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ANIMAL NUTRITION |
Department of Animal Science, Cornell University, Ithaca, NY 14853
Abstract
The objective of this study was to determine possible synergistic effects of supplementing one of three fungal phytases: Aspergillus fumitagus PhyA (AFP), A. niger PhyA (ANP), or Peniophora lyci phytase (PLP) with an Escherichia coli AppA phytase (EP) in diets for pigs. Three experiments, each lasting for 4 wk, were conducted with a total of 106 weanling pigs (5 wk old). The corn-soybean meal basal diet (BD) contained no supplemental inorganic P. In Exp. 1, 35 pigs (8.6 ± 1.0 kg BW) were fed (as-fed basis) BD + AFP at 750 U/kg of feed, BD + inorganic P (0.2% P), or BD + PLP at 500, 750, or 1,000 U/kg feed. Pigs fed BD + AFP or BD + 0.2% P had higher (P < 0.05) plasma inorganic P concentrations than those fed BD + PLP at the end of the trial (wk 4). In Exp. 2, 35 pigs (8.1 ± 0.9 kg BW) were fed BD + AFP, EP, PLP, a 1:1 mix of AFP:EP, or a 1:1 mix of PLP:EP at 500 U/kg. Pigs fed the AFP:EP mixture had growth performance and plasma measures similar to those fed either enzyme alone. Pigs fed the PLP:EP mixture had lower (P < 0.05) plasma alkaline phosphatase activity than those fed BD + PLP. Pigs fed BD + PLP had lower (P < 0.05) plasma inorganic P concentrations than pigs fed BD + EP, and higher (P < 0.05) plasma alkaline phosphatase activity than all other groups at wk 4. In Exp. 3, 36 pigs (9.1 ± 1.2 kg BW) were fed BD + ANP, EP, or a 1:1 mix of ANP:EP at 500 U/kg feed. Pigs fed the two enzymes together had lower (P < 0.05) plasma inorganic P concentration than those fed BD + EP and lower (P < 0.05) plasma alkaline phosphatase activity than pigs fed BD + ANP at wk 4. In conclusion, although the four phytases showed different effects on plasma P status of weanling pigs, there was no synergistic effect between any of the three fungal phytases and the bacterial phytase on the plasma measures or growth performance under the conditions of the present study.
Key Words: Alkaline Phosphatase • Phosphorus • Phytase • Pigs • Plasma
Introduction
Effectiveness of supplemental phytase in improving dietary phytate-P utilization by pigs has been repeatedly shown in a variety of conditions (Cromwell et al., 1993
; Radcliffe et al., 1998; Sands et al., 2001; Traylor et al., 2001). Because most of available phytases are unable to withstand the heat inactivation (60 to 90°C) in feed pelleting, phytases with improved thermostability will certainly expand their practical applications. Until now, two heat-stable phytases have been reported. One is produced by submerged fermentation of Aspergillus oryzae carrying a gene from Peniophora lyci (PLP, Lassen et al., 2001), and made heat-resistant using a chemical coating method (Ward, 2000). The other is a naturally occurring PhyA phytase isolated from A. fumigatus (Pasamontes et al., 1997), which is overexpressed in a yeast system (AFP, Rodriguez et al. 2000). A bacterial phytase from Escherichia coli (AppA) has been expressed in Pichia pastoris as an extracellular phytase (EP, Rodriguez et al., 1999a), and has been tested in young pigs (Stahl et al., 2000). Compared with A. niger PhyA phytase (ANP) or the two heat-stable phytases (PLP and AFP), EP is different with regard to the initiation site, optimal pH, and catalytic efficiency in phytate hydrolysis and/or susceptibility to proteolysis (Greiner et al., 1993; Rodriguez et al., 1999a,b). Thus, there may be a synergistic effect between the EP and the fungal phytases on phytate-P hydrolysis in the gastrointestinal tract of pigs due to the heterogeneity in the compositions of feed phytate and in the conditions of gastrointestinal pH and proteolysis (Pallauf and Rimbach, 1997). Therefore, the objective of this study was to determine whether combining one of the three fungal phytases with EP was more effective than feeding each phytase alone in improving plasma P status and growth performance of weanling pigs.
Materials and Methods
Phytases
The PLP (Ronozyme P, Roche Vitamins, Nutley, NJ) and ANP (Natuphos, BASF, Mt. Olive, NJ) contained a specific activity of 2,400 and 5,000 U/g of product by analysis, respectively. The expression and preparation of EP and AFP in P. pastoris X33 was described elsewhere (Rodriguez et al., 1999a; 2000), and the specific activity was adjusted to 1,200 U/g using wheat middlings as a carrier. To make activity comparison practically relevant, we determined phytase activity of all sources used in the present study by the release of inorganic P from sodium phytate in 0.2 M citrate buffer, pH 5.5, at 37°C (Han et al., 1998). One unit of phytase activity was defined as the amount of enzyme needed to release 1 µmol of inorganic P per minute from sodium phytate under the assay conditions.
Animals, Diets, and Measures
The protocols for the animal experiments of this study were approved by the Institutional Animal Care and Use Committee of Cornell University. Three experiments, each lasting for 4 wk, were conducted with a total of 106 weanling pigs (5 wk old). In all experiments, pigs were Landrace-Yorkshire-Duroc crossbreds from the Cornell University Swine Farm, were weaned at 4 wk of age, and were fed a corn-soybean meal basal diet (BD, Table 1) supplemented with 0.1% inorganic P (as dicalcium phosphate) before the experiments. They were allotted into treatment groups on the basis of BW, litter, and sex. In Exp. 1, 35 pigs (8.6 ± 1.0 kg BW) were divided into five groups (n = 7). Because we were initially uncertain of the appropriate dose of PLP for the synergistic study, three groups of pigs were fed (as-fed basis) BD + PLP at 500, 750, or 1,000 U/kg of feed to examine its dose-dependent effectiveness. The other two groups of pigs were fed BD + AFP (750 U/kg of feed) or BD + inorganic P (0.2% P) to compare the relative efficacy of PLP with that of AFP. In Exp. 2, 35 pigs (8.1 ± 0.9 kg BW) were divided into five treatment groups (n = 7) and were fed BD + AFP, EP, PLP, a mix of AFP:EP (1:1), or a mix of PLP:EP (1:1) at 500 U/kg feed to determine the relative efficacy of AFP or PLP alone or in combination with EP. In Exp. 3, 36 pigs (9.1 ± 1.2 kg BW) were divided into three groups (n = six pens, two pigs per pen) and were fed BD + ANP, EP, or a mix of ANP:EP (1:1) at 500 U/kg feed to determine the relative efficacy of ANP or EP alone or in combination.
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), but no supplemental inorganic P, and a reduced Ca level (0.51%). The ratios of Ca:Ptotal in all experimental diets were close to 1.2:1 (Lei et al., 1994; Liu et al., 1998). Pigs in Exp. 1 and 2 were individually penned and pigs in Exp. 3 were housed in a group of two per pen in an environmentally controlled barn (23 to 25°C; light:dark cycle, 12 h) and allowed free access to feed and water. Feed waste was collected daily, and BW of pigs was measured weekly for calculation of ADG, ADFI, and G:F. Blood samples of individual, overnight-fasted (for 8 h) pigs were collected from the anterior vena cava into heparinized syringes at the start and at the end of trial to assay for plasma alkaline phosphatase activity and plasma inorganic P concentration.
Biochemical Analysis
Plasma was prepared by centrifuging ice-chilled whole blood samples at 3,000 x g (GS-6KR centrifuge, Beckman Instruments Inc.) for 10 min at 4°C. For determination of inorganic P concentration, plasma was deproteinated with 12.5% trichloroacetic acid and assayed using Elon (p-methylaminophenol sulfate) solution (Gomori, 1942). Plasma alkaline phosphatase activity was determined by the hydrolysis of p-nitrophenol phosphate to p-nitrophenol (Bowers and McComb, 1966). The enzyme unit was defined as the amount of activity that releases 1 µmol of p-nitrophenol per minute at 30°C.
Statistical Analysis
Data were analyzed as completely randomized design using ANOVA by SAS (SAS Inst., Inc., Cary, NC). Pen was used as the experimental unit. The Bonferroni t-test was used to compare treatment means, and P < 0.05 was set as the significance level (Gill, 1986).
Results
Experiment 1
Initial plasma inorganic P concentrations of pigs were not different among all treatment groups, whereas the final concentrations at wk 4 were 20 to 30% lower (P < 0.05) in pigs fed BD + PLP than those in pigs fed BD + AFP or BD + 0.2% P (Figure 1). Plasma inorganic P concentrations were not different between pigs fed various levels of PLP or between pigs fed BD + AFP and BD + 0.2% P at wk 4. Overall ADG, ADFI, and G:F of pigs were not affected (P = 0.30 to 0.98) by the dietary treatments (Table 2).
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). At the end of trial (wk 4), plasma inorganic P concentrations in pigs fed the two enzymes together were not different from pigs fed either AFP or PLP alone, but were marginally lower (P = 0.15) than that of pigs fed BD + EP. Pigs fed BD + PLP had 20% lower (P < 0.05) plasma inorganic P concentrations than those of pigs fed BD + EP. Initial plasma alkaline phosphatase activities were not different among the five treatment groups (Figure 3). The enzyme activity was 50% higher (P < 0.05) in pigs fed BD + PLP than in pigs fed BD + EP at wk 4. The other three groups of pigs had 20 to 40% lower (P < 0.05) plasma alkaline activities than those fed BD + PLP. Overall growth performance of pigs was not different (P = 0.39 to 0.62) among the five treatment groups (Table 2
).
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). At the end of trial (wk 4), pigs fed the two enzymes together had a plasma inorganic P concentration that was 9% lower (P < 0.05) than that of pigs fed BD + EP, but that was similar to that of pigs fed BD + ANP. There was a 17% difference in plasma inorganic P concentrations between the pigs fed ANP and EP alone. Plasma alkaline phosphatase activity in pigs fed the two enzymes together was similar to that of pigs fed BD + EP, but was 33% lower (P < 0.05) than that in pigs fed BD + ANP (Figure 5). There were no differences (P = 0.24 to 0.56) in growth performance between the treatment groups (Table 2).
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Results from the present study show no synergistic effect between the bacterial phytase and the three fungal phytases on dietary phytate-P hydrolysis for supporting growth or maintaining plasma inorganic P concentrations. Although there were positive effects (reductions) on plasma alkaline phosphatase activity from the combination of PLP or ANP with EP over supplementing the fungal phytases alone, no benefit from these combinations over EP alone was seen. Similarly, the combination of AFP and EP provided no benefit over feeding either alone. Although our results are in line of those of Augspurger et al. (2003) from chicks fed ANP mixed with PLP or EP, the lack of apparent synergism between these distinctly different phytases is still somewhat intriguing. This is because there are rather large differences in optimal pH, substrate specificity, initiation site of catalysis, and proteolysis resistance between the fungal phyases and the bacterial enzyme. Specifically, ANP is a 3-phytase that initiates the phytate-P release at the 1- or 3-carbon position of the inositol ring. In contrast, EP is a 6-phytase that initiates the hydrolysis at the 6-carbon position (Greiner et al., 1993). Combining ANP and EP may enable simultaneous hydrolysis of phytate-P at two sites, resulting in an accelerated hydrolysis rate. Conversely, EP has an acidic pH optimum ranging from 2.5 to 3.5 (Rodriguez et al., 1999a), whereas less acidic effective pH range has been reported for AFP (4 to 6.5) (Pasamontes et al., 1997; Rodriguez et al., 2000) and PLP (4 to 5) (Lassen et al., 2001). Combining EP with AFP or PLP may result in much broader effective pH ranges to enhance dietary phytate-P hydrolysis, due to the heterogeneity in the compositions of feed phytate and in the pH of gastrointestinal tracts of pigs (Pallauf and Rimbach, 1997). Because the present study did not show these biochemical synergistic potentials between EP and AFP, ANP, or PLP, future research will be needed to determine whether: 1) dietary conditions such as pH (adding acidifiers) should be modified; 2) older pigs with more acidic stomach should be tested; and 3) different ratios of various enzymes in the diets, rather than simply a 1:1 mixture, should be applied to show possible synergistic effects of these distinct phytases.
Our study represents the first test of the feeding efficacy of the heat-stable AFP expressed in Pichia yeast (Rodriguez et al., 2000). In Exp. 1, pigs fed AFP at 750 U/kg feed had growth performance and plasma inorganic P concentrations similar to those of pigs fed 0.2% P. Using the same enzyme produced in a fungal system, Simoes Nunes and Guggenbuhl, (1998) demonstrated that AFP was effective in releasing phytate-P and might partially replace inorganic P supplementation in diets for pigs. Because the heat stability of AFP is a naturally occurring property (Pasamontes et al., 1997; Rodriguez et al., 2000), its potential in helping to overcome the loss of phytase activity at feed pelleting (Wyss et al., 1998) warrants more research.
In Exp.1, there was no dose-dependent effect of PLP from 500 to 1,000 U/kg of feed on growth performance or plasma inorganic P concentrations. In Exp. 2, we chose 500 U/kg of feed, a dose of phytase activity that is normally added to commercial diets, to compare the efficacy of PLP with that of AFP or EP. Pigs fed PLP had lower plasma inorganic P concentrations and/or higher plasma alkaline phosphatase activities compared with pigs fed AFP or EP. Previous studies on the dose-dependent responses of PLP have generated mixed results (Brady et al., 2002). In vitro, a strong dose-response effect (0, 750, 1,500, and 3,000 U/kg) was seen only when the enzyme was incubated with rice bran, but not with soybean meal (Ward, 2000). In a recent chick study by Augspurger et al. (2003), increasing supplementation of PLP to a P-deficient diet from 500 to 1,000 U/kg of feed resulted in greater weight gain and G:F, but had no effect on tibia ash or bioavailable P release. It is unclear whether processing of PLP as a multicoated granule for heat stability reduced its solubility upon ingestion by pigs. Because the PLP formulation was designed for use in pelleted diets, the lipid coating might have limited the complete release of the enzyme in the mash diets used in the present study and hence its efficacy within the gastrointestinal tract of the pigs.
As shown by higher (P < 0.05) plasma inorganic P concentrations and lower (P < 0.05) plasma alkaline phosphatase activities, pigs fed EP had an improved P nutritional status, compared with pigs fed PLP or ANP at 500 U/kg. The better efficacy of EP compared with ANP or PLP, measured as growth performance, bone strength, and P balance, has been reported in both swine and poultry diets (Applegate et al., 2003; Augspurger et al., 2003). The better efficacy of EP than the two fungal phytases may be partially related to its more acidic optimal pH, greater catalytic efficiency, and stronger resistance to pepsin digestion (Greiner et al., 1993; Rodriguez et al., 1999a,b; Golovan et al., 2000). With all of these attributes, 500 U of EP, measured at pH 5.5 in test tubes, may have more functioning potency in the stomach of pigs (Yi and Kornegy, 1996) than that of the fungal phytases. However, caution should be given in specifying the criteria for the efficacy comparison of EP and ANP or PLP, as there was no difference in growth performance between pigs fed these enzymes at 500 U/kg of feed, despite their differences in plasma measures. In an earlier study (Stahl et al., 2000), we did not see any significant difference between EP and ANP in affecting plasma inorganic P concentrations or alkaline phosphatase activity of weanling pigs. The relatively high supplemental levels of EP and ANP (700 to 1,200 U/kg of feed) in that study might preclude the possible efficacy difference between these two enzymes.
One might question the validity of using plasma inorganic P concentration and plasma alkaline phosphatase activity as the criteria to assess the efficacy of different phytases. As expected, growth performance of pigs, in particular with only a limited number of replicates within treatment groups, does not normally show consistent responses to marginal P deficiency or graded levels of phytase activity within relatively short periods of time (Stahl et al., 2000). In contrast, decreases in plasma inorganic P concentrations and elevations of plasma alkaline phosphatase activity are observed within a week in pigs fed P-deficient diets without added phytase or inorganic P (Lei et al., 1993; Han et al., 1998, Stahl et al., 2000). When pigs are deprived of, or limited in, P supply, alkaline phosphatase is released to mobilize P from bones for critical metabolic needs (Boyd et al., 1983; Pointillart et al., 1987). Although Jongbloed and Mroz (1999) failed to obtain consistent responses of these biochemical measures in their studies, we were able to use these measures to determine phytase efficacy (Gentile et al., 2003). More convincingly, strong correlations between these plasma measures and bone strength or body P retention have been documented in many phytase studies by us (Lei et al., 1993; Han et al., 1997, 1998; Gentile et al., 2003) and by others (Pointillart et al., 1987; Simoes Nunes and Guggenbuhl, 1998). In the present study, there were positive correlations (r = 0.4 to 0.8, P < 0.05) between overall ADG and plasma inorganic P concentrations of individual pigs within each experiment (data not shown), although the effects of dietary treatments on ADG were not statistically significant (P = 0.2 to 0.7). Thus, we consider that plasma inorganic P concentration and plasma alkaline phosphatase activity are reliable indicators for the efficacy assay of dietary phytase or P supplementation. Compared with other methods, such as true P digestibility (Shen et al., 2001), these indicators offer the convenience and benefit of being able to track the P status of individual animals over time.
Implications
A bacterial phytase (Escherichia coli AppA phytase) was combined with either two commercially available fungal phytases (Aspergillus niger PhyA phytase and Peniophora lyci phytase or PLP) or a naturally occurring heat-stable Aspergillus fumigatus phytase in corn-soybean meal diets for weanling pigs. Although differences were observed between these enzymes at 500 and/or 750 U/kg of feed alone in maintaining normal plasma status of phosphorus nutrition in pigs, no benefit over feeding the bacterial enzyme alone was observed by combining it with the fungal enzymes.
Footnotes
1 This research was supported in part by the Biotechnology Program of Cornell Univ., and the Cornell Research Foundation holds U.S. patents 6,451,572 and 6,511,699 on the bacterial phytase. We thank BASF (Mt. Olive, NJ) and Roche Vitamins (Nutley, NJ) for the donation of microbial phytases, and are grateful for the assistance of J. R. Thornton, J. M. Gentile, and T. W. Kim in animal care and laboratory analysis. 
2 Current address: Iowa State University, Dept. of Anim. Sci., 201 Kildee Hall, Ames 50011.
3 Correspondence: Morrison Hall 252 (phone: 607-254-4703; fax: 607-255-9829; e-mail: XL20{at}cornell.edu).
Received for publication September 8, 2003. Accepted for publication February 19, 2004.
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