Published November 25, 2014
Estimation of standardized phosphorus
retention for inorganic phosphate sources in broilers1
S. B. Liu,*† J. J. Xie, * L. Lu,* S. F. Li,*‡ L. Y. Zhang,* Y. Jiang,* and X. G. Luo*2
*Mineral Nutrition Research Division, Institute of Animal Science, Chinese Academy of Agricultural
Sciences, Beijing 100193, P. R. China; †Wen’s Foodstuffs Group Corporation Ltd., Yunfu 527439, P. R. China; and
‡Department of Animal Science, Hebei Normal University of Science and Technology, Qinhuangdao 066004, P. R. China
ABSTRACT: Two experiments were conducted to
estimate standardized P retention (SPR) values of
dicalcium phosphate (DCP), monocalcium phosphate
(MCP), and monopotassium phosphate (MKP) in
broilers. In total, ninety-six 22-d-old male broilers with
similar BW (780 g average) were used in each experiment.
The chicks were randomly allotted to 1 of 4 treatments
(P-free, DCP, MCP, or MKP diets) with 6 replicate cages
of 4 chicks each in a completely randomized design. After
3-d acclimation, chicks were fasted for 24 h and then fed
P-free, DCP, MCP, or MKP diets for 4 h in Exp. 1 or 72 h
in Exp. 2. Excreta samples were collected for a total of 28
or 52 h (24 or 48 h after feed withdrawal) in Exp. 1 and
96 or 120 h (24 or 48 h after feed withdrawal) in Exp. 2,
respectively. The excreta collection time of 52 h in Exp.
1 or 96 h in Exp. 2 was adequate for the estimation of
SPR. The estimated basal endogenous P losses (EPL)
in chicks fed the P-free diet were 109 ± 4 mg/52 h per
bird and 49.2 ± 4.0 mg/96 h per bird in Exp. 1 and 2,
respectively. The SPR values of inorganic phosphate
sources corrected by the above basal EPL differed (P <
0.001) in Exp. 2 but not in Exp. 1. However, these SPR
values were very similar between the 2 experiments with
68.7, 69.8, or 76.6% in Exp. 1 and 71.8, 70.6, or 78.3% in
Exp. 2 for DCP, MCP, or MKP, respectively. The results
from the current study indicated that, compared with the
72-h feeding and 96-h excreta collection procedure, the
4-h feeding and 52-h excreta collection procedure was
a relatively quicker time- and labor-saving method for
estimating the SPR values of inorganic P sources in
broilers. The estimated SPR values of commonly used
inorganic P sources (MCP and DCP) were about 70%.
Key words: broiler, dicalcium phosphate, monocalcium phosphate, monopotassium phosphate,
standardized phosphorus retention
© 2013 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2013.91:3766–3771
doi:10.2527/jas2012-5729
INTRODUCTION
Inorganic P sources are usually incorporated into
poultry diets to meet the P requirements of the bird (NRC,
1994; Dilger and Adeola, 2006). Nutritionists often
assume that inorganic P could be completely available for
broilers in the diet formulation (Leske and Coon, 2002;
Coon et al., 2007). However, the determined apparent
P retention (APR) values from inorganic P sources
1Supported by The Special Fund for the Innovative Team of the
Chinese Academy of Agricultural Sciences (Beijing, P. R. China),
China Agriculture Research System (Project No. CARS-42; Beijing,
P. R. China) and the Special Fund for Agro-scientific Research in the
Public Interest (Project No. 200903006; Beijing, P. R. China).
2Corresponding author: [email protected]
Received August 7, 2012.
Accepted May 9, 2013.
indicated that chicks did not fully use P in diet (Van der
Klis and Versteegh, 1996; De Groote and Huyghebaert,
1997; Leske and Coon, 2002; Coon et al., 2007).
Furthermore, because of the absence of reliable values
for endogenous P losses (EPL; Dilger and Adeola, 2006),
the standardized P retention (SPR) in inorganic P sources
may not have been reported. Recently, the standardized
total tract digestibility of P in feed grade P has been
reported and successfully used in the diet formulation
for pigs (Petersen and Stein, 2006; Widmer et al., 2007;
Almeida and Stein, 2010, 2012; Kim et al., 2012; Rojas
and Stein, 2012). Our previous studies demonstrated that
a P-free diet could be used for measuring the basal EPL
of broilers and then estimating the SPR values of plant
feedstuffs and diet in broilers (Liu et al., 2012a,b).
Monocalcium phosphate (MCP) and dicalcium
phosphate (DCP) are the main forms of inorganic P
3766
Standardized phosphorus retention in broilers
Table 1. Analyzed Ca and P contents in inorganic P sources1
P source2
Ca, %
P, %
DCP
22.74
17.82
MCP
14.59
22.41
MKP
ND3
22.52
1Each value based on triplicate determinations.
2DCP = dicalcium phosphate; MCP = monocalcium phosphate; and MKP =
monopotassium phosphate.
3ND= not detectable.
sources used in poultry feed industry, and monopotassium
phosphate (MKP) often served as a standard reference
in studies aimed at measuring relative bioavailability of
inorganic P sources (Harrold et al., 1983; Li et al., 2000;
Peter and Baker, 2002; Amezcua and Parsons, 2007; Kim
et al., 2008). Therefore, the objective of the current study
was to estimate SPR coefficients of DCP, MCP, and MKP
in broilers, which can be used to more accurately meet P
requirements of broilers in the diet formulation.
MATERIALS AND METHODS
All experimental procedures were approved by the
Animal Research Center at the Veterinarian Office of
Beijing, P. R. China.
Experimental Design, Diets, and Birds
A completely randomized design was used in the 2
experiments. There were a total of 4 dietary treatments,
including P-free, DCP, MCP, and MKP diets. All 4
diets were formulated to meet or exceed the nutrient
requirements of growing broilers from 3 to 6 wk of age
recommended by NRC (1994), except for Ca and P. These
diets contained equal contents of ME and CP. The P-free
diet was mainly composed of cornstarch, gelatin, and
synthetic AA and contained 0.005% of P. The DCP, MCP,
and MKP diets were formulated as described by Van der
Klis and Versteegh (1996) and had the same P content
(0.20%) and a Ca to P ratio of 2.4:1. The analyzed Ca and
P contents of DCP, MCP, and MKP are shown in Table 1.
The composition of the 4 diets is presented in Table 2.
Four hundred 1-d-old male Arbor Acres broiler chicks
were obtained from a local hatchery (Huadu Broiler
Breeding Corp., Beijing, China) and housed in electrically
heated, thermostatically controlled stainless cages coated
with plastic (100 by 50 by 45 cm) and equipped with
fiberglass feeders and waterers. Feed and tap water were
available ad libitum. Tap water contained no detectable
P. During 1 to 21 d after hatching, chicks were fed a
standard broiler starter diet (containing 12.54 MJ/kg of
ME, 21.40% of CP, 1.0% of Ca, and 0.45% of nonphytate
P) and maintained on a 24-h constant light schedule.
3767
Table 2. The compositions of experimental diets
(as-fed basis)1
Item
P-free
DCP
MCP
MKP
Ingredient, %
Corn starch
47.42
46.79
46.63
46.79
Sucrose
20.64
20.64
20.64
20.64
Soybean oil
3.60
3.80
3.85
3.80
Gelatin2
19.46
19.46
19.46
19.46
Cellulose3
3.00
3.00
3.00
3.00
DCP
–
1.05
–
–
MCP
–
–
0.86
–
MKP
–
–
–
0.86
CaCO34
1.28
0.66
0.96
1.28
NaCl4
0.30
0.30
0.30
0.30
K2CO34
0.53
0.53
0.53
0.10
Vitamin and mineral premix5
0.38
0.38
0.38
0.38
dl-Met (98%)
0.19
0.19
0.19
0.19
l-Lys HCl (98.5%)
0.24
0.24
0.24
0.24
l-Thr (98.5%)
0.44
0.44
0.44
0.44
l-Trp (98.5%)
0.17
0.17
0.17
0.17
l-Ile (99%)
0.49
0.49
0.49
0.49
l-Leu (99%)
0.64
0.64
0.64
0.64
l-Phe (99%)
0.47
0.47
0.47
0.47
l-Val (99%)
0.75
0.75
0.75
0.75
Total
100
100
100
100
Analyzed and calculated nutrients6
ME, MJ/kg
12.81
12.80
12.80
12.78
CP, %
19.73
19.74
19.83
19.90
DM, %
91.90
91.68
91.50
91.47
Met + Cys, %
0.72
0.72
0.72
0.72
Lys, %
1.00
1.00
1.00
1.00
Ca, %
0.50
0.50
0.50
0.49
Total P, %
0.005
0.21
0.21
0.21
1DCP = dicalcium phosphate; MCP = monocalcium phosphate; MKP =
monopotassium phosphate.
2Obtained from Gelita Gelatine USA Inc. (Sioux City, IA).
3Obtained from Yuanju Biotech Inc. (Shanghai City, China).
4Reagent grade.
5Provided per kilogram of diet: vitamin A (all-trans retinol acetate),
10,000 IU; cholecalciferol, 3,000 IU; vitamin E (all-rac-α-tocopherolacetate),
16 IU; vitamin K (menadione sodium bisulfate), 2.0 mg; thiamin (thiamin
mononitrate), 2.0 mg; riboflavin, 6.4 mg; vitamin B6, 2.0 mg; vitamin B12,
0.012 mg; calcium pantothenate, 10 mg; niacin,26 mg; folic acid, 1.0 mg;
biotin, 0.10 mg; choline (choline chloride), 1000 mg; Cu (CuSO4·5H2O), 8
mg; Mn (MnSO4·H2O), 80 mg; Fe (FeSO4·7H2O), 80 mg; Zn (ZnSO4·7H2O),
40 mg; I (KI), 0.35 mg; and Se (NaSeO3), 0.15 mg.
6CP, DM, Ca, and total P were analyzed, but all others were calculated
(NRC, 1994).
In Exp. 1, on d 22 at 0800 h, 96 male chicks with
similar BW (780 ± 19 g) were selected and randomly
allotted to 1 of 4 dietary treatments with 6 replicate
cages of 4 birds each. Anesthesia and analgesia were
induced by intravenous injections mainly composed of
haloperidol, dihydroetrophine, and xylidinothiazoline
(SuMianXin II, 0.1 mL/kg; Quartermaster University of
PLA, Changchun, China). Chicks were sutured with a
threaded hollow plastic cap around the vent for screwing
3768
Liu et al.
a plastic bag to collect excreta (Adeola et al., 1997), and
the wounds of all chicks were treated with penicillin G
procaine (30,000 IU) to desensitize. Birds were allowed
to recover from the surgery and acclimated for 3 d. On
d 24 at 2200 h, feeds were withdrawn and all chicks
were fasted overnight (8 h). On d 25 at 0600 h, all chicks
were fed a P-free diet for 4 h first and then fasted for 24
h to clear residues in the gastrointestinal tract (Liu et
al., 2012a,b). On d 26 at 1000 h, feeders (with feeds)
and fecal-collecting bags were installed in the same
order (from cages 1 to 24), and P-free or test diets
were introduced for 4 h and then feeds were withdrawn.
Excreta collections started from feeding and lasted for
a total of 28 or 52 h (24 or 48 h after the end of the 4-h
feeding period; Liu et al., 2012a,b).
In Exp. 2, on d 22 at 0800 h, 96 male chicks with
similar BW (780 ± 22 g) were selected and randomly
allotted to 1 of 4 dietary treatments with 6 replicate cages
of 4 birds each and acclimated to the environment for 3
d. On d 24 at 2200 h, feed was removed and chicks were
fasted for 8 h. On d 25 at 0600 h, all chicks were fed
the P-free diet for 4 h and then fasted for 24 h to empty
feed residues in the gastrointestinal tract of broilers. On
d 26 at 1000 h, feeders (with feed) and fecal collection
trays were installed with cages, and all 4 diets were
introduced for 72 h, and then feeds were withdrawn.
Excreta collections started from feeding and lasted for a
total of 96 or 120 h (24 or 48 h after the end of the 72-h
feeding period; Liu et al., 2012a,b).
Sample Collections and Analyses
In Exp. 1, excreta samples were collected at about 4-h
intervals, because the excreta-collecting bag attached to
the anus was fully filled with excreta in about 4 h. In Exp.
2, excreta samples were collected twice a day at 0900
and 1800 h (Liu et al., 2012b). The excreta samples were
transferred into plastic bags according to cage number
and then dried in a forced-air oven at 55°C for 96 h.
Dried excreta samples were ground through a 0.45-mm
sieve using a grinding mill (Yanshanzhengde, Inc., Bejing,
China) to facilitate analyses. Diets and fecal samples were
analyzed for DM contents (procedure 4.1.06; AOAC,
2000), and diets were analyzed for Kjeldahl N (Thiex et
al., 2002). Concentrations of Ca in inorganic P sources
and diets were determined by inductively coupled plasma
spectroscopy (Model IRIS Intrepid II; Thermal Jarrell
Ash, Waltham, MA) as described by Li et al. (2011). Total
P concentrations in inorganic P sources, diets, water, and
fecal samples were determined using a spectrophotometer
(procedure 3.4.11; AOAC, 2000; Model Cary 100, Varian
Inc., Palo Alto, CA).
Calculations and Statistical Analyses
The APR (%) and SPR (%) of inorganic P
sources were individually calculated according to the
following equations:
APR = (PI – PO)/PI × 100, and
SPR = [PI – (PO – EPLB)]/PI × 100,
in which PI is the total P intake (mg) of birds fed the
tested diet, PO is the total excreta P output (mg) of birds
fed the tested diet, and EPLB is the total excreta P output
(mg) of chicks fed the P-free diet.
Statistical analyses of the SPR data at 2 collection times
in Exp. 1 and 2 were performed with the student’s t test using
TTEST procedure (SAS Inst. Inc., Cary, NC). The SPR data
of inorganic P sources were analyzed by 1-way ANOVA
using the GLM procedure of SAS. Differences among
means were tested by the LSD method. The cage served as
the experimental unit for all statistical analyses, and the P <
0.05 was considered to be statistically significant.
RESULTS
Chicks in all treatments were healthy throughout the
Exp. 1 and 2 and readily consumed their diets. The data
for basal EPL and P retention for inorganic P sources in
broilers are presented in Tables 3 and 4. In Exp. 1, the
average feed intake did not differ among the birds fed the
P-free, DCP, MCP, or MKP diets, and the average P intake
was similar among the birds fed the different inorganic P
source diets. The basal EPL values of the birds fed the
P-free diet and fecal P output values of the birds fed the
DCP, MCP, or MKP diets increased (P < 0.001) with the
extending total excreta collection time from 28 to 52 h. The
basal EPL values were estimated to be 38.9 ± 5.5 or 109 ±
4 mg/chick when the total excreta collection time was 28
or 52 h (24 or 48 h after feed withdrawal), respectively.
There was no effect of excreta collection time on the SPR
values of inorganic P sources. When the total excreta
collection time was 28 or 52 h, the determined values of
SPR for DCP, MCP, and MKP were 71.7 or 68.7%, 74.0
or 69.8%, and 77.6 or 76.6%, respectively, whereas the
determined values of APR for DCP, MCP, and MKP were
7.6 or –110.0%, 12.2 or –103.0%, and 20.6 or –83.0%,
respectively. There were no differences in SPR values
among DCP, MCP, and MKP.
In Exp. 2, the average feed intake did not differ among
the birds fed the P-free, DCP, MCP, or MKP diets, and
the average P intake was similar among the birds fed the
different inorganic P source diets. The basal EPL values
of the birds fed the P-free diet and fecal P output values of
the birds fed the DCP, MCP, or MKP diets increased (P <
0.001) with the extending total excreta collection time
from 96 to 120 h (Table 4). The basal EPL values were
3769
Standardized phosphorus retention in broilers
Table 3. Determined basal endogenous phosphorus loss (EPL) values, apparent phosphorus retention (APR) and
standardized phosphorus retention (SPR) values of inorganic P sources for broilers in Exp. 11,2
DCP
MCP
Item
28 h3
52 h3
SEM
28 h
52 h
Feed intake,4 g DM/chick
26.4
26.4
1.1
27.3
27.3
Excreta, g DM/chick
4.66
6.71
0.19
4.72
6.95
P intake, mg/chick
60.7
60.7
2.5
63.0
63.0
Excreta P output, mg/chick
56.1b
128.0a
3.0
55.3b
128.0a
APR, %
7.6
–110.0
9.0
12.2
–103.0
EPL,5 mg/chick
38.9b
109.0a
7.0
38.9b
109.0a
SPR, %
71.7
68.7
5.5
74.0
69.8
a,bMeans with different superscripts within the same row differ (P < 0.001).
1DCP = dicalcium phosphate; MCP = monocalcium phosphate; MKP = monopotassium phosphate.
2Values represent means of 6 replicate cages of 4 chicks each.
3A total of excreta collection time.
4Average feed DMI of birds fed the P-free diet was 24.3 ± 3.1 g/chick.
5Basal EPL estimated by the P-free gelatin–cornstarch diet (n = 6).
estimated to be 49.2 ± 4.0 or 86.3 ± 4.0 mg/chick when
the total excreta collection time was 96 or 120 h (24 or 48
h after feed withdrawal), respectively. There was no effect
of excreta collection time on the SPR values of DCP, MCP,
and MKP. When the total excreta collection time was 96
or 120 h, the determined values of SPR for DCP, MCP,
and MKP were 71.8 or 68.5%, 70.6 or 69.6%, and 78.3
or 75.2%, respectively, whereas the determined values of
APR for DCP, MCP, and MKP were 59.1 or 46.3%, 59.2
or 49.0%, 66.5 or 54.5%, respectively. The SPR for MKP
was greater (P < 0.001) than those for DCP and MCP, but
the SPR for DCP was not different from MCP. In addition,
although different procedures were used in the Exp. 1 and
2, the determined values of SPR for DCP, MCP, and MKP
in Exp. 1 were similar to those in Exp. 2.
DISSCUSSION
The values of APR exhibited huge differences. In
Exp. 1, negative APR values of all inorganic P sources
were observed at the total excreta collection time of 52 h,
showing considerable effect of EPL on APR coefficients.
A similar phenomenon was also observed in our previous
study (Liu et al., 2012b). In Exp. 2, however, the
determined values of APR for all inorganic P sources were
over 46.0% at any excreta collection time. Obviously, the
disagreement was mainly due to the great difference in
the EPL values of birds between the 2 experiments.
Our previous study demonstrated that the P-free
gelatin–cornstarch diet could be used for determining the
basal EPL and then estimating the SPR values of plant
feedstuffs and corn–soybean meal diet in broilers (Liu et
al., 2012b). However, the basal EPL varied greatly with
different experimental procedures. In the current study, the
estimated EPL was elevated after longer excreta collection
within the same experiment (in Exp. 1: 109 mg/52 h vs.
SEM
1.1
0.22
2.6
2.0
6.0
7.0
3.8
28 h
29.6
5.13
68.3
54.1b
20.6
38.9b
77.6
MKP
52 h
29.6
6.37
68.3
125.0a
–83.0
109.0a
76.6
SEM
2.2
0.15
5.1
2.0
10.5
7.0
3.5
38.6 mg/28 h; in Exp. 2: 86.3 mg/120 h vs. 49.2 mg/96
h) as expected, but the longer experimental period resulted
in less EPL between experiments. Similar results were
also observed in our previous studies (Liu et al., 2012a,b).
Although a total excreta collection time was much longer in
Exp. 2 (96 vs. 120 h) than in Exp. 1 (28 vs. 52 h), the relative
fasting extent (the ratio of the fasting time to the total
excreta collection time) during the excreta collection was
much smaller in Exp. 2 (0.25 vs. 0.40) than in Exp. 1 (0.86
vs. 0.92). Our previous studies have already shown that
fasting substantially affected the excretion of endogenous
P in broilers (Liu et al., 2012a,b). In addition, the broilers
in Exp. 2 were likely to be more severely P deficient than
those in Exp. 1 and, therefore, could have less endogenous
P excreted from the digestive tract of birds (Dilger and
Adeola, 2006). Therefore, both the extent of fasting during
the excreta collection and the extent of P deficiency of birds
might explain why the longer experimental period resulted
in less EPL in the present study. Furthermore, those EPL
values of broilers in the present study were also less than
those (123 mg/52 h or 85.4 mg/96 h per bird) observed
in our previous study (Liu et al., 2012b). One possible
explanation might be that the Ca content (0.50%) in the
present P-free diet was greater than that (0.39%) in our
previous study. Al-Masri (1995) reported that the EPL of
birds decreased from 135 to 30 mg/d as the Ca to P ratios
increased from 1.0:1 to 2.5:1, indicating that the EPL of
birds decreased as dietary Ca content increased. In addition,
it might be related to the difference in BW of birds between
our present and previous studies. In the current study, the
average BW of broilers was 780 g, which was lower than
that in our previous study (819 g; Liu et al., 2012b). It has
been found that the EPL value was affected by age and/or
BW of broilers (Liu et al., 2012a).
Although the EPL values differed substantially
between 2 experiments, the determined SPR of each
3770
Liu et al.
Table 4. Determined basal endogenous phosphorus loss (EPL) values, apparent phosphorus retention (APR) and
standardized phosphorus retention (SPR) values of inorganic P sources for broilers in Exp. 21,2
DCP
MCP
Item
96 h3
120 h3
SEM
96 h
120 h
Feed intake,4 g DM/chick
169
169
5
187
187
Excreta, g DM/chick
28.4
30.3
1.9
30.0
31.7
P intake, mg/chick
389
389
11
429
429
Excreta P output, mg/chick
159b
209a
8
176b
220a
APR, %
59.1
46.3
2.9
59.2
49.0
EPL,5 mg/chick
49.2b
86.3a
5.8
49.2b
86.3a
SPR, %
71.8b
68.5b
2.5
70.6b
69.6b
a,bMeans with different superscripts within the same row differ (P < 0.001).
1DCP = dicalcium phosphate; MCP = monocalcium phosphate; MKP = monopotassium phosphate.
2Values represent means of 6 replicate cages of 4 chicks each.
3A total of excreta collection time.
4Average feed DMI of birds fed the P-free diet was 173 ± 4 g/chick.
5Basal EPL estimated by the P-free gelatin–cornstarch diet (n = 6).
inorganic P supplement, corrected by EPL, did not
show much variation. The major differences between
experiments were the feeding time and excreta collection
time. In Exp. 1, the total excreta collection time of 28
or 52 h did not affect the SPR of inorganic P source,
which is not in agreement with our previous study (Liu
et al., 2012b). The results showed that the total excreta
collection time of 28 or 52 h affected the SPR of soybean
meal (70.4 vs. 50.5%) and inorganic P-unsupplemented
corn–soybean meal diet (53.6 vs. 44.4%) in broilers,
indicating that the total excreta collection time of 52 h
was required for the estimation of SPR of the soybean
mean and corn–soybean meal diet. The purified diets used
in the current study contained less fiber and phytate than
plant ingredient-based diets, which might lead to quicker
transition time for diets passing through the digestive tract
(Fleming and Lee, 1983; Watson et al., 2006).
Therefore, compared with soybean meal and corn–
soybean meal diet, purified diets containing inorganic P
sources in the present study may have moved faster in the
digestive tract of birds, and, therefore, a shorter excreta
collection time could be suitable for the estimation of
their SPR in broilers. However, considering the fact that
inorganic P sources are generally added to plant ingredientbased diets to meet P requirements of broilers, the excreta
collection time of 52 h should be considered more suitable
for the estimation of SPR of inorganic P sources in broilers
when the 4-h feeding procedure was adopted. In Exp. 2, the
total excreta collection time of 96 or 120 h did not affect the
SPR of inorganic P sources in broilers either, which was in
agreement with our previous report for determining the SPR
of corn, soybean meal, and inorganic P-unsupplemented
corn–soybean meal diet in broilers (Liu et al., 2012b).
The results indicated that the total excreta collection time
of 96 h was sufficient for the estimation of SPR of plant
SEM
5
2.1
12
9
2.5
5.8
2.3
96 h
181
30.7
396
140b
66.5
49.2b
78.3a
MKP
120 h
181
32.7
396
194a
54.5
86.3a
75.2Aa
SEM
8
3.9
18
10
2.2
5.8
2.0
feedstuffs, inorganic P sources, and diet in broilers when
the 72-h feeding procedure was adopted.
Our previous study (Liu et al., 2012b) demonstrated
that there was a good additivity of estimated SPR of corn
and soybean meal in the inorganic P-unsupplemented
corn–soybean meal diet when the procedure of 4-h
feeding plus 52-h excreta collection was adopted whereas
the additivity of estimated SPR of corn and soybean meal
was not good mainly due to the interference from a high
intake of P when the procedure of 72-h feeding plus 96-h
excreta collection was adopted. In the present study, we
did not test the additivity of the above estimated SPR
values of inorganic P sources in the diet formulation of
broilers. However, in our another trial, we determined the
SPR (57.5%) of the corn–soybean meal diet supplemented
with DCP with the 4-h feeding plus 52-h excreta collection
procedure and found that there was a good additivity of
the estimated SPR for DCP in the corn–soybean meal
diet formulation of broilers (Liu, 2012). Therefore, the
4-h feeding plus 52-h excreta collection procedure should
be a reliable method for estimating the SPR for plant
feedstuffs and inorganic P sources in broilers. Furthermore,
the chicks fed the P-free diet for 72 h in the 72-h feeding
plus 96-h excreta collection procedure are more likely to
develop the potential P deficiency compared with those
fed the P-free diet for 4 h in the 4-h feeding plus 52-h
excreta collection procedure. This procedure of the total
feeding and excreta collecting time (52 h) is relatively
quicker and time and labor saving than that used in Exp.
2. Therefore, the 4-h feeding plus 52-h excreta collection
procedure would be suggested for estimating the SPR of
inorganic P sources, plant feedstuffs, and diets in broilers.
Further studies are needed to check the additivity of the
estimated SPR values of inorganic P sources in the diet
formulation of broilers.
Standardized phosphorus retention in broilers
It is generally assumed that inorganic P (MCP and
DCP) could be 100% available for broilers in the diet
formulation (Leske and Coon, 2002; Coon et al., 2007).
After the procedure of 4-h feeding plus 52-h excreta
collection, the determined SPR values of commonly
used inorganic P sources (MCP and DCP) in broilers
were 68.7 and 69.8%, respectively, which were much less
than expected. The results indicated that supplemental
inorganic P was not 100% available for broiler chickens.
The reasons for low SPR of inorganic P might be due to
the short gut of birds, which made inorganic P sources
have a short P absorption or retention time in the gut
(Mitchell and Smith, 1991; Barton and Houston, 1993).
However, exact reasons need to be further investigated.
In conclusion, the 4-h feeding plus 52-h excreta
collection procedure in the current study was a relatively
quicker, time- and labor-saving method for estimating
the SPR values of inorganic P sources in broilers. Using
this procedure, the estimated SPR values of MCP and
DCP, commonly used inorganic P supplements, were
68.7 and 69.8%, respectively.
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