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The Effect of Dietary Phosphorus Level and Phytase Supplementation on Growth Performance, Bone-Breaking Strength, and Litter Phosphorus Concentration in Broilers¹

S. Powell^*, S. Johnston^*, L. Gaston and L. L. Southern^*,2

^* School of Animal Sciences, and School of Plant, Environmental, and Soil Sciences, Louisiana State University Agricultural Center, Baton Rouge 70803

² Corresponding author: lsouthern{at}agcenter.lsu.edu

	ABSTRACT

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This research was conducted to determine the effects of feeding different P levels with and without phytase supplementation on broiler growth performance, bone-breaking strength (BBS), and litter P concentration. An experiment with 4 trials was conducted with 7,840 Ross x Ross straight-run broilers. For each trial, 1,960 broilers were allotted on d 0 to treatments, with 7 replications each and with 70 broilers per replication. The broilers were fed a 4-period feeding program consisting of starter (0 to 14 d), grower (14 to 32 d), finisher (32 to 41 d), and withdrawal (41 to 50 d) periods. For each trial, the same pen was used continuously for each treatment-replication combination, and the litter was not removed between trials. Broilers were fed a control diet [0.43, 0.40, 0.36, or 0.32% nonphytate P (nPP)] in the starter, grower, finisher, and withdrawal periods, respectively, a low Ca and P (LCaP) diet with a 0.05% reduction in nPP in each period, and these 2 diets supplemented with phytase at 600 phytase units/kg (nPP and Ca were reduced by 0.094% in diets with phytase). Diet did not affect (P > 0.10) broiler performance in the starter or withdrawal periods. Generally, both phytase addition and the LCaP diet decreased some aspects of growth performance during the grower and finisher periods. There was no main effect of phytase on BBS, but BBS was decreased in the broilers fed the LCaP diet with phytase addition (nPP x phytase, P < 0.01) in the grower period, and BBS was decreased in the finisher (P < 0.02) and withdrawal (P < 0.01) periods for broilers fed the LCaP diet. Total P, soluble P (SP), and reactive soluble P (RSP) were decreased (P < 0.04) in the litter of broilers fed the LCaP diets. Total P, SP, and RSP were decreased (P < 0.01) in the litter of broilers fed phytase. These data indicate that phytase supplementation at 600 phytase units/kg reduces growth in some periods, has no effect on BBS, and reduces total P, SP, and RSP in the litter.

Key Words: broiler • phosphorus • phytase • litter phosphorus

	INTRODUCTION

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Phosphorus is an essential nutrient for plants and animals and is critically important to the optimal production of poultry. However, there is a concern worldwide regarding the quantity of P that is released into the environment generated from land application of poultry litter from commercial production. This concern arises from the fact that P contributes to the eutrophication of water. This enrichment of surface waters by plant nutrients, according to Withers et al. (1995), is a form of pollution that restricts the potential use of affected water. This problem has led to vigorous research to reduce the quantity of P released into the environment as a product of the poultry industry.

Recent research has reported substantial differences in the nonphytate P (nPP) requirement of broilers compared with those published by the NRC (1994). Waldroup et al. (2000) reported that the nPP requirement for the starter phase ranges from 0.37 to 0.39%. Angel et al. (2000a, b) determined the nPP requirement to be between 0.32 and 0.28% nPP (0.80% Ca) for the grower period (18 to 32 d), between 0.24 and 0.19% nPP (0.70% Ca) for the finisher period (32 to 42 d), and 0.11% nPP (0.61% Ca) in the withdrawal period (42 to 49 d). Dhandu and Angel (2003) determined the nPP requirement in a 4-period system and reported a requirement of 0.20% nPP for the finisher period and 0.16% nPP in the withdrawal period. These nPP requirement results are considerably lower than the recommendation by the NRC (1994). These data suggest that it is possible to reduce the P concentration of the diet in an effort to reduce the quantity of P in the litter, without reducing broiler growth performance, while reducing the potential for P pollution. Researchers are in agreement that a reduction of supplemental P in the diet results in a decrease in total P in broiler litter; however, there is a need to establish this response in a 4-period feeding program in reused litter. Researchers also are in general agreement that the supplementation of phytase to the diets of broilers can replace approximately 0.1% of dietary P. However, the data are inconsistent regarding the effect of phytase on the soluble P (SP) concentration in litter runoff water during rainfall simulation (DeLaune et al., 2001). This is a major concern because the SP in the litter is readily available to aquatic plants, and it is often considered the key factor contributing to accelerated eutrophication of surface waters (Pote, 2000).

Although considerable improvements have been made in recent years in the reduction of P in poultry excreta or litter, research needs to be conducted in many areas. Therefore, the objectives of this research were to investigate the effects of lowering the P concentration and adding phytase in the diet on growth performance, bone-breaking strength (BBS), and P in the litter of broilers in a 4-period feeding program in reused litter.

	MATERIALS AND METHODS

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All methods used in this experiment regarding animal care were approved by the Louisiana State University Agricultural Center Animal Care and Use Committee. An experiment was conducted with 7,840 Ross x Ross 508 commercial broilers from House of Raeford (Gibsland, LA). The experiment consisted of 4 trials. For each trial in the experiment, 1,960 broilers were allotted on the day of hatch to 4 treatments, with 7 replications per treatment and 70 broilers per replication. Each trial lasted 50 d. The broilers were housed in 1.52 x 3.05 m pens at the Louisiana State University Poultry Farm in one room of a tunnel-ventilated house equipped with cool cells and fans. The pens contained 12 to 14 cm of fresh litter for the first trial. Litter was raked and a top dressing of fresh litter was applied before the start of each of the remaining 3 trials. For each trial, the same pen was used continuously for each treatment-replication combination, and the litter was not removed between trials. A lighting schedule similar to commercial conditions was used in this study. Lighting was via incandescent lighting and hours of light for a 24-h period consisted of 4 d of 24 h of light, followed by 5 d of 20 h of light, 6 d of 18 h of light, and 16 h of light for the remainder of the project. The temperature in the house was maintained at 29 to 32°C for the first week and was decreased by 2°C every week until the house temperature was 21 to 24°C, weather permitting. Feed and water were offered for ad libitum consumption throughout the experimental period. Feed was fed in a mash form via a feed tray for the first week and then by 2 hanging tube feeders (43 cm in diameter) per pen. Water was provided via one automatic waterer with 9 nipples in each pen. The broilers were fed a 4-period feeding program consisting of starter (0 to 14 d), grower (14 to 32 d), finisher (32 to 41 d), and withdrawal (41 to 50 d) periods.

Broilers were fed a control diet (0.43, 0.40, 0.36, or 0.32% nPP in the starter, grower, finisher, and withdrawal periods, respectively), a low Ca and P (LCaP) diet with a 0.05% reduction in nPP in each period, and these 2 diets supplemented with phytase at 600 phytase units/kg (nPP was reduced by 0.094% in diets with phytase). The level of nPP in the control diet was based on a review of the literature (Angel et al., 2000a,b; Waldroup et al., 2000; Dhandu and Angel, 2003). For the starter period, the diets were formulated to contain 3,034 kcal of ME/kg, 1.26% total Lys, and 0.91% TSAA (Table 1). For the growing period, the diets were formulated to contain 3,116 kcal of ME/kg, 1.14% total Lys, and 0.86% TSAA (Table 2). For the finishing period, the diets were formulated to contain 3,160 kcal of ME/kg, 0.96% total Lys, and 0.78% TSAA (Table 3). For the withdrawal period, the diets were formulated to contain 3,192 kcal of ME/kg, 0.87% total Lys, and 0.66% TSAA (Table 4). All other nutrients met or exceeded the NRC (1994) requirement. Natuphos 1200 (BASF Corporation, Mt. Olive, NJ) was included in diets 3 and 4 at 0.05% to provide 600 phytase units/kg of diet. The nPP concentrations were reduced by 0.094% in the diets with added phytase for all growth periods. The phytase nutrient matrix values evaluated by Shelton et al. (2004) were used in the diets with phytase to account for the nutrient-sparing effect of phytase on ME (31 kcal/kg) and amino acids (TSAA 0.008% and Lys 0.015%).

Data were analyzed by ANOVA procedures appropriate for a randomized complete block design (Steel and Torrie, 1980) by using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC). The model included trial and the trial x treatment interaction. The trial x treatment interaction was significant for most variables, but in general, they were due to changes in magnitude. Contrast statements were included to examine phytase, nPP, and the phytase x nPP interaction as a 2 x 2 factorial arrangement of treatments. The PROC MIXED procedure was used in the analysis of litter data. The pen of broilers was the experimental unit for all data.

	RESULTS

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Diet did not affect (P > 0.10) broiler performance in the starter period. During the grower period, phytase decreased (P < 0.01 to 0.05) ADG, ADFI, G:F, and BW; and the LCaP diet decreased (P < 0.03 to 0.08) ADFI and G:F. Phytase decreased ADG and G:F more in broilers fed the control diet than in those fed the LCaP diet (nPP x phytase, P < 0.10). During the finisher period, phytase decreased ADFI (P < 0.10) and BW (P < 0.01), and the decrease in ADFI was greater in broilers fed the control diet than in those fed the LCaP diet (nPP x phytase, P < 0.01). During the withdrawal period, diet did not affect (P < 0.10) growth performance. The overall data showed no effect (P > 0.10) of the LCaP diet on growth performance. However, phytase supplementation decreased (P < 0.02 to 0.05) ADG, ADFI, and G:F. The overall effect of phytase was a 1.6% decrease (P < 0.07) in final BW (Table 5).

View larger version (23K): [in this window] [in a new window]   Figure 1. Phosphorus concentration in the litter of broilers fed a control diet [0.43, 0.40, 0.36, or 0.32% nonphytate P (nPP) in the starter, grower, finisher, and withdrawal periods, respectively], a low Ca and P (LCaP) diet with a 0.05% reduction in nPP in each period, and these 2 diets supplemented with phytase (phy) at 600 phytase units/kg.

	DISCUSSION

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Neither the nPP level fed nor phytase supplementation affected broiler growth performance in the starter period. These data are in agreement with published results (Brugalli et al., 1999; Waldroup et al., 2000; Applegate et al., 2003; Angel et al., 2005). However, Yan et al. (2000) reported an increase in BW at 21 d for broilers with the addition of phytase. These results indicate that a 0.05% reduction of the nPP concentration from 0.43 to 0.38% in the LCaP diets and a further 0.094% reduction in nPP with phytase supplementation had no negative effect on broiler growth performance in the starter period. This is in agreement with the requirement of 0.39% nPP reported by Waldroup et al. (2000) and the 0.31% reported by Brugalli et al. (1999). These data suggest that the nPP concentration required to maximize growth performance in the starter period is lower than the NRC (1994) recommended level of 0.45% nPP.

During the grower period, phytase decreased ADG, ADFI, G:F, and BW. This general decrease in growth performance during the grower period is not consistent with the results of Angel et al. (2005), who reported no difference in growth performance in broilers when the nPP concentration of the diet was reduced by 0.07%, from 0.33 to 0.26%, with phytase supplementation. In addition, Yan et al. (2003) reported that a reduction of 0.05% from 0.20% nPP with the addition of phytase resulted in no difference in growth performance among broilers fed phytase. The levels of nPP fed in the grower period (0.40, 0.35, 0.31, and 0.26%) are higher than the levels reported by Angel et al. (2000a), Yan et al. (2001), and Dhandu and Angel (2003) to maximize broiler growth performance (0.28, 0.186, and 0.20% nPP, respectively). The start of the grower period in this research differs from the others in that the grower period started at d 14 and not at d 17 or 18. However, Shelton et al. (2004) started the grower period at d 15 and reported no difference in growth performance of broilers when using the same nutrient matrix value for phytase as in this research. Thus, the results obtained in the present research, in which phytase decreased ADG and G:F more in broilers fed the control diet than in those fed the LCaP, indicates that the effect of phytase supplementation is dependent on the level of dietary P fed, with the lower levels of dietary P receiving the positive benefits.

The lower BW in broilers fed phytase in the finisher and withdrawal periods seems to be a carryover effect from the grower period because there was no difference in ADG and G:F for these periods. However, during the finisher period, phytase supplementation decreased ADFI, and this decrease was greater in broilers fed the control diet than in those fed the LCaP diet. This response again seems to be due to the level of 0.26% nPP fed in this period; this level of nPP is higher than the 0.16% reported by Dhandu and Angel (2003) and the 0.23% reported by Yan et al. (2003).

The overall data indicate that phytase supplementation decreased final BW by 1.6% compared with broilers not fed phytase. Yan et al. (2000), using a high available P hybrid of corn, reported a decrease of 3% in BW in 56-d-old broilers fed phytase with a reduction of 0.075% in dietary P from the NRC recommended values, and a 5.7% increase in BW for the broilers whose diet was reduced by 0.15% dietary P with phytase supplementation. The increase in BW was not observed in broilers fed phytase in the LCaP diet in this experiment. A possible explanation is that the increase in availability of amino acids and ME from phytase was used in the formulation of diets for this experiment, but they were not considered in the work of Yan et al. (2000) because phytase was added on top of their diets. These data indicate that the effect of phytase supplementation on growth performance is dependent on the concentration of dietary P.

Bone-breaking strength was not affected by phytase supplementation in any period of growth. This response indicates that the release of nPP by phytase was adequate for normal bone development. This response also indicates that the decrease in growth performance is not a result of P deficiency, because BBS would be expected to be the first variable affected by phytase supplementation. Bone-breaking strength in the grower period was decreased in broilers fed the LCaP with the addition of phytase, which indicates that the 0.35% (0.26% without phytase) nPP fed in this diet was inadequate to maximize BBS. This nPP level is below the 0.28 to 0.32% nPP reported by Angel et al. (2000a) to maximize BBS in the grower period. Bone-breaking strength was decreased in the finisher and withdrawal periods for broilers fed the LCaP diet. This response indicates that the level of nPP fed was inadequate to maximize BBS. However, Ling et al. (2000) reported that nPP levels of 0.26 and 0.19% were needed to maximize BBS in the finisher and withdrawal periods, respectively. The nPP levels of 0.31 (0.22%) and 0.27% (0.18%) should have been adequate.

Total P, SP, and RSP were reduced by 9.7, 9.7, and 10.9%, respectively, in the litter of broilers fed the diets with LCaP. This response indicates that if broilers were fed closer to the requirement for P, then the concentration of P in the litter would be decreased, resulting in a reduction in the potential of litter P to pollute waterways. Total P was decreased in the litter of broilers fed phytase by 22.6% in the control diet and by 21.5% in the LCaP diet. Soluble P and RSP also decreased by 11.7 and 14.3%, respectively, with phytase supplementation. These data are similar to those reported by Applegate et al. (2003) and Shelton et al. (2004) for TP. However, the decrease in SP and RSP with phytase supplementation was not reported by these researchers. These data indicate that there is a positive correlation between the concentration of P in the diet and TP in the litter.

In summary, these data indicate that phytase supplementation at 600 phytase units/kg reduces growth in the grower period, has no negative effect on BBS during any period, and reduces the TP, SP, and RSP concentrations of poultry litter. These data also indicate that a 0.05% reduction in nPP and Ca from the control nPP levels of 0.43, 0.40, 0.36, and 0.32 for the starter, grower, finisher, and withdrawal periods, respectively, has no negative effect on overall growth performance, but decreases BBS in the finisher and withdrawal periods. However, the reduction in BBS during the finisher and withdrawal periods must be investigated further to establish the BBS that is required to minimize loss during processing. Total P, SP, and RSP were reduced in the litter of broilers fed the LCaP and phytase-supplemented diets.

	FOOTNOTES

 
¹ Approved for publication by the Director of the Louisiana Agricultural Experiment Station as manuscript number 07-18-0285.

Received for publication July 17, 2007. Accepted for publication February 4, 2008.

	REFERENCES

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Angel, R., T. J. Applegate, and M. Christman. 2000a. Effects of dietary nonphytate phosphorus on performance and bone measurements in broilers fed on a four phase feeding system. Poult. 79(Suppl. 1):21–22. (Abstr.)

Angel, R., T. J. Applegate, M. Christman, and A. D. Mitchell. 2000b. Effect of dietary nonphytate phosphorus level on broiler performance and bone measurements in the starter and grower phase. Poult. Sci. 79(Suppl. 1):21–22. (Abstr.)

Angel, R., W. W. Saylor, A. S. Dhandu, W. Powers, and T. J. Applegate. 2005. Effects of dietary phosphorus, phytase, and 25-hydroxycholecalciferol on performance of broiler chickens grown in floor pens. Poult. Sci. 84:1031–1044.[Abstract/Free Full Text]

Applegate, T. J., B. C. Joern, D. L. Nussbaum-Wagler, and R. Angel. 2003. Water-soluble phosphorus in fresh litter is dependent upon phosphorus concentration fed but not on fungal phytase supplementation. Poult. Sci. 82:1024–1029.[Abstract/Free Full Text]

Bender, M. R., and W. C. Wood. 2000. Total phosphorus in residual materials. Pages 77–82 in Methods of Phosphorus Analysis for Soils, Sediments Residuals and Waters. Southern Cooperative Series Bull. No. 396. G. M. Pierzynski ed. North Carolina State Univ., Raleigh.

Brugalli, I., D. J. Silva, L. F. T. Albino, P. C. Gomes, H. S. Rostagno, and A. Silva. 1999. Available phosphorus requirement and effect of particle size on phosphorus bioavailability from meat and bone meal for broiler chicks. Rev. Bras. Zootec. 28:1288–1296.

Dhandu, A. S., and R. Angel. 2003. Broiler nonphytin phosphorus requirement in the finisher and withdrawal periods of a commercial four-phase feeding system. Poult. Sci. 82:1257–1265.[Abstract/Free Full Text]

DeLaune, P. B., P. A. Moore, Jr., D. C. Carmen, T. C. Daniel, and A. N. Sharply. 2001. Development and validation of a phosphorus index for pastures fertilized with animal manure. Pagess 239–247 in Proc. Int. Symp. Addressing Anim. Prod. Environ. Issues, Research Triangle Park, Raleigh, NC.

Ling, B., C. R. Angel, T. J. Applegate, N. G. Zimmermann, and A. S. Dhandu. 2000. The nonphytate phosphorus requirements of broilers in a four-phase feeding program. Poult. Sci. 79(Suppl. 1):11. (Abstr.)

NRC. 1994. Nutrient Requirements of Poultry. 9th rev. ed. Natl. Acad. Press, Washington, DC.

Pote, D. H. 2000. Analyzing for total phosphorus and total dissolved phosphorus in water samples. Pages 91–93 in Methods of Phosphorus Analysis of Soils, Sediments, Residuals, and Water. Southern Cooperative Series Bull. No. 396. G. M. Pierzynski, ed. North Carolina State Univ., Raleigh.

Self-Davis, M. L., and P. A. Moore Jr. 2000. Determining water-soluble phosphorus in animal manure. Pages 74–76 in Methods of Phosphorus Analysis of Soils, Sediments, Residuals, and Water. Southern Cooperative Series Bull. No. 396. G. M. Pierzynski, ed. North Carolina State Univ., Raleigh.

Shelton, J. L., L. L. Southern, L. A. Gaston, and A. Foster. 2004. Evaluation of the nutrient matrix values for phytase in broilers. J. Appl. Poult. Res. 13:213–221.[Abstract/Free Full Text]

Steel, R. G. D., and J. H. Torrie. 1980. Principles and Procedures of Statistics: A Biometrical Approach. 2nd ed. McGraw-Hill Book Co., New York, NY.

Waldroup, P. W., J. H. Kersey, E. A. Saleh, C. A. Fritts, F. Yan, H. L. Stilborn, R. C. Crum Jr., and V. Raboy. 2000. Nonphytate phosphorus requirement and phosphorus excretion of broiler chicks fed diets composed of normal or high available corn with and without microbial phytase. Poult. Sci. 79:1451–1459.[Abstract/Free Full Text]

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Yan, F., J. H. Kersey, C. A. Fritts, and P. W. Waldroup. 2003. Phosphorus requirements of broiler chicks six to nine weeks of age as influenced by phytase supplementation. Poult. Sci. 80:455–459.

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