Phosphorus Requirements of Broiler Chicks Six to Nine Weeks of Age as Influenced by Phytase Supplementation
Published: July 4, 2016
By: F. Yan, J. H. Kersey, C. A. Fritts, and P. W. Waldroup
Poultry Science Department, University of Arkansas, Fayetteville, Arkansas
Summary
Two trials of similar design were conducted to determine the nonphytate phosphorus (NPP) requirements for broilers from 42 to 63 d of age in diets with or without phytase supplementation. Male broilers of a commercial strain were grown to 42 d on nutritionally complete diets with NRC (1994) recommended levels of Ca and NPP. At 42 d, the birds were placed on experimental diets and fed to 63 d. The experimental treatments consisted of a 2 × 6 factorial arrangement with two levels of phytase (0 or 800 U/kg) and six levels of NPP (0.10 to 0.35% in 0.05% increments). Body weight gain, feed conversion, and mortality were determined during the period. At 49, 56, and 63 d, excreta samples were taken, and samples of birds were killed for tibia ash determination. The lowest level of NPP, with or without phytase supplementation, was sufficient for maximum BW gain, feed conversion, and livability. Using nonlinear regression, levels of NPP needed to optimize tibia ash in the absence of phytase were 0.31 ± 0.004%, 0.23 ± 0.02%, and 0.22 ± 0.029% at 49, 56, and 63 d, respectively. When diets were supplemented with 800 U/kg of phytase, the NPP requirement for optimum tibia ash was 0.15 ± 0.049% at 49 d. At 56 and 63 d, no more than 0.10% NPP (lowest level tested) was sufficient to maximize tibia ash. Compared to current NRC (1994) recommendations, the application of these reduced dietary phosphorus levels could markedly reduce excreta excretion of phosphorus by broilers.
(Key words: broiler, phosphorus, phytase, eutrophication, waste management)
2003 Poultry Science 82:
Introduction
The poultry industry is facing growing concerns about the possible contribution of land application of poultry litter to eutrophication of surface waters (Edwards and Daniel, 1992; Sharpley, 1999). Attention has focused on means of reducing phosphorus excretion while maintaining productivity. Because of the demands for adequate skeletal development of rapidly growing broilers, it is necessary to provide adequate levels of phosphorus with a sufficient margin of safety in broiler diets.
Chickens are lacking or limited in phytase, the enzyme necessary for breakdown of the phytate molecule and subsequent release of phytate-bound phosphorus in plant feedstuffs (Nelson, 1967; O’Dell et al., 1972; Raboy, 1990). The ability of exogenous phytase to improve the availability of phytate-bound phosphoruswas demonstrated by Nelson et al. (1968, 1971). 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 (Ravindran et al., 1995; Sebastian et al., 1998). Numerous studies have demonstrated that dietary phosphorus levels in broiler diets can be reduced by supplementation with phytase (Simons et al., 1990; Broz et al., 1994; Denbow et al., 1995; Kornegay et al., 1996; Yi et al., 1996). It is generally recognized that the phosphorus requirements of chicks decrease with age (NRC, 1994); however, few studies have focused on phosphorus requirements after 3 or 4 wk of age when the broiler consumes the greatest percentage of total feed and thus the greatest portion of the excreta excretion occurs. The NRC recommendations for broilers of this age are based primarily upon studies by Waldroup et al. (1963, 1974), Sauveur (1978), and Yoshida and Hoshii (1982) using birds with far less growth potential than those used today. Several recent studies have explored the utilization of phytase from of 3 to 6 wk of age (Sohail and Roland, 1999; Yan et al., 2001), but to our knowledge, none have evaluated needs after 6 wk of age. The objective of the present study was to determine the dietary requirements of the broiler chicken for nonphytate phosphorus (NPP) during the period from 6 to 9 wk of age using corn-soybean meal diets with and without supplementation with microbial phytase. | Table 1. Composition (g/kg) and calculated analysis of diet for broiler chickens 6 to 9 wk of age.  1Alpharma, Inc., Ft. Lee, NJ 07024.2Elanco Animal Health division of Eli Lilly & Co., Indianapolis, IN. 3Provided per kilogram of diet: vitamin A (from vitamin A acetate), 7,714 IU; cholecalciferol, 2,204 IU; vitamin E, 16.53 IU; vitamin B12, 0.013 mg; riboflavin, 6.6 mg; niacin, 39 mg; pantothenic acid, 10 mg; choline, 465 mg; menadione (from menadione dimethylpyrimidinol), 1.5 mg; folic acid, 0.9 mg; thiamin (from thiamine mononitrate), 1.54 mg; pyridoxine (from pyridoxine HCl), 2.76 mg; D-biotin, 0.066 mg; ethoxyquin, 125 mg; Se, 0.1 mg. 4Provided per kilogram of diet: Mn (from MnSO4_H2O), 100 mg; Zn (from ZnSO4_7H2O), 100 mg; Fe (from FeSO4_7H2O) 50 mg; Cu (from CuSO4_5H2O), 10 mg; I (from Ca(IO3)2_H2O), 1 mg. 5Variable ingredients included 18.50 g/kg limestone and 6.20 g/kg washed builders sand for low-phosphorus diet and 11.51 g/kg limestone and 13.19 g/kg for high-phosphorus diet. 6Calculated from NRC (1994). |
Materials and methods
Two trials of identical design were conducted. A diet was formulated to meet the nutrient requirements of the broiler from 6 to 9 wk as suggested by NRC (1994). Minimum levels of amino acids were 110% of those recommended by NRC to provide margins of safety. The diet was formulated to contain 0.35% NPP with 0.80% calcium (Table 1). Removal of the supplemental dicalcium phosphate and adjustment of the level of ground limestone and inert filler (washed builders sand) produced a diet with 0.10% NPP and 0.80% calcium.
Diets were adequately fortified with vitamins and trace minerals using supplements obtained from commercial producers.
A large batch of the basal diet void of dicalcium phosphorus, limestone, and inert filler was mixed and divided into two sublots. The sublots were then fortified with dicalcium phosphate, limestone, and inert filler as indicated in Table 1 to produce low-phosphorus (0.10% NPP) and high-phosphorus (0.35% NPP) basal diets. Each of these two diets was then divided into two sublots; one sublot of each was treated with 800 U/kg phytase enzyme.2 The enzyme was sprayed on to the mixed feed; one part of enzyme was mixed with 10 parts of distilled water and slowly applied to the feed in a mixer. Feed not treated with phytase was sprayed with an equivalent amount of distilled water. Samples of the mixed feeds were assayed for phytase content to verify adequate mixing. Additional samples were analyzed for calcium and total phosphorus content.
After obtaining the results of the mineral assays, portions of the low-phosphorus and high-phosphorus diets, with and without phytase, were blended in quantities calculated to provide levels of NPP ranging from 0.10 to 0.35% in increments of 0.05%. This design resulted in a total of 12 experimental diets in a 2 × 6 factorial arrangement of two levels of phytase (0 or 800 U/kg) with six levels of NPP. Each of the 12 diets was fed to four replicate pens of 50 male chicks each in two consecutive studies.
In each study, male chicks of a commercial strain3 were obtained from a local hatchery and grown to 6 wk of age on nutritionally complete diets with adequate levels of phosphorus to maximize bone development [0.45% NPP to 3 wk, 0.35% to 6 wk as suggested by NRC (1994)]. At 6 wk, birds were randomly assigned to pens with built-up softwood shavings litter. Fifty birds were placed in each of 48 pens (5.6 m2) with four pens assigned to each dietary treatment. The experimental diets in mash form and tap water were provided for consumption ad libitum.
Body weights by pen were determined at 42, 49, 56, and 63 d; pen feed consumption was measured for the same period. Birds that died during the study were weighed; feed utilization was adjusted for mortality. Three birds per pen were removed at 46, 53, and 60 d and placed in finishing batteries with raised wire floors. They were fed the test diets for an additional 3 d with excreta samples collected during that time and freezedried prior to phosphorus assay. Excreta samples were analyzed in quadruplicate in each of the two trials.4 At 49, 56, and 63 d the birds in the battery pens were killed by CO2 inhalation followed by cervical dislocation, and the tibia was removed for bone ash determination as described by AOAC (1990).
Penmeans served as the experimental unit for statistical analysis. Data were subjected to analysis of variance as a factorial arrangement of treatments with NPP level and phytase supplementation as the main effects and the interaction of NPP and phytase supplementation.
Table 2. Analysis of calcium and total phosphorus content of experimental diets1
1Analyses conducted by Agricultural Diagnostic Laboratory, University of Arkansas, Fayetteville, AR, using inductively coupled plasma-atomic energy spectroscopy following HNO3 digestion.2Means ± standard deviation (n = 16).
Analysis used the general linear models procedure of SAS software (SAS Institute, 1991). Initial BW served as a covariate for analyzing BW gain. Mortality data were transformed to √n + 1 prior to analysis; data are presented as natural numbers. Statements of probability are based upon P ≤ 0.05. When significant differences among or between treatment means were found, means were separated using repeated t tests using probabilities generated by the least squares means option. Following these analyses, nonlinear regression analysis was conducted using the PROC NLIN procedure of SAS (SAS Institute, 1991) to estimate the requirement for selected variables. Variables that were subjected to the regression analysis included BW gain, feed conversion ratio, and bone ash content.
Results and discussion
The analyzed level of total phosphorus in the basal diet (estimated 0.10%NPP)was slightly lower than originally calculated, but the amounts of added phosphorus in the test diets, as determined by subtraction of the amount in the basal diet, were in good agreement with calculated values (Table 2). Calcium levels were in good agreementwith the calculated 0.80%. Results of the phytase assays of the low-phosphorus and high-phosphorus basal diets indicated good agreement with calculated levels (860 ± 63 and 805 ± 56 U/kg for the low- and high-phosphorus basal diets, respectively).
As there were no interactions of trial × treatment, data from the two studies were combined. The level of NPP or phytase supplementation had no significant effect on BW gain (Table 3), feed conversion (Table 4), or mortality (Table 5) at any age during the study, indicating that the lowest dietary level of NPP was sufficient to support these live parameters for birds of this age. High mortality occurred from 56 to 63 d as a result of increased house temperature coupled with the stress caused to the birds while handling them during weighing at 56 d. [AUTH QUERY: Previous sentence OK as edited?]
No significant interaction between dietary NPP level and phytase supplementation was observed for BW gain, feed conversion, or mortality. Waldroup et al. (1974) reported that in two of three trials, 0.12% NPP (lowest level tested) was adequate for BWgain and feed conversion in broilers 4 to 8 wk of age; in a third trial no more than 0.24% was required. Tortuero and Tardon (1983) found that no more than 0.29% NPP (lowest level tested) was satisfactory for BW gain, feed conversion, and tibia ash in broilers 35 to 53 d of age. More recently Skinner et al. (1992a; 1992b) reported that removal of supplemental phosphate sources from corn-soybean meal diets fed to broilers from 42 to 49 d or 42 to 56 d did not adversely affect BW gain, feed conversion, or tibia ash, so long as calcium levels of 0.48% or more were maintained and that broilers had previously been fed adequate levels of calcium and phosphorus. The reduced phosphorus diets in the Skinner studies contained 0.12% NPP, similar to the present study.
Table 3. Effect of nonphytate phosphorus level and phytase supplementation on BW gain of male broilers from 6 to 9 wk of age (means of four replicate pens of 50 male broilers in two successive trials)
1With or without addition of 800 U/kg phytase (Natuphos, BASF Corporation, Mt. Olive, NJ).2Used as a covariate for body weight gain analyses.
Table 4. Effect of nonphytate phosphorus level and phytase supplementation on feed conversion by male broilers from 6 to 9 wk of age (means of four replicate pens of 50 male broilers in two successive trials)
1With or without addition of 800 U/kg phytase (Natuphos, BASF Corporation, Mt. Olive, NJ).Tibia ash at 49, 56, and 63 d was significantly affected by level of dietary NPP, phytase supplementation, and by the interaction between NPP and phytase (Table 6). Nonlinear regression analysis was used to estimate the NPP requirement for optimum tibia ash for broilers fed diets with and without phytase supplementation; the requirement was established as the inflection point of the one-slope regression model (Robbins et al., 1979; Yu and Morris, 1999; Waldroup et al., 2000). When no phytase was added to the diets, the NPP requirement for optimum tibia ash was 0.31 ± 0.004% (mean ± SE) at 49 d, in close agreement with the NRC (1994) recommendation of 0.30%. This value was reduced to 0.23 ± 0.020% and 0.22 ± 0.029% NPP at 56 and 63 d, respectively. When diets were supplemented with phytase, the NPP requirement for optimum tibia ash was 0.15 ± 0.049% at 49 d. At 56 and 63 d, no more than 0.10% NPP (lowest level tested)was sufficient tomaximize tibia ash.
The dietary NPP level and phytase supplementation had a marked impact upon excreta phosphorus content (Table 7). As reported in previous studies from our laboratory (Waldroup et al., 2000), excreta phosphorus rose gradually as dietary NPP increased until the needs for optimumtibia ash weremet and then increased sharply. A feeding strategy that reduced dietary NPP levels to no more than that needed to optimize tibia ash could have a marked impact upon excreta phosphorus content.
Estimates of excreta phosphorus excretion at the NPP levels selected to maximize tibia ash were determined by plotting the excreta phosphorus values shown in Table 6 and finding the intercept of the estimated NPP level with the point on the excreta phosphorus response line. The excreta phosphorus content (dry matter basis) of birds fed the NRC (1994) recommended NPP levels in a diet without phytase supplementation was estimated to be 1.27, 1.53, and 1.25% at 49, 56, and 63 d, respectively. The excreta phosphorus content of birds fed the NPP levels estimated for optimumtibia ash without phytase supplementation were estimated to be 1.29, 1.1, and 1.08% at 49, 56, and 63 d, reductions of 0, 28, and 15%, respectively, compared to the NRC levels. The excreta phosphorus contents from birds fed the NPP levels estimated for optimum tibia ash with phytase supplementation were estimated to be 0.77, 0.74, and 0.71% (dry matter basis) at 49, 56, and 63 d, reductions of 39, 52, and 43%, respectively, compared to the NRC levels. A recent agricultural survey5 indicated that the mean level of NPP in broiler finisher diets in the United States was 0.32% per 3,200 ME kcal/kg, slightly more than current NRC (1994) recommendations and similar to that estimated at 49 d without phytase supplementation. Application of the reduced levels of dietary phosphorus in conjunction with phytase supplementation should allow for markedly reduced excretion of phosphorus in the litter with no reduction in live performance or in bone development.
Table 5. Effect of nonphytate phosphorus level and phytase supplementation on mortality by male broilers from 6 to 9 wk of age (means of four replicate pens of 50 male broilers in two successive trials)
1With or without addition of 800 U/kg phytase (Natuphos, BASF Corporation, Mt. Olive, NJ).Table 6. Effect of nonphytate phosphorus level and phytase supplementation on tibia ash of male broilers from 6 to 9 wk of age (means of three tibiae from each of four replicate pens in two successive trials)
a–gWithin comparisons, means with common superscript do not differ significantly (P ≤ 0.05).1With or without addition of 800 U/kg phytase (Natuphos, BASF Corporation, Mt. Olive, NJ).
Table 7. Effect of nonphytate phosphorus level and phytase supplementation on excreta phosphorus content of male broilers from 6 to 9 wk of age.
1Means ± standard deviation (n = 8). Analyses conducted by Agricultural Diagnostic Laboratory, University of Arkansas, Fayetteville, AR, using inductively coupled plasma-atomic energy spectroscopy following HNO3 digestion.2With or without addition of 800 U/kg phytase (Natuphos, BASF Corporation, Mt. Olive, NJ).
Acknowledgments
This study was supported in part by a grant from the U.S. Poultry and Egg Association, Tucker, GA. Contributions of phytase and phytase assays by BASF Corporation, Mt. Olive, NJ, are greatly appreciated.
References
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4 de julio de 2016
What about broilers raised to shorter period. We kill birds at age of 35 to 40 days as we sell whole bird. The basal ration consist of Sorghum and ground nut cakes
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