J. Appl. Poult. Res.
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J APPL POULT RES 2006. 15:518-524
© 2006 Poultry Science Association
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Research Reports

Biological Availability of Phosphorus Sources in Prestarter and Starter Diets for Broiler Chicks

A. R. Garcia, A. B. Batal and N. M. Dale1

Department of Poultry Science, University of Georgia, Athens 30602

1 Corresponding author: ndale{at}uga.edu


   SUMMARY
TOP
 SUMMARY
DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Two of the most widely used phosphate sources for broiler diets are defluorinated tricalcium phosphate (DFP) and dicalcium phosphate (DCP). Reports in the literature have shown that the biological availability of P in DFP for broilers and laying hens is lower than that in DCP. If this difference in bioavailability is even greater in young chicks, it might preclude the inclusion of DFP in prestarter and possibly starter diets. To address this question, 2 experiments were conducted to compare the P bioavailability of DFP and DCP in young broilers during the prestarter (1 to 8 d) and starter (9 to 15 d) periods. In Experiment 1, the first 3 treatments contained DFP, DCP, or raw rock phosphate, which were added to the diets to meet 0.32% available P (AP). Additionally, in 3 other treatments that served as positive controls, K2HPO4 was added to meet AP levels of 0.24, 0.32, and 0.40%. No significant difference was observed at 4, 8, and 15 d of age between the foot ash percentage of chickens fed the DFP and DCP diets, indicating that the biological availability of P in DFP was not significantly inferior to that of DCP. In Experiment 2, chick responses to 2 levels of either DFP or DCP, added to meet AP levels of 0.28 and 0.34%, were compared with those of chicks receiving K2HPO4, which was added to meet 3 AP levels (0.22, 0.28, and 0.34%). Foot ash results at 6 and 15 d of age indicated that the P utilization of chickens fed diets containing DFP was not significantly different to that of chickens fed the DCP diets. The difference in P bioavailability between DFP and DCP at 6 or 15 d of age was not greater than 10%. These results indicate that DFP can be satisfactorily utilized by young chicks during the prestarter and starter period and do not support the view that DFP should be excluded from diets for young chickens.

Key Words: defluorinated phosphate • dicalcium phosphate • bioavailability • prestarter diet • broiler chicken


   DESCRIPTION OF PROBLEM
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Recent research conducted with young poultry has documented physiological changes in the gastrointestinal tract occurring during the first week of age [1, 2]. Nutrient uptake [3], digestive enzymatic activity [4], and nutrient utilization in chickens [5, 6] have been found to gradually increase during and after the first week of life. Increased attention is now being given to the nutritional needs of the chicken during the first week posthatching, not only because this period has become recognized as being ever more critical in the development of modern broilers but also because broilers are reaching market weight in a shorter period [7]. As a strategy to compensate for an initially immature digestive system, interest in the use of prestarter diets has arisen [8], with the goal of providing either a higher concentration of nutrients or more digestible ingredients so as to facilitate nutrient utilization during the first week of life.

Because the available P (AP) from common feedstuffs used in practical diets is usually not sufficient to fulfill the P requirement of chickens, inorganic P sources are generally added to the feed. The concentration and availability of P in commercial phosphates must receive proper attention in feed formulation, not only because absolute concentrations of P may vary but also because differences in bioavailability of different commonly used phosphates have been well documented [9, 10, 11, 12, 13, 14]. Two of the most popular inorganic phosphate supplements are dicalcium phosphate (DCP) and defluorinated tricalcium phosphate (DFP), the former being frequently used as a standard source in relative bio-availability (RBV) studies [15], whereas the later is popular because of increased nutrient density (Ca + P + Na totals approximately 55% vs. 39% in DCP) and is used as an aid in improving pelleting efficiency [16, 17]. In several studies, it has been reported that the RBV of P in DFP is 5 to 10% lower than that in DCP [9, 10, 12, 13]. However, these studies have been largely conducted in laying hens, turkey poults, or broiler chickens after 21 d of age. To date, there is a lack of research regarding the bioavailability of P supplements during the first week of age, when most digestive functions are still in a developmental stage and P utilization could be affected. Should the bio-availability of P in DFP in chicks be markedly lower than that of DCP during the first week of life, this might preclude the inclusion of DFP in broiler prestarter or even starter diets. Therefore, the objective of the present research was to evaluate and compare the biological availability of P in DFP and DCP during the first 2 wk of age so as to determine if DFP is a suitable P source for chicks during the first week posthatch.


   MATERIALS AND METHODS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
General Procedures
Two experiments were conducted to evaluate the P bioavailability of DFP and DCP in young chicks. In Experiment 1, the objective was to compare DFP and DCP as inorganic P sources for broiler diets during the prestarter (1 to 8 d of age) and starter (9 to 15 d of age) periods. Five hundred eighty 1-d-old, straight-run broiler chicks (Cobb 500) [18], obtained from a commercial hatchery, were placed in battery brooders [19] with raised wire floors in environmentally controlled rooms. The birds were initially weighed and sorted so that the pens had a similar initial weight and weight distribution and randomly assigned to 6 dietary treatments, with 6 replicates of 16 chicks each. In both experiments, the basal diet provided 0.13% nonphytin P (calculated). To establish a response pattern from a highly available reagent grade phosphate, K2HPO4 (KP; diabasic) [20] was added to 3 dietary treatments to meet AP levels of 0.24, 0.32, and 0.40% (0.11, 0.19, and 0.27% P from the inorganic source). In addition to these, 3 other treatments contained DFP, DCP, or raw rock phosphate (RRP), which were added to the diets to meet a level of 0.32% AP (0.19% P from the inorganic source). The final phosphate source (RRP) served as a negative control to test the sensitivity of the assay.

The objective of Experiment 2 was to first confirm the general observations made in the initial experiment and also to directly compare the RBV of DFP and DCP during the prestarter and starter periods. Four hundred seventy 1-d-old, straight-run, broiler chicks [18] obtained from a commercial hatchery were placed in battery brooders as described for Experiment 1. In the first 3 treatments, increasing amounts of KP were added to the diets to meet AP levels of 0.22, 0.28, and 0.34% (0.09, 0.15, and 0.21% P added from the inorganic source), which again served as standard. The 2 test phosphates, DFP and DCP, were added to the diets at variable concentrations to meet AP levels of 0.28 and 0.34% for each source (0.15 and 0.21% P from the inorganic source), totalizing 4 dietary treatments. Thus, a total of 7 dietary treatments were included in the experimental design, each with 6 replications of 11 birds.

Body weight and feed intake (FI) were recorded at 4, 8, and 15 d of age in Experiment 1 and at 6 and 15 d of age in Experiment 2 to calculate BW gain (BWG) and gain:feed (GF). These data were corrected for mortality, which was recorded daily. Additionally, 5 chicks per pen were randomly selected and euthanized by CO2 asphyxiation at 4, 8, and 15 d in Experiment 1 and at 6 and 15 d of age in Experiment 2. From each bird, the right foot was removed for determination of foot ash (FA), according to the method of Garcia and Dale [21]. Because FA is highly correlated to tibia bone ash (r2 = 0.92) [21], FA was used as the parameter to evaluate P utilization.

Diets
The composition of the diets is presented in Tables 1Go and 2Go. Diets were based on corn and soybean meal and formulated to be isocaloric and isonitrogenous. Nutrient levels were similar to those used in commercial starter diets [22]. In both experiments, for purposes of diet formulation, 100% availability of the P in all phosphate sources was assumed. Samples of DFP, DCP, and RRP were submitted to a commercial laboratory [23] for analysis of Ca and P before diet formulation. Concentrations of P and Ca of these phosphates were 17.33 and 32.2%, 18.21 and 25.4%, and 14.04 and 24.3% for DFP, DCP, and RRP, respectively. Diets were fed ad libitum for 15 d in both experiments.


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  		Table 1. Composition of the diets, Experiment 1
 

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  		Table 2. Composition of the diets, Experiment 2
 
Statistical Analysis
Data for BWG, FI, GF, and FA from both experiments were analyzed by ANOVA, and when significant differences were found (P < 0.05), means were separated and compared by Tukey’s multiple comparison procedure through SAS [24]. Data for FA and supplemental P intake (Experiment 2) were fitted to a linear model using PROC REG of SAS [24]. Coefficients of RBV for DFP and DCP were obtained through the parallel lines [25] and the standard curve assay, both methods as outlined by Littell et al. [26].


   RESULTS AND DISCUSSION
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
In Experiment 1, a significant increase in BWG was observed as AP increased from 0.24 to 0.40% in the groups fed KP at both 4 and 8 d (Table 3Go). At 15 d, there were no significant differences in weight gain between dietary treatments, with the exception of the group fed the RRP, in which growth was significantly depressed. No significant differences were detected in FI at 4 d. However, at 8 and 15 d, the chicks fed the RRP diet had the lowest FI. With the exception of the chicks fed the lowest level of KP at 4 d of age, there were no significant differences in GF in any treatments. Mortality was not significant or associated to any dietary treatment. There was a significant increase in FA at 4, 8, and 15 d in the groups fed the KP diets as AP increased (Table 4Go), indicating that the assay was sensitive enough to detect changes in FA due to AP level changes. The birds fed RRP as the P source had a significant reduction in FA, as compared with birds fed KP, DFP, and DCP. Such reduction was observed at 4, 8, and 15 d and confirmed again the sensitivity of the assay. The depression in FA in birds receiving RRP was expected and is in agreement with previous studies [27, 28], because biological availability of P in RRP has been reported to be low (from 25 to 65%), depending upon the geographical region. No significant differences were found between the FA of chicks receiving DFP or DCP during either the prestarter or starter periods (Table 4Go). These results suggest that if in fact there is a reduced bioavailability of DFP, it was too small to be detected under these assay conditions and was certainly not exaggerated in the very young chicks.


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  		Table 3. Growth performance1 of broiler chickens at 4, 8, and 15 d of age in response to supplemental inorganic P from different sources, Experiment 1
 

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  		Table 4. Foot ash percentage1 of broiler chickens at 4, 8, and 15 d of age in response to supplemental inorganic P from different sources, Experiment 1
 
As cited previously, many reports using tibia bone ash as a response parameter [9, 10, 12, 13] found DFP to have a lower biological availability than DCP. However, in different studies conducted with broilers receiving either DCP or DFP as their inorganic P supplement, no significant differences were found in the tibia bone ash at 41 d of age [29, 30], which is in agreement with the results obtained in the present research. Since growth performance results and FA percent observed in Experiment 1 do not suggest that DCP had a markedly greater P bioavailability than DFP, a second experiment was conducted to more critically investigate this point.

In Experiment 2, no significant differences were found at 6 d of age for BWG or at 6 or 15 d for FI and GF (Table 5Go). The chickens fed 0.22% AP containing KP had the lowest BWG at 15 d. At levels of 0.28 and 0.34% AP, no significant differences were observed in the BWG of chicks due to phosphate sources. There was a significant increase in FA at 6 and 15 d of age when increasing levels of KP were fed (Table 6Go). However, no significant differences were found in FA percentage between DFP and DCP at the 2 levels of dietary P tested (0.28 and 0.34%) at either 6 or 15 d of age. After fitting the FA data to a linear model, the test for equality slopes was significant (P < 0.0001); thus, the RBV was calculated through the parallel lines assay as outlined by Littell et al. [26]. The parameter estimates obtained at 6 and 15 d of age were as follows: slope = 9.24 and 5.59, respectively; intercepts: –6.39, –7.23, and –7.58 at 6 d and –2.22, –2.70, and –2.60 at 15 d for KP, DFP, and DCP, respectively. Additionally, coefficients of RBV were calculated by the standard curve method, as outlined by Littell et al. [26]. The regression equations for the response to KP, which was used as the standard, were as follows: FA = 9.37107 + 0.0269 (mg of P intake) and FA = 11.5557 + 0.00286 (mg of P intake) at 6 and 15 d of age, respectively. Coefficients of RBV are presented in Table 7Go. At 6 d, regardless of the method of estimation, the RBV of DFP was below 80%, whereas for DCP the RBV was above 80%. The difference between DFP and DCP ranged from 6.67 to 9.1 percentage points. At 15 d, the RBV of both phosphates was greater than 80%, although the RBV of DFP was approximately 3.5 percentage points greater than that of DCP. However, when comparing the parallel line model intercepts for DCP and DFP, there was no indication of any significant differences between the sources (Table 7Go). Regardless of the method of estimation, the difference observed between the RBV of both phosphates was in the range of 5 to 10% that has been reported in studies conducted with older birds [16, 30]. In neither case, however, was there an indication that DFP had a markedly lower bioavailability than DCP for very young chicks. The coefficients of RBV at 6 and 15 d of age obtained from this study were somewhat lower than those obtained in work with older birds [9, 10, 12, 13]. However, both the standard P sources and the methodology used to calculate the RBV often differ among laboratories, a point which has been recognized in reviewing such assays [31]. In the parallel lines assay, which was applied in the present research, the coefficients of RBV are usually 10 to 18% lower than those obtained by slope ratio [26]. In the present research, however, there was a close agreement in the RBV values obtained from parallel lines and the standard curve methodology.


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  		Table 5. Growth performance1 of broiler chickens at 6 and 15 d of age in response to supplemental inorganic P from different sources, Experiment 2
 

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  		Table 6. Foot ash percentage1 of broiler chickens at 6 and 15 d of age in response to supplemental inorganic P from different sources, Experiment 2
 

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  		Table 7. Relative biological availability1 (%) of P from defluorinated tricalcium phosphate (DFP) and dicalcium phosphate (DCP) for broiler chickens at 6 and 15 d of age, Experiment 2
 
The objective of the current research was to determine if DFP might have a markedly lower bioavailability than DCP for very young chicks. If this were the case, in spite of its advantages in total nutrient density and improvements in pelleting efficiency, the use of DFP might be constrained in prestarter and starter diets. This was in fact found not to be the case, and there appears to be no reason to exclude DFP from rations for very young chicks. Thus, for the formulation of prestarter and starter diets, where highly digestible ingredients are desired, inclusion of DFP as an inorganic P source is acceptable.


   CONCLUSIONS AND APPLICATIONS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
REFERENCES AND NOTES
 

  1. The bioavailability of P in DFP is not greatly inferior to that of DCP for chicks during the first or second wk of age.
  2. Defluorinated tricalcium phosphate is a satisfactory source of inorganic P for prestarter and starter diets for broiler chickens.


   REFERENCES AND NOTES
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 

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  3. Noy, Y., and D. Sklan. 2001. Yolk and exogenous feed utilization in the posthatch chick. Poult. Sci. 80:1490–1495.[Abstract/Free Full Text]
  4. Nitsan, Z., G. Ben-Avraham, Z. Zoref, and I. Nir. 1991. Growth and development of the digestive organs and some enzymes in broiler chicks after hatching. Br. Poult. Sci. 32:515–523.[Web of Science][Medline]
  5. Noy, Y., and D. Sklan. 1995. Digestion and absorption in the young chicks. Poult. Sci. 74:366–373.[Web of Science][Medline]
  6. Batal, A. B., and C. M. Parsons. 2002. Effects of age on nutrient digestibility in chicks fed different diets. Poult. Sci. 81:400–407.[Abstract/Free Full Text]
  7. Lilburn, M. S. 1998. Practical aspects of early nutrition for poultry. J. Appl. Poult. Res. 7:420–424.[Abstract/Free Full Text]
  8. Rocha, P. T., J. H. Stringhini, M. A. Andrade, N. S. M. Leandro, M. L. Andrade, and M. B. Café. 2003. Protein and metabolizable energy levels in prestarter rations (1–7 days) on broiler performance from 1 to 21 days. Braz. J. Anim. Sci. 32:162–170.
  9. Nelson, T. S., and A. C. Walker. 1964. The biological evaluation of phosphorus compounds. A summary. Poult. Sci. 43:94–98.
  10. Peeler, H. T. 1972. Biological availability of nutrients in feeds: Availability of major minerals. J. Anim. Sci. 35:695–712.[Abstract/Free Full Text]
  11. Potter, L. M. 1988. Bioavailability of phosphorus from various phosphates based on body weight and toe ash measurements. Poult. Sci. 67:96–102.[Web of Science][Medline]
  12. Nelson, T. S., L. K. Kirby, and Z. B. Johnson. 1990. The relative biological value of feed phosphates for chicks. Poult. Sci. 69:113–118.[Web of Science][Medline]
  13. Sullivan, T. W., J. H. Douglas, N. J. Gonzalez, and P. L. Bond Jr. 1992. Correlation of biological value of feed phosphates with their solubility in water, dilute hydrogen chloride, dilute citric acid, and neutral ammonium citrate. Poult. Sci. 71:2065–2074.[Web of Science][Medline]
  14. Wendt, P., and M. Rodehutscord. 2004. Investigations on the availability of inorganic phosphate from different sources with growing white Pekin ducks. Poult. Sci. 83:1572–1579.[Abstract/Free Full Text]
  15. Lima, F. R., C. X. Mendonça Jr., J. C. Alvarez, J. M. F. Garzillo, E. Ghion, and P. M. Leal. 1997. Biological evaluations of commercial dicalcium phosphates as sources of available phosphorus for broiler chicks. Poult. Sci. 76:1707–1713.[Abstract/Free Full Text]
  16. Behnke, K. C. 1981. Pellet mill performance as affected by mineral source. Feedstuffs 53:34–36.
  17. Verner, W. A. 1988. Phosphates in pelleting: Best cost versus least cost. Feed Manage. 39:56–58.
  18. Cobb 500, Cobb-Vantress Inc., Siloam Springs, AR.
  19. Petersime Incubator Co., Gettysburg, OH.
  20. J. T. Baker Inc., Phillipsburg, NJ.
  21. Garcia, A. R., and N. Dale. 2006. Foot ash as a means of quantifying bone mineralization in chicks. J. Appl. Poult. Res. 15:103–109.[Abstract/Free Full Text]
  22. Agri-Stats Inc., Fort Wayne, IN.
  23. Phoslab Inc., Lakeland, FL.
  24. SAS Institute. 1990. SAS STAT User’s Guide Release 6.08. SAS Inst. Inc., Cary, NC.
  25. The percentage of FA data for the standard and the test phosphate sources obtained in Experiment 2 was fitted to a linear model with 6 parameters, according to the formula FA = ß0 + ß1x1 + ß2x2 + ß3x3 + {varepsilon} where ß0 = the intercept of the GLM; ß1, ß2, and ß3 = the corresponding slopes for each phosphate source; and x1, x2, and x3 = the supplemental P intake for each phosphate source. Thereafter, an F-test for reduction of terms to 4 parameters was applied, with the formula Fv1,v2 = [SSE(reduced model) SSE(full model)/df(lost)]/[SSE(full model)/df(full model)] where v1 = the df of the numerator; v2 = the df of the denominator; and SSE = the sum of squares for error. Two fitted models were tested: one with a common slope and one with a common intercept. Because the P-value of the test for a common slope was lower (P = 0.08) than that for a common intercept (P = 0.12), the former model was chosen to estimate the RBV. Having 3 intercepts and 1 common slope means that 3 parallel lines are being compared, thus the RBV was calculated by the parallel lines assay. Data of P supplemental intake were logarithmically transformed and then regressed to FA percentage and fitted to the linear models as described above. The RBV was calculated with the following formula: Antilog [(intercept of the test source – intercept of standard source)/ slope] x 100, as outlined by Littell et al. [26].
  26. Littell, R. C., A. J. Lewis, and P. M. Henry. 1995. Statistical evaluation of bioavailability assays. Pages 5–31 in Bioavailability of Nutrients for Animals: Amino Acids, Minerals and Vitamins. C. B. Ammerman, D. H. Baker, and A. J. Lewis, ed. Acad. Press, New York, NY.
  27. Osorio, J. G., and L. S. Jensen. 1986. Biological availability of phosphorus from a Venezuelan rock phosphate for broiler chicks. Nutr. Rep. Int. 33:545–552.
  28. Borges, F. M. O., M. A. O. Furtado, J. A. F. Veloso, and N. C. Baião. 1997. Disponibilidade do fósforo de fontes inorgânicas para frangos de corte. Arq. Bras. Med. Vet. Zootec. 49:639–647.
  29. Rama Rao, S. V., and V. Ramasubba Reddy. 2001. Utilisation of different phosphorus sources in relation to their fluorine content for broiler and layers. Br. Poult. Sci. 42:376–383.[Web of Science][Medline]
  30. Rama Rao, S. V., and V. Ramasubba Reddy. 2001. Relative bio-availability of different phosphorus supplements in broiler and layer chicken diets. Asian-Australas. J. Anim. Sci. 14:979–985.
  31. De Groote, G., and G. Huyghebaert. 1997. The bioavailability of phosphorus from feed phosphates for broilers as influenced by bio-assay method, dietary Ca-level and feed form. Anim. Feed Sci. Technol. 69:329–340.




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