J. Anim Sci. 2008. 86:858-870. doi:10.2527/jas.2007-0312
© 2008 American Society of Animal Science
Effect of low doses of Aspergillus niger phytase on growth performance, bone strength, and nutrient absorption and excretion by growing and finishing swine fed corn-soybean meal diets deficient in available phosphorus and calcium1
T. L. Veum2 and
M. R. Ellersieck
Agricultural Experiment Station and Division of Animal Sciences, University of Missouri, Columbia 65211
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Abstract
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Two experiments were conducted to evaluate the efficacy of low doses of Aspergillus niger (AN) phytase for growing and finishing pigs fed corn-soybean meal (SBM) diets with narrow Ca:P ratios that were about 0.9 g/kg deficient in available P and Ca. Experiment 1 utilized 120 pigs with an early finisher period from 51.5 ± 0.2 to 89.7 ± 0.9 kg of BW and a late finisher period that ended at 122.5 ± 2.0 kg of BW. During each period, treatments were the low-P diets with 0, 150, 300, or 450 units (U) of AN phytase added/kg of diet, and a positive control (PC) diet. There were linear increases (P 
0.001) in bone strength and ash weight, the absorption of P (g/d and %) and Ca (%), and overall ADG (P = 0.01) with increasing concentration of AN phytase. Pigs fed the diets with 150, 300, or 450 U of AN phytase/kg did not differ from pigs fed the PC diet in growth performance overall, and pigs fed the diets with 300 or 450 U of AN phytase did not differ in P and Ca absorption (g/d) or bone ash weight from pigs fed the PC diet. However, only pigs fed the diet with 450 U of AN phytase/kg had bone strength similar to that of pigs fed the PC diet. Experiment 2 utilized 120 pigs in a grower phase from 25.3 ± 0.1 to 57.8 ± 0.8 kg of BW and a finisher phase that ended at 107.6 ± 1.0 kg of BW. Treatments were the low-P diet with AN phytase added at 300, 500, or 700 U/kg of grower diet, and 150, 250, or 350 U/kg of finisher diet, respectively, resulting in treatments AN300/150, AN500/250, and AN700/350. Growth performance and the absorption (g/d) of P and Ca for the grower and finisher phases were not different for pigs fed the diets containing AN phytase and pigs fed the PC diets. However, pigs fed the PC diets excreted more fecal P (g/d, P 0.01) during the grower and more P and Ca (g/d, P < 0.001) during the finisher phases than the pigs fed the diets with phytase. There were linear increases (P 0.05) in bone strength and bone ash weight with increasing concentration of AN phytase. However, pigs fed the PC diets had a greater bone strength and bone ash weight than pigs fed diets AN300/150, AN500/250 (P 0.02), or AN700/350 (P 0.08). There were no treatment responses for N or DM digestibility in either experiment. Phytase supplementation reduced fecal P excretion from 16 to 38% and fecal Ca excretion from 21 to 42% in these experiments. In conclusion, 450 U of AN phytase/kg was effective in replacing 0.9 g of the inorganic P/kg of corn-SBM diet for finishing swine based on bone strength, whereas 300 or 150 U of AN phytase/kg of diet maintained growth performance of grower or finisher pigs, respectively.
Key Words: calcium • growing-finishing pig • nutrient absorption • nutrient excretion • phosphorus • phytase
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INTRODUCTION
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Most of the phytate P in grain-oil seed meal diets is excreted in the manure because swine produce little to no intestinal phytase (Pointillart et al., 1984
, 1987). However, supplementation of corn-soybean meal (SBM) diets that are deficient in available P (aP) with an Aspergillus niger (AN) phytase increases P absorption and decreases P excretion by swine from weaning to finishing (Han et al., 1997; Harper et al., 1997; Liu et al., 1998). Studies with growing pigs in the Netherlands showed that 500 to 2,000 units (U) of AN phytase/kg of diet deficient in aP released 0.8 to 1.0 g of aP/kg of diet, with phytase having a greater efficacy in a corn-SBM diet than a practical Dutch diet (Jongbloed et al., 1996, 2000). For growing-finishing pigs fed corn-SBM diets deficient in aP, 500 U of AN phytase/kg of diet was equivalent to about 0.7 g of inorganic P/kg for ADG, and 1.1 g of inorganic P/kg for P digestibility and 10th-rib shear force (Harper et al., 1997). The efficacy of phytase is affected by physiological age, diet, and management factors (Mroz et al., 1994; Kemme et al., 1997a,b). Decreasing dietary Ca to narrow the Ca:total P (tP) ratio will also increase the efficacy of AN phytase (Lei et al., 1994; Qian et al., 1996; Liu et al., 1998). The dose-response relationship of AN phytase fits an exponential curve with maximal efficacy up to about 500 U/kg of diet (Jongbloed et al., 2000), with efficacy demonstrated up to 15,000 U/kg of pig diet (Kies et al., 2006).
Two experiments were conducted with group-fed finishing and growing-finishing pigs to evaluate decreased concentrations of AN phytase (Natuphos) in corn-SBM diets deficient in aP and Ca, and with narrow Ca:tP ratios to enhance the efficacy of AN phytase for nutrient absorption. Response criteria were growth performance, metacarpal bone characteristics, and the apparent total-tract absorption and fecal excretion of Ca, P, N, and DM.
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MATERIALS AND METHODS
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Phytase Source
A transgenic microbial phytase that contains genetic material derived from Aspergillus ficuum (Heinzl, 1996) and is produced commercially in Aspergillus niger (AN; Natuphos in meal form, BASF Corp. Inc., Florham Park, NJ) was used in 2 experiments. This AN phytase has pH optima at 2.5 and 5.0, and initiates dephosphorylation of phytate (myoinositol hexakisphosphate) at the 3-position compared with plant phytases that initiate dephosphorylation at the 6-position (Kies, 1996). The AN phytase product was analyzed in quadruplicate for phytase activity before mixing the diets, and the phytase activity was 5,203 U/g of product. One U of enzyme activity is defined as the amount of enzyme that liberates 1.0 µmol of inorganic P per min from 5.1 mM sodium phytate at 37°C and pH 5.5 (Engelen et al., 1994, 2001).
Animals, Housing, and Diets
These experiments were approved by the University of Missouri Animal Care and Use Committee.
Exp. 1.
For 3 wk before beginning this experiment, all pigs were fed a corn-SBM diet containing 6.0 g/kg of Ca and 5.0 g/kg of tP. Crossbred finishing pigs (70 barrows and 50 gilts, GenetiPorc US, LLC, Morris, MN) were allotted to 5 dietary treatments by litter, sex, and BW in a randomized complete block design. This experiment had an early finishing period 1 (experimental d 0 to 39) with a beginning BW of 51.5 ± 0.2 at 90 ± 2 d of age, and a late finishing period 2 (experimental d 39 to 75) with beginning and ending BW of 89.7 ± 0.9 and 122.5 ± 2.0 kg, respectively. Pigs were housed 3 per pen (4 m2) in an enclosed building with a concrete slated floor. There were 8 BW blocks (pens)/treatment with sex equalized within blocks. Temperature was maintained between 18 and 21°C with thermostatically controlled exhaust fans and heaters. Each pen had a nipple drinker and a self feeder. Pigs and feeders were inspected daily during the experiment.
To increase the consistency of the diet composition, stocks of yellow corn and SBM were set aside for use in this experiment and analyzed for Ca, P, N, and DM. Stocks of feed grade dicalcium phosphate and ground limestone were analyzed for Ca and P, and Ca, respectively, with the bioavailability of P and Ca from these sources estimated at 100% (NRC, 1998). The analyzed nutrient values of the ingredients were used to formulate the basal low-P batch mixes and the positive control (PC) diets. The analyzed P values for corn and SBM were multiplied by the bioavailability of P values (%) from the NRC (1998) to obtain estimated aP values for the batch mixes. Dicalcium phosphate was added to the basal low-P period 1 batch mix, and the period 1 and 2 batch mixes were made to have calculated aP and Ca deficiencies of 0.9 g/kg based on the NRC (1998) requirements for pigs in the BW ranges of 50 to 80 kg and 80 to 120 kg, respectively (Table 1). Therefore, the Ca:tP ratios for the basal batch mixes and PC diets were within a narrow range of 1.1:1 to 1.2:1.
After mixing, the basal batch mixes that were deficient in aP and Ca and the PC diets were sampled and analyzed, and the analyzed values were used to determine the digestibility and fecal excretion (g/d and %) of Ca, P, N, and DM in period 2. The basal period 1 and 2 batch mixes used in the current experiment met all other nutrient requirements (NRC, 1998) and were subdivided and supplemented with 0 (negative control), 150, 300, or 450 U of AN phytase/kg of diet to make dietary treatments AN0, AN150, AN300, or AN450, respectively. The fifth dietary treatment was the PC, with diets for periods 1 and 2 that met the NRC (1998) nutrient requirements for finishing pigs. All the diets were prepared in meal form and fed to appetite in self feeders. Chromic oxide was added to the period 2 diets at 0.5 g/kg from d 39 to 52 of the experiment to determine nutrient digestibility.
Exp. 2.
Crossbred growing pigs (76 barrows and 44 gilts, GenetiPorc US, LLC, Morris, MN) with an average starting BW of 25.3 ± 0.1 kg at 54 ± 1 d of age were allotted by litter, sex, and BW to 4 dietary treatments in a 2-phase experiment with a randomized complete block design. Pigs were housed 3 per pen in the same facility used for Exp. 1. There were 10 BW blocks (pens)/treatment, with sex equalized within BW blocks. Temperature was maintained between 19 and 21°C during the grower phase (experimental d 0 to 35) and 17 to 19°C during the finisher phase (experimental d 35 to 83) with beginning and ending BW of 57.8 ± 0.8 and 107.6 ± 1.0 kg, respectively.
Stocks of yellow corn, SBM, feed grade dicalcium phosphate, and ground limestone were set aside for this experiment and analyzed for nutrient content as described for Exp. 1. Analyzed nutrient values of the ingredients were used to formulate the basal batch mixes that were deficient in aP and Ca and the PC diets for the grower and finisher phases. The analyzed P values for corn and SBM were multiplied by the bioavailability of P values from the NRC (1998) to obtain estimated aP values for the basal batch mixes. The basal grower and finisher low-P batch mixes contained supplemental dicalcium phosphate and were made to have calculated deficiencies of 1.0 g/kg for aP and 0.9 g/kg for Ca for both growing and finishing pigs in the BW ranges of 20 to 50 kg and 50 to 80 kg, respectively (NRC, 1998). Therefore, similar to Exp. 1, all diets had a narrow range in Ca:tP ratio of 1.1:1 to 1.2:1. After mixing, the basal batch mixes and the PC diets were sampled and analyzed, and the analyzed values were used to determine the digestibility and fecal excretion (g/d and % of intake) of Ca, P, N, and DM during the grower and finisher phases (Table 2). For the grower phase, the basal batch mix was subdivided and supplemented with 300, 500, or 700 phytase U/kg of diet.
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Table 2. Ingredient and chemical composition (%) of air-dried basal grower and finisher diets, as-fed basis, for Exp. 21
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For the finisher phase, phytase supplementation of the dietary treatments was decreased to 50% of the concentration used in the grower diets, with AN phytase added at 150, 250, or 350 phytase U/kg of basal diet, respectively. Therefore, the 3 dietary treatment combinations made by supplementation of the basal grower and finisher batch mixes with AN phytase were AN300/150, AN500/250, and AN700/350, respectively. The fourth treatment was the grower and finisher PC diets that met the NRC (1998) nutrient requirements for aP (calculated) and Ca. The diets were prepared in meal form and fed to appetite in self feeders. Chromic oxide was added to the diets at 0.5 g/kg from experimental d 14 to 26 of the grower phase and d 42 to 54 of the finisher phase to determine nutrient digestibility.
Measurements
Exp. 1.
Pigs were weighed individually on d 0, 39, 46, and 75 (the end) of the experiment. Pen feed consumption was determined for periods 1 and 2 and for the 6-d fecal collection during period 2. Fresh fecal grab-samples (about 100 g) were collected from individual pigs once daily from d 47 to 52 of the experiment (average pig BW of 96.0 ± 1.1 kg on d 46). Samples from individual pigs within pens were pooled and frozen in plastic freezer bags until analyzed. Before analysis, fecal collections for each pen were thawed, pooled, and air-dried at 55°C. The dried fecal samples and samples of the low-P basal batch mixes and the PC diets were ground to pass through a 1.0-mm screen. Duplicate subsamples of feces and quadruplicate subsamples of the low-P basal batch mixes and PC diets were utilized for Ca, P, Cr, N, and DM analyses (AOAC, 1990). The subsamples were wet-ashed for mineral analysis, and the digests were analyzed for the concentration of tP by the molybdovanadate colorimetric method (Spectra Rainbow Microplate Reader, Tecan Inc., Durham, NC) and for the concentrations of Ca and Cr by atomic absorption spectrophotometry (Spector AA-30, Varian Analytical Instruments, San Fernando, CA). Analyzed values (Table 1
) were used to determine the total-tract digestibility and excretion of P, Ca, N, and DM for period 2.
At the end of the experiment, the pigs were killed (electrocution followed by exsanguination). The right front foot of each pig was removed and refrigerated at 2°C. The third metacarpal bone was excised and cleaned of all adhering tissue within 3 d for bone size and weight measurements and the determination of breaking strength and ash weight. A caliper (model CDS6, Mitutoyo Corp., Kawasaki, Japan) was used to measure metacarpal bone length and the midshaft widths at the narrowest and widest points. Breaking strength of the fresh bones was determined using an Instron testing machine (Model TML, Instron Corp., Canton, MA) similar to the procedure described by Crenshaw (1986). Force was applied to the center of the bone, which was held by 2 supports spaced 3.0 cm apart. After the determination of breaking strength, the bones were wrapped with cheesecloth, boiled in deionized water for 2 h, dried at 55°C for 24 h, and extracted with ethyl ether for 4 d. Ash weight was determined after the fat-free bones were dried at 55 and 100°C for 18 and 2 h, respectively, and ashed in a muffle furnace at 600°C for 16 h (AOAC, 1990).
Exp. 2.
Pigs were weighed individually on d 0, 21, 35, 49, and 83 of the experiment. Pen feed consumption was determined for the grower and finisher phases, and for the 5-d fecal collections during experimental d 22 to 26 of the grower phase (average pig BW on d 21 of 42.6 ± 0.7 kg) and experimental d 50 to 54 of the finisher phase (average pig BW of 72.1 ± 0.09 on d 49). Fresh fecal samples were collected and stored, and both diet and fecal samples were processed and analyzed for Ca, P, Cr, N, and DM, as described for Exp. 1 (Table 2). At the end of the experiment, pigs were killed and the third metacarpal bone was removed from the right front foot of each pig to determine breaking strength and other bone characteristics, as described for Exp. 1.
Statistical Analysis
All data for both experiments were analyzed by ANOVA as a randomized complete block design (Snedecor and Cochran, 1989) using the GLM procedure (SAS Inst. Inc., Cary, NC). Pens of pigs were the experimental units. Significance was taken at P 0.05, with a trend being between P 
0.06 and P 0.10. For Exp. 1, the preplanned single df comparisons were the linear and quadratic responses for the diets AN0, AN150, AN300, and AN450, and the PC diet vs. each individual AN phytase treatment, AN0, AN150, AN300, or AN450. For Exp. 2, the preplanned single df comparisons were the linear and quadratic responses for the 3 grower/finisher dietary treatment combinations of AN300/150, AN500/250, and AN700/350, respectively, and the PC diet vs. each individual AN phytase grower/finisher treatment combination of AN300/150, AN500/250, or AN 700/350.
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RESULTS
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Pig Growth Performance
Exp. 1.
All pigs completed the experiment. For period 1, there were linear increases (P = 0.01) in ADG with increasing concentration of AN phytase in diets AN0, AN150, AN300, and AN450 (Table 3). Also for period 1, pigs fed the PC diet had a greater ADG than pigs fed diets AN0 (P < 0.001) or AN150 (P = 0.06), and a greater (P = 0.05) ADFI than the pigs fed diet AN0. For period 2, there was a quadratic response (P = 0.06) in G:F with increasing concentration of AN phytase. Overall from d 0 to 75, there were linear (P = 0.07) and quadratic (P = 0.03) responses in G:F with increasing concentration of AN phytase, and pigs fed the PC diet had a greater overall ADG (P = 0.01) and G:F (P = 0.03) than pigs fed diet AN0. The quadratic responses for G:F in period 2 and overall occurred because the G:F of pigs fed diet AN450 was not greater than that of pigs fed diet AN300. For period 1, growth performance was not different for pigs fed the PC diet compared with pigs fed diets AN300 or AN450. For period 2 and overall, growth performance was not different for pigs fed the PC diet compared with pigs fed diets AN150, AN350, or AN450.
Exp. 2.
Two pigs on AN phytase treatment AN500/250 died during the experiment, and the cause of death was unrelated to the treatment. There were no linear or quadratic responses for ADG, ADFI, or G:F with increasing concentrations of AN phytase in diets AN300/150, AN500/250, or AN700/350, respectively, for the grower or finisher phases or for the entire experiment overall (Table 4). In addition, there were no differences in ADG, ADFI, or G:F for pigs fed the PC diet compared with pigs fed the diets containing AN phytase for the grower or finisher phases or for the experiment overall.
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Table 4. Effect of Aspergillus niger (AN) phytase supplementation on growth performance of growing-finishing pigs in Exp. 21
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Metacarpal Bone Characteristics
Exp. 1.
There were linear increases (P < 0.001) in metacarpal bone breaking strength, fresh bone weight, fat-free dry weight, and ash weight with increasing concentration of AN phytase (Table 5). Pigs fed the PC diet had a greater (P 0.003) bone breaking strength than pigs fed diets AN0, AN150, or AN300, whereas the bone breaking strength of pigs fed the PC diet or diet AN450 did not differ from each other. Pigs fed the PC diet also had greater fat-free dry bone and bone ash weights than pigs fed diet AN0 (P < 0.001) or diet AN150 (P = 0.01). There were linear (P = 0.005) and quadratic (P = 0.10) increases in metacarpal bone length, and a linear increase (P = 0.07) in midshaft width at the narrowest point with increasing concentration of AN phytase. However, there were no treatment differences for midshaft width taken at the widest point (experimental mean ± SE of 20.74 ± 0.33 mm, data not provided). Also, there were no differences in metacarpal bone characteristics for pigs fed the PC diet compared with pigs fed diet AN450.
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Table 5. Effect of Aspergillus niger phytase supplementation on metacarpal bone characteristics of finishing pigs in Exp. 11
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Exp. 2.
There were linear increases (P 0.05) in metacarpal bone breaking strength, fat-free dry weight, and ash weight with increasing dietary concentration of AN phytase (Table 6). However, pigs fed the PC grower and finisher phase diets had greater metacarpal bone breaking strength, fat-free dry weight, and ash weight than pigs fed dietary treatments AN300/150 (P < 0.001), AN500/250 (P 0.02), or AN700/350 (P 0.08).
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Table 6. Effect of Aspergillus niger phytase supplementation on metacarpal bone characteristics of growing-finishing pigs in Exp. 21
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Apparent Total-Tract Absorption and Excretion of P, Ca, and N, and DM Digestibility.
Exp. 1.
The intakes of P and Ca were greater (g/d, P 0.01) for pigs fed the PC diet than for pigs fed the low-P diets with or without AN phytase (Table 7). There was a linear increase (g/d, P < 0.001) in the apparent total-tract absorption of P, and linear decreases (g/d, P 0.01) in the apparent fecal excretion of P and Ca with increasing dietary concentrations of AN phytase. In addition, there was a quadratic response in fecal Ca excretion (g/d, P = 0.08) because the fecal Ca excretion by the pigs fed diet AN450 was not less than that of the pigs fed diet AN300.
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Table 7. Effect of Aspergillus niger phytase supplementation on the apparent total tract absorption and excretion of P and Ca of finishing pigs in Exp. 11
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The apparent absorption of P was greater (g/d, P 0.001) for pigs fed the PC diet than for pigs fed diets AN0 or AN150, and pigs fed the PC diet excreted more (g/d, P 0.006) P than pigs fed diets AN150, AN300, or AN450. In addition, pigs fed the PC diet excreted more (g/d, P 0.01) Ca than the pigs fed diets AN0, AN150, AN300, or AN450.
Expressed as percentages of intake, there were linear increases (P 0.001) and quadratic responses (P 0.02) in the absorption of P and Ca, and associated linear decreases and quadratic responses in the fecal excretion of P and Ca, with increasing dietary concentration of AN phytase. The quadratic responses occurred because the percentages of P and Ca absorbed and excreted by pigs fed diets AN300 or AN450 were not different. Pigs fed diets AN300 or AN450 absorbed greater (P 0.01) percentages of P and Ca, and excreted less (P 0.01) fecal P and Ca than the pigs fed the PC diet. In addition, there were trends for the percentages of Ca absorbed and excreted to be greater and smaller (P = 0.06), respectively, for pigs fed diet AN150 than for pigs fed the PC diet.
There were no linear or quadratic responses and no preplanned treatment comparison differences for N or DM (data not provided). The experimental means ± SE for N intake, apparent N absorption, and fecal N excretion in g/d, and DM digestibility (%), respectively, were 62.8 ± 3.9, 51.2 ± 3.0, 11.6 ± 1.3, and 88.0 ± 0.4.
Exp. 2.
Pigs fed the PC diet had greater intakes of P and Ca (g/d, P < 0.001) than pigs fed the diets containing AN phytase (AN300/150, AN500/250, or AN700/350) for the grower and finisher phases (Table 8). Pigs fed the PC diet also excreted more P (g/d, P 0.01) during the grower phase, and more fecal P and Ca (g/d, P < 0.001) during the finisher phase than pigs fed any of the diets containing AN phytase. However, the grams of P and Ca absorbed per day were not different for pigs fed the PC diet or pigs fed the diets containing AN phytase for the grower or finisher phases.
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Table 8. Effect of Aspergillus niger phytase supplementation on the apparent total tract absorption and excretion of P and Ca by growing and finishing pigs in Exp. 21
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Expressed as percentages of intake, there were no treatment comparison differences for the apparent percentages of P and Ca absorbed or excreted during the grower phase. For the finisher phase, there was a linear trend for increases (P = 0.10) in the apparent absorption of P and Ca, with corresponding decreases in the percentages of P and Ca excreted. Pigs fed the PC diets also excreted more P and Ca than the pigs fed diets AN500/250 (trend at P 0.10) or AN700/350 (P 0.01). There were no linear or quadratic responses, and no preplanned grower or finisher phase treatment comparison differences for N or DM (data not provided). The experimental grower phase means ± SE for N intake, apparent N absorption, and fecal N excretion in grams/day, and DM digestibility (%), respectively, were 60.6 ± 2.2, 49.7 ± 1.6, 10.9 ± 0.8, and 88.4 ± 0.4. The experimental finisher phase means ± SE for N intake, apparent N absorption, and fecal N excretion in grams/day, and DM digestibility (%), respectively, were 71.3 ± 1.7, 56.8 ± 1.3, 14.5 ± 1.0, and 87.3 ± 0.6.
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DISCUSSION
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The AN phytase used in these experiments with group-fed finishing and growing-finishing pigs was effective in hydrolyzing phytate in corn-SBM diets that were about 0.9 g/kg below the NRC (1998) dietary requirements for aP and Ca. For the finishing pigs in Exp. 1 (51.5 to 122.5 kg of BW), there were linear increases in ADG, metacarpal bone breaking strength and ash weight, and the apparent absorption of P (g/d and %) and Ca (%) with increasing concentration of AN phytase up to 450 U/kg of low-P diet, the greatest concentration fed. More importantly, finishing pigs fed the low-P diets containing 150, 300, or 450 U of AN phytase/kg did not differ from pigs fed the PC diet in growth performance (ADG, ADFI, and G:F), and finishing pigs fed the low-P diets containing 300 or 450 U of AN phytase/kg did not differ from pigs fed the PC diet in the grams of P and Ca absorbed/day, or in the grams of metacarpal bone ash. However, only finishing pigs fed the low-P diet containing 450 U of AN phytase/kg had metacarpal bone strength comparable with that of pigs fed the PC diet. Therefore, 450 U of AN phytase/kg of diet replaced all of the inorganic P (0.9 g/kg of diet) for late-finisher pigs from 89.7 to 122.5 kg of BW. Other experiments with growing-finishing pigs fed corn-SBM diets deficient in aP also showed that AN phytase concentrations of about 500 U/kg of diet were required to obtain bone strength or P absorption values comparable with those of pigs fed the PC diets, whereas lower concentrations of AN phytase were adequate for growth performance (Harper et al., 1997; Liu et al., 1997). Cromwell et al. (1993, 1995) also showed linear increases in growth performance criteria, bone breaking strength, and bone ash with increasing concentration of AN phytase up to 1,000 U/kg in corn-SBM diets deficient in aP fed to growing-finishing pigs. However, the lower efficacy of the AN phytase observed in the experiments by Cromwell et al. (1993, 1995) may be the result of greater dietary Ca concentrations and wider Ca:tP ratios in those experiments compared with the current experiments and other experiments with growing or growing-finishing pigs (Harper et al., 1997; Kemme et al., 1997b; Liu et al., 1998). It is well known that a wide range in Ca:tP ratio has negative effects on pig growth performance (Lei et al., 1994; Cromwell et al., 1995; Qian et al., 1996), bone development (Nielsen et al., 1971), digestibility of P and other nutrients (Liu et al., 1998; Johnston et al., 2004), and the efficiency of phytase to release P from phytate (Lantzsch et al., 1994). Lowering the Ca:tP ratio in low-P corn-SBM diets to 1.0:1 or 1.2:1 increased the efficacy of AN phytase to hydrolyze phytate P for weaning and growing-finishing pigs compared with wider Ca:tP ratios (Qian et al., 1996; Liu et al., 1998, 2000).
For the current growing-finishing pig experiment (25.3 to 107.6 kg of BW), there were no linear or quadratic responses for growth performance criteria or for the grams of P and Ca absorbed or excreted daily, although there was a linear increase in metacarpal bone breaking strength and bone ash weight with increasing concentration of AN phytase. In addition, the growth performance responses of pigs fed the PC diets were not different from pigs fed any of the AN phytase treatment combinations (AN300/150, AN500/250, or AN700/350 U/kg) for the grower or finisher phases or for the entire experiment. Harper et al. (1997) also showed that 250 U of AN phytase/kg of diet was adequate for growth performance and the absorption (%) of P and Ca by pigs fed corn-SBM diets that were deficient in aP by 1.0 or 0.5 g/kg during the grower or finisher phases, respectively, compared with pigs fed a PC diet. In another experiment with corn-SBM grower and finisher diets that were deficient in aP by 0.8 g/kg, 167 U of AN phytase/kg was adequate for growth performance and Ca absorption (%), although 333 U of AN phytase/kg was required for adequate P absorption (%) compared with pigs fed the PC diet (Harper et al., 1997). At our station, the efficacy of 250 U of AN phytase/kg of corn-SBM diet deficient in aP was increased 2-fold for growth performance by soaking before feeding compared with feeding as a dry meal, with the growth performance of growing pigs fed the soaked diet containing 250 U of AN phytase/kg being equivalent to that of pigs fed the dry PC diet (Liu et al., 1997).
For metacarpal bone strength in the current growing-finishing experiment, pigs fed the PC diet had stronger bones than pigs fed grower/finisher diets AN300/150 or AN500/250, with a trend for stronger bones than pigs fed grower/finisher diet AN700/350. Therefore, even though the efficacy of AN phytase may increase with increasing physiological age (Kemme et al., 1997a), the 50% reduction in phytase concentrations in the finisher diets compared with the phytase concentrations in the grower diets in the current grower/finisher experiment did not provide adequate phytase in the finisher diets to maintain bone strength compared with pigs fed the PC diet. Nevertheless, we did not observe any differences among treatment groups in lameness, activity in the pens, or in the ability to walk to the scale when the pigs were weighed individually. In another experiment, mobility score and fat-free dry metatarsal bone weight of weanling pigs fed a corn-SBM diet deficient in aP with 500 U of microbial phytase/kg of diet were not different from pigs fed the PC diet (Omogbenigun et al., 2003). Whereas 350 U of AN phytase/kg of finisher diet in the current experiment (0.9 g/kg deficient in aP) was not adequate for metacarpal bone strength compared with pigs fed the PC diet, Harper et al. (1997) showed that 333 U of AN phytase/kg of finishing diet (0.8 g/kg deficient in aP) was adequate with 10th-rib shear force as the criterion compared with pigs fed the PC diet.
The lack of an AN phytase effect on the N response criteria or DM digestibility (%) by growing or finishing pigs in the current 2 experiments is in agreement with some other experiments in which AN phytase did not increase the total-tract apparent percentage absorption of N or DM in corn-SBM diets deficient in aP fed to swine (Sands et al., 2001; Johnston et al., 2004; Radcliffe et al., 2006). Also, AN phytase did not increase the apparent ileal or total-tract digestibilities of soybean protein or amino acids in semipurified diets fed to growing swine (Yi et al., 1996; Traylor et al., 2001), or in a high phytate diet containing rice bran fed to growing pigs (Liao et al., 2005). In addition, 2 different Escherichia coli-derived phytase enzyme products did not improve protein utilization from SBM or corn gluten meal for chicks (Augspurger and Baker, 2004) or from a corn-SBM diet fed to growing pigs (Veum et al., 2006).
For the current finishing experiment (Exp. 1), pigs fed the diets containing 150, 300, or 450 U of AN phytase/kg of diet excreted 28, 37, and 38% less P, respectively, and 38, 48, and 42% less Ca, respectively, than the pigs fed the PC diet (g/d comparisons from Table 7). In other experiments at our station, supplementation of corn-SBM diets deficient in aP and Ca with 500 U of AN phytase/kg reduced P excretion from 36 to 40% and Ca excretion from 35 to 64% by growing or growing-finishing pigs compared with pigs fed PC diets (Liu et al., 1997, 1998). At another station, supplementation of a corn-SBM diet that was adequate in Ca and deficient in aP with 500 U of AN phytase/kg reduced P excretion 31% compared with finishing pigs fed the PC diet (Cromwell et al., 1995).
For the current growing-finishing experiment (Exp. 2), pigs fed the grower phase diets containing 300, 500, or 700 U of AN phytase/kg excreted 21, 16, and 26% less P, respectively, and 21, 23, and 21% less Ca, respectively, than pigs fed the grower PC diet (g/d comparisons from Table 8). For the finishing phase, pigs fed the diets containing 150, 250, or 350 U of AN phytase/kg excreted 24, 30, and 31% less P, respectively, and 22, 28, and 29% less Ca, respectively, than the pigs fed the finisher PC diet. These reductions in P excretion are within the range of values reported in other experiments with growing-finishing pigs that were group-fed corn-SBM diets deficient in aP containing 167 to 500 U of AN phytase/kg of diet (Harper et al., 1997) or 240 to 830 U of AN phytase/kg of diet (Cromwell et al., 1995) compared with pigs fed PC diets (Ca excretion was not reported in those experiments). Supplementation of a corn-SBM-rapeseed meal diet deficient in aP with 1,000 U of AN phytase/kg of diet reduced P and Ca excretion by 42 and 21%, respectively (Han et al., 1997). Supplementation of a grain sorghum-canola meal diet deficient in aP with 200 to 600 U of AN phytase also reduced the fecal excretion of P by 15 to 22% and Ca by 12 to 25% (Veum, 1996b).
An estimate of the % P released by AN phytase in the late-finishing low-P diets in Exp. 1 may be calculated utilizing the data in Table 7. The estimated aP in the basal (negative control) diet is 0.057% (1.87 g of absorbed P/d divided by 3,280 g of ADFI multiplied by 100). The % aP in the basal diet is subtracted from the total % aP in each diet containing AN phytase to obtain the estimated % P released by AN phytase. Using this method of calculation, the P released by AN phytase in diets AN150, AN300, and AN450 is estimated at 0.045, 0.072, and 0.076%, respectively. The estimated aP provided by dicalcium phosphate in the PC diet is 0.08%, close to the % aP released by AN phytase in diet AN450. The estimated P release calculations from Exp. 1 with late-finishing pigs are in agreement with the experimental results of Kornegay (1996) and Jongbloed et al. (1996) that demonstrated a decline in the effectiveness of AN phytase with increasing concentrations of AN phytase in low-P diets fed to young and growing-finishing swine.
The lower effective concentrations of AN phytase ( 500 U/kg of diet) that replaced about 0.9 g/kg of the aP and Ca required for growing and finishing pigs fed corn-SBM diets in the current experiments, and replaced from 0.8 to 1.0 g/kg of the aP in the experiments conducted by Harper et al. (1997) may be due to the fact that the Ca concentrations were reduced in those experiments, with narrow Ca:tP ratios that ranged from 1.1 to 1.2:1. The efficacy of AN phytase for weanling and growing-finishing pigs is enhanced by narrow Ca:tP ratios (Qian et al., 1996; Veum, 1996a; Liu et al., 1998) compared with wide Ca:P ratios (Lantzsch et al., 1994; Lei et al., 1994; Cromwell et al., 1995). However, even with wide Ca:tP ratios ( 1.6), supplementation of corn-SBM-rapeseed meal grower and finisher diets deficient in aP with 1,200 or 1,000 U of AN phytase/kg, respectively, improved pig growth performance criteria and bone breaking strength comparable with that of the pigs fed the PC diets (Han et al., 1997).
When the P release equivalency of AN phytase was compared with an inorganic P source in 2 other experiments, 500 U of AN phytase/kg was equivalent to about 0.7 g of inorganic P for ADG and 1.1 g of inorganic P for P digestibility and 10th-rib shear force (Harper et al., 1997). The enzymatic efficiency of AN phytase was also equivalent to that of an E. coli-derived phytase in 2 experiments with weanling pigs based on growth performance criteria, plasma inorganic P concentration, and pig mobility score (Stahl et al., 2000). However, other experiments that used an inorganic P standard for comparison showed that the P release equivalency of an E. coli-derived phytase was greater than that of AN phytase (Augspurger et al., 2003; Jendza et al., 2006). The AN phytase used in the current experiments was efficacious for P digestibility with graded doses up to 15,000 U/kg of weaner pig diet deficient in aP (Kies et al., 2006). A genetically engineered E. coli phytase was also efficacious for young pigs with doses up to 12,500 U/kg of corn-SBM diet deficient in aP based on growth performance, P digestibility, and bone strength (Veum et al., 2006). Therefore, the most advantageous phytase concentration for future use in swine diets will depend on a combination of factors such as economics, environment, and nutritional demands.
In conclusion, the current experiments and the experiments of Harper et al. (1997) have shown that concentrations of AN phytase below 500 U/kg will support adequate growth performance of growing and finishing pigs that are group-fed corn-SBM diets that are 0.8 to 1.0 g/kg deficient in aP and Ca with a narrow Ca:tP ratio ( 1.2:1). However, these experiments have also demonstrated that concentrations of AN phytase below 500 U/kg will not support adequate bone strength or P absorption (g/d) compared with pigs fed a PC diet containing supplemental inorganic P that meets the minimum aP requirements for swine (NRC, 1998). The differences in the sensitivity ranking of the response criteria in the current experiments and the experiments of Harper et al. (1997) are in general agreement with other experiments that showed apparent total-tract absorption of P and bone measurements were more sensitive criteria than blood measurements or growth performance for estimating the bioavailability of P in swine diets (Koch et al., 1984; Dellaert et al., 1990; Yi and Kornegay, 1996). Adequate bone strength is essential for market hogs that must be ambulatory when slaughtered, and for structural soundness of replacement gilts that enter the breeding herd. Therefore, the current experiments with group-fed pigs are in agreement with the recommendations of Parr (1996), Harper et al. (1997), and Jongbloed et al. (2000) that 500 U of AN phytase/kg of diet may effectively replace about 0.8 to 1.0 g/kg of the inorganic P in corn-SBM diets for growing and finishing swine.
Aspergillus niger phytase added at 450 units/kg of corn-soybean meal diet replaced all of the inorganic P (about 0.9 g/kg of diet) required by late-finishing pigs based on bone strength. However, 300 or 150 units AN phytase/kg of grower or finisher diet, respectively, replaced about 0.9 g/kg of the inorganic P and Ca required for growth performance, although these concentrations of AN phytase were not adequate for bone strength. Pigs fed the low-P finishing diet with 450 units of AN phytase/kg excreted 38 and 42% less fecal P and Ca, respectively, than pigs fed the PC diet. Growing-finishing pigs fed the low-P diets that contained from 150 to 700 units of AN phytase/kg excreted 16 to 31% less P and 21 to 29% less Ca than pigs fed the PC diets. The use of AN phytase in diets deficient in aP and Ca should greatly reduce the excretion of P and Ca in manure, and the environmental benefits will enhance the sustainability of the swine industry worldwide.
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Footnotes
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1 Thanks to D. W. Bollinger, J. Liu, K. Jennings, S. Krumpelman, C. Mitchell, C. Tiemeyer, and L. Vanskike for assistance with animal care and data collection, and the BASF Corporation, Florham Park, NJ, for providing the Natuphos phytase. 
2 Corresponding author: veumt{at}missouri.edu
Received for publication May 30, 2007.
Accepted for publication December 18, 2007.
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LITERATURE CITED
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Abstract
INTRODUCTION
