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ANIMAL PRODUCTION |
* Departments of Animal Science and
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Agronomy, Iowa State University, Ames 50011;
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Department of Animal and Avian Sciences, University of Maryland, College Park 20742
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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Key Words: excretion • low-phytate soybean • phosphorus • swine
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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), resulting in the unavailable fraction being excreted. There is concern that P excretion is a large contributor to surface water quality deterioration (Sweeten, 1992).
Inclusion of exogenous phytase in swine diets improves overall diet P availability, resulting in less P excreted (Cromwell et al., 1993, Adeola et al., 1995; Cromwell et al., 1995) and reduced concentrations of inorganic P added to the diet (Kornegay and Qian, 1996; Kemme et al., 1997; Adeola et al., 1998). Phytase efficacy is less than 100%, resulting in a portion of the P in a corn-SBM diet still being unavailable (Kemme et al., 1997; Sands et al., 2001). Development of a corn with high available P has demonstrated promise in further increasing overall diet P availability (Spencer et al., 2000a; Sands et al., 2001; Veum et al., 2001).
When phytase is added, and dietary inorganic P reduced appropriately, the solubility of excreted P should not be changed significantly (Applegate et al., 2003; Baxter et al., 2003; Angel et al., 2005). A controversy exists as to the effect of phytase on manure water soluble P (WSP) concentrations (DeLaune et al., 2004). Potential alternatives to phytase for increasing the availability of P in soybean meal are important to investigate.
A low-phytate soybean line has been developed that has similar total P compared with conventional soybean cultivars but contains only 25% of total P as phytate P compared with 71% of total P as phytate P in conventional cultivars (Oltmans et al., 2005).
The objectives of this study were to quantify the total P and WSP excretion from pigs fed low-phytate (LP) and traditional P (TP) SBM and to determine if supplemental phytase fed with the LP SBM further reduced total P (tP) and WSP excretion.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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). The SBM with TP content was obtained from conventional soybeans processed by American Natural Soy, Cherokee, IA. Both types of soybeans were expeller-processed by American Natural Soy during the same week.
Samples of the SBM were analyzed for specific amino acid profile (AOAC, 1990) at the University of Missouri Experiment Station Chemical Laboratories after diet formulation (Table 1). Before diet formulation, SBM and corn samples were analyzed for total Kjeldahl nitrogen content (microKjeldahl method 984.13, AOAC, 1990). Soybean meal and corn samples were analyzed for total P content using a wet acid digestion procedure (method 7.123 AOAC, 1980) and for nonphytin P content at the University of Maryland, before diet formulation. To determine nonphytin P content, phytate content was measured and subtracted from total P content.
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and modified by Newkirk and Classen (1998). Briefly, samples were extracted with 0.5 N HCl by shaking with an orbital shaker at 2,500 x g for 3 h. Lipid was then removed from the samples with HPLC-grade chloroform. Extracts were analyzed on an HPLC equipped with an anion-exchange column (50 x 4.6 mm PRP X-500 column, Hamilton, Reno, NV) and a 6.3 x 11.2 mm precolumn. Samples were eluted over a 20-min gradient (0 to 0.5 M NaNO3, 0.01 M 1-methylpiperzine, pH 4.0). The elutant was reacted postcolumn with 0.015% FeCl3 (in 0.15% sulfosalicylic acid), and the in-line absorbance was determined at 500 nm. Resultant peak areas were then quantified using a standard curve of peak areas obtained from purified phytic acid (Sigma Chemicals, St. Louis, MO).
Animals and Housing
Experiments were approved by the Iowa State University Committee on Animal Care. Ninety-six cross-bred PIC (406 x C22, PIC Inc., Franklin, KY) barrows weighing approximately 18 ± 0.3 kg were allocated by BW to pens, 4 pigs/pen with 6 replications/treatment. To minimize variation in beginning BW, pigs were selected from 13 litters within a single farrowing. Pens were not balanced by litter, but rather they were balanced by weight. All pens contained partially slatted concrete floors. Pigs were provided ad libitum access to nipple waterers and self-feeders.
Dietary Treatments
Pens were randomly assigned to 1 of 4 dietary treatments in a 2 x 2 x 4 factorial arrangement consisting of a common corn source along with LP or TP SBM, 0 or 500 phytase units of phytase/kg [Ronozyme P (CT) 2500; DSM Nutritional Products; Basel, Switzerland], and 4 feeding phases. Diets were formulated to contain 1.0% available Lys; 0.73% Ca; 3,306 kcal of ME/g as fed, and 0.39% nonphytin P during the first feeding phase; 1.0% available Lys; 0.67% Ca; 3,322 kcal of ME/ g as fed, and 0.35% nonphytin P during the second feeding phase; 0.88% available Lys; 0.62% Ca; 3,330 kcal of ME/g as fed, and 0.30% nonphytin P during the third feeding phase; and 0.76% available Lys; 0.59% Ca; 3,330 kcal of ME/g as fed, and 0.30% nonphytin P during the fourth feeding phase.
Diet composition and analyzed nutrient concentrations are provided in Tables 2 and 3. Note that formulation of the second-phase diets was intended to maintain available lysine content similar to that formulated during the first phase. However, because the analyzed diets indicated that available lysine was below the targeted concentration, the amount of SBM included during the second phase was slightly more than that included in the first feeding phase. Ingredients were not analyzed for Ca content before mixing, and diets within a phase were formulated to contain similar Ca content irrespective of phytase inclusion.
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Measurements and Analytical Procedures
After a 5-d acclimation period, urine and fecal grab samples were collected from each pig on d 6 and 14 of each 2-wk feeding phase for determination of apparent digestibility. Urine was collected by waiting for each pig to urinate and inserting a cup into the urine stream. On collection, fecal samples were pooled by pen (200 g/ pig) and mixed in a blender. Feces and feed samples were dried in a forced-air oven (model 500, Fisher Scientific, Hanover, IL) at 55°C until a constant weight was achieved, ground through a 0.5-mm sieve (3383-L10 series Thomas Scientific, Swedesboro, NJ), and ashed in a muffle furnace at 550°C for 4 h (Isotemp basic, Fisher Scientific). Samples were then digested and subjected to total P analysis (method 7.123 AOAC, 1980) using a standard curve that contained 5 standard solutions of P. Acid insoluble ash content of diets and feces was determined to quantify the indigestible marker content of each (Vogtmann et al., 1975). Feces were analyzed for WSP content using a 2-h water-extraction method that was modified from Self-Davis and Moore (2000). A 50-mL aliquot of urine from each pig was pooled to establish a pen sample. Urine samples were digested and analyzed for P content (method 7.123 AOAC, 1980).
Pen weights were determined using individual BW and pen feed disappearance on weekly sample collection days. Individual pig BW changes were summed by pen and averaged. Feed samples were collected on d 6 and 14 of each feeding phase and analyzed as separate samples for acid insoluble ash content, P content, and non-phytin P content. A composite sample of each diet was analyzed at the University of Missouri Experiment Station Chemical Laboratories for amino acid profile, including available lysine (methods 975.44 and 982.30, AOAC, 1990). Feed disappearance was divided by the number of pigs per pen (n = 4) to provide pig ADFI.
Statistical Analyses
Data were analyzed as a 2 x 2 x 4 factorial arrangement of treatments consisting of 2 SBM types (LP and TP), 2 phytase inclusion concentrations (0 and 500 phytase units of phytase/kg), and 4 feeding phases. Pen served as the experimental unit. Analysis was performed using the GLM procedure of SAS (2005) and included the main effects of SBM source, phytase inclusion, feeding phase, and all 2-way and 3-way interactions of the main effects. Significance was declared at P < 0.05.
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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). Significant feeding phase effects were observed for ADFI and BW gain.
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). In general, OM and DM digestibility increased as pigs aged with a less clear pattern for P digestibility.
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). Apparent digestibility of P was greater when pigs were fed diets containing LP SBM (48.9%) vs. TP SBM (42.4%; P < 0.001; Table 5). Apparent digestibility of P was greater in pigs fed diets supplemented with phytase (47.0%) compared with pigs fed diets without supplemental phytase (44.3%; P < 0.001; Table 5).
Phosphorus Excretion
Total P, WSP, and WSP as a percentage of tP (DM basis) increased from the first to the second feeding phase (Table 6), whereas the contents of these variables were not different from one another during the second, third, and fourth feeding phases.
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). Fecal tP content decreased 19%, whereas WSP content decreased 17%. The percent of WSP in tP was not different between feces from pigs fed diets with either SBM type. Supplementing diets with phytase reduced tP excretion 16% (15.9 vs. 18.4 g/kg of tP) and WSP by 6%, leading to a 7% reduction in WSP as a percentage of tP. Inclusion of phytase in the LP SBM diets decreased tP and WSP in the feces even further, 17 and 8%, respectively, but WSP as a percentage of tP increased 11%. Pigs fed the LP SBM diets supplemented with phytase showed decreased tP and WSP content by 8 and 6%, respectively, with no differences observed for WSP as a percentage of tP. No treatment effects were observed for urine P content (11.4 mg/L; P = 0.20). However, as pigs aged, urine P decreased (14.7, 9.8, 9.0, and 8.1 mg/L for phases 1, 2, 3, and 4, respectively; P < 0.01).
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DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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; Veum et al., 2001) and high available P corn in broilers (Huff et al., 1998) and laying hens (Snow et al., 2003). Other studies have demonstrated improved performance in pigs fed low-phytate grain diets, formulated based on a total P rather than on a nonphytin P basis (Sands et al., 2001; Veum et al., 2002). Their findings therefore reflect greater use of P from the low-phytate grains. In the current study, because diets were formulated on a nonphytin P basis, reflecting the difference in nonphytin P content between SBM sources, no difference in performance would be expected. Apparent digestibility of P was similar to that reported by Spencer et al. (2000a), whose estimates ranged from 48 to 55% in low-phytate corn diets and 46% in traditional P corn diets supplemented with dicalcium phosphate. Veum et al. (2002) reported apparent P absorptions of 40% when traditional grain was fed and 66% when low-phytate barley was fed. The observed age effect on urine P content likely reflects a change in dietary formulation that more nearly proximated nutrient needs of the animals.
The interest in low-phytate grains is driven by the need to minimize potential environmental impacts of animal production. Results from the current study showed that feeding the LP SBM, in conjunction with formulating the diets reflecting the potential availability of the P from the 2 SBM sources (on nonphytin P basis), resulted in an improved apparent digestibility of P. Findings were consistent with other research where low-phytate corn (Spencer et al., 2000a and b; Veum et al., 2001) and low-phytate barley (Veum et al., 2002) were fed to swine. Similarly, Yamka et al. (2005) reported improved digestibility of P when dogs were fed diets containing LP SBM vs. TP SBM.
Whereas availability of P was improved in diets containing LP SBM, feed intake was not affected by soybean source, resulting in reduced fecal P from pigs fed the LP diets as compared with those fed the TP diets. These results are in agreement with previous reports of decreased fecal P when pigs were fed diets containing LP SBM (Wienhold and Miller, 2004), high available P corn (Spencer et al., 2000a; Sands, et al., 2001; Veum et al., 2001), or LP barley (Veum et al., 2002), and when dogs were fed LP SBM (Yamka et al., 2005). Sands et al. (2001) reported a decrease in fecal P of 16% when high available P corn was fed as compared with traditional corn. In our study a decrease of 20% was observed when LP SBM diets were fed as compared with feeding TP SBM diets. Addition of phytase to the LP diets further reduced fecal P content. A similar effect was reported by Sands et al. (2001), in which the inclusion of phytase in diets containing high available P corn reduced fecal P in growing pigs. Wienhold and Miller (2004) reported that whereas total P and WSP were lower in feces from swine fed LP SBM diets vs. those fed TP SBM diets, the proportion of total P that was constituted by WSP remained unchanged. The current study demonstrated that feeding the LP SBM reduced total P intake and decreased fecal WSP content, an effect also found in recent research with reduced P intake in poultry (Applegate et al., 2003; Angel et al., 2005). In swine, no effect of reducing dietary P on WSP concentration has been reported (Angel et al., 2005).
Only DeLaune et al. (2004) have demonstrated increased WSP content as a result of phytase inclusion in diets, but our study showed the opposite with the inclusion of phytase in swine diets decreasing WSP content. A similar decrease in WSP was reported by Angel et al. (2005) when phytase was included in broiler and turkey diets but no change when phytase was included in swine diets. Others have also reported decreases in WSP in litter where broilers have been grown on feeds containing phytase (Saylor et al., 2001; Applegate et al., 2003; Maguire et al., 2004).
Water-soluble P, as a fraction of total P, increased in the current study as a result of feeding the LP SBM and phytase. The increase in the fraction of total P that was WSP when the LP diets were fed resulted from a proportionately greater decrease in total fecal P than in WSP. The increased WSP as a fraction of tP that resulted from LP SBM and phytase could be interpreted to suggest that LP SBM and phytase result in manures that pose a greater environmental risk (P runoff). However, it is important to recognize that because ADFI was not different as a result of either SBM source or phytase inclusion and apparent digestibility of P in swine fed the LP SBM diets was greater, the mass of P and WSP excreted was less in the LP SBM diets. Therefore, the environmental impact of feeding the LP diets remains positive because the load or mass of WSP and total P potentially going into the environment as fertilizer decreased. Whereas the apparent digestibility of P was decreased in swine offered the phytase diets by 3 percentage units, the lower P content of the phytase diets (Table 3) resulted in an overall effect of decreased WSP content of feces and reduced mass of excreted WSP. The primary focus when applying manure to soils should be on the mass of total P and WSP in the manure. Both of these were reduced when LP SBM or phytase or both were fed to swine.
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IMPLICATIONS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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Footnotes |
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2 The authors thank the United Soybean Board for their financial support of this project.
3 Corresponding author: wpowers{at}iastate.edu
Received for publication November 10, 2005. Accepted for publication February 5, 2006.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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