J. Anim Sci. 2006. 84:3364-3374. doi:10.2527/jas.2006-212
© 2006 American Society of Animal Science
Efficacy and equivalency of an Escherichia coli-derived phytase for replacing inorganic phosphorus in the diets of broiler chickens and young pigs1
J. A. Jendza*,
R. N. Dilger*,
J. S. Sands
and
O. Adeola*,2
* Department of Animal Sciences, Purdue University, West Lafayette, IN 47907-2054; and
and
Danisco Animal Nutrition, Marlborough, SN8 1XN, UK
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Abstract
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Two studies were conducted to determine the efficacy of an Escherichia coli-derived phytase (ECP) and its equivalency relative to inorganic phosphorus (iP) from monosodium phosphate (MSP). In Exp. 1, one thousand two hundred 1-d-old male broilers were used in a 42-d trial to assess the effect of ECP and iP supplementation on growth performance and nutrient digestibility. Dietary treatments were based on corn-soybean meal basal diets (BD) containing 239 and 221 g of CP, 8.2 and 6.6 g of Ca, and 2.4 and 1.5 g of nonphytate P (nPP) per kg for the starter and grower phases, respectively. Treatments consisted of the BD; the BD + 0.6, 1.2, or 1.8 g of iP from MSP per kg; and the BD + 250, 500, 750, or 1,000 phytase units (FTU) of ECP per kg. Increasing levels of MSP improved gain, gain:feed, and tibia ash (linear, P < 0.01). Increasing levels of ECP improved gain, gain:feed, tibia ash (linear, P < 0.01), apparent ileal digestibility of P, N, Arg, His, Phe, and Trp at d 21 (linear, P < 0.05), and apparent retention of P at d 21 (linear, P < 0.05). Increasing levels of ECP decreased apparent retention of energy (linear, P < 0.01). Five hundred FTU of ECP per kg was determined to be equivalent to the addition of 0.72, 0.78, and 1.19 g of iP from MSP per kg in broiler diets based on gain, feed intake, and bone ash, respectively. In Exp. 2, forty-eight 10-kg pigs were used in a 28-d trial to assess the effect of ECP and iP supplementation on growth performance and nutrient digestibility. Dietary treatments consisted of a positive control containing 6.1 and 3.5 g of Ca and nPP, respectively, per kg; a negative control (NC) containing 4.8 and 1.7 g of Ca and nPP, respectively, per kg; the NC diet plus 0.4, 0.8, or 1.2 g of iP from MSP per kg; and the NC diet plus 500, 750, or 1,000 FTU of ECP per kg. Daily gain improved (linear, P < 0.05) with ECP addition, as did apparent digestibility of Ca and P (linear, P < 0.01). Five hundred FTU of ECP per kg was determined to be equivalent to the addition of 0.49 and 1.00 g of iP from MSP per kg in starter pigs diets, based on ADG and bone ash, respectively.
Key Words: broiler • equivalency • Escherichia coli • monosodium phosphate • phytase • pig
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INTRODUCTION
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Inorganic phosphorus is added to diets for monogastric animals to compensate for their inefficient utilization of phytate P, the main storage form of P in mature cereal grains and oilseeds. Much of the P in animal waste is undigested phytate-bound P. Research has demonstrated definitively that microbial phytase can be used to reduce P excretion by increasing phytate P availability. To reduce the amount of P being excreted into the environment, microbial phytase is routinely added to diets to improve P utilization (Baxter et al., 2003
; Angel et al., 2005). Augspurger et al. (2003) recently demonstrated that P release in broiler chicks by an Escherichia coli-derived phytase was 0.124% at 500 phytase units (FTU) per kg compared with 0.032 or 0.028% for an equivalent dose of commercial preparations of Aspergillus niger or Peniophora lycii phytase, respectively. These results indicate that the efficacy of feed grade phytases varies widely, and other recent studies have reported different P release values for different phytases (Angel et al., 2001; Timmons et al., 2001).
The current study was conducted to evaluate the efficacy of an E. coli-derived phytase and determine its equivalency relative to P from monosodium phosphate (MSP) using growth performance and nutrient digestion in broiler chickens and young pigs.
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MATERIALS AND METHODS
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All protocols used in this study were approved by the Purdue University Animal Care and Use Committee.
Efficacy and Equivalency in Broilers (Exp. 1)
One thousand two hundred 1-d-old male broiler chicks were weighed individually, sorted based on BW, and assigned to 8 diets, such that the average BW across dietary treatments was similar. There were 6 replicate pens with 25 birds per pen. A schedule of 23:1 h of light to dark was maintained. Pen temperatures from d 0 to 7, 8 to 14, and 15 to 42 were 35, 32, and 27°C, respectively. Pens with wood shavings were 1.5 x 2.4 m, providing 0.14 m2/bird.
The chicks were fed starter diets for 3 wk. The starter diets were based on a basal diet (BD) formulated to contain 3,200 kcal of ME, 224 g of CP, 7.7 g of Ca, and 2.4 g of nonphytate P (nPP) per kilogram and adequate in all other nutrients, according to the recommendations of the NRC (1994; Table 1). The BD also contained 2.5 g of Cr2O3 per kg as an indigestible marker. The starter diets consisted of the BD; the BD plus 0.6, 1.2, or 1.8 g of inorganic P (iP) from MSP; and the BD plus 250, 500, 750, or 1,000 FTU per kg of an E. coli-derived phytase. The phytase used in the present research was an E. coli-derived phytase expressed in Schizosaccaromyces pombe (Phyzyme XP, Danisco Animal Nutrition, Marlborough, UK). All diets were fed in a mash form, and the phytase was added as a powder.
Chicks were switched to grower diets at the end of wk 3 and maintained on the grower diets for 3 wk. The grower diets were based on a BD containing 3,200 kcal of ME, 202 g of CP, 6.1 g of Ca, and 1.4 g of nPP per kg, and adequate in all other nutrients (NRC, 1994). Grower diets were supplemented with MSP and phytase at levels identical to those in the starter diets. Body weights and feed intake were recorded at the end of wk 3 and 6.
On d 21, 5 chicks closest to the average weight for each pen were selected as a group and assigned to battery cages for excreta collection as described by Adedokun et al. (2004). A schedule of 23:1 h of light to dark was maintained, and battery temperatures were 27°C. From d 21 to 23, excreta samples were collected from each cage. On d 23, chicks were euthanized via CO2 inhalation. Digesta samples were collected from the ileum, and the tibia was taken from each bird for analysis. Also on d 21, floor pens were normalized to 18 birds/pen to account for losses in some pens.
Efficacy and Equivalency in Young Pigs (Exp. 2)
Pigs were weaned at approximately 21 d and fed a diet containing 220 g of CP and 11.5 g of Lys per kg of diet for 14 d before the pigs were selected for use in the experiment. Eight dietary treatments consisted of a positive control (PC) containing 7.1 g of Ca, 2.4 g of nPP per kg with no supplemental phytase and adequate in all nutrients (NRC, 1998; Table 1
), a negative control (NC) containing no supplemental phytase or iP with 5.3 g of Ca, 0.8 g of nPP per kg, and a Ca:P ratio similar to that of the PC; the NC plus 0.4, 0.8, or 1.2 g of P from MSP per kg; and the NC plus an E. coli-derived phytase at 500, 750, or 1,000 FTU per kg. All diets contained 3.0 g of Cr2O3 per kg as an indigestible marker.
Forty-eight pigs weighing approximately 10 kg were sorted based on BW and sex and housed individually in stainless-steel pens. Pigs were assigned to 8 dietary treatments with 6 pigs per treatment. The pens (0.76 x 0.89 m), each equipped with a nipple waterer, stainless-steel feeder, and plastic-coated expanded metal floor, were located in an environmentally regulated building maintained at 23 ± 2°C, with a 12-h light to dark cycle.
Pigs were weighed and feed intake was recorded once a week. Fresh fecal grab samples were collected on d 22 to 28, pooled by pig, and stored at –18°C until analysis. On d 28, pigs were euthanized, and the left third and fourth metacarpals were excised for determination of bone ash.
Chemical Analysis
Excreta and fecal samples were dried at 55°C in a forced-draft oven, and ileal digesta samples were freeze-dried (Freezemobile 12SL, The Virtis Co. Inc., Gardiner, NY) for 5 d. Excreta, fecal, ileal, and feed samples were ground through a 1-mm screen. Samples were then used to determine DM content by oven drying at 105°C for 24 h. Nitrogen content of the diets was determined by the combustion method (model FP2000, Leco Corp., St. Joseph, MI) according to the AOAC (2000), and GE was determined by adiabatic bomb calorimetry (model 1261, Parr Instrument Co., Moline, IL).
Samples from broilers were analyzed for AA, Ca, Cr, and P (Missouri Experiment Station Chemical Laboratory, University of Missouri, Columbia). Samples for AA analysis were prepared by a 24-h hydrolysis in 6 N HCl at 110°C under an N atmosphere. For Met and Cys analysis, samples were oxidized using performic acid before acid hydrolysis. Samples for Trp analysis were hydrolyzed using barium hydroxide. Amino acids in the hydrolysate were determined by HPLC after postcolumn derivatization (AOAC, 2000). Amino acid concentrations were not corrected for incomplete recovery resulting from hydrolysis. Calcium, Cr, and P concentrations of samples were determined by the inductively coupled plasma, atomic emission spectroscopy method (AOAC, 2000) after wet-ash digestion with nitric and perchloric acids.
Fecal and feed samples from pigs were prepared using wet-ash digestion (AOAC, 2000), and Cr was determined by measuring absorption at 540 nm (Spectronic 21D, Milton Roy Company, Rochester, NY). Calcium in wet-ashed samples was determined by an atomic absorption spectrometer (AAnalyst 300, Perkin Elmer, Norwalk, CT). Phosphorus concentration was determined using a colorimetric assay. Acid molybdate and Fiske’s SubbaRow reducer solution were added to wet-ash samples to form a phosphomolybdenum complex. Color intensity was proportional to P concentration and was determined with a spectrophotometer using absorbance at 620 nm (AOAC, 2000; SpectraCount, Model # AS1000, Packard, Meriden, CT). Phytase activity was determined by the method of Engelen et al. (1994). One FTU is defined as the quantity of enzyme required to hydrolyze 1 µmol of iP from an excess of 15 µM sodium phytate per min at pH 5.5 and 37°C (International Union of Biochemistry, 1979). Left metacarpal bones from pigs and broiler tibias were excised at slaughter, defleshed by blunt dissection, lipid-extracted with ether, and ashed for 16 h at 600°C in a muffle furnace to determine bone ash.
Statistical Analysis
All data were evaluated for violation of the basic assumptions for ANOVA and transformed by the Box-Cox method (Montgomery, 2001) when necessary. Growth performance, digestibility, retention, and bone ash data were analyzed by the GLM procedure (SAS Inst. Inc., Cary, NC) appropriate for a randomized complete block design. Untransformed means are reported, but for subsequent analysis, transformed values were substituted where necessary, and means were compared by orthogonal polynomial contrasts. Linear and nonlinear regression analyses were conducted on several response criteria using the JMP statistical package from SAS. The linear regression model used was
where a is the y intercept, b is the slope of the line, and X is level of supplemental iP from MSP or FTU from E. coli-derived phytase per kg. The nonlinear regression model used was the mechanistic growth model:
where 
1 is the y maximum, 2 controls the y intercept, 3 controls the degree of curvature, and X is level of supplemental iP from MSP or FTU from E. coli-derived phytase per kg. Dependent variables (response criteria) were regressed against independent variables (calculated iP from supplemental MSP or phytase intake from supplemental E. coli-derived phytase). Phosphorus equivalency of phytase was determined through solution of the equations for the independent variable at an equivalent level of the dependent variable.
The second-order Akaike’s Information Criterion (AICc) was used to determine whether the linear or nonlinear regression was a better fit to the data (Motulsky and Christopoulos, 2003). The AICc is calculated for each line using the equation
where N is the number of data points, Ln is the natural log, K is the number of parameters fitted by the regression equation plus 1, and SS is the error sums of squares. The probability that the nonlinear regression equation is correct was calculated using the following equation:
where 
equals the AICc of the nonlinear equation minus the AICc of the linear equation. The sum of the probabilities for the 2 equations explaining the same data is 1, with a probability 
0.5 indicating a nonlinear curve is appropriate, probabilities 
0.5 indicating a linear curve is more appropriate, and probabilities around 0.5 considered ambiguous. If the data for 1 supplement were better fit by a linear equation and the data for the other supplement were better fit by the nonlinear equation, the supplement with the higher probability determined the set of equations to be used.
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RESULTS
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In Exp. 1, the activity of the 4 phytase-containing diets was determined to be 215, 515, 552, or 1,015 in the starter diets, and 382, 657, 896, or 1,215 in the grower diets formulated to contain 250, 500, 750, or 1,000 FTU per kg, respectively. Body weight gain per bird increased linearly and quadratically (P < 0.01) to increasing levels of both MSP and E. coli–derived phytase supplementation in the 0 to 21 (starter), 21 to 42 (grower), and 0 to 42 d (overall) periods (Table 2). Broilers increased their feed intake linearly (P < 0.01) in all 3 periods with increasing levels of MSP or phytase, and quadratically (P < 0.05) in the grower and overall periods with increasing levels of phytase. Feed efficiency increased linearly (P < 0.01) in all 3 periods and quadratically in the starter and overall (P < 0.05) periods in response to increasing supplementation with MSP. Feed efficiency increased linearly (P < 0.01) in the grower and overall periods and quadratically (P < 0.05) in the starter period as E. coli-derived phytase supplementation increased. Percent tibia ash increased linearly (P < 0.01) in response to MSP and E. coli-derived phytase supplementation at the end of the starter period and experiment, and quadratically to the increase in MSP (P < 0.05) and phytase (P < 0.01) supplementation at the end of the experiment.
Gain per bird and percent bone ash were better fit by the nonlinear equation based on probabilities of greater than 86%. However, feed intake was described better by the linear regression equation for iP with a probability greater than 80% and only marginally better by the nonlinear equation for phytase (Table 3). As a result, equivalency was calculated using the nonlinear equation for gain per bird and bone ash, and the linear equation was used for feed intake in broilers. Five hundred FTU of E. coli-derived phytase per kilogram of diet was determined to be equivalent to the addition of 0.72, 0.78, or 1.19 g of iP per kg from MSP using gain per bird, feed intake, and bone ash, respectively, in Exp. 1 (Table 4).
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Table 3. Regressions of growth performance and bone ash content on inorganic P (iP) and Escherichia coli phytase supplementation in Exp. 1
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Table 4. Equivalency of Escherichia coli phytase relative to inorganic P (iP) for growth performance and bone ash content of broilers in Exp. 1
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At d 21, linear decreases were observed in apparent ileal digestibility of DM, energy, N, and Ca (P < 0.05), and quadratic responses were observed in DM and energy (P < 0.01) to increasing concentrations of MSP (Table 5). Ileal digestibility of N (P < 0.05) and P (P < 0.01) increased linearly as phytase supplementation increased. Similarly, linear increases were observed in ileal digestibility of Arg, His, Trp, Tyr (P < 0.01), Phe, Asp, Cys, Glu, Gly, and Pro (P < 0.05) in birds in response to phytase supplementation (Table 6).
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Table 5. Apparent ileal digestibility and apparent retention coefficients of energy and nutrients at d 21 in broilers in Exp. 11
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The response of broilers to increasing concentrations of iP from MSP in P retention at d 21 was negative (linear and quadratic, P < 0.01; Table 5). Their response to MSP supplementation was quadratic for DM, energy, N, Ca, or P retention (P < 0.01). As phytase activity of the diet increased, broilers responded linearly and quadratically (P < 0.05) in apparent retention of DM and energy and quadratically (P < 0.05) in N retention. Apparent retention of P increased (linear and quadratic, P < 0.01) as phytase supplementation increased.
In Exp. 2, the phytase activity of the diets formulated to contain 500, 750, or 1,000 FTU per kg was determined to be 586, 832, or 1,226 FTU per kg, respectively. Pigs fed the NC diet had lower average daily gain, final BW, and percent bone ash than pigs fed the PC diet (P < 0.05; Table 7). Increasing levels of MSP resulted in linear increases in ADG, final BW, and percent bone ash (P < 0.05). Increasing supplemental E. coli-derived phytase increased ADG (linear and quadratic, P < 0.05) and percent bone ash (linear, P < 0.05).
The nonlinear equation failed to converge for data from pigs fed diets supplemented with iP from MSP, and the linear equation fit the data for phytase-supplemented diets with probabilities over 90% for ADG and percent bone ash (Table 8). As a result, the equivalency equations were calculated using the results of the linear regression analysis. Five hundred FTU per kg of E. coli-derived phytase were determined to be equivalent to the addition of 0.49 or 1.00 g of iP per kg from MSP using ADG and bone ash, respectively, in Exp. 2 (Table 9).
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Table 8. Regressions for growth performance and bone ash on inorganic P (iP) and Escherichia coli phytase supplementation for young pigs in Exp. 2
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Table 9. Equivalency of Escherichia coli phytase relative to inorganic P (iP) for growth performance and bone ash content of young pigs in Exp. 2
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Pigs responded to increasing phytase activity in the diet with increases in apparent digestibility of Ca (linear, P < 0.01) and P (linear and quadratic, P < 0.01; Table 10). Increasing levels of supplemental MSP resulted in a linear increase in apparent digestibility of P (P < 0.01) and a quadratic response in apparent digestibility of Ca (P < 0.01). Phosphorus digestibility was lower in pigs fed the NC than the PC (P < 0.01).
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DISCUSSION
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The results obtained from these 2 studies showed that the E. coli-derived phytase investigated is effective in improving P availability in corn-soybean meal diets fed to broilers and young pigs. As supplemental iP and phytase increased, gain, feed intake, and gain:feed in broilers and ADG in young pigs increased linearly.
Traditional industry diets use dicalcium phosphate as the source of supplemental iP. However, NRC (1994 However, NRC (1998) states that dicalcium phosphate is 95 to 100 percent bioavailable, with bioavailability generally expressed as a percentage of MSP or monocalcium phosphate. Johnston et al. (2004), Liu et al. (2000), and Ballam et al. (1984) reported that the efficacy of phytase can be influenced by the ratio of Ca to P, with the efficacy decreasing dramatically when Ca concentration is 2 or more times that of P. In an attempt to minimize the possibility of confounding effects, we decided to use MSP as our iP reference.
The weight gain response of birds to phytase supplementation indicated that the efficacy of this enzyme could peak or plateau around 500 FTU per kg because of the diminishing response to phytase supplementation. This is supported by the fact that the nonlinear equation was 6.5-fold (86.73/13.27%) better fit than the linear equation (Motulsky and Christopoulos, 2003). Interestingly, Onyango et al. (2005) did not see a plateau; instead they reported 17 and 20% increases in gain per bird from d 8 to 22 by supplementing a low-P diet with 500 and 1,000 FTU per kg of an evolved-E. coli phytase, respectively. Dilger et al. (2004) reported 6 and 19% improvements in gain from d 8 to 22 with 500 and 1,000 FTU of the same E. coli-derived phytase used in the current study per kg, respectively, and 9, 14, and 14% increases in gain from d 0 to 42 in male broiler chicks with 500, 750, and 1,000 FTU of Phyzyme XP per kg, respectively. These results, in conjunction with the results of Onyango et al. (2005), indicate that the plateau may not be observed within the range of 0 to 1,000 FTU per kg in broiler chicks fed an adequate P diet from d 0 to 7 and then the phytase-supplemented diet from d 8 to 22. With such a design, chicks build up a sufficient P reserve, thus possibly masking the plateau we have observed at higher supplementation levels.
Addition of phytase to broiler diets increased ileal digestibility of 4 essential and most of the nonessential AA on d 21. Adeola and Sands (2003) documented some instances in the literature where small increases in digestibility of AA were observed. However, those observed increases rarely translated into improved growth performance after accounting for the effect of improved phytate P availability. Adeola and Sands (2003) also pointed to a larger body of reports in which no response was observed in AA utilization to phytase supplementation.
Effects on apparent retention in boilers were far less pronounced at d 21. Increasing levels of MSP negatively affected P retention. Addition of phytase improved retention of P but decreased retention of DM and energy.
Denbow et al. (1995), Harper et al. (1997), and Ravindran et al. (2001) used r2 as the criterion for selecting either linear or nonlinear regression model to describe the changes in certain response criteria to graded levels of phytase and supplemental iP. Neter et al. (1996), however, indicated that r2 is not a meaningful statistic for nonlinear regression because the product of the error sum of squares and the regression sum of squares is not necessarily equal to the total sum of squares. Motulsky and Christopoulos (2003) indicated that the 2 best methods for comparing 2 regression equations for goodness of fit of the same data are an F-test if the 2 equations are nested or AICc if they are not. Because it is not possible to get the linear equation by setting some of the parameters of the mechanistic growth model (Y = 1 x (1 – 2 x e(–3 x X))), , to zero or one, the AICc is the only valid means of comparison in this situation.
The r2 values of linear models generated from the poultry growth performance data were lower than those observed in the literature (Denbow et al., 1995; Yi et al., 1996a; Adedokun et al., 2004). The differences may be attributed to duration of study and age of birds. Denbow et al. (1995) and Yi et al. (1996a) conducted 21-d trials, whereas our trial was 42 d in duration. Adedokun et al. (2004) used only linear regression equations and obtained high r2 values using the same E. coli-derived phytase. However, the duration of their study was 14 d after allowing birds ad libitum access to a standard P-adequate starter diet for 7 d. The higher r2 values of Adedokun et al. (2004) could be the result of P stores accumulated during the first 7 d, which may have decreased variability by modifying the response to lower iP in the diet. They could also be the result of a shorter observational period because we had 4 more weeks for variance to increase as the birds grew. The equivalent of between 0.92 and 1.82 g of P from MSP would be released by 1,000 FTU of E. coli-derived phytase per kilogram of diet in broilers depending on the performance criteria used. The most reliable predictor of equivalency in this study, based on a combination of highest r2 value and probability from AICc, was gain per bird with 1,000 FTU per kg being equivalent to 0.92 g of iP from MSP per kg. This is slightly lower than 1.01, or 1.03 g of P per kg for BW gain and the average of all response criteria, respectively, reported by Adedokun et al. (2004).
The weanling pigs responded to supplemental MSP or E. coli-derived phytase with linear improvements in ADG, percent bone ash, and BW at the end of 4 wk of study. Using a different E. coli-derived phytase for 28 d in weanling pigs, Adeola et al. (2004) observed 17 and 10% increases in ADG and final BW, respectively, over the NC with 1,000 FTU per kg, compared with improvements of 19 and 8% observed for those response criteria, respectively, in the current study. However, the greatest difference in ADG, percent bone ash, or final BW between the NC and phytase supplementation was observed with the NC + 750 FTU per kg of diet, indicating the diminishing response to phytase supplementation in pigs as well. Similar responses were observed in the nutrient digestibility. Phosphorus digestibility increased by 0.22, 0.13, and 0.02 as phytase supplementation increased from 0 to 500, 500 to 750, and 750 to 1,000 FTU per kg, respectively.
The r2 values for the performance prediction equations generated from the weanling pig growth performance data were lower than those reported by Yi et al. (1996b) and Harper et al. (1997). Those researchers developed regressions using treatment means rather than the individual observations, which may have resulted in elevated r2 values. Harper et al. (1997) reported that 500 units of fungal-derived phytase was equivalent to the addition of between 0.87 and 0.96 g of iP from dicalciummonocalcium phosphate supplements, whereas Yi et al. (1996b) reported that it was equal to the addition of 1.28 g of iP from defluorinated phosphate. Five hundred FTU of E. coli-derived phytase per kg used in the current study was found to be equivalent to the addition of 0.49 and 1.00 g of iP from MSP per kg of diet based on ADG and bone ash, respectively. The differences between our results and those of Yi et al. (1996b) and Harper et al. (1997) could be greater than reported because of the use of different sources of iP as standards. Phosphorus availability is similar for monocalcium phosphate and MSP (NRC, 1998), but de-fluorinated phosphate is only 80% available compared with MSP (Soares, 1995). Kemme et al. (1997) indicated that the efficacy of phytase in releasing digestible P is influenced by the physiological status of pigs with grow-finishing pigs ranking above starter pigs. Phytase has been shown to be more efficacious in reducing water-soluble P excretion in grower pigs than starter pigs (J. A. Jendza and O. Adeola, unpublished data). Starter pigs may lack the ability to adequately capitalize on phytase supplementation due to a lack of gut maturity or insufficient retention time.
In summary, the E. coli-derived phytase used in the current study is capable of partially alleviating the deleterious effect of feeding a P-deficient corn-soybean meal-based diet on growth performance in broiler chicks and weanling pigs, as well as influencing the digestibility of several essential AA in broilers. When supplementing P-deficient diets with 500 FTU per kg, the E. coli-derived phytase is equivalent to the addition of between 0.72 and 1.19 g in broiler diets and between 0.49 and 1.00 g of iP from MSP per kg in weanling pig diet.
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Footnotes
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1 Journal paper No. 2006-17863 of the Purdue University Agricultural Research Programs. The authors thank Danisco Animal Nutrition, Marlborough, UK, for financial support of this research, and the staff of the Purdue University Swine Research Unit for care of experimental animals. 
2 Corresponding author: ladeola{at}purdue.edu
Received for publication April 5, 2006.
Accepted for publication July 18, 2006.
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Abstract
INTRODUCTION
