©2009 Poultry Science Association, Inc.
Evaluation of equivalency values of microbial
phytase to inorganic phosphorus
in 22- to 42-day-old broilers
J. C. Han,*† X. D. Yang,* H. X. Qu,† M. Xu,* T. Zhang,* W. L. Li,* J. H. Yao,*1
Y. R. Liu,‡ B. J. Shi,§ Z. F. Zhou,§ and X. Y. Feng§
*College of Animal Science and Technology, Northwest Agriculture and Forestry
University, Yangling, China 712100; †Department of Life Science, Shangqiu Normal
University, Shangqiu, China 476000; ‡Shenzhen Kondarl (Gaoling) Feed Co. Ltd.,
Gaoling, China 710200; and §Guangdong VTR Bio-Tech Co. Ltd., Zhuhai, China 519000
Primary Audience: Nutritionists, Feed Formulators, Researchers
SUMMARY
This experiment was conducted to evaluate the equivalency values of microbial phytase to
inorganic phosphorus (Pi) in 22- to 42-d-old broilers fed a corn-soybean meal diet. Ten dietary
treatments were designed in which diet 1 was the basal diet [calcium 0.90%, total phosphorus
0.35%, nonphytate phosphorus (NPP) 0.13%] and diet 4 was control (calcium 0.90%, total
phosphorus 0.57%, NPP 0.35%). Diets 2 and 3 included 0.20 and 0.27% of NPP, and diets 5
to 10 contained graded levels of microbial phytase (125, 250, 500, 1,000, 2,000, and 4,000 U/
kg of diet). Body weight gain, feed intake, phosphorus retained, plasma Pi concentration, tibia
ash content, and tibia-breaking strength increased, but plasma calcium concentration decreased
with increasing dietary NPP content (from 0.13 to 0.35%) or phytase activity. Microbial phytase
caused an increase, whereas dietary NPP caused a decrease in phytate phosphorus (PP) retention. When 4,000 U of phytase was added to the basal diet with 0.13% NPP, 95% PP was
released based on tibia ash content, and broiler BW gain and feed intake were equal to those
of broilers fed the control diet (NPP 0.35%). Microbial phytase at 125, 250, 500, 1,000, 2,000,
and 4,000 U/kg of diet was determined to be equivalent to the addition of 0.035 to 0.208% of
Pi from dicalcium phosphate in 22- to 42-d-old broilers. These data suggest that high levels
of microbial phytase could release almost all dietary PP and replace all supplemental Pi in
growing-finishing broilers.
Key words: equivalency value, microbial phytase, broiler
2009 J. Appl. Poult. Res. 18:707–715
doi:10.3382/japr.2009-00029
DESCRIPTION OF PROBLEM
The primary constituents of diets for monogastric animals are plant-based ingredients,
primarily from the seeds of plants. Most of the
stored phosphorus in plants is found in seeds
1
Corresponding author: [email protected]
and mainly in the form of phytate phosphorus
(PP), which is poorly available to nonruminant
animals, including poultry. Therefore, their diets are supplemented with inorganic phosphorus
(Pi).
JAPR: Research Report
708
The enzyme phytase hydrolyzes phosphate
groups from the phytin molecule, potentially
making the hydrolyzed phosphorus from phytin
available to the animal. Previous studies showed
that total phosphorus (tP) retention began to plateau around 500 U/kg of phytase when tP-deficient diets were supplemented with up to 2,000
U/kg of phytase [1, 2]. However, recent research
indicated that phytase at a high level (12,000 U/
kg) hydrolyzed almost all the dietary PP in 16-dold broilers [3]. No report was found on the effect of a high level of microbial phytase on the
degradation of PP in 22- to 42-d-old broilers fed
a corn-soybean meal diet.
Zhang et al. [4, 5] proposed a linear relationship between the dose of enzyme and the performance of the animal. Based on this notion,
Shirley and Edwards [3] proposed a model between dietary phytase and growth performance
in starter broilers. To determine the equivalency
values of microbial phytase to nonphytate phosphorus (NPP), a linear model was used in this
study.
The first objective of this experiment was
to verify the hypothesis that if all the PP in a
broiler finisher diet were hydrolyzed by phytase
in a diet containing 0.35% tP (0.13% NPP), then
optimal performance could be achieved with no
addition of Pi. The second aim was to investigate
the equivalency values of microbial phytase to
Pi in 22- to 42-d-old broilers fed a corn-soybean
meal diet.
MATERIALS AND METHODS
Birds and Dietary Treatments
All procedures used during this study were
approved by the Animal Care Committee of
Northwest Agriculture and Forestry University. On the day of hatch, 480 male Arbor Acres
chicks [6] were randomly and equally assigned
to 40 cages (68 × 66 × 33 cm), with 12 chicks
per cage. All chicks were fed a typical commercial broiler starter pellet diet (AME 2,926 kcal/
kg, CP 19.7%, calcium 0.95%, tP 0.70%, NPP
0.48%, Lys 1.07%, Met + Cys 0.81%) until 3
wk of age. On d 21, broilers were individually
weighed, transferred to growing-finishing cages
(200 × 50 × 35 cm), and assigned to 1 of the
10 dietary treatments, with 4 replicates per treat-
ment. According to the NRC (1994) [7] recommendation, the first 4 diets were formulated as
follows: basal diet with 0.13% NPP (no Pi addition), and diets 2 to 4 with NPP at 0.20, 0.27,
and 0.35%, respectively (Table 1). Diet 4 with
0.35% NPP and 0.57% tP served as the control
diet. Diets 1 to 4 were made individually. Microbial phytase at 125, 250, 500, 1,000, 2,000, and
4,000 U/kg was supplemented to the basal diet to
become diets 5 to 10, respectively. All diets had
the same calcium level of 0.90%. Throughout
the 22- to 42-d experiment, chicks were given
access to mash feed and water ad libitum, with
an 18-h lighting schedule.
Microbial Phytase
Microbial phytase was derived from Trichoderma strain and expressed in the yeast Pichia
pastoris [8]. The product was determined to have
5,000 U/g of phytase, where 1 U is equivalent to
1 phytase unit and is the amount of enzyme that
liberates 1 μmol of Pi/min from 0.0051 mol/L
of sodium phytate at 37°C and at pH 5.50. The
enzyme was analyzed premix and added to the
diet in powder form.
Samples Collection
All broilers were individually weighed on d
21 and 42. On d 42, two chicks were randomly
selected from each cage and weighed, a heparinized blood sample was obtained from the wing
vein, and the bird was killed by carbon dioxide
asphyxiation. Blood samples were collected,
centrifuged for 10 min at 3,000 × g, and frozen
at −4°C [9]. The left and right tibias from individual birds were excised, sealed in plastic bags,
and stored at −4°C for further analysis [10].
Excreta were collected using a classical total
collection procedure for 96 h from d 37 to 40
with collections every 8 h, and stored at −4°C.
Before analysis, the excreta samples were dried
at 65°C for 24 h and ground to pass through a
1-mm mesh screen.
Phytate phosphorus and tP of the diet and excreta were determined using the method of Rutherfurd et al. [11]. Calcium was determined using the AOAC method [12]. Crude protein and
energy content were determined using a Kjeltec
2300 analyzer [13] and Automatic Bomb Calorimeter [14], respectively.
Han et al.: PHYTASE EQUIVALENCY VALUES
709
Table 1. Composition of the experimental diets1
Experimental diets 1 to 4
Item1
Ingredient, %
Corn
Soybean meal
Soybean oil
Swine lard
Corn gluten meal
Limestone
Dicalcium phosphate
l-Lysine
dl-Methionine
Vitamin premix3
Trace mineral premix4
Choline chloride
Sodium chloride
Dietary analysis, %
AME, kcal/kg, calculated
CP, calculated
CP, determined
Lys, calculated
Met, calculated
Ca, calculated
Ca, determined
tP, calculated
tP, determined
PP, calculated
PP, determined
0.13% NPP2
0.20% NPP
0.27% NPP
0.35% NPP
66.80
26.40
1.53
—
2.11
2.29
—
0.18
0.06
0.03
0.10
0.20
0.30
66.47
26.40
1.53
0.12
2.15
2.01
0.45
0.18
0.06
0.03
0.10
0.20
0.30
66.12
26.40
1.53
0.24
2.20
1.77
0.87
0.18
0.06
0.03
0.10
0.20
0.30
65.76
26.40
1.53
0.36
2.25
1.48
1.35
0.18
0.06
0.03
0.10
0.20
0.30
2,988
18.50
19.37
1.00
0.38
0.90
0.93
0.35
0.36
0.22
0.23
2,988
18.50
19.35
1.00
0.38
0.90
0.94
0.42
0.41
0.22
0.21
2,987
18.50
19.37
1.00
0.38
0.90
0.93
0.49
0.49
0.22
0.22
2,987
18.50
19.27
1.00
0.38
0.90
0.91
0.57
0.56
0.22
0.21
1
tP = total phosphorus; PP = phytate phosphorus.
NPP = nonphytate phosphorus. The NPP of the basal diet was 0.13%. Diets 5 to 10 were supplemented with microbial phytase
at the levels of 125, 250, 500, 1000, 2,000 and 4,000 U/kg on the basal diet.
3
Vitamin premix provided the following (per kg of diet): vitamin A, 6,000 IU; vitamin D3, 500 IU; vitamin E, 30 IU; menadione, 0.5 mg; thiamine, 2.0 mg; riboflavin, 5.0 mg; niacin, 30 mg; pyridoxine, 3.0 mg; vitamin B12, 0.01 mg; pantothenic acid,
10.0 mg; folic acid, 0.55 mg; biotin, 0.15 mg.
4
Trace mineral premix provided the following (per kg of diet): iron, 60 mg; zinc, 80 mg; copper, 8 mg; manganese, 60 mg;
iodine, 0.6 mg; and selenium, 0.3 mg.
2
The retention of PP, tP, calcium, and the CP,
P retained, and AME values were calculated as
described in the References and Notes [15].
Statistical Analysis
Pen means served as the experimental unit
for statistical analysis. The data were analyzed
by the ANOVA procedure of SAS software [16]
to estimate the significance of treatment effects.
Duncan’s multiple means comparison was used
for differences of means. Linear and quadratic
effects of NPP (diets 1 to 4) and phytase (diet
1 and diets 5 to 10) on growth, parameters of
the tibia and plasma, and nutrient retention were
tested using orthogonal polynomials. Linear and
quadratic models were Y = a + bX and Y = a +
bX + cX2, respectively, where Y is the response
(BW gain and tibia ash) and X is NPP or phytase
(g/kg of diet). For evaluation of the equivalency
of phytase to NPP, the linear model Y = a + bX
was used, where Y is the response [BW gain,
feed intake (FI), phosphorus retained, and tibia
ash] and X is 0.13 to 0.35% of NPP or 0.025,
0.05, 0.10, 0.20, 0.40, and 0.80 g/kg of phytase.
The equivalency of phytase to NPP was calculated by subtracting the obtained values from
NPP of the basal diet. Statements of probability
are based on P ≤ 0.05.
RESULTS AND DISCUSSION
Growth Performance
The increase in dietary NPP content improved BW gain (linear, P < 0.001; quadratic,
JAPR: Research Report
710
P = 0.024), FI (linear, P < 0.001; quadratic, P
< 0.001), and phosphorus retained (linear, P <
0.001; quadratic, P < 0.001) in 22- to 42-d-old
broilers (Table 2). It has been demonstrated that
deficiencies of phosphorus cause decreased BW
gain, FI, and G:F [17, 18]. Similar results were
found in this experiment. Mortality was 0 in the
basal diet treatment and was not affected by dietary NPP.
Phytase supplementation also increased BW
gain (linear, P < 0.001), FI (linear, P < 0.001),
and phosphorus retained (linear, P < 0.001;
quadratic, P < 0.001) in 22- to 42-d-old broilers (Table 2). When the phytase level was increased to 4,000 U/kg, BW gain, FI, and G:F
became equivalent to those of broilers fed the
control diet (0.35% NPP). Research has shown
that phytase addition increases BW gain and FI
in chicks fed diets formulated to be deficient
in phosphorus [3, 19, 20]. The increase in BW
gain was a result of the increase in FI [19, 21];
thus, phytase generally did not have an effect on
FE [18, 22]. However, some researchers have
reported an increase in FE in chicks fed diets
with added phytase [23, 24]. Kornegay et al.
[25] reported an increase in G:F in 1- to 21-dold chicks fed diets containing phytase, but only
when the diets contained 0.20% NPP; at higher
concentrations of NPP, there was no response in
FE. Gordon and Roland [26] also reported an
increased G:F in chickens fed diets with added
phytase, but only in a corn-soybean meal diet
not supplemented with Pi. In this study, Pi was
not added to the basal diet (0.13% NPP), and
BW gain and FI were significantly improved by
phytase supplementation.
Plasma Parameters
The enhancement of dietary NPP level increased plasma Pi content (linear, P < 0.001) but
decreased plasma calcium concentration (linear,
P < 0.001) in 42-d-old broilers (Table 3). In this
study, the same calcium levels were used in all
diets, and the balance between calcium and Pi
was disrupted in the low-NPP diet and then recovered with the increase in dietary tP. The ratio
of calcium to Pi in plasma shifted from 4.35:1 in
the basal diet to 1.48:1 in the control diet. This
shift in calcium to phosphorus retention resulted
in an improvement in broiler growth, tibia ash
content, and tibia-breaking strength [3, 27].
Phytase supplementation to the basal diet increased plasma Pi content (linear, P < 0.001) and
decreased plasma calcium concentration (linear,
P = 0.003; quadratic, P = 0.004; Table 3). Supplemental phytase of 4,000 U/kg overcame the
tP deficiency of the basal diet, and plasma calcium and Pi values became 11.8 and 8.0 mg/100
mL, which were equivalent to those of birds fed
the control diet. Plasma Pi content increased
with the increase in phytase in this experiment,
Table 2. Effect of nonphytate phosphorus (NPP) and phytase on the growth of 22- to 42-d-old broilers1
NPP treatment,2 %
0.13
0.20
0.27
0.35
0.13
0.13
0.13
0.13
0.13
0.13
SEM
P-value
a–f
Phytase treatment, U/kg
0
0
0
0
125
250
500
1,000
2,000
4,000
BW gain,3 g
1,360e
1,574abcd
1,643abc
1,680a
1,471d
1,549bcd
1,558bcd
1,538cd
1,565abcd
1,665ab
17.6
<0.001
Feed intake,4 g
2,533e
2,901b
3,026a
3,039a
2,798bcd
2,857bc
2,707d
2,762cd
2,899b
3,019a
26.6
<0.001
Phosphorus retained,5 g
G:F, g/g
4.39f
7.22d
8.83b
9.80a
5.98e
6.40e
7.20d
7.91c
8.64b
8.95b
0.254
<0.001
0.537b
0.543b
0.543b
0.553ab
0.526b
0.542b
0.576a
0.557ab
0.540b
0.552ab
0.003
0.090
Means in a column with no common superscript are significantly different.
Each mean represents 4 pens (12 birds per pen).
2
Nonphytate phosphorus (formulated).
3
Phosphorus effect (linear, P < 0.001; quadratic, P = 0.024); phytase effect (linear, P < 0.001).
4
Phosphorus effect (linear, P < 0.001; quadratic, P < 0.001); phytase effect (linear, P < 0.001).
5
Phosphorus effect (linear, P < 0.001; quadratic, P < 0.001); phytase effect (linear, P < 0.001; quadratic, P < 0.001).
1
Han et al.: PHYTASE EQUIVALENCY VALUES
711
and these results agreed with the findings of
Shirley and Edwards [3]. The increase in plasma
Pi content resulted from the improvement in PP
and tP retention.
ed from the improvements in PP and tP retention.
Tibia Parameters
The increase in dietary NPP content caused a
decline in PP retention (linear, P < 0.001) but enhanced tP retention (linear, P = 0.018; quadratic,
P = 0.002; Table 5). It has been demonstrated
[27, 29] that increasing the NPP levels depresses PP retention in broiler diets. Similar results
were obtained in this experiment. Research has
shown that the endogenous phytase present in
the intestinal epithelium of chicks is capable of
hydrolyzing some dietary phytate but that this
process is made less efficient in the presence of
higher NPP levels [30–33]. Therefore, intestinal phytase activity was lower and the quantity
of PP hydrolysis was reduced with high levels
of dietary NPP. Different results were obtained
for the relationship between dietary NPP levels
and the retention of energy and protein, which
showed that in starter broilers, the amount of
energy retained responded positively to [34] or
was not influenced by dietary NPP levels [35],
whereas in the growing-finishing phase, the
enhancement of dietary NPP increased energy
retention in female broilers but decreased it in
male broilers [35]. Other studies [3, 36] showed
that reductions in dietary NPP led to a decrease
Tibia ash weight (linear, P < 0.001) and percentage (linear, P < 0.001; quadratic, P = 0.006)
and tibia-breaking strength (linear, P < 0.001;
quadratic, P < 0.001) increased with the increase in dietary NPP (Table 4). Deficiencies of
phosphorus decreased bone ash content in other
studies [18, 19]. Similar results were found in
this experiment. In another study [28], with an
increase in dietary NPP, bone ash content was
improved; therefore, tibia ash and strength were
enhanced.
Phytase supplementation increased tibia ash
weight (linear, P < 0.001; quadratic, P = 0.004),
percentage (linear, P < 0.001; quadratic, P =
0.02), and breaking strength (linear, P < 0.001;
quadratic, P = 0.02; Table 4). When 4,000 U of
phytase was added to the basal diet, tibia ash
weight and breaking strength were lower than
those of broilers fed the control diet. Phytase increased bone ash in chickens fed diets deficient
in phosphorus [18, 20, 24]. In this experiment,
phytase had a positive effect on tibia ash weight,
percentage, and breaking strength, which result-
Nutrient Retention
Table 3. Effect of nonphytate phosphorus (NPP) and phytase on plasma minerals and total protein in 42-d-old
broilers1
NPP treatment,2 %
0.13
0.20
0.27
0.35
0.13
0.13
0.13
0.13
0.13
0.13
SEM
P-value
a–e
Phytase
treatment, U/kg
Calcium,3
mg/100 mL
Pi,4 mg/100 mL
Total protein,5
g/100 mL
0
0
0
0
125
250
500
1,000
2,000
4,000
17.2a
16.5a
12.3bcd
11.3d
13.6b
13.3bc
12.1bcd
11.8cd
12.0cd
11.8cd
0.35
<0.001
4.0c
4.3c
7.9a
7.6a
4.1c
4.0c
5.0bc
8.5a
5.8b
8.0a
0.31
<0.001
4.4cd
4.3cd
5.5a
3.9cde
4.0cde
3.8de
3.3e
4.6bc
3.9cde
5.2ab
0.12
<0.001
Means in a column with no common superscript are significantly different.
Each mean represents 4 pens (12 birds per pen).
2
Nonphytate phosphorus (formulated).
3
Phosphorus effect (linear, P < 0.001); phytase effect (linear, P = 0.003; quadratic, P = 0.004).
4
Inorganic phosphorus; phosphorus effect (linear, P < 0.001); phytase effect (linear, P < 0.001).
5
Phosphorus effect (quadratic, P = 0.032); phytase effect (linear, P = 0.002).
1
JAPR: Research Report
712
Table 4. Effect of nonphytate phosphorus (NPP) and phytase on tibia parameters in 42-d-old broilers1
NPP treatment,2
Phytase
%
treatment, U/kg
0.13
0.20
0.27
0.35
0.13
0.13
0.13
0.13
0.13
0.13
SEM
P-value
Tibia-breaking
strength,3 kg
Tibia ash,4 g
Tibia ash,5 %
Tibia
phosphorus, %
Tibia
calcium, %
12.99e
14.54de
18.64bc
29.81a
17.36cd
17.33cd
16.64cde
20.31bc
21.47b
22.19b
0.80
<0.001
1.30g
1.83f
2.30bcd
2.68a
1.90ef
2.08de
1.95ef
2.17cd
2.32bc
2.40b
0.06
<0.001
42.27d
47.96abc
50.05abc
51.06a
46.99c
46.70c
48.35abc
47.13bc
50.99a
50.41ab
0.50
<0.001
7.12b
7.85ab
8.60a
8.80a
8.32a
7.81ab
8.12ab
8.21a
8.44a
8.44a
0.12
0.088
17.37
19.78
19.70
20.03
20.18
18.67
18.13
18.93
19.48
19.50
0.27
0.344
0
0
0
0
125
250
500
1,000
2,000
4,000
a–g
Means in a column with no common superscript are significantly different.
Each mean represents 4 pens (12 birds per pen).
2
Nonphytate phosphorus (formulated).
3
Phosphorus effect (linear, P < 0.001; quadratic, P < 0.001); phytase effect (linear, P < 0.001; quadratic, P = 0.02).
4
Phosphorus effect (linear, P < 0.001); phytase effect (linear, P < 0.001; quadratic, P = 0.004).
5
Phosphorus effect (linear, P < 0.001; quadratic, P = 0.006); phytase effect (linear, P < 0.001; quadratic, P = 0.02).
1
in nitrogen retention in broilers. In this experiment, the retention of energy and CP were not
affected by dietary NPP levels.
When the basal diet was supplemented with
graded levels of phytase, retention of PP (linear,
P < 0.001; quadratic, P < 0.001) and tP (linear,
P < 0.001; quadratic, P < 0.001) increased, but
calcium retention decreased (linear, P < 0.001;
Table 5). Crude protein and energy retention
was not affected by phytase addition. Wu et al.
[35] indicated that when 2,000 U of phytase was
added to the basal diet, the apparent ileal digestion of PP ranged from 72 to 79% in 38- to 41-dold broilers. In this experiment, the PP retention
was 77% when 4,000 U of phytase was supplemented and broiler growth in the treatment with
Table 5. Effect of NPP and phytase on nutrient retention in 37- to 42-d-old broilers1
NPP treatment,2 %
0.13
0.20
0.27
0.35
0.13
0.13
0.13
0.13
0.13
0.13
SEM
P-value
a–e
Phytase
treatment, U/kg
PP,3
%
tP,4
%
Calcium,5
%
AME,
kcal/kg
CP,
%
0
0
0
0
125
250
500
1,000
2,000
4,000
42.2d
37.5
28.2e
23.0e
58.3c
55.6c
60.8bc
65.5b
75.6a
77.1a
2.93
<0.001
49.5e
59.3cd
59.6cd
56.5d
61.0cd
64.0c
76.0b
81.8a
85.2a
84.7a
2.02
<0.001
59.3a
57.1a
57.7a
57.8a
59.9a
59.0a
56.4ab
57.8a
55.0ab
52.1b
0.54
0.035
3,045
3,096
3,094
3,025
3,053
3,033
3,153
3,061
3,151
3,051
15.7
0.593
57.1
60.6
56.7
59.6
60.0
61.1
58.3
60.4
61.4
60.6
0.46
0.222
Means in a column with no common superscript are significantly different.
Each mean represents 4 pens (12 birds per pen).
2
Nonphytate phosphorus (formulated).
3
Phytate phosphorus; phosphorus effect (linear, P < 0.001); phytase effect (linear, P < 0.001; quadratic, P < 0.001).
4
Total phosphorus; phosphorus effect (linear, P = 0.018; quadratic, P = 0.002); phytase effect (linear, P < 0.001; quadratic, P
< 0.001).
5
Phytase effect (linear, P < 0.001).
1
Han et al.: PHYTASE EQUIVALENCY VALUES
713
Table 6. Regression equations between performance and dietary NPP and phytase in 22- to 42-d-old broilers
NPP effect1
Item
Equation
BW gain
Y = 1,234.4 + 1,389.2X
Y = 789.7 + 5,568.9X – 8,687.5X2
Y = 2,347.8 + 2,219X
Y = 1,465.3 + 10,514X − 17,241X2
Y = 0.534 + 6.2768X
Y = 0.0213 + 11.095X − 10.016X2
Y = 38.673 + 38.562X
Y = 26.847 + 149.7X − 231.01X2
Y = 1.8039 + 24.235X
Y = −3.1609 + 70.897X − 96.988X2
Feed intake
Tibia ash weight
Tibia ash content
Phosphorus retained
Phytase effect2
r2
r2
Equation
0.659
0.772
0.741
0.938
0.933
0.943
0.741
0.858
0.893
0.957
y = 1,472.3 + 254.21x
y = 1,455.8 + 487.89x − 296.42x2
y = 2,703.3 + 413.82x
y = 2,688.9 + 618.17x − 259.21x2
y = 1.8127 + 0.9093x
y = 1.6769 + 2.8385x − 2.4471x2
y = 45.919 + 7.2347x
y = 44.778 + 23.442x − 20.558x2
y = 6.0478 + 4.5225x
y = 5.3466 + 14.482x − 12.634x2
0.394
0.418
0.486
0.495
0.460
0.614
0.341
0.468
0.633
0.860
1
X = NPP percentage of diet.
x = grams of phytase per kilogram of diet.
2
4,000 U of phytase was equivalent to that of
broilers fed the control diet. Research has shown
that tP retention could be improved with graded
levels of phytase in tP-deficient broiler diets [1,
3, 25, 37, 38]. Similar results were found in this
study. The maximum retention value of tP was
approximately 85% when 2,000 U of phytase
was added to the basal diet. Previous research
showed that adding phytase improved the retention of dietary CP and energy [3, 39–42] in
chicks, but in other experiments this had no effect [31, 43–46].
0.12% Pi from monosodium phosphate in broiler
diets. The data in this experiment indicated that
81 to 95% of PP was released by 4,000 U of
phytase, and Pi would not need to be added to
22- to 42-d-old broiler diets.
CONCLUSIONS AND APPLICATIONS
Equivalency of Microbial Phytase
Relative to Pi
Shirley and Edwards [3] found that tP retention could be improved in a dose-response manner with graded levels of phytase in tP-deficient
broiler diets. In this experiment, linear models
were used to evaluate the NPP equivalency of
phytase (Table 6, 7). Based on equations for BW
gain, FI, and tibia ash, amounts of NPP equivalent to 125, 250, 500, 1,000, 2,000, and 4,000 U/
kg of phytase in 22- to 42-d-old broilers were
determined to range from 0.035 to 0.208%, and
the percentage of the dietary phytate P released
was calculated to range from 16 to 95% (Table
8).
Previous studies showed that the amount of
available P released from PP by phytase ranged
from 31 to 60% for 250 to 2,000 units of U/kg of
feed [1, 21, 39, 47]. Jendza et al. [48] reported
that 500 U/kg of microbial phytase was determined to be equivalent to the addition of 0.07 to
1. Body weight gain, FI, plasma Pi, tibia
ash weight, tibia ash percentage, tibiabreaking strength, and tibia phosphate of
22- to 42-d-old broilers increased with
dietary NPP concentration. The dietary
NPP concentrations required for tibia
ash percentage, BW gain, and FI were
0.32, 0.32, and 0.30%, respectively.
2. Phytase supplementation improved
growth, plasma Pi, tibia ash weight, tibia
ash percentage, tibia-breaking strength,
tibia phosphate, and retention of PP and
tP.
3. Phytase levels of 125, 250, 500, 1,000,
2,000, and 4,000 U/kg of diet were
Table 7. Equivalency equation of phytase relative
to inorganic phosphorus for growth, tibia ash, and
phosphorus retained of broilers
Item
Equivalency equation1
Model
BW gain
Feed intake
Tibia ash weight
Tibia ash content
Phosphorus retained
y = 0.0412 + 0.1830x
y = 0.0302 + 0.1865x
y = 0.0737 + 0.1449x
y = 0.0579 + 0.1876x
y = 0.0451 + 0.1866x
Linear
Linear
Linear
Linear
Linear
1
y = NPP percentage of diet; x = gram of phytase per kilogram of diet.
JAPR: Research Report
714
Table 8. Equivalency of phytase to nonphytate phosphorus for growth performance and tibia ash in 22- to 42-d-old
broilers
Item
0.025 g of
phytase/kg of
diet or 125 U
of phytase/kg
of diet
0.05 g of
phytase/kg of
diet or 250 U
of phytase/kg
of diet
0.046
0.035
0.077
0.063
0.050
0.050
0.040
0.081
0.067
0.054
0.40 g of
0.10 g of
0.20 g of phytase/ phytase/kg of
phytase/kg of
kg of diet or
diet or
diet or 500 U
1,000 U of
2,000 U of
of phytase/kg
phytase/kg
phytase/kg
of diet
of diet
of diet
0.80 g of
phytase/kg
of diet
or 4,000 U
of phytase/kg
of diet
Equivalency of phytase to NPP, %
BW gain
Feed intake
Tibia ash weight
Tibia ash content
Phosphorus retained
0.060
0.049
0.088
0.077
0.064
0.078
0.068
0.103
0.095
0.082
0.114
0.105
0.132
0.133
0.120
0.188
0.179
0.190
0.208
0.194
48 to 60
81 to 95
% of phytate phosphorus
Phosphorus released
16 to 35
18 to 37
equivalent to the addition of 0.035 to
0.208% of Pi from dicalcium phosphate
in 22- to 42-d-old broilers.
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Acknowledgments
This study was supported by Shaanxi Scientific and
Technological Innovation Project (2007ZDKG-15, Xi’an,
China). The authors are grateful to W. Y. Song for his valuable corrections to the manuscript.