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Distribution of supplemental Escherichia coli AppA2 phytase activity in digesta of various gastrointestinal segments of young pigs¹

Department of Animal Science, Cornell University, Ithaca, NY 14853

	Abstract

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The objective of this study was to determine the functional location and disappearance of activity of a supplemental Escherichia coli AppA2 phytase and its impact on digesta P and Ca concentrations in the gastrointestinal tract of pigs. In Exp. 1, 18 pigs (8.3 ± 0.2 kg of BW) were allotted to 3 groups (n = 6 each) and fed a low-P (0.4%) corn-soybean meal, basal diet (BD), BD + phytase [500 units (U)/kg of feed], or BD + inorganic P (iP, 0.1%) for 4 wk. In Exp. 2, 30 pigs (14.5 ± 0.2 kg of BW) were allotted to 3 groups (n = 10 each) and fed BD, BD + 500 U of phytase/kg of feed, or BD + 2,000 U of phytase/kg of feed for 2 wk. Five or six pigs from each treatment group were killed at the end of both experiments to assay for digesta phytase activity and soluble P concentration in 6 segments of the digestive tract and digesta total P and Ca concentrations in stomach and colon. Compared with pigs fed BD, pigs fed BD + 500 U of phytase/kg of feed in Exp. 1 and BD + 2,000 U of phytase/kg of feed in Exp. 2 had greater (P < 0.05) phytase activities in the digesta of the stomach and upper jejunum (2 m aborally from the duodenum). No phytase activity was detected in the digesta of the lower jejunum (2.12 m cranial to the ileocecal junction) or ileum from any of the treatment groups in either trial. Concentrations of digesta-soluble P peaked in the upper jejunum of pigs fed BD in Exp. 1 and 2, but showed gradual decreases between the stomach and the upper jejunum of pigs fed BD + phytase or BD + iP. In both experiments, pigs fed only BD had greater (P < 0.05) colonic digesta phytase activity and soluble P concentrations than those fed phytase. In Exp. 2, total colonic digesta P or Ca concentrations, or both, of pigs displayed a phytase-dose-dependent reduction (P < 0.05). In conclusion, supplemental dietary AppA2 mainly functioned in the stomach and was associated with a reduced phytase activity in colonic digesta of weanling pigs.

Key Words: calcium • colon • digesta • phytase • phytate-phosphorus • pig

	INTRODUCTION

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Microbial phytase supplementation has been effectively used to improve utilization of phytate-P in diets of pigs (Cromwell et al., 1993, Sands et al., 2001; Traylor et al., 2001) and poultry (Johnston and Southern, 2000), reducing their fecal P excretion and releasing phytate-chelated minerals for absorption by these species (Lei et al., 1993). Jongbloed et al. (1992) and Yi and Kornegay (1996) have shown the stomach as the major site for supplemental Aspergillus niger fungal PhyA phytase in hydrolyzing digesta phytate-P in pigs.

Recently, several bacterial phytases have been expressed and characterized (Rodriguez et al., 1999). The Escherichia coli phytase AppA2, isolated from pig colon, has been shown to be more effective than fungal phytases in releasing phytate-P in diets for swine and poultry (Applegate et al., 2003; Augspurger et al., 2003). The superior performance of this bacterial phytase is likely attributed to a more acidic optimal pH and a greater resistance to pepsin digestion than that of fungal PhyA phytase (Rodriguez et al., 1999). However, it is unclear if these distinct enzymatic properties of bacterial phytase lead to actions and fates in the gastrointestinal tract different from fungal phytases.

Thus, the objective of this study was to determine the effects of supplemental dietary E. coli AppA2 phytase on total phytase activity distribution, soluble and total P, and total Ca in digesta from stomach, duodenum, upper jejunum, lower jejunum, ileum, and colon of young pigs.

	MATERIALS AND METHODS

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Animals, Diets, and Treatments
The protocol was approved by the Institutional Animal Care and Use Committee of Cornell University. All pigs used in the study were weanling crossbreds (Landrace-Hampshire-Duroc) selected from the Cornell University Swine Farm and allotted into treatment groups based on BW, litter, and sex. Before the experiments, the pigs were weaned at 4 wk of age and fed a corn-soybean meal basal diet (BD, Table 1) without supplemental inorganic P (iP). In Exp. 1, 18 pigs (6-wk old, 8.3 ± 0.2 kg of BW) were allotted to 3 groups (n = 6 each), and fed BD, BD + 500 U of phytase/kg of feed), or BD + iP (0.1%) on an as-fed basis for 4 wk. In Exp. 2, 30 pigs (8-wk-old, 14.5 ± 0.2 kg of BW) were divided into 3 groups (n = 10 each), and fed BD, BD + 500 U of phytase/kg of feed, or BD + 2,000 U of phytase/ kg of feed for 2 wk. The phytase used in both experiments was an E. coli AppA2 [40,750 units (U)/g, OptiPhos, JBS United Inc., Sheridan, IN] and added into the diets at mixing. The actual phytase activity in the experimental diets was analyzed (Kim and Lei, 2005) and is listed in the footnote of Table 1. The BD had no supplemental iP and a reduced Ca concentration, but contained adequate concentrations of all other nutrients (NRC, 1998). The ratios of Ca:P in all diets were maintained at 1.24:1 to ensure the function of phytase (Lei et al., 1994). All pigs were penned (1 x 2.5 m) individually in an environmentally controlled barn (21 to 26°C; 12:12 h, light:dark cycle) and allowed ad libitum access to feed and water.

Digesta samples were collected from the stomach, duodenum [12 cm aborally (i.e., in a direction away from the stomach) from the pylorus], upper jejunum (2 m aborally from the duodenal segment), lower jejunum (2.12 m cranial to the ileocaecal junction), ileum (12 cm cranial to ileocaecal junction), and colon (midpoint) for determination of phytase activity, soluble P concentration, total P concentration, and total Ca concentration. Saline prepared with ultrapure water was added at 1:1 to the stomach contents for thorough mixing before sampling. All collected digesta samples were frozen immediately in liquid N and stored at –20°C until freeze-dried for various analyses.

Laboratory Analyses
All chemicals were purchased from Sigma Chemical Co. (St. Louis, MO). Plasma was separated from whole blood samples that were chilled on ice and then centrifuged at 3,000 x g (GS-6KR centrifuge, Beckman Instruments Inc., Palo Alto, CA) for 10 min at 4°C. Plasma iP concentration was determined using Elon (p-methyl-aminophenol sulfate) solution after deproteination with 12.5% tricholoacetic acid (Gomori, 1942). Plasma alkaline phosphatase activity was measured by the hydrolysis of p-nitrophenol phosphate to p-nitrophenol (Bowers and McComb, 1966). The enzyme unit was defined as 1 µmol of p-nitrophenol released per min at 30°C. Phytase activity in the digesta and feed was determined by the release of iP from sodium phytate in 0.2 M citrate buffer, pH 5.5, at 37°C (Kim and Lei, 2005). Soluble P in digesta samples was first extracted in 0.2 M citrate buffer, pH 5.5 at room temperature for 30 min, and then the supernatant was collected by centrifugation of the mixture at 35,600 x g for 15 min. Thereafter, soluble P in 200 µL of supernatant was measured using the same procedure as for the determination of free P released in the phytase activity assay (Kim and Lei, 2005). Total P and Ca concentrations of stomach and colon digesta samples were analyzed using an Inductively Coupled, Argon Plasma Emission Spectrometer (Model: ICAP 61E Trace Analyser, Thermo Jerrel Ash Corporation, Franklin, MA; Eppard et al., 1985). Stomach digesta samples in Exp. 2 were dissolved in deionized water (0.1 g into 4 mL) and vortexed for measuring pH using a pH meter (Accumet Model 630, Fischer Scientific, Pittsburgh, PA).

Statistical Analyses
All data were analyzed using the GLM procedure (SAS Inst. Inc., Cary, NC). Individually penned pigs were considered the experimental unit. The main effects of dietary treatments on growth performance, plasma iP concentrations, and plasma alkaline phosphatase activities were analyzed using 1-way ANOVA, with time-repeated measurements (Gill, 1986). The main effect of dietary treatments on digesta phytase activity, soluble P concentrations, and total Ca or P concentrations were analyzed using 1-way ANOVA. Because of the relatively large variation, digesta phytase activity data were normalized by log transformation (log of activity + 1) for statistical analysis, but were presented as the original values. Bonferroni’s t-test was used to compare treatment means. Selected correlations (digesta phytase activity vs. soluble P, digesta phytase activity vs. pH, and total digesta P vs. Ca) in Exp. 2 were analyzed using PROC CORR of SAS. The significance level was set at P < 0.05 for all analyses.

	RESULTS

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Experiment 1
Growth Performance and Plasma Measures.
Compared with those fed BD, pigs fed the BD + 500 U of phytase/kg of feed and BD + 0.1% iP had 28 and 34% greater (P < 0.05) overall ADG, respectively (Table 2). These 2 groups of pigs also had 13 to 21% greater (P < 0.05) G:F ratios than the pigs fed BD only. There was no significant difference in overall ADFI among the pigs fed the 3 diets. Initial plasma iP concentrations and plasma alkaline phosphatase activities were similar among treatment groups. At wk 4, pigs fed BD had 35 to 38% lower (P < 0.05) plasma iP concentration, but 67% to 1.2-fold greater (P < 0.05) plasma alkaline phosphatase activity than pigs fed BD + 500 U of phytase/kg of feed or BD + 0.1% iP, respectively. Weekly analyses of growth performance and plasma measures showed the same dietary treatment effects as those of the overall or final time-point (data not shown).

View larger version (11K): [in this window] [in a new window]   Figure 1. Phytase activity of freeze-dried digesta samples from various segments of the digestive tract of pigs fed basal diet (BD), BD + 500 U of phytase/kg of feed (500 U/kg), or BD + 0.1% iP (0.1% iP) in Exp. 1. Data were normalized by log transformation. Values are the untransformed means ± SE of individually penned pigs (n = 5 to 6 per dietary group because some samples had an inadequate amount for all analyses).A,BFor each segment, means not sharing a common letter differ (P < 0.05), and SEM were stomach, 10; duodenum, 17; upper jejunum, 21; and colon, 79. *Only 1 duodenum digesta sample was available from the BD group for analysis.

View larger version (14K): [in this window] [in a new window]   Figure 2. Soluble P concentrations of freeze-dried digesta from various segments of the digestive tract of pigs fed basal diet (BD), BD + 500 U of phytase/kg of feed (500 U/kg), or BD + 0.1% iP (0.1% iP) in Exp. 1. Values are the means ± SE of individually penned pigs (n = 3 to 6 per dietary group because some samples had an inadequate amount for all analyses). The inset is a magnification of the changes between the stomach and ileum for a better view of the relatively low values. A,BFor each segment, means not sharing a common letter differ (P < 0.05), and SEM were stomach, 1.9; duodenum, 1.2; upper jejunum, 2.1; lower jejunum, 0.4; ileum, 0.6; and colon, 11.1. B* indicates significance at P = 0.07. *Only 1 duodenum digesta sample was available for analysis from the BD group.

View larger version (18K): [in this window] [in a new window]   Figure 3. Total P and Ca concentrations of freeze-dried stomach and colon digesta samples from pigs fed basal diet (BD), BD + 500 U of phytase/kg of feed (500 U/kg), or BD + 0.1% iP (0.1% iP) in Exp. 1. Values are means ± SE of individually penned pigs (n = 6 per dietary group). A,BWithin each segment and mineral, means not sharing a common letter differ (P < 0.05), and SEM for total P and Ca concentrations were stomach, 0.1 and 0.5; and colon, 0.9 and 1.5, respectively.

View larger version (10K): [in this window] [in a new window]   Figure 4. Phytase activity of freeze-dried digesta samples from various segments of the digestive tract of pigs fed basal diet (BD), BD + 500 U of phytase/kg of feed (500 U/kg), and BD + 2,000 U of phytase/kg of feed (2,000 U/kg) in Exp. 2. Data were normalized by log transformation. Values are the untransformed means ± SE of individually penned pigs (n = 4 to 5 per dietary group because some samples had an inadequate amount for all analyses). A–CFor each segment, means not sharing a common letter differ (P < 0.05), and SEM were stomach, 115; duodenum, 130; upper jejunum, 144; and colon, 261.

View larger version (15K): [in this window] [in a new window]   Figure 5. Soluble P concentrations of freeze-dried digesta samples from various segments of the digestive tract of pigs fed basal diet (BD), BD + 500 U of phytase/kg of feed (500 U/kg), and BD + 2,000 U of phytase/kg of feed (2,000 U/kg) in Exp. 2. The inset is a magnification of the changes between the stomach and ileum for a better view of the relatively low values. Values are the means ± SE of individually penned pigs (n = 3 to 5 per dietary group because some samples had inadequate amount for all analyses). A,BFor each segment, means not sharing a common letter differ (P < 0.05), and SEM were stomach, 1.7; duodenum, 0.8; upper jejunum, 0.7; lower jejunum, 1.6; ileum, 1.0; and colon, 20.8.

View larger version (16K): [in this window] [in a new window]   Figure 6. Total P and Ca concentrations of freeze-dried stomach and colon digesta samples from pigs fed basal diet (BD), BD + 500 U of phytase/kg of feed (500 U/kg), and BD + 2,000 U of phytase/kg of feed (2,000 U/kg) in Exp. 2. Values are means ± SE of individually penned pigs (n = 5 per dietary group). A–CWithin each segment and mineral, means not sharing a common letter differ (P < 0.05), and SEM for total P and Ca concentrations were stomach, 0.25 and 0.51; and colon, 2.7 and 2.2, respectively. B* vs. B, P = 0.06.

	DISCUSSION

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An interesting finding from the current study is that colon digesta phytase activity was negatively affected by supplemental phytase. In both experiments, pigs fed 500 U of phytase/kg of feed phytase had decreased colon digesta phytase activity compared with pigs fed BD. In Exp. 2, pigs fed BD + 2,000 U of phytase/kg of feed had lower colon digesta phytase activity than those fed BD + 500 U of phytase/kg of feed. Colon digesta soluble P concentrations followed similar trends. The inverse relationship between dietary and colonic digesta phytase activities may be explained by greater phytate hydrolysis in the upper gastrointestinal tract leaving less available substrate to induce the production of colon microbial phytase (Porres et al., 1999). Consequently, the enhanced phytate-hydrolysis upstream by dietary phytase led to reduced dietary-P reaching the colon for the degradation by colonic phytase and thereby reducing soluble P in colon digesta (Schlemmer et al., 2001; Leytem et al., 2004). Although there was no significant difference in colon digesta phytase activity or soluble P concentrations between pigs fed BD + iP and BD + 500 U of phytase/kg of feed in Exp. 1, the total P concentration in colon digesta was greater in pigs fed BD + iP. Apparently, supplemented phytase hydrolyzed phytate in the upper digestive tract and rendered more soluble P absorbed in the upper intestine (Liu et al., 2000). Thus, this would lead to a decreased release of soluble P into the environment from phytate-P degradation in colon because the colon is unlikely a major site for absorption of digesta P (Civitelli and Avioli, 1994).

Profiles of soluble P concentrations in digesta from various segments of pigs fed BD + phytase or BD + iP were apparently different from those of pigs fed only BD, although the differences did not reach statistical significance in all occasions. In the phytase or iP-supplemented pigs, digesta soluble P concentrations displayed a trend of a decrease between the stomach and the duodenum, followed by slight or negligible changes until the lower jejunum. If digesta P extraction was related to P absorption, our data were consistent with the report by Lantzsch et al. (1992) who demonstrated that phytate-P was mainly absorbed in the upper intestine of pigs fed corn. In contrast, digesta soluble P concentrations in pigs fed BD in Exp. 2 showed an opposite trend (a sharp increase) from the stomach to the upper jejunum, followed by a sharp decrease in lower jejunum. These pigs also had digesta soluble P concentrations lower in ileum, but greater in colon than pigs fed phytase.

As expected, total P and Ca concentrations in the stomach digesta of pigs fed BD did not differ from those of pigs fed BD + 500 or 2,000 U/kg, but were lower than pigs fed BD + iP. In the colon digesta, there was a positive correlation between total P and Ca concentrations. Pigs fed BD had greater concentrations of total P and Ca in colon digesta than pigs fed BD + 500 or 2,000 U of phytase/kg of feed. This scenario was probably associated with the formation of phytate and Ca chelates (Vohra et al., 1965). Likely, the phytate-chelated Ca moved into the colon to be released with phytate-P by the microbial phytase if digesta phytate was not degraded in the upper gastrointestinal tract. Previously, phytase supplementation has been shown to improve absorption of dietary P and Ca in the upper intestine (Liu et al., 1997). It is unclear if the released Ca from phytate by colonic phytase was absorbed. In summary, our research has demonstrated that the stomach was the main functional location of E. coli AppA2 phytase. The supplemental enzyme maintained fairly similar activities in digesta from stomach to upper jejunum and resulted in substantial reductions in colonic digesta phytase activity. Consequently, the phytase-supplemented pigs have low concentrations of P and Ca in the colon digesta and therefore a high probability of low excretion of these elements into the environment.

	Footnotes

 
¹ This project was developed under the auspices of the Cornell University Center for Biotechnology, a NYSTAR Designated Center for Advanced Technology supported by New York State. We thank Mike Rutzke of the USDA (ARS, Ithaca, NY) for his help in digesta mineral analysis and Taewan Kim, Jiming Li, Carol A. Roneker, Michael Scimeca, Erin Peterson, Jeremy Weaver, and Koji Yasuda (Cornell University, Ithaca, NY) for their help in animal care and digesta collection.

² Corresponding author: XL20{at}cornell.edu

Received for publication February 27, 2006. Accepted for publication February 22, 2007.

	LITERATURE CITED

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This Article Abstract Full Text (PDF) All Versions of this Article: jas.2006-111v1 85/6/1444    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Pagano, A. R. Articles by Lei, X. G. Search for Related Content PubMed PubMed Citation Articles by Pagano, A. R. Articles by Lei, X. G.