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Efficacy of an Escherichia coli Phytase in Broilers Fed Adequate or Reduced Phosphorus Diets and Its Effect on Carcass Characteristics

Department of Poultry Science, University of Arkansas, Fayetteville 72701

¹ Corresponding author: jemmert{at}uark.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Five experiments (EXP) were conducted to assess the efficacy of an Escherichia coli phytase compared with 2 commercially available fungal phytases. In EXP 1 and 2, male broiler chicks were fed experimental diets that included a P-deficient control (0.13% available P; 0.88% Ca) alone or with graded levels of KH₂PO₄ (0, 0.05, 0.10, or 0.15%) or phytase at levels of 250, 500, 1,000, 2,000, or 4,000 phytase units/kg of E. coli phytase (EXP 1 and 2), fungal phytase 1 (EXP 2), or fungal phytase 2 (EXP 2). In EXP 1 and 2, weight gain and tibia ash (mg/chick and %) responded linearly (P < 0.05) to inorganic P addition. In EXP 2, each level of E. coli phytase released more P than either fungal phytases 1 or 2, whether based on tibia ash weight (mg/chick) or percentage. In EXP 3, 4, and 5, dietary treatments containing adequate or deficient levels of P were fed with or without supplemental E. coli phytase. In EXP 3, weight gain and tibia ash were reduced (P < 0.05) by P deficiency, but gain and tibia ash of chicks fed E. coli phytase (250, 500, or 1,000 phytase units/kg) did not differ (P > 0.05) from that of chicks fed the P-adequate diet. In addition, carcass yield of broilers fed E. coli phytase was not reduced (P > 0.05). In EXP 4, E. coli phytase effectively supported weight gain, tibia ash, breast yield, and leg yield compared with birds fed the P-adequate diet, but clavicle breakage during processing was increased in birds fed E. coli phytase. In EXP 5, E. coli phytase again effectively supported weight gain, and no differences (P > 0.05; compared with the P-adequate diet) were noted for clavicle ash, diameter, or breaking strength. No differences (P > 0.05) in bone breakage during processing were noted among treatments. These results indicate that the addition of E. coli phytase to P-deficient broiler diets improves growth, bone, and carcass performance and is more effective at releasing phytate-bound P than the other phytase products that were tested.

Key Words: phosphorus • broiler chick • bioavailability • phytase

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
A major issue facing the broiler industry is maintaining bone integrity while reducing feed cost and reducing environmental pollution. Bone breakage in broilers is not only an economic issue for processors but a welfare issue as well (Rath et al., 2000), with quality of nutrition playing an important role. The use of phytase enzymes may prove to be a method to address both issues. The effectiveness of phytase in releasing bound Ca, P, and other divalent minerals important in bone development has been well established (Biehl and Baker, 1997; Harper et al., 1997; Zanini and Sazzad, 1999; Boling-Frankenbach et al., 2001; Augspurger et al., 2003; Augspurger and Baker, 2004a,b; Shelton et al., 2004; Onyango et al., 2005). It has been estimated that phytase releases at least 0.09% bound Ca and P (Augspurger et al., 2003; Augspurger and Baker, 2004b; Shelton et al., 2004) and improves digestibility of these nutrients (Harper et al., 1997; Zanini and Sazzad, 1999; Jalal and Scheideler, 2001; Dilger et al., 2004).

With the importance of P in the environment, phytase source and efficacy has become an important issue to the poultry industry. Dephosphorylation of the phytate molecule occurs at different reaction sites, depending on the origin of the phytase enzyme that is catalyzing the reaction (Rodriguez et al., 1999b; Tamim et al., 2004). Furthermore, phytase enzyme origin also affects the pH at which the enzyme is most effective and its ability to resist breakdown in the stomach and small intestine (Rodriguez et al., 1999a; Augspurger et al., 2003), hence the differences in the efficacy of different phytase enzymes. Recent research has indicated that a new Escherichia coli phytase (OptiPhos, JBS United Inc., Sheridan, IN) is more efficacious than other commercially available phytases in releasing at least 0.10% P (Augspurger et al., 2003).

Although information provided in these research findings is invaluable, there exists a lack of information about the effect of phytase enzymes on carcass characteristics such as the incidence of bone breakage during processing. Breakage of bones, such as the tibia, clavicle, and coracoid, affects both product condemnation rates and food safety, which are extremely important for the broiler industry. Five experiments (EXP) were conducted with the objectives of assessing the relative P-releasing ability of E. coli phytase and comparing its efficacy to 2 commercially-available fungal phytase products [fungal phytase 1 (FP1; Natuphos, BASF, Mount Olive, NJ) and fungal phytase 2 (FP2; Ronozyme, DSM Nutritional Products Inc., Parsippany, NJ)]. The effect of E. coli phytase on growth performance, tibia and clavicle ash, and bone breakage during processing in commercial broilers was measured.

	MATERIALS AND METHODS

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All procedures were approved by the University of Arkansas Institutional Animal Care and Use Committee. Before the beginning of EXP 1 and 2 and throughout EXP 3, 4, and 5, male Cobb x Cobb (Cobb-Vantress Inc., Siloam Springs, AR) broilers were housed in floor pens with pine shavings, hanging tube feeders, and Plasson waterers. Before the initiation of EXP 1, 2, and 3, chicks were fed a common corn–soybean meal starter diet that contained 24% CP and met or exceeded all NRC (1994) nutrient recommendations. Water and feed were freely available.

A review of the differences among the different phytase enzymes used in these EXP is given by Rodriguez et al. (1999b), Applegate et al. (2003b), Augspurger et al. (2003), and Onyango et al. (2005). Dietary additions of phytase were made according to the experimental procedures of Augspurger et al. (2003) and Augspurger and Baker (2004a), who assayed the same phytases used herein and defined phytase activity as the quantity of the enzyme that will liberate 1 µmol of inorganic P per min from 5.1 mM Na phytate at a pH of 5.5 and temperature of 37°C. Thus, dietary additions in each EXP were made to accomplish dietary phytase activity levels as defined under the aforementioned conditions.

EXP 1 and 2
On d 9 or 8 posthatching (EXP 1 and 2, respectively), chicks were weighed, wing-banded, and randomly allotted to dietary treatments such that each pen within an EXP would have a similar average initial weight and weight range. Each EXP consisted of 5 replicates of 5 chicks per replicate housed in batteries with raised wire floors, and a 24-h photoperiod was used. Experimental diets (Table 1) were fed until d 23 or 22 posthatching (EXP 1 and 2, respectively), at which time chicks and feed were weighed for determination of weight gain, feed intake, and feed efficiency. At the termination of each EXP, chicks were killed by cervical dislocation, and right tibias were collected for subsequent analysis of ash weight per chick (mg/chick) and percentage of ash.

EXP 3
Experiment 3 consisted of 5 dietary treatments, replicated 8 times, with each replicate containing 20 birds. All diets were based on corn and soybean meal and met or exceeded NRC (1994) recommendations for all nutrients, with the exception of P, when appropriate (Table 1). Experimental diets (Table 1) were fed from 3 to 21 d and 21 to 42 d, and treatments consisted of the following diets: 1) a positive control containing adequate levels of Ca (1.0 and 0.9% during the starter and grower periods, respectively) and iP (0.47 and 0.46% during the starter and grower periods, respectively); 2) a negative control containing an adequate level of Ca (1.0 and 0.9% during the starter and grower periods, respectively) and a deficient level of iP (0.31 and 0.28% during the starter and grower periods, respectively); and 3), 4), and 5) diet 2 with graded levels of E. coli phytase (250, 500, and 1,000 FTU/kg). Birds and feed were weighed at EXP initiation, during phase changes, and at assay termination (d 42) to calculate weight gain, feed intake, feed efficiency, and livability for each period and overall. Feeders were removed from experimental pens 10 h before EXP termination. Following weighing, 5 birds per pen were randomly selected for processing at the University of Arkansas Poultry Processing Plant.

EXP 4 and 5
In EXP 4, there were 6 dietary treatments with 7 replicate pens (20 birds per pen); in EXP 5, there were 4 dietary treatments with 4 replicate pens (15 birds per pen). All diets were based on corn and soybean meal and met or exceed NRC (1994) recommendations for all nutrients, with the exception of Ca and P, when appropriate (Table 1). Birds and feed were weighed at EXP initiation, during phase changes, and at assay termination (d 50 or 56 in EXP 4 and 5, respectively) to calculate weight gain, feed intake, feed efficiency, and livability for each period and overall. Feeders were removed from experimental pens 10 h before EXP termination. Following weighing, 5 birds per pen (EXP 4) were randomly selected for processing at the University of Arkansas Poultry Processing Plant; all birds from EXP 5 were processed.

In EXP 4, chicks were weighed and placed on treatment diets on d 1 posthatch. Experimental diets (Table 1) were fed as follows: starter (1 to 18 d), grower (18 to 32 d), finisher (32 to 40 d), and withdrawal (40 to 50 d). Dietary treatments consisted of the following diets: 1) a positive control adequate in all essential nutrients for the respective phases; 2) diet 1 with Ca reduced by 0.05% and P reduced by 0.10%; 3) diet 1 with 300 FTU/kg of E. coli phytase; 4) diet 2 with 300 FTU/kg of E. coli phytase; 5) diet 1 with dietary Ca reduced by 0.05% and dietary P reduced by 0.15% P and 600 FTU/kg of E. coli phytase; and 6) diet 1 with dietary Ca reduced by 0.05% and dietary P reduced by 0.20% and 1,000 FTU/kg of E. coli phytase. Treatment additions to the basal diet were made at the expense of cornstarch. Due to concerns over the detrimental effects of feeding birds diets that were too deficient in Ca and iP for the whole duration of the project, corresponding negative controls for treatments 5 and 6 were not formulated. Experiment 5 was similar to EXP 4, with the exception of the EXP initiation (d 8) and termination (d 56) and the dietary treatments, which included only treatments 1, 2, 4, and 6 from EXP 4.

Processing Variables
After arrival at the processing plant, birds were hung on a shackle line and commercially processed to evaluate carcass and parts yields, and the incidence of bones that were broken or disjointed. Birds were electrically stunned (11 V, 11 mA, 11 s), manually bled by severing the left carotid artery and jugular vein, bled out (1.5 min), soft-scalded (129°F, 2 min), and feathers were picked with the use of inline commercial defeathering equipment. Eviscerating and rinsing followed, after which carcasses were placed in a prechill tank at 12 C for 15 min. Carcasses were then moved to an immersion chiller (1°C) for 45 min, after which carcasses were removed, packed in ice, and aged at 4°C until time of deboning (EXP 4 and 5) at 4 h postmortem. Carcasses were separated into breast (pectoralis major and pectoralis minor), wings, legs, and frame, followed by weighing and removal of the tibia from the legs for subsequent ash analysis.

Bone Response Variables
Tibias were autoclaved for 45 min to remove adhering muscle and cartilage, dried at 110°C for 24 h, and subsequently weighed. Dry tibias were ashed in a muffle furnace at 600°C for 18 h. After cooling, tibia ash was weighed for determination of ash weight and bone ash percentage. In EXP 4 and 5, the incidence of broken bones (tibia, coracoid, clavicle, and radius and ulna) and disjointed wings that had occurred during processing were noted at the time that birds were separated into parts. The incidence of broken or disjointed bones was expressed as a percentage of the number of birds selected for processing. For clavicles, the incidence rate reflects the sum of clavicles broken on the shaft or at the point of fusion. In EXP 5, clavicles were collected at the time of deboning for measurement (on the same d) of diameter, tension force, and break force. Intact clavicles (at time of collection) were subjected to a tension test, in which tension force (the force required to separate the clavicles at the point of fusion) was measured in newtons on a texture analyzer (TA-XT2i, Texture Technologies Corp., Scarsdale, NY) equipped with a 5-kg load cell and 2 attached adjustable grips (TA-96, Texture Technologies Corp.) placed opposite each other on the machine. The ends of the bone (opposite of midpoint) were trimmed so that the bone could be mounted in adjustable grips. The clavicle was placed in the grip 15 mm away from the midpoint of the clavicle on both sides of the bone. The clavicle bone was then pulled apart until broken at a speed of 5 mm/sec with tension strength (N) measurements being recorded. Following the tension test, these bones, in addition to the bones that were previously broken at the point of fusion during processing, were broken by using a 3-point bend-breaking method on 1 side of the clavicle. The 3-point bend test was conducted using the texture analyzer (TA-XT2i, Texture Technologies Corp.) fitted with a 1.5 x 11 mm incisor knife blade (TA-45, Texture Technologies Corp.) attachment at a speed of 5 mm/sec. Force (N) required to break bones was recorded and represented break force. Any clavicles which were broken along the shaft before testing were not used in bone strength analysis; all clavicles were subjected to ash analysis (following strength measurements) as described for tibias.

Statistical Analysis
Data were subjected to ANOVA (SAS Institute, 2004) appropriate for a completely randomized design; treatment means were separated using the least significant difference multiple-comparison procedure or Duncan’s multiple range test (in the case of missing replicate values). Single df contrasts were used to test overall effects of phytase (when appropriate). Standard curves were established (SAS Institute, 2004), with tibia ash (mg/chick or %) as the dependent variable and consumption (g) of supplemental P as the independent variable for EXP 1 and 2. By insertion of replicate values for tibia ash (mg/chick or %) into the standard curve equation, the amount of P released by the enzyme was calculated for treatments 6 to 10 (EXP 1). Pens served as the experimental unit for all data analyzed, and means were considered significant at P < 0.05.

	RESULTS

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EXP 1
Growth and bone response variables are represented in Table 2. Increasing iP resulted in a linear increase in weight gain and feed intake (P < 0.01); adding E. coli phytase resulted in a linear and quadratic increase in weight gain (P < 0.05). Feed efficiency increased with increasing iP and E. coli phytase levels (P < 0.05). Increasing iP resulted in a linear increase in tibia weight and tibia ash (P < 0.05). Standard curve regression equations (Table 2) were as follows: for percentage of tibia ash, Y = 38.95 + 8.48X (r² = 0.72) and for milligrams of tibia ash, Y = 272.98 + 163.62X (r² = 0.65). Bioavailable P release estimates ranged from 0.11 to 0.19% for 250 to 10,000 FTU/kg of supplemented E. coli phytase when based on tibia ash weight (mg/chick) and 0.09 to 0.19% for 250 to 10,000 FTU/kg of supplemented E. coli phytase when based on tibia ash expressed as a percentage (Table 2). It should be noted that the tibia ash values for birds fed diets with 750 FTU of E. coli phytase/kg or greater exceeded the tibia ash value for birds fed 0.15% supplemental iP (diet 4).

EXP 5
Growth performance and bone response variables for EXP 5 are shown in Table 7. In this EXP, slightly decreasing dietary iP and Ca (diet 2) reduced (P < 0.05) weight gain compared with birds fed the other diets. No differences (P > 0.05) among treatments were noted for clavicle ash (%), but clavicle diameter and tension force (force required to separate the clavicles at the point of fusion) was reduced (P < 0.05) in birds fed diet 2. No differences (P < 0.05) in clavicle diameter or tension force were noted in birds fed diet 1 or the diets containing E. coli phytase. Break force (force required to break the clavicle) did not differ (P > 0.05) among treatments, although break force for clavicles from birds fed diet 2 was numerically lower. As for EXP 4, bone breakage rates in EXP 5 were variable, and no differences (P < 0.05) in the incidence of bone breakage during processing were observed. It should be noted that, for clavicles, the majority (>80%; data not shown) of breakage occurred at the point of fusion.

	DISCUSSION

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The addition of phytase to diets deficient in available P at various production phases of broilers has been shown to increase growth and improve bone (usually tibia) response variables (Zyla et al., 2000a,b; Applegate et al., 2003a; Augspurger et al., 2003; Augspurger and Baker, 2004a,b; Dilger et al., 2004; Shirley and Edwards, 2003). The degree of response has been the subject of much investigation, and researchers have estimated that fungal phytases release an amount of available P ranging from less than 0.05% (Angel et al., 2001) to as much as 0.113% (Biehl et al., 1995). The level of improved P utilization and growth seems largely dependent on the source of phytase supplementation, as some of the major constraints to the catalytic properties of phytase enzyme are pH and time limitations with regard to the unique nature of the gastrointestinal tract of the broiler (Zyla et al., 2004).

Augspurger et al. (2003) reported greater P-release values from phytase produced by E. coli expressed in yeast when compared with phytase derived from FP1 and FP2 for young chicks and pigs during the starter phases of production. Applegate et al. (2003b) reported that turkeys fed diets supplemented with an E. coli-derived phytase had a consistently higher iP-sparing effect than FP1 and FP2. Augspurger et al. (2003) attributed the greater P release by E. coli phytase to the different activation levels of FP1 (pH 2.5 and 5.5), FP2 (pH 4.0 to 4.5), and the E. coli-derived phytase (pH 2.5 to 3.5). Rodriguez et al. (1999a) reported that the E. coli phytase enzyme expressed in Pichia pastoris released more P from phytate in soybean meal than Aspergillus niger phyA at each enzyme’s optimum pH. Moreover, E. coli phytase appears to be more resistant to pepsin breakdown; Rodriguez et al. (1999b) reported that another E. coli phytase had a 30% increase in phytase activity after being incubated in pepsin at a pH of 2, whereas FP1 had a 58 to 77% decrease in activity under the same experimental conditions. However, FP1 was more resistant to trypsin degradation at a pH of 7 than E. coli phytase enzyme.

Our results confirm the efficacy of E. coli phytase (Table 2) and indicate an increased ability of E. coli phytase to release bound P, compared with the fungal phytases that were used (Table 3). As described previously (Rodriguez et al., 1999a,b; Applegate et al., 2003b; Augspurger et al., 2003), attributes of E. coli phytase (resistance to pepsin degradation, optimum pH) appear to enhance its P-releasing ability. Based on tibia ash, we noted improvements in estimated iP release ranging from 23 to 200% (depending on phytase level) for E. coli phytase, compared with FP1, and 118 to 700% (depending on phytase level) for E. coli phytase, compared with FP2. As previously noted, at the higher levels of E. coli phytase supplementation in EXP 1 and 2, tibia ash values exceeded those of the standard curve; although this brings into question the accuracy of E. coli phytase efficacy estimates at the higher levels of E. coli phytase supplementation, it does suggest that E. coli phytase releases >0.15% iP. Our iP-sparing values for the various phytase enzymes are similar to those reported by Augspurger et al. (2003).

In other farm species of economic importance, investigators have largely focused on the effect of phytase in conjunction with varying amino acid and energy levels on carcass quality of pigs and drakes (Harper et al., 1997; Attia, 2003; Walz and Pallauf, 2003; Shelton et al., 2004). The effect of phytase enzyme supplementation on carcass yield in pigs appears to be variable (O’Quinn et al., 1997; Liu et al., 1998), and Walz and Pallauf (2003) reported that although phytase increased apparent digestibility of P, Ca, and Zn, it had no effect on carcass and meat characteristics in barrows. Similar results have been obtained in drakes supplemented with phytase, Lys, or both, with no difference in carcass yield and meat quality reported by Attia (2003). However, Shelton et al. (2004) reported that the inclusion of phytase to diets deficient in Ca, P, and trace minerals reversed the negative effects of these deficient diets on carcass lean content, weight, dressing percentage, and bone associated with the removal of these minerals in growing-finishing pigs.

The effect of phytase on carcass characteristics in broilers is also important, but it is limited. In the current EXP, the inclusion of the E. coli phytase enzyme not only returned bone ash percentage to that of the control in broilers fed P-deficient diets (Tables 2, 3, 4, and 6), but it also prevented negative effects on carcass and breast yield in birds fed diets containing substantially reduced P in EXP 4. It should be noted that corresponding negative control diets were not fed in EXP 4 and 5 because of welfare concerns associated with feeding such drastic reductions in Ca and P over the duration of the trials, but in a separate trial, short-term feeding of negative control diets (diets 5 and 6 in EXP 4 and diet 4 in EXP 5 fed without E. coli phytase) verified that these diets substantially reduce growth and tibia ash in the absence of E. coli phytase (data not shown).

Bone integrity has an important role to play in total yield of the carcasses intended for the whole-bird market and the further-processing market (Rath et al., 2000) and in the rate of product loss due to bone breakage. Chen and Moran (1994) reported that reducing the level of P in the withdrawal phase of production resulted in increased defects and decreased production of grade-"A" carcasses. We were interested in determining whether phytase would affect the incidence of bone breakage during processing. In EXP 4, bone breakage results were highly variable, and we were surprised by the high incidence of broken clavicles. We have also noted high rates of clavicle breakage (approaching 50%) in other research projects involving processing of broilers raised on nutritionally-adequate diets. The departmental processing plant in which birds were processed must accommodate a wide range of bird sizes, and it is possible that evisceration equipment was not optimally adjusted for birds in our trial, resulting in a higher clavicle breakage rate. Because of this, and because the rate of wing breakage in EXP 4 was so variable (and seemingly illogical), portions of EXP 4 were repeated in EXP 5. Although variability associated with bone breakage was still high in EXP 5, clavicle and wing breakage rates were lower overall, and results indicated that bone breakage should not be increased in broilers fed diets containing low levels of iP combined with supplemental phytase.

In conclusion, based on the data obtained from these EXP, E. coli phytase releases more P than the fungal phytases that were tested. When based on tibia ash weight (mg/chick or %), the amount of available P released ranged from 0.119 to 0.239% for E. coli phytase, compared with 0.07 to 0.18% from FP1 and 0.03 to 0.11% from FP2 at phytase supplementation levels of 250 and 4,000 FTU/kg, respectively. When based on tibia ash weight (mg/chick), P release appeared to be maximized at a level of 1,000 FTU/kg of E. coli phytase. Results also indicate that E. coli phytase is effective at maintaining carcass yield characteristics without increasing the incidence of bone breakage (based on EXP 5).

Received for publication March 23, 2006. Accepted for publication June 11, 2006.

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