibility values in corn were affected (P < 0.05) by P contents in the assay diets. The apparent ileal and fecal P digestibility values increased from −51.0 to 33.3% and from −41.4 to 39.1%, respectively, as P content increased from 0.7 to 2.8 g/kg DMI. Linear relationships (P < 0.05), expressed as g/kg DMI, between the apparent ileal and fecal digestible P and the total intake of dietary P, suggested that true P digestibility and the endogenous P outputs associated with corn can be determined by the regression analysis technique. There were no differences (P > 0.05) in true P digestibility values (54.0 ± 6.5 vs. 59.8 ± 8.5%) and the endogenous P outputs (0.693 ± 0.128 vs. 0.670 ± 0.160 g/kg DMI) between the ileal and the fecal determinations. The endogenous fecal P output represented 12.3% and 25.8% of the daily total and available P requirements in growing pigs recommended by the National Research Council in 1998. The present literature data of apparent digestibility and availability underestimate the true digestive utilization of P in corn for growing pigs by ∼35%. Current diet formulation on the bases of total, apparent P digestibility and availability values in corn inevitably leads to P overfeeding and excessive P excretion in pigs.

This study was conducted to determine true ileal AA digestibility coefficients and the endogenous AA outputs associated with barley samples for growing-finishing pigs using the regression analysis technique with dual digestibility markers. Six barrows, with 30.5 and 58.6 kg average initial and final BW, were fitted with a simple T-cannula at the distal ileum and fed six barley-based diets at close to ad libitum feed intake according to a 6 x 6 Latin square design. The six diets contained 97% of six barley samples varying from low to high in CP and AA contents (8.5, 9.2, 9.8, 11.5, 12.6, and 15.6% CP, respectively, on DM basis). The dietary NDF content ranged from 16.8 to 23.8% on DM basis. Chromic oxide (Cr2O3) and acid-insoluble ash (AIA) were used as digestibility markers. Each experimental period lasted 7 d. Ileal digesta were collected, at 2-h intervals, for a total of 24 h during d 6 and 7. There were linear relationships (P < 0.01) between dietary contents of apparent ileally digestible and total CP and AA as determined by using either Cr2O3 or AIA as a digestibility marker. The use of Cr2O3 vs AIA affected (P < 0.01) the determination of true ileal AA digestibility coefficients and the endogenous CP and AA outputs. However, there were no differences (P > 0.01) in the true ileal AA digestibility coefficients in barley samples between this study and the average values reported in the literature. The endogenous CP and AA outputs determined in this study were higher (P < 0.01) than reported values (35.1+/-3.0 vs 14.7+/-1.1 g CP/kg DMI). It is concluded that dual digestibility markers should be used to measure true ileal AA digestibility coefficients and endogenous AA outputs when dietary fiber content is high and the ileal digesta is collected through a simple T-cannula in the pig. True rather than apparent ileal AA digestibility coefficients determined in barley samples should be used in diet formulation for swine. The gastrointestinal endogenous AA secretion, recycling, and output losses are important in whole-body AA utilization and homeostasis, especially when fiber-enriched diets are fed to growing-finishing pigs.