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Research Reports |
* Faculdade de Ci
ncias Agrárias e Veterinárias, Universidade Estadual Paulista, Jaboticabal 14884900, São Paulo, Brazil; and Danisco Animal Nutrition, St. Louis, MO 63104
1 Corresponding author: sakomura{at}fcav.unesp.br
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SUMMARY |
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 TOP SUMMARY DESCRIPTION OF PROBLEMMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONS AND APPLICATIONSREFERENCES AND NOTES |
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Key Words: broiler chick • nutrient digestibility • phytase matrix
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DESCRIPTION OF PROBLEM |
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TOPSUMMARYDESCRIPTION OF PROBLEMMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONS AND APPLICATIONSREFERENCES AND NOTES |
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Phytases are enzymes naturally found in some seeds and microorganisms [7]. One of the first studies to investigate phytase (PHY) produced by the fungus Aspergillus ficuum in diets for broilers was conducted by Nelson et al. [8]. The results showed the benefits of this enzyme on the hydrolysis of phytic P. However, only at the end of the 1980s did commercial production of PHY begin. It is currently produced by various companies. Exogenous PHY has been used in diets to improve performance and to reduce production costs and environmental impact. Consequently, it has become nutritionally and economically viable in commercial broiler production.
The nutritional matrix of PHY shows how much Ca, P, ME, and amino acids can be made available by adding this enzyme to the diet [9]. However, many factors can influence the action of PHY on nutrient utilization, such as the level of the enzyme and nutrients in the diet, phytic acid in the ingredients, dietary Ca:P ratio, age of the bird, and other factors.
This study was conducted to evaluate the effect of increasing levels of PHY supplementation on nutrient digestibility, energy utilization, and performance of a commercial strain of broilers fed a series of 3 corn-soybean-based negative control diets that differed in nutrient content and were formulated to contain lower nutrient content than the positive control diet.
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MATERIALS AND METHODS |
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TOPSUMMARYDESCRIPTION OF PROBLEMMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONS AND APPLICATIONSREFERENCES AND NOTES |
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ncias Agrárias e Veterinárias. All methods used in these experiments followed recommended guidelines for the care and use of animals in agricultural research [10].
Dietary Treatments
Practical type corn-soybean mash diets were used, but a constant (5.5%) amount of rice bran was included to increase the level of phytin P (0.31% of starter diets and 0.29% of grower diets). The composition of starter diets (1 to 21 d) and grower diets (22 to 42 d) are presented in Table 1
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Digestibility Assays
Two assays were conducted, one during d 14 to 21 (starter phase) and the other during d 28 to 35 (grower phase).One thousand two hundred sixty male (Cobb 500) chicks [12] were housed in floor pens containing wood shavings litter and received a diet formulated with normal levels of nutrients (PC). At the beginning of assays, the chicks were weighed to get similar initial mean body weights (356 ± 18 g at 14 d and 1,100 ± 42 g at 28 d of age) and were allocated to cages (50 x 45 x 38cm). For each assay, 630 birds were distributed into 7 dietary treatments, with 6 replicates of 15 birds. Digestibilities of nutrients were determined by 2 methods. A first series of measurements was based on excreta collection to determine AME of diets. For excreta collection, the birds were fed the experimental diets for a 7-d period. Excreta samples were collected on the last 2 d and dried [13]. A second series was based on ileal digesta collection to determine apparent ileal crude protein digestibility (AICPD), apparent ileal amino acid digestibility (AIAAD), and mineral absorption. A source of acid insoluble ash was added at 1% [14] to all diets as an indigestible marker. At 21 d in the first and at 35 d in the second assay, all birds were killed by cervical dislocation, and the contents of the distal 20 cm of the ileum were collected. The ileum was defined as that portion of the small intestine extending from the Meckel’s diverticulum to a point 40 mm proximal to the ileo-cecal junction. The digesta samples were frozen immediately and, subsequently, freeze-dried.
Chemical Analyses
Diets, excreta, and digesta samples were analyzed for amino acids by high-pressure liquid chromatography [15], energy by adiabatic bomb calorimeter [16], and N according to the AOAC [17]. Mineral content (P, Ca, Mg, K, and Zn) of diets and digesta were measured after sulfuric acid digestion [18]. Bone minerals were also determined [19], and bone concentrations of Ca, Mg, K, Na, and Zn were analyzed with a coupled flame emission spectrometer [20] and P by a colorimetric procedure [19]. The acid insoluble ash of the diets, excreta, and ileal digesta samples was determined after ashing the samples and treating with 4 mol–1 HCl according to the AOAC [17].
Performance Trial
A total of 1,960 one-day-old male broiler (Cobb 500) chicks [12] were allocated into 49 pens, 40 chicks per pen (3.30 m2). Each floor pen had 1 feeder (1:40 birds), 1 drinker (1:80 birds), and was covered with wood shavings litter. The chicks were distributed into 7 replicate pens for each treatment. At the beginning of the trial, the chicks were individually weighed and distributed to get similar initial pen body weight means.
The lighting program consisted of 24 h of light. Birds had ad libitum access to feed and water.
Measurements of feed intake (FI), weight gain, and feed conversion (FC) were taken from 1 to 21 d and 1 to 42 d, respectively. Mortality was recorded daily and used to calculate the mortality-corrected feed intake.
At 42 d, 4 broiler chicks were randomly selected from each pen, fasted for 12 h, and then killed by cervical dislocation. The right and left tibias were removed and processed [21]. The right tibia was analyzed for bone resistance [22] (bone-breaking strength measured as kg of force/cm2). The left tibia was used to determine ash, Ca, P, Mg, K, Zn, and Na.
The cost of PHY supplementation in diets was evaluated by using the bioeconomic index (BEI) according to Guidoni et al. [23].
Statistical Analyses
The data were analyzed by the general linear models procedure [24], by ANOVA with 7 treatments compared by Duncan’s multiple range test at 5% level of probability.
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RESULTS AND DISCUSSION |
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TOPSUMMARYDESCRIPTION OF PROBLEMMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONS AND APPLICATIONSREFERENCES AND NOTES |
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).
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). Compared with the corresponding NC diet, the addition of PHY generally increased AME in both ages. From 14 to 21 d, the AME values of NC1 with PHY (3,517 kcal/kg) and the PC (3,526 kcal/kg) diets were not significantly different. However, AME values for the NC2 (3,327 kcal/kg) and NC3 (3,333 kcal/kg) with PHY were significantly less than the PC (P < 0.05). From 28 to 35 d, the addition of PHY in the NC2 (3,572 kcal/kg) and NC3 (3,624 kcal/kg) diets resulted in significantly higher AME values than that obtained with the PC (3,503 kcal/kg). The AME (3,455 kcal/kg) of NC1 plus PHY was not different from that of the PC.
On an 88% dry matter basis, the average calculated ME of the 3 NC diets at d 14 to 21 and d 28 to 35 were 3,373 and 3,455 kcal/kg, respectively (Table 2). During d 14 to 21, PHY significantly increased the AME of NC1 diet by 5.8%. Similary in the 28 to 35 d period, the supplementation of 750 and 1,000 U of PHY increased AME in 5.7% in NC2 (from 3,379 to 3,572 kcal/kg) and NC3 (from 3,429 to 3,624 kcal/kg) diets, respectively. These increases in AME were superior in magnitude to those reported by Ravindran et al. [4], who found that PHY addition increased diet AME by 3.5%. Namkung and Leeson [25] reported an improvement of 1% in AME due to supplemental PHY.
These results suggest that the addition of 500, 750, and 1,000 U of PHY on NC1, NC2, and NC3 diets, respectively, provides increases on AME of diets from 65 to 195 kcal/kg at 21 d. However, at 35 d, the supplementation on NC1 did not increase dietary AME but on NC2 and NC3 provided increases of 193 and 195 kcal/kg, respectively. The effect of PHY on energy availability is likely a result of incremental improvements in protein [4], starch [26], and fat [27] digestibility.
In both ages, birds fed the NC and PC diets had similar AICPD (Table 2). This result can be explained by the relatively minor reductions of crude protein made in the NC diets so that the protein deficiency was not enough to influence digestibility in these treatments. However, supplementation with 500 and 750 U of PHY in NC1 and NC2 diets, respectively, provided superior AICPD (P < 0.05) to that obtained with the PC diet at 21 and 35 d. This improvement was likely due to the capacity of PHY to hydrolyze complexes formed by phytic acid and protein [28, 29]. In both ages, supplementation with 1,000 U of PHY in NC3 did not increase AICPD (P > 0.05).
At 21 d, the addition of PHY to NC1 and NC2 diets increased the AICPD by 5.9 and 4.6%, respectively. At 35 d, PHY supplementation in NC1 and NC2 diets improved AICPP by 2.1 and 4.3%, respectively. These results were similar to those reported by Lan et al. [30], who found an improvement in AICPD of 3.7 and 2.3% with 500 and 750 U of PHY/kg in the diet, respectively. The coefficients of amino acid ileal digestibility at 21 d are shown in Table 3. The digestibility coefficients for Ala, Cys, Gly, His, Lys, Met, and Thr of the NC1, NC2, and NC3 diets were lower than those determined for the PC diet. However, for Glu, Arg, Phe, Ile, Leu, Tyr, and Val, there were no differences among NC and PC diets. For Asp, Pro, and Ser, the results were not consistent across the NC diets. Averaged across all amino acids, the PC treatment gave an average AIAAD of 83.4%; the value for the NC diets was 80.9%. The reduced level of Ca in NC diets may have been a contributing factor to the lower AIAAD, due to lower activity of proteolitic enzymes [4, 6, 25]. The inhibition of these enzymes may be caused by either complexing Ca with phytic acid, because this mineral is necessary for the activity of trypsin and 
-amylase, or by the interaction of phy-tate with substrates of these enzymes [31].
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Supplementation of NC1 and NC2 with 500 and 750 U of PHY, respectively, increased (P < 0.05) the AIAAD, except for Ile. However, the supplementation of 1,000 U of PHY on the NC3 diet did not increase the AIAAD (P < 0.05). The higher Ca:P ratio may have limited AIAAD and AICPD responses in the NC3 diet, an effect also verified by Qian et al. [33]. Ravindran et al. [27] observed linear effects on AIAAD with PHY supplementation in a Lys-deficient diet.
The AIAAD of the NC diets were superior (P < 0.05) to those of PC, except for Arg, Cys, and His at 35 d (Table 4). Similar results were observed for Ca, K, and Zn absorption (Table 5). This increase in amino acids and some mineral digestibility in birds fed NC diets may be due to a decrease in FI of nutritionally deficient diets, which improved nutrient digestibility.
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), PHY did not result in a similar response for all the amino acids. For Gly, Lys, Ser, Thr, and Phe, there was an increase in AIAAD with PHY in the NC1 and NC2 diets, whereas for Cys, Pro, Val, Tyr, and Iso, PHY improved AIAAD only in the NC3. No effect was detected with PHY supplementation for Asp, Glu, Arg, His, Leu, Met, and Ala. According to Ravindran [4], the magnitude of the response to PHY supplementation on protein and amino acid digestibility can be determined by several factors, such as phytic acid concentration, structure, solubility, and availability of amino acids. Thus, the variation of PHY response in this study may be due to difference in chemical structure of each amino acid, because the level of phytic acid was the same in the diets. The increases in the AIAAD by the addition of PHY to the NC diets varied from 0.53% for Ile to 4.89% for Cys and Thr, resulting in a mean increase of 2.71% for all amino acids. This response was lower than the 3.4% response cited by Ravindran et al. [27] for supplementation of 500 U of PHY/kg of diet; however, it was higher than the range of responses (1.3 to 2.3%) reported in other studies [28, 32].
Mineral Absorption
The absorption of Ca, P, Mg, K, and Zn as determined in broilers from 14 to 21 d and 28 to 35 d is shown in Table 5.
From 14 to 21 d, birds fed the NC1 diet had lower absorption of P, Mg, and Zn than those fed the PC. From 28 to 35 d, Ca, K, and Zn digestibility was higher from the NC diets without PHY when compared with the PC diet. The nutritionally marginal levels of P in NC2 and and NC3 promoted decreased FI (Table 6) and consequently decreased Ca and Zn intakes at both ages. The birds probably improved their capacity for absorption of these minerals to help meet their requirements.
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). At 21 d, compared with the NC without enzyme, the addition of PHY to NC1 and NC2 diets increased (P < 0.05) the digestibility coefficient of P by 36.9 and 23.8% (relative increase calculated considering the difference between NC without and with PHY, expressed in percentage), Mg by 111.5 and 41.4%, and Zn by 466.7 and 80.1%, respectively. Phytase only affected Ca digestibility in birds fed the NC1 diet (increase of 22.7%), whereas it improved K digestibility in birds fed the NC2 and NC3 diets (1.4 and 1.3%, respectively). At d 35, PHY did not affect P and Zn digestibility in birds fed the NC1 diet. However, in birds fed the NC3 diet, PHY improved Ca, Mg, and K digestibility. For P digestibility, the increases obtained by PHY addition in NC2 and NC3 were 24.1 and 40.3%, whereas for Zn, increases were 123.8 and 111%, respectively. The magnitude of response to PHY in the NC3 diets was an improvement in digestibility of 8.6, 93.8, and 5.5% for Ca, Mg, and K, respectively.
The higher Ca:P ratio may have contributed to the poor efficacy of PHY in the NC3 diet at d 21. For efficient activity of PHY it is important to keep ideal Ca:P ratio. According to Shafey [34], a high Ca:P ratio could increase intestinal pH and reduce mineral solubility and, consequently, its digestibility. The increase in Ca:P ratio would increase insoluble mineral-bound phytin crystals, which may be resistent to hydrolysis by PHY. Moreover, extra Ca in relation to P could affect PHY activity by competing for the active sites of the enzymes [7, 33].
The improvement of mineral absorption is due to the action of PHY on mineral-phytate complexes, making the minerals available for absorption, increasing their utilization, and decreasing their excretion [5].
Considering that all diets were formulated to contain the same level of phytic acid (0.31 and 0.29%, respectively, in the starter and grower diets), it is possible to presume that the greater responsiveness with PHY supplementation on mineral digestibility in the NC2 and NC3 diets was due to the higher level of enzyme added to these diets.
Performance Results
Table 6 shows the results of FI, digestible P intake (PdI), body weight gain (BWG), and FCR of broilers from 1 to 21 d and from 1 to 42 d and the BEI of the diets.
In both phases, FI and PdI of birds fed the NC1, NC2, and NC3 diets were lower (P < 0.05) than that observed for birds consuming the PC diet. The FI of birds fed NC diets with PHY supplementation elicited a response and consumptions similar to those of the PC. Phytase addition increased PdI in all NC diets in the starter phase; however, from 1 to 42 d, there was effect of supplementation only in NC2 and NC3 diets. The birds fed the PC diet had the highest PdI due to the greater level of Pd in this diet. Phytase supplementation of the NC diets showed that during each period PHY was efficient in recovering the decrease in FI of NC and that the greatest increase in FI due to PHY was seen in the NC3 diet (410 g in starter phase and 1,238 g from 1 to 42 d). Phosphorus deficiency results in FI reduction [5, 7, 35]. Phytase acts on the P-phytic acid complex, releasing this mineral for absorption, thus ameliorating the FI reduction.
Birds fed NC diets had lower BWG compared with the PC. However, in the starter phase, only the birds fed the NC1 with PHY had BWG similar to those fed the PC. From 1 to 42 d, the BWG of birds fed NC1 and NC2 diets supplemented with PHY were similar to those fed the PC. Although the addition of PHY to NC1, NC2, and NC3 diets increased BWG by 4.7, 19.4, and 31.3%, respectively, BWG of birds fed the NC3 and PHY diet was lower than that of the birds fed the PC diet. The increase of PdI by PHY addition could explain the improvement in BWG, because BWG is is positively correlated with FI. However, limitations either on release of nonmineral nutrients or an imbalance may be limiting further growth response in the NC3 diet. Viveros et al. [7]. reported similar BWG in birds fed a PC diet and those fed an NC diet with a low P level (0.35% available P) and supplemented with 500 U/kg of PHY.
In both phases, the broilers fed the NC3 diet with the lowest nutrient levels had a better FC; however, this result was due to the decrease in FI. Phytase supplementation did not improve FC in NC1 and NC2 diets. The effect of adding PHY to the NC3 diet was to increase FC, due to the increased FI without a matching increase in BWG. These results were similar to those found by Ahmad et al. [36] and Viveros et al. [7]. However, Tejedor et al. [37] observed a better FC with PHY supplementation in corn-soybean-based diets.
The performance results support those obtained for nutrient digestibility (Tables 2, 3, 4 and 5). The performance improvement of broilers fed the NC diets with PHY supplementation can be explained by the improved utilization of energy, protein, amino acids, as well as macro-and microminerals.
According to Guidoni et al. [23], the BEI is a function of BWG, diet, chick cost, and feed intake, where BEI = BWG – (diet cost/chick cost) x feed consumption. Therefore, the highest index represents the best cost-benefit or economic value. Because the PC diet was the highest cost diet, it had the lowest bioeconomic index. Phytase supplementation improved BEI of the NC diets by 7.9%, an indication of the economic viability of using PHY in diets with nutrient reduction. It is also worth noting that the BEI of NC diets containing PHY (average 0.725) was about 30% greater than the BEI (0.590) of the PC diet.
Bone Mineralization
Table 7 gives the values at 42 d of age for bone resistance (bone-breaking strength or kg of force/cm2) and ash as well as the concentration of Ca, P, Mg, K, Zn, and Na in the tibias at 42 d. The reduced nutrient levels in the NC diets decreased bone resistance and ash as well as tibial Zn compared with those obtained with the PC diet. There was no significant difference among the PC and NC for bone Ca and Na content. Compared with the PC diet, lower tibial Mg and K concentrations were observed in broilers fed NC1. Broilers fed the NC2 diet had 19.30% lower tibial P compared with PC. Lan et al. [21] observed a reduction of 12.79% in tibial Ca and P concentrations of broilers fed a diet with 0.24% available P when compared with broilers fed a PC diet with 0.35% available P.
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Sebastian et al. [5], Lan et al. [30], Ahmad et al. [36], and Broz et al. [38] found improvement in bone mineralization with PHY supplementation. The adition of PHY to the NC1 diet increased bone concentration of Mg by 65.63% and K by 12.50% in relation to NC without PHY. Bone Na concentration was not affected by dietary treatments.
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CONCLUSIONS AND APPLICATIONS |
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TOPSUMMARYDESCRIPTION OF PROBLEMMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONS AND APPLICATIONSREFERENCES AND NOTES |
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ACKNOWLEDGMENTS |
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REFERENCES AND NOTES |
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TOPSUMMARYDESCRIPTION OF PROBLEMMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONS AND APPLICATIONSREFERENCES AND NOTES |
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