METABOLISM AND NUTRITION

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1 METABOLISM AND NUTRITION Evaluation of Normal Yellow Dent Corn and High Available Phosphorus Corn in Combination with Reduced Dietary Phosphorus and Phytase Supplementation for Broilers Grown to Market Weights in Litter Pens 1 F. Yan,* J. H. Kersey,* C. A. Fritts,* P. W. Waldroup,*,2 H. L. Stilborn,,3 R. C. Crum, Jr., D. W. Rice,,3 and V. Raboy *Poultry Science Department, University of Arkansas, Fayetteville, Arkansas 72701; Pioneer Hi-Bred International, Johnston, Iowa 50131; USDA-ARS, National Small Grains Research Facility, Aberdeen, Idaho ABSTRACT A study was conducted to determine the and tibia ash that were equal to or superior to those fed extent fecal P levels could be reduced while maintaining performance. Various strategies were employed including the use of a high available phosphorus hybrid of corn (HAPC), supplementation with phytase enzyme, and reduced dietary P levels. The use of HAPC resulted in a 50% reduction in phytate-bound dietary P as compared with a normal yellow dent corn (YDC) diet. Dietary nonphytate P was maintained at either NRC (1994) recommendations for appropriate age periods or reduced by or 0.15%. Portions of the diets were supplemented with 1,000 units of phytase/kg. Male chicks of a commercial strain were grown to 56 d on the test diets. Broilers fed diets with HAPC had BW, feed conversion, livability, diets with YDC with considerably reduced fecal P content at any dietary level of nonphytate P. Phytase supplementation enabled birds to maintain live performance at lower levels of nonphytate P, further reducing the fecal P output. One of the greatest contributions of phytase was a reduction in mortality at the lower levels of nonphytate P. Dietary P levels could be reduced by 0.075% under NRC (1994) recommendations without adversely affecting live performance; a reduction of 0.15% in conjunction with phytase supplementation maintained BW, feed conversion, and livability but reduced tibia ash. The extent to which dietary P levels can be reduced over the entire feeding program is subject to further research. (Key words: high available phosphorus corn, phytase, phytic acid, broilers, fecal phosphorus) 2000 Poultry Science 79: INTRODUCTION Concerns about the possible contribution of P runoff from the application of poultry litter to eutrophication of surface waters has focused attention on means of reducing phosphorus excretion (Edwards and Daniel, 1992; Sharpley, 1999). Because of the demands for adequate skeletal development of the rapidly growing broiler and the variability of phosphorus content in animal byproduct feeds used to provide a major share of this mineral, it is necessary to provide an adequate margin of safety in broiler diets. A considerable amount of the phosphorus in poultry diets is in the form of phytate phosphorus. This organically bound form of the mineral is poorly available to Received for publication August 18, Accepted for publication March 22, Published with the approval of the director of the Arkansas Agricultural Experiment Station. Manuscript No To whom correspondence should be addressed: pwaldro@comp. uark.edu. 3 Present address: Optimum Quality Grains, L.L.C., Justin Drive, Des Moines, IA Pioneer Hi-Bred International, Johnston, IA chickens because monogastrics are lacking or limited in phytase, the enzyme that is necessary for breakdown of the molecule and subsequent release of phosphorus for absorption (O Dell et al., 1972; Raboy, 1990). Nelson et al. (1968, 1971) demonstrated that addition of phytase to broiler diets was an effective means of improving the availability of phytate-bound phosphorus. Recent commercial development of phytase enzymes offers promise in reducing phosphorus excretion by increasing the ability of the chick to utilize a portion of the phytatebound phosphorus (reviewed by Ravindran et al., 1995; Sebastian et al., 1998). Another approach to reducing phosphorus in excreta is to develop feedstuffs with modified levels of phytatebound phosphorus. A corn mutation with low phytate phosphorus and high available phosphorus content has been developed by the USDA (Raboy and Gerbasi, 1996; Raboy, 1997) and has been bred into a hybrid by a major seed company 4 using the low phytic acid 1-1 (lpal-1) Abbreviation Key: FCR = feed conversion ratio; HAPC = high available phosphorus corn; NPP = nonphytate phosphorus; YDC = yellow dent corn. 1282

2 PHOSPHORUS REDUCTION IN LITTER 1283 allele of the corn LPA1 gene. This hybrid, designated as high available phosphate corn (HAPC), contains approximately 0.27% total phosphorus, of which 0.17% is estimated to be available to the chicken. The nonphytate phosphorus in HAPC has been found to be equivalent in biological value to a commercial dicalcium phosphate (Ertl et al., 1998; Waldroup et al., 1999). In contrast, normal yellow dent corn (YDC) contains similar levels of total phosphorus but only about 0.03% available phosphorus. Previous studies with HAPC have been limited primarily to birds grown to 3 wk of age (Ertl et al., 1998; Waldroup et al., 1999). Huff et al. (1998) grew broilers to 49 d using diets with YDC or HAPC; however, phosphorus levels used in the diets were greater than NRC recommendations. The present study was conducted to evaluate the use of YDC and HAPC in reduced-phosphorus diets for broilers grown to market weights with phytase supplementation to enhance utilization of phytatebound phosphorus. MATERIALS AND METHODS Floor Pen Studies Using nutrient values provided by the seed company (Table 1), diets were formulated for growing broilers to 8 wk with either YDC or HAPC (Table 2). The YDC used in the study was the isogenic normal phytate counterpart to the HAPC. Both corns were grown in the same location during the same year. The diets contained a minimum of 110% of NRC (1994) suggested amino acid requirements and were formulated to contain NRC (1994) recommended levels of nonphytate phosphorus (NPP; 0.45% NPP for 0 to 21 d, 0.35% for 21 to 42 d, and 0.30% for 42 to 56 d) with either YDC or HAPC. By varying the level of supplemental dicalcium phosphorus and limestone in the diet, additional test diets were produced that contained reduced levels of NPP [ 0.0%, 0.075, and 0.15% of NRC (1994)] for both corn types. Each of these diets was mixed and divided into two subplots. One lot was treated with microbial phytase enzyme at 1,000 units/kg 5 ; this level of phytase was considered to be sufficient for maximum economical release of phosphorus (Kornegay et al., 1996; Van der Klis and Versteegh, 1996; Yi et al., 1996). The combination of two corn sources, with and without phytase supplementation, at three levels of NPP resulted in 12 experimental treatments. Each treatment was fed to four replicate pens of 50 male broilers. Diets were fed in pellet form (starter diets were crumbled) with the phytase enzyme sprayed on the feeds in a mixer after the pelleting process. Samples of diets were ana- 5 Natuphos, BASF Corporation, Mt. Olive, NJ One unit of phytase activity is defined as the quantity of enzyme required to produce 1 µmol of inorganic P/min from 5.1 mmol/l of sodium phytate at a ph of 5.5 and a water bath temperature of 37 C. 6 Cobb-Vantress, Inc., Siloam Springs, AR TABLE 1. Nutrient profile of normal yellow dent corn (YDC) and high available phosphorus (HAPC) corn (as-fed basis) 1 Nutrient YDC HAPC TME (kcal/kg) 3, , Dry matter, % CP, % Crude fiber, % Ash, % Crude fat, % Ca, % Total P, % Phytate P, % Nonphytate P, % Alanine, % Arginine, % Aspartic acid, % Cystine, % Glutamic acid, % Glycine, % Histidine, % Isoleucine, % Leucine, % Lysine, % Methionine, % Phenylalanine, % Proline, % Serine, % Threonine, % Tyrosine, % Tryptophan, % Valine, % Values provided by Pioneer Hi-Bred International, Inc., Johnston, IA lyzed for calcium, total phosphorus, and phytase activity. Day-old male chicks of a commercial broiler strain (Cobb ) were obtained from a local hatchery and were randomly distributed into pens in a commercialtype house with new wood shaving litter over concrete floors. Fifty birds were placed in each of 48 pens (5.2 m 2 ). Each pen was equipped with two tube feeders and an automatic water font. The birds were placed on their respective test diets at 1 d of age and were fed to 56 d with the test feeds and tap water provided ad libitum. Cage Studies Portions of the test diets were fed to cohort birds maintained in wire-floored battery pens in a temperaturecontrolled room for bone ash and fecal phosphorus determination. Each diet was fed to eight pens of chicks with eight birds per pen. Measurements Birds in the floor pens were group weighed by pen at 21, 42, and 56 d of age, and pen feed consumption was determined. Mortality was checked twice daily; any bird that died was weighed, and the weight used to adjust feed conversion. Feed conversion ratio (FCR; grams of feed per gram of gain) was calculated by dividing total feed consumed by weight of live plus dead birds. Two birds from each battery pen (16 per treatment) were killed by CO 2 inhalation at 21, 42, and 56 d for

3 1284 YANETAL. tibia ash determination as outlined by AOAC (1990). At the same ages, fecal samples were collected on aluminum foil, pooled from the eight replicate pens, and freeze-dried, and phosphorus content was determined. Statistical Analysis Data were subjected to analysis of variance as a factorial arrangement of treatments with corn source, phosphorus level, and phytase supplementation as main effects; all possible interactions among and between the main effects were evaluated. Mortality data were transformed to n+1 prior to analysis; data are presented as natural numbers. Analysis used the general linear model of SAS (SAS Institute, 1991). Significant differences among or between means were separated by repeated t-tests using the lsmeans option of SAS. Statements of probability were based on P RESULTS AND DISCUSSION The calculated and analyzed levels of calcium and total phosphorus are shown in Table 3. There was good agreement between calculated and analyzed levels of these two minerals. Results of phytase assays indicated that all phytase supplemented diets contained activity commensurate with expected levels; mean phytase values were 1,020, 935, and 998 units/kg for starter, grower, and finisher diets, respectively. A summary of the statistical analyses for the performance parameters is shown in Table 4. Body Weight There were no significant differences in body weight between birds fed the two types of corn at any age (Table 5). Overall, addition of phytase to the diets significantly improved body weight at 21 d; however, there was no significant improvement in body weight at 42 or 56 d from phytase supplementation. As expected, phosphorus level significantly influenced body weight. At every age, birds fed diets with 0.075% NRC levels did not differ significantly in body weight from those fed the NRC level; birds fed diets with 0.15% NRC were significantly lighter than birds fed NRC or 0.075% NRC diets. Several interactions between main effects were observed. There was a significant interaction between type of corn and phytase supplementation at 56 d; body weight of chicks was significantly improved by phytase supplementation when they were fed YDC diets but not when fed HAPC diets. Because HAPC contains approximately half of the phytate-bound phosphorus that could TABLE 2. Composition and calculated nutrient content of broiler starter, grower, and finisher diets with normal yellow dent corn (YDC) or high available phosphate corn (HAPC) 0to21d 21to42d 42to56d Ingredient YDC HAPC YDC HAPC YDC HAPC (g/kg) YDC HAPC Soybean meal (48% CP) Poultry oil DL-Methionine (98%) Lysine HCl (98%) Threonine Salt BMD Coban Broiler vitamin mix Trace mineral mix Variable , , , , , , ME, kcal/kg 3, , , , , , CP, % Ca, % P, % Nonphytate P, % Alpharma, Inc., Ft. Lee, NJ Provides 110 g/kg bacitracin activity as bacitracin methylene disalicylate. 2 Elanco Animal Health, division of Eli Lilly & Co., Indianapolis, IN Provides 132 g monensin/kg as monensin sodium. 3 Provides per kilogram of diet: 7,714 IU vitamin A, 2,204 IU cholecalciferol, IU vitamin E, mg vitamin B 12, 6.6 mg riboflavin, 39 mg niacin, 10 mg pantothenic acid, 465 mg choline, 1.5 mg vitamin K, 0.9 mg folic acid, 1.54 mg thiamin, 2.76 mg pyridoxine, mg d-biotin, 125 mg ethoxyquin, and 0.1 mg Se. 4 Provides per kilogram of diet: Mn (from MnSO 4 H 2 O), 100 mg; Zn (from ZnSO 4 7H 2 O), 100 mg; Fe (from FeSO 4 7H 2 O), 50 mg; Cu (from CuSO 4 5H 2 O), 10 mg; and I (from Ca(IO 3 ) 2 H 2 O),1mg. 5 Variable amounts of dicalcium phosphate, limestone, or washed builders sand as required to adjust level of nonphytate phosphorus.

4 PHOSPHORUS REDUCTION IN LITTER 1285 TABLE 3. Calculated (C) and analyzed (A) levels of calcium and phosphorus in test diets containing normal yellow dent corn (YDC) or high available phosphorus corn (HAPC) Treatment 0 21 d d d YDC (NRC) Ca (A) Total P (C) Total P (A) YDC ( 0.075% of NRC) Ca (A) Total P (C) Total P (A) YDC ( 0.15% of NRC) Ca (A) Total P (C) Total P (A) HAPC (NRC) Ca (A) Total P (C) Total P (A) HAPC ( 0.075% of NRC) Ca (A) Total P (C) Total P (A) HAPC ( 0.15% of NRC) Ca (A) Total P (C) Total P (A) be released by phytase supplementation as compared to YDC, this interaction was expected and is in agreement with previous research from our laboratory (Waldroup et al., 1999). There was a significant interaction between phytase supplementation and level of NPP in 56-d body weights; phytase supplementation significantly improved body weights when added to diets containing 0.15% NRC but not when added to diets containing NRC or 0.075% NRC. These two levels of NPP appeared to be adequate to maintain body weight and, thus, would not be expected to respond to phytase supplementation. Feed Conversion Feed conversion by birds fed the experimental diets is shown in Table 6. These data may be influenced in part by the relatively high mortality experienced at the lowest level of nonphytate phosphorus. Even though data were adjusted to account for the weight of birds that died during the study, this adjustment is imperfect at best. This adjustment resulted in numerous interactions between and among the main effects. Overall, FCR by birds fed diets containing HAPC was equal (21 and 42 d) or superior (56 d) to that of chicks fed diets with YDC. Phytase supplementation resulted in superior overall FCR at 56 d. At 42 d, the FCR of birds fed the phytase-supplemented diets with reduced phosphorus (%) levels was inexplicably greater than that of birds fed the unsupplemented diets. At 56 d, there were several interactions among and between the main effects. Phytase supplementation significantly improved FCR of diets based on YDC but not when added to diets containing HAPC; note that the diets with HAPC had less phytate-bound phosphorus to be released by the phytase. Phytase supplementation also had a greater influence on FCR when added to diets with reduced phosphorus levels, having a greater influence on low-phosphorus diets containing YDC compared with diets containing the HAPC. Mortality Mortality of birds fed the experimental diets is shown in Table 7. Mortality was higher than anticipated, especially at the later ages, and was exacerbated by heat stress between 42 and 56 d. Mortality was not significantly influenced by the type of corn used in the diets but was significantly influenced by dietary phosphorus level. At 42 and 56 d, birds fed the diets with 0.15% NRC had significantly higher mortality than those fed diets with NRC or 0.075% NRC. Birds fed diets supplemented with phytase had significantly lower mortality than TABLE 4. Results of statistical analysis of performance parameters Source Starter Grower Finisher Probability > F Body weight Corn source Phytase P level Corn phytase Corn P level Phytase P Level Corn phytase P Level CV % Feed utilization Corn source Phytase P level Corn phytase Corn P Level Phytase P level Corn phytase P Level CV % Mortality Corn source Phytase P level Corn phytase Corn P level Phytase P level Corn phytase P level CV % Tibia ash Corn source Phytase P level Corn phytase Corn P level Phytase P level Corn phytase P level CV %

5 1286 YANETAL. TABLE 5. Effect of normal yellow dent corn (YDC) or high available phosphate corn (HAPC), phytase supplementation, and level of nonphytate phosphorus on body weight of male broilers Dietary P level 1 Corn Added source phytase 2 NRC 0.075% 0.15% Mean 21-d Weight (g) YDC HAPC Yes x... No y YDC Yes YDC No HAPC Yes HAPC No a 703 a 679 b 42-d Weight (g) YDC... 2,218 2,174 2,033 2,142 HAPC... 2,158 2,134 2,064 2, Yes 2,198 2,136 2,066 2, No 2,178 2,172 2,031 2,127 YDC Yes 2,224 2,205 2,054 2,161 YDC No 2,211 2,143 2,013 2,123 HAPC Yes 2,172 2,068 2,078 2,106 HAPC No 2,144 2,200 2,049 2, ,188 a 2,154 a 2,048 b 56-d Weight (g) YDC... 3,401 3,367 3,230 3,333 HAPC... 3,404 3,358 3,263 3, Yes 3,391 ab 3,311 b 3,343 ab 3, No 3,413 a 3,415 a 3,150 c 3,326 YDC Yes 3,389 3,364 3,383 3,378 a YDC No 3,413 3,371 3,078 3,287 b HAPC Yes 3,394 3,258 3,302 3,318 ab HAPC No 3,413 3,458 3,223 3,365 a ,402 x 3,363 x 3,247 y a c; x,y Within comparisons, means with common superscript do not differ significantly (P 0.05). 1 Indicates reduction (% of diet) from NRC (1994) recommended level. 2 With or without 1,000 units of phytase/kg. those fed unsupplemented diets, with a significant interaction between phosphorus level and phytase supplementation. Addition of phytase significantly reduced mortality at the lower levels of phosphorus, especially at 42 and 56 d. This reduction in mortality by phytase supplementation may be one of the greatest contributions of phytase in a feeding strategy to minimize fecal excretion of phosphorus by broilers. Tibia Ash Tibia ash at different ages is shown in Table 8. Tibia ash was not influenced by corn source, indicating that the NPP found in the HAPC was utilized as well as the dicalcium phosphate supplement used in the diets with YDC, in agreement with studies by Ertl et al. (1998) and Waldroup et al. (1999). Phytase supplementation resulted in significant improvements in tibia ash at all ages. Tibia ash of birds fed diets with the reduced phosphorus levels was significantly lower than that of birds fed the diets with NRC recommended levels at all ages, even with phytase supplementation. There was a significant interaction between phosphorus level and phytase supplementation; phytase supplements improved tibia ash to a greater extent at the lowest level of phosphorus supplementation. At 21 d, but not at older ages, phytase was more effective in improving tibia ash when added to diets containing YDC than in diets with HAPC. Fecal Phosphorus The phosphorus content of freeze-dried feces at different ages is shown in Table 9. These data are expressed in actual quantity and as relative amounts. The relative amount represents the percentage fecal phosphorus in relation to the YDC diet with the NRC-recommended phosphorus level with no phytase supplementation. Fecal phosphorus was markedly reduced by reducing the dietary phosphorus level and by substitution of HAPC for YDC. Addition of phytase had little effect on actual TABLE 6. Effect of normal yellow dent corn (YDC) or high available phosphate corn (HAPC), phytase supplementation, and level of nonphytate phosphorus on feed conversion by male broilers Dietary P level 1 Corn Added source phytase 2 NRC 0.075% 0.15% Mean 21-d feed:gain ratio (g:g) YDC HAPC Yes No YDC Yes YDC No HAPC Yes HAPC No d feed:gain ratio (g:g) YDC HAPC Yes b b a a... No ab c b b YDC Yes YDC No HAPC Yes HAPC No d feed:gain (g:g) YDC x HAPC y... Yes b b b y... No b b a x YDC Yes c bc bc y YDC No bc b a x HAPC Yes c bc bc y HAPC No bc bc bc y b b a a c; x,y Within comparisons, means with common superscript do not differ significantly (P 0.05). 1 Indicates reduction (% of diet) from NRC (1994) recommended level. 2 With or without 1,000 units of phytase/kg.

6 PHOSPHORUS REDUCTION IN LITTER 1287 TABLE 7. Effect of normal yellow dent corn (YDC) or high available phosphate corn (HAPC), phytase supplementation, and level of nonphytate phosphorus on mortality by male broilers Dietary P level 1 Corn Added source phytase 2 NRC 0.075% 0.15% Mean 21-d mortality (%) YDC HAPC Yes No YDC Yes YDC No HAPC Yes HAPC No d mortality (%) YDC HAPC Yes 9.25 b 5.75 b 8.00 b 7.66 y... No 7.00 b b a x YDC Yes YDC No HAPC Yes HAPC No b 7.87 b a 56-d mortality (%) YDC HAPC Yes c c c y... No bc b a x YDC Yes YDC No HAPC Yes HAPC No b b a a c; x,y Within comparisons, means with common superscript do not differ significantly (P 0.05). 1 Indicates reduction (% of diet) from NRC (1994) recommended level. 2 With or without 1,000 units of phytase/kg. fecal phosphorus output when dietary phosphorus was reduced by 0.075% but had a greater impact on reduction of fecal phosphorus when dietary phosphorus was reduced by 0.15%. It must be noted, however, that addition of phytase to these diets reduced mortality and allowed the birds to grow at these lower phosphorus levels; thus, phytase supplementation is an important contributor to the overall strategy for reducing fecal phosphorus content. Results of this study suggest that fecal phosphorus content can be markedly reduced without sacrificing live performance and skeletal integrity by the use of normal YDC or HAPC in conjunction with reduced dietary phosphorus content and phytase supplementation. Reducing dietary phosphorus levels in YDC diets to 0.15% below NRC recommendations along with phytase supplementation resulted in a 37.5% reduction in fecal phosphorus levels. A similar phosphorus level and phytase supplementation with HAPC diets reduced fecal phosphorus by 58.2%, as compared with broilers fed the YDC diet with NRC-recommended phosphorus levels. Although tibia ash was lower with these diets as compared with those fed the NRC-recommended levels, no apparent leg problems or excessive mortality was noted. Phytase supplementation appeared to be especially beneficial in reducing mortality associated with the lower dietary phosphorus levels, in agreement with the report by Waldroup et al. (1999). The extent to which dietary phosphorus levels may be reduced over the growing period of the broiler needs further study, utilizing diets designed for specific age periods. The greatest part of the skeletal development of the broiler takes place during the first 3 wk of life (Skinner and Waldroup, 1995); after this time phosphorus levels may be greatly reduced with no adverse effects on performance (Waldroup et al., 1974; Sauveur, 1978; Yoshida and Hoshii, 1982; Nys et al., 1983; Tortuero and Tardon, 1983; Skinner et al., 1992). The extent to which tibia ash must be maximized to prevent breaking problems during processing must also be determined (Yoshida and Hoshii, 1982). TABLE 8. Effect of normal yellow dent corn (YDC) or high available phosphate corn (HAPC), phytase supplementation, and level of nonphytate phosphorus on tibia ash content of male broilers maintained in battery brooders Dietary P level 1 Corn Added source phytase 2 NRC 0.075% 0.15% Mean 21-d Tibia ash (%) YDC HAPC Yes a b b x... No a b c y YDC Yes a YDC No c HAPC Yes ab HAPC No b a b c 42-d Tibia ash (%) YDC HAPC Yes a b b x... No a b c y YDC Yes YDC No HAPC Yes HAPC No a b c 56-d Tibia ash (%) YDC b c d HAPC a c d Yes ab bc cd x... No a d e y YDC Yes YDC No HAPC Yes HAPC No a b c a e; x,y Within comparisons, means with common superscript do not differ significantly (P 0.05). 1 Indicates reduction (% of diet) from NRC (1994) recommended level. 2 With or without 1,000 units of phytase/kg.

7 1288 YANETAL. TABLE 9. Effect of source of corn, phytase supplementation, and level of nonphytate phosphorus on phosphorus content of freeze-dried feces from male broilers maintained in battery brooders Fecal P 1 Dietary treatment 21 d 42 d 56 d (%) YDC (100.0) (100.0) (100.0) YDC + phytase (99.6) (100.3) (101.9) YDC ( 0.075% P) (83.0) (73.4) (80.5) YDC ( 0.075% P) + phytase (92.7) (84.7) (74.3) YDC ( 0.15% P) (72.0) (69.6) (69.8) YDC ( 0.15% P) + phytase (64.1) (54.3) (62.5) HAPC (92.3) (77.0) (79.5) HAPC + phytase (83.0) (81.8) (85.9) HAPC ( 0.075% P) (72.2) (62.3) (63.2) HAPC ( 0.075% P) + phytase (76.0) (66.4) (66.9) HAPC ( 0.15% P) (52.9) (45.1) (45.2) HAPC ( 0.15% P) + phytase (54.0) (43.6) (41.8) 1 Values in parentheses represent percentage fecal phosphorus in relation to normal corn diets at NRCrecommended level of nonphytate phosphorus. 2 Yellow dent corn (YDC) diets contain NRC recommended level of nonphytate phosphorus. 3 Addition of 1,000 units of phytase/kg. HAPC = high available phosphorus corn. ACKNOWLEDGMENTS This study was supported by donation of the corn and a grant from Pioneer Hi-Bred International, Johnston, IA 50131, and a grant from the US Poultry and Egg Association, Tucker, GA Donation of phytase and phytase assays by BASF, Mt. Olive, NJ 07828, is greatly appreciated. REFERENCES Association of Official Analytical Chemists, Official Methods of Analysis. 15th ed. AOAC, Arlington, VA. Edwards, D. R., and T. C. Daniel, Environmental impacts of on-farm poultry waste disposal A review. Bioresource Tech. 41:9 33. Ertl, D. S., K. A. Young, and V. Raboy, Plant genetic approaches to phosphorus management in agricultural production. J. Environ. Quality 27: Huff, W. E., P. A. Moore, Jr., P. W. Waldroup, A. L. Waldroup, J. M. Balog, G. R. Huff, N. C. Rath, T. C. Daniel, and V. Raboy, Effect of dietary phytase and high available phosphorus corn on broiler chicken performance. Poultry Sci. 77: Kornegay, E. T., D. M. Denbow, Z. Yi, and V. Ravindran, Response of broilers to graded levels of microbial phytase added to maize-soyabean-meal-based diets containing three levels of non-phytate phosphorus. Br. J. Nutr. 75: National Research Council, Nutrient Requirements of Poultry. 9th rev. ed. National Academy Press, Washington, DC. Nelson, T. S., T. R. Shieh, R. J. Wodzinski, and J. H. Ware, The availability of phytate phosphorus in soybean meal before and after treatment with a mold phytase. Poultry Sci. 47: Nelson, T. S., T. R. Shieh, R. J. Wodzinski, and J. H. Ware, Effect of supplemental phytase on the utilization of phytate phosphorus by chicks. J. Nutr. 101: Nys, Y., B. Sauveur, A. Oya, and P. Mongin, Effect of different levels of dietary sodium and phosphorus on 4 to 7 week chick growth performance. Nutr. Rep. Int. 28: O Dell, B. L., A. R. de Boland, and S. R. Koirtyohann, Distribution of phytate and nutritionally important elements among the morphological components of cereal grains. J. Agric. Food Chem. 20: Raboy, V., Biochemistry and genetics of phytic acid synthesis. Pages in: Inositol Metabolism in Plants. D. J. Moore, W. Boas, and F. A. Loewus, ed. Wiley-Liss, New York, NY. Raboy, V., Accumulation and storage of phosphate and minerals. Pages in: Advances in Cellular and Molecular Biology of Plants. Vol. 4. Cellular and Molecular Biology of Plant Seed Development. B. A. Larkins and I. K. Vasil, ed. Kluwer Publishers, Dordrecht, The Netherlands. Raboy, V., and P. Gerbasi, Genetics of myoinositol phosphate synthesis and accumulation. Pages in: Subcellular Biochemistry. Vol. 26. Myoinositol Phosphates, Phosphoinositides, and Signal Transduction. B. B. Biswas and S. Biswas, ed. Plenum Press, New York, NY. Ravindran, V., W. L. Bryden, and E. T. Kornegay, Phytates: Occurrence, bioavailability, and implications in poultry nutrition. Poult. Avian Biol. Rev. 6: SAS Institute, SAS User s Guide: Statistics. Version 6.03 Edition. SAS Institute Inc., Cary, NC. Sauveur, B., Phosphorus requirements in finishing broilers, aged 4 to 8 weeks. Arch. Geflugelk. 42: Sebastian, S., S. P. Touchburn, and E. R. Chavez, Implications of phytic acid and supplemental microbial phytase in poultry nutrition: A review. World s Poultry Sci. J. 54: Sharpley, A., Symposium: Reducing the environmental impact of poultry production: Focus on phosphorus. Poultry Sci. 78: Skinner, J. T., A. L. Izat, and P. W. Waldroup, Effects of removal of supplemental calcium and phosphorus from broiler finisher diets. J. Appl. Poult. Res. 1: Skinner, J. T., and P. W. Waldroup, Allometric bone development in floor-reared broilers. J. Appl. Poult. Res. 4: Tortuero, F., and M. V. Diez Tardon, Possibilities in the use of low phosphorus concentrations for broiler diets during the finishing period. Adv. Aliment. Mejora Anim. 24:63 66.

8 PHOSPHORUS REDUCTION IN LITTER 1289 Van der Klis, J. D., and H.A.J. Versteegh, Phosphorus nutrition of poultry. Pages in: Recent Advances in Animal Nutrition. P. C. Garnsworthy, J. Wiseman, and W. Haresign, ed. Nottingham University Press, Nottingham, UK. Waldroup, P. W., J. H. Kersey, E. A. Saleh, C. A. Fritts, H. L. Stilborn, R. C. Crum, Jr., and V. Raboy, Nonphytate phosphorus requirement and phosphorus excretion of broiler chicks fed diets composed of normal or high available phosphate corn with and without microbial phytase. Poultry Sci. 79:(in press). Waldroup, P. W., R. J. Mitchell, and K. R. Hazen, The phosphorus needs of finishing broilers in relation to dietary nutrient density level. Poultry Sci. 53: Yi, Z., E. T. Kornegay, V. Ravindran, and D. M. Denbow, Improving phosphorus availability in corn and soybean meal for broilers using microbial phytase and calculation of phosphorus equivalency values for phytase. Poultry Sci. 75: Yoshida, M., and H. Hoshii, Re-evaluation of requirement of calcium and available phosphorus for finishing meat-type chickens. Jpn. Poult. Sci. 19: