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Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1 and * Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5
4To whom correspondence should be addressed. E-mail: mfan{at}uoguelph.ca.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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25%. True rather than
apparent P digestibility values should be determined and used in diet
formulation for pigs. In addition, this study shows that the
gastrointestinal endogenous P output is important in whole-body P
requirement and homeostasis.
KEY WORDS: • phosphorus • endogenous outputs • digestion and absorption • pigs
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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. As a crucial component of all forms of life on earth,
inorganic phosphates are a limited and nonrenewable natural resource
and the conservation of phosphorus has been a global issue
(2)
. P is the third most expensive nutrient after energy
and protein in swine nutrition and feeding (3)
.
Furthermore, excessive P output in swine manure is a key nutrient
contributing to environmental pollution (4)
. These aspects
have made research on improving efficiency of P utilization by pigs one
of the most important issues in swine nutrition.
Accurate determination of bioavailability of P in feeds and the
formulation of swine diets on the basis of bioavailable P supply are
essential to ensure efficient utilization (5
6
7)
.
Bioavailability of P in feed ingredients is usually measured by
digestibility studies and the slope-ratio assay. Digestibility
studies indirectly estimate P availability by measuring its digestive
utilization.
Mechanisms of phosphate digestion and absorption at the cellular and
molecular level are becoming better understood. After enzymatic
hydrolysis and release, inorganic phosphates are absorbed via
transcellular and paracellular routes (8
,9)
. The
transcellular pathway includes transport across the brush border
membrane of the enterocyte by the Na+-phosphate
cotransporter and extrusion across the basolateral membrane of the cell
by the Na+-independent phosphate transporter
(8
,10)
.
However, the determination of P digestion and absorption at the
whole-animal level is still challenged and confounded by the
presence of the gastrointestinal endogenous P contribution (Fig. 1
). Without correction for endogenous contribution, P digestibility
values determined are usually referred to as apparent P digestibility
values. At present, apparent P digestibility values in feed ingredients
for pigs are used in diet formulation due to the lack of a valid
technique for quantification of the endogenous P outputs
(5
,11
,12)
. Three major issues face the use of apparent P
digestibility values in diet formulation. First, reported apparent P
digestibility values are very variable within the same ingredients. For
example, apparent P digestibility values in soybean meal (SBM) for pigs
varied between 15 and 34% (5
,12)
. Second, apparent P
digestibility values likely underestimate the true digestive
utilization of P by 20–25% (13)
. Third, apparent P
digestibility values measured in single feed ingredients are not always
additive when used for diet formulation (14)
. Thus, it is
essential to determine the gastrointestinal endogenous P outputs and
true P digestibility values in feed ingredients for pigs.
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pioneered studies to measure true P
availability in pigs by using the 32P tracer.
Because of fast recycling of tracers within the gastrointestinal tract
and difficulties in handling radioactive materials in routine
whole-animal studies, this area of research has not been explored
much since then. Alternatively, the regression analysis technique, by
using the linear relationships between amino acid outputs in ileal
digesta or feces and their dietary inputs, has been developed and used
to determine the endogenous amino acid outputs and true amino acid
digestibility values in feed ingredients for pigs (16
,17)
.
Logically, if the same linear relationship exits for P, the endogenous
P output and true P digestibility values can also be measured by the
regression analysis technique. Using SBM as a "model" ingredient, this study was designed to address the following objectives: 1) to examine the effect of dietary P content on the determination of apparent P digestibility values; 2) to determine whether the regression analysis technique can be used to determine the gastrointestinal endogenous P outputs and true P digestibility values; and 3) to examine the role of the large intestine in the endogenous P outputs and P digestion in pigs.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Determination of the gastrointestinal endogenous P outputs by the
regression analysis technique relies on establishing linear
relationships between P outputs in ileal digesta or feces and their
dietary inputs (17)
.
The total outputs of P in ileal digesta and feces, expressed as g/kg
dry matter (DM) diet intake, are calculated from Equation (1)
according
to the previous studies (17)
.
 | (1) |
where PO represents the outputs of P in digesta or feces (g/kg DM diet intake), PI is the content of P in ileal digesta or feces (g/kg DM digesta or feces), ID is the Cr2O3 concentration in the diets (g/kg DM diet) and II is the Cr2O3 concentration in ileal digesta or feces (g/kg DM digesta or feces).
The outputs of P in ileal digesta and feces have both dietary and
endogenous origins. If there are linear relationships between P outputs
in ileal digesta or feces and the graded levels of P inputs from diets,
when expressed as g/kg DM diet intake, their relationships can be
expressed according to Equation (2)
.
 | (2) |
where POi represents the outputs of P in
ileal digesta or feces collected from animals fed the ith
assay diet, determined using Equation (1)
(g/kg DM diet intake),
PE represents the levels of the
gastrointestinal endogenous P in ileal digesta or feces (g/kg DM diet
intake), DI is the percentage of
dietary P that is truly indigestible going through the gastrointestinal
tract (%) and PDi is the P content in
the ith assay diet (g/kg DM diet). DT
is the true ileal and fecal P digestibility values (%) in the
P-containing assay ingredient and can be calculated according to
Equation (3)
, once DI is estimated
from regression analysis according to Equation (2)
.
 | (3) |
Equation (2) represents a simple linear regression model in which POi and PDi are the dependent and independent variables, respectively. PE and DI are the regression coefficients and are estimated by fitting the simple linear regression model. If there are linear relationships between P outputs in ileal digesta or feces and graded levels of P inputs from the diets with significant intercepts, then the endogenous P level in ileal digesta or feces can be determined directly by extrapolating the dietary inputs of P to zero by obtaining the intercepts of the linear regression equations (PE).
To determine true ileal and fecal P digestibility values in a P-containing ingredient, a series of assay diets are formulated to contain graded dietary levels of P but only from the assay ingredient. The contents of other dietary factors such as antinutritive factors that likely affect P digestion and endogenous P outputs should be controlled between the assay diets.
Animals, diets and experimental design.
Four Yorkshire barrows, with an average initial body weight of 6.8 kg,
were surgically fitted with a simple T-cannula at the distal ileum
according to procedures adapted from previous studies
(18)
. After surgery, the pigs were housed individually in
stainless steel metabolic crates in a temperature-controlled barn
(20–22°C). During a 7-d recovery period, the barrows were fed a 210
g/kg crude protein weaning diet. A detailed description of pre- and
postoperative care was previously presented (18)
.
After recovery, the barrows were fed one of the four experimental diets
(Table 1
) according to a 4 x 4 Latin square design. They were fed twice
daily, equal amounts each meal, at 0800 and 2000 h. The dietary
allowances were 500, 680, 780 and 880 g/d during periods 1, 2, 3 and 4,
respectively. Water was freely available from a low pressure drinking
nipple. The barrows were electrically stunned before they were killed
at the conclusion of the experiment and dissected to determine whether
cannulation had caused intestinal abnormalities. The average body
weight of the barrows at the conclusion of the experiment was 20.8 kg.
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). Corn oil was included to bring the digestible energy
content up to the level recommended by NRC standards (3)
and to reduce the dustiness of the diets; lactose and dextrose were
included to improve the palatability of the diets. Vitamins and
minerals were supplemented according to NRC standards (3)
.
Chromic oxide was included in the diets to act as the digestibility
marker for the determination of the digestibility values of the
nutrients that were measured. The inclusion of antibiotics in the diets
was for the prevention of postweaning diarrhea according to the current
swine industry practice. Each experimental period comprised 8 d. After a 4-d adaptation period, all possible fecal samples were collected on d 5 and 6. Ileal digesta samples were collected for a total of 24 h, i.e., from 0800 to 1000 h on d 7 and every 2 h thereafter until 0800 h on d 8 and from 1000 to 1200 h on d 8 and every 2 h thereafter until 0800 h on d 9. Ileal digesta were collected in soft plastic tubing (length, 10 cm; i.d., 1.5 cm) which was attached to the barrel of the cannula with Velcro tape. The tubing contained 10 mL of a solution of formic acid (2.86 mol/L) to minimize further bacterial activity. The tubing was removed and replaced as soon as it was partially filled with digesta. Digesta were immediately frozen at -20°C.
The experimental proposal, surgical procedures, and procedures for care
and treatment of the barrows were reviewed and approved by the
University of Guelph Animal Care Committee. The animals used in this
experiment were cared for in accordance with the guidelines established
by Canadian Council on Animal Care (19)
.
Chemical analyses.
After the conclusion of the experiment, the digesta and fecal samples were freeze-dried, pooled within the same barrow and period for the same diet, ground through a mesh screen and mixed before analysis. The samples of the diets and SBM were ground similarly. Analyses were performed in duplicate.
Analyses for DM were carried out according to AOAC methods
(20)
. Analyses for neutral-detergent fiber were
carried out according to an established procedure (21)
.
Chromic oxide was determined (22)
by using an atomic
absorption spectrometer (SpectrAA-10/20, Varian, Mulgrave, Australia).
Diet ( 1.0 g) and 0.4–0.6 g of digesta and fecal samples were
weighed into 60-mL Pyrex beakers and ashed overnight at 550°C.
Cr2O3, as part of the ash, was then oxidized to
dichromate by digestion in 6 mL of phosphoric acid (16.7
mol/L)-manganese sulfate (13.5 mmol/L) solution mixed with 8 mL of
potassium bromate (0.27 mol/L) solution on a hot plate. Potassium
dichromate was used as standard.
Analyses of total inorganic P in samples were carried out by
spectrophotometric analysis at 355 nm (23)
. Potassium
monobasic phosphate was used as standard. To partition total P contents
in diet, digesta and fecal samples into water-soluble inorganic
phosphate-P and water-insoluble P, 1.0 g of sample was
weighed into 50-mL centrifuge tubes, mixed and centrifuged at 2000
x g for 20 min to precipitate large particles. The
supernatant was transferred into a 250-mL volumetric flask and assayed
for the content of inorganic phosphate-P. Because the color
reaction reagents did not react with any water-soluble organic
phosphates in the supernatant samples, the difference between the total
P and the water-soluble inorganic P contents was defined to be the
water-insoluble P (24)
.
Calculations and statistical analyses.
The apparent ileal and fecal digestibility values of DM and P in the
experimental diets were calculated according to Equation (4)
.
 | (4) |
where DAi represents the apparent ileal and fecal P digestibility values in the assay diets (%, on as-fed basis), ID is the digestibility marker concentration in the ith assay diet (%, on as-fed basis), PI is the P concentration in ileal digesta or feces (%, on as-fed basis), PD is the P concentration in the ith assay diet (%, on as-fed basis) and II is the digestibility marker concentration in ileal digesta or feces (%, on as-fed basis).
On the basis of the apparent ileal and fecal P digestibility values and
the levels of endogenous P extrapolated with regression analysis, the
true P digestibility values in the assay diets and also in the test
ingredient, SBM, can be determined according to Equation (5)
.
 | (5) |
Alternatively, the endogenous P outputs corresponding to
individual diets can also be calculated according to Equation (6)
, if
corresponding true ileal and fecal P digestibility values are
determined.
 | (6) |
where DTi represents the true ileal and fecal P digestibility values in the assay diets (%), DAi represents the apparent ileal and fecal P digestibility values in the assay diets (%), PE represents the levels of endogenous P in ileal digesta and feces (g/kg DM diet intake) and PDi is the P concentration in the assay diets (g/kg DM diet).
The digestibility values were first subjected to ANOVA for a 4 x 4 Latin square design. The intervals between the treatment level of P
were designed to be equal by adding an equal amount of SBM (136 g/kg)
to the diets at the expense of cornstarch. The treatment effect was
therefore partitioned and tested according to equally spaced orthogonal
polynomial analyses (25)
. The ANOVA and the orthogonal
polynomial analyses were carried out using the General Linear
Procedures of SAS (26)
. Related linear and curve linear
regression analyses were conducted by using the Fig.P program (Fig.P, 1993 , Biosoft,Cambridge,UK). The comparison of true P digestibility
values and the endogenous P outputs between ileal digesta and feces was
conducted according to the pooled t test (27)
.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Solvent-extracted SBM was used as a test ingredient; it contained 6.4
g/kg total P on an as-fed basis. This type of SBM usually contains
52 ± 3.7% of total P as phytate-P and 8 ± 8% units/kg
intrinsic phytase activity (28)
.
Graded levels of dietary protein, calcium and P intake, as a result of
graded levels of SBM inclusion, did not affect normal digestive
functions as was reflected by changes in DM digestibility values
(Table 2
). There was a linear decrease (P < 0.01) in the
apparent ileal and fecal DM digestibility values from diets 1 to 4,
which was a direct result of replacing cornstarch with SBM, indicating
that SBM has a lower apparent ileal DM digestibility value than
cornstarch. There was an increase (P < 0.01) in the
apparent ileal and fecal P digestibility values in SBM when the dietary
P content was increased from 1.1 to 4.3 g/kg DM diet. For ileal P
digestibility, the increase was 61.9%. For fecal P digestibility, the
increase was 26.4% (Table 2)
.
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). The presence of significant linear relationships between the ileal
and fecal outputs and dietary inputs of P in this study suggests that
the ileal and fecal total outputs of P at different dietary levels can
be linearly partitioned into the components of P of endogenous and
exogenous sources (Fig. 2)
. Thus the gastrointestinal endogenous P
outputs in ileal digesta and feces were determined according to
Equations (2) and (6)
. As shown in Figure 3A
, the endogenous P output was higher (P < 0.05) in
ileal digesta than in feces (0.86 ± 0.09 vs. 0.31 ± 0.06
g/kg DM diet intake). True ileal and fecal P digestibility values in
SBM were determined according to Equations (2)
, (3) and (5). As shown
in Figure 3
B, there was no difference (P > 0.05) between the true ileal (50.7 ± 7.1) and fecal (48.5 ± 5.4%) P digestibility values in SBM.
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and
4;T3,4>). The patterns of P flows were similar between ileal
digesta and feces. In general, there were linear and (or) quadratic
increases (P < 0.01) in the total ileal P outputs,
expressed as g/kg DM for digesta, feces or diet, as dietary P levels
increased from diets 1 to 4. There were quadratic decreases
(P < 0.01) in the levels of endogenous P outputs in
ileal digesta and feces between the diets when these were expressed as
g/kg DM digesta or feces. However, the levels of endogenous P in ileal
digesta and fecal were not different (P > 0.05)
between the diets when these results were expressed as g/kg DM diet
intake. On the other hand, ileal and fecal outputs of P of dietary
origin showed linear and quadratic patterns of increases (P
< 0.01) when these were expressed as g/kg DM digesta or feces or
DM diet intake from diets 1 to 4 (Tables 3
and 4)
. Furthermore, it is
noteworthy that when expressed as g/kg DM diet intake, the endogenous P
flow was dramatically lower (P < 0.05) at the fecal
than at the ileal level, whereas there were no differences
(P > 0.05) between the levels of P originating from
dietary sources between the fecal and the ileal levels (Tables 3
and 4)
.
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. Thus,
differences in the dietary levels of P had dramatic effects on the
apparent ileal and fecal P digestibility values. However, these had no
effects on the true P digestibility values (Fig. 4A
and
B). On the other hand, relative contributions of endogenous P outputs, as
a percentage of total dietary P content, were not constant and
decreased exponentially (P < 0.05) in response to the
increases in the dietary P contents (Fig. 5
). These results show that the endogenous P contributions have
relatively larger effects on their respective apparent digestibility
values at lower than at higher levels of dietary P.
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). Between 64 and 88% of total dietary P was not water-soluble
inorganic phosphate-P and had to be hydrolyzed before absorption.
In ileal digesta, only 10% of total P remained water-soluble
inorganic phosphate-P; however, the majority of P (90%) existed as
the water-insoluble P that was not readily available for absorption
as shown in Figure 6A
. In feces, between 30 and 43% of total P was converted into
water-soluble inorganic phosphate-P. However, these P escaped
absorption and were excreted in feces as shown in Figure 6
B.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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By using SBM as an assay ingredient, for the first time, the presence
of linear relationships was demonstrated between the total P outputs in
ileal digesta and feces and the dietary inputs when P flow was
expressed as g/kg DM diet intake. This further suggests that the
gastrointestinal endogenous P outputs and true P digestibility values
in feed ingredients for pigs can be determined by the regression
analysis technique. The methodological aspects of measuring the
gastrointestinal endogenous amino acid outputs and true ileal amino
acid digestibility values by the regression analysis technique were
examined previously (17
,29)
. In this study, the endogenous
P outputs were determined to be 0.86 ± 0.09 g/kg DM diet intake
in ileal digesta and 0.31 ± 0.06 g/kg DM diet intake in feces.
Thus, for pigs between 5 and 20 kg with voluntary feed intake at 5%
of body weight, the endogenous P outputs were estimated to be
0.19–0.77 g/d in ileal digesta and 0.07–0.28 g/d in feces. Fecal
endogenous P output was reported to be between 0.09 and 0.12 g/d in
humans (9)
. There is very little other information
available from the literature.
Total and available P requirements were recommended to be 3.25–6.00
and 2.00–3.20 g/d, respectively, for piglets between 5 and 20 kg body
weight (3)
. In this study, the ileal endogenous P output
represents 5.8–12.8% of the pig’s (5–20 kg) daily requirement
for total P and 9.5–24.1% of the pig’s daily requirement for
available P. Fecal endogenous P output represents 2.1–4.7% of the
pig’s daily requirement for total P and 3.5–8.9% of the pig’s
(5–20 kg) daily requirement for available P. Therefore, fecal
endogenous P output represents a significant portion of the P
requirement.
The higher level of the endogenous P output (P < 0.05)
in ileal digesta than in feces (0.86 ± 0.09 vs. 0.31 ± 0.06
g/kg DM diet intake) suggests that 64% of the endogenous P output
at the end of the small intestine was likely reabsorbed in the large
intestine by aid of microbial fermentation. Thus, the large intestine
may play an important role in whole-body P homeostasis by recycling
endogenous P that was secreted in the upper gastrointestinal tract.
As illustrated in Figure 1
, total endogenous P secretions into the
gastrointestinal tract potentially include P from salivary, gastric,
biliary and exocrine pancreatic juices, as well as P from intestinal
secretions and sloughed mucosal cells. Technically, it is difficult to
measure the efficiency of reabsorption of the total gastrointestinal
endogenous P secretions. It is usually assumed that 75% of the
total gastrointestinal endogenous nutrient secretions, which include
amino acids and minerals, is absorbed (9
,30)
. Based on
this assumption, it can be calculated that the total gastrointestinal
endogenous P secretion likely ranges between 0.28 and 1.12 g/d for pigs
between 5 and 20 kg in body weight, suggesting that a large proportion
of the total daily P required is being recycled within the
gastrointestinal tract in pigs.
By aid of the regression analysis technique, the true ileal and fecal P
digestibility values in SBM were determined, and there was no
difference between true ileal and fecal P digestibility values (50.7
± 7.1 vs. 48.5 ± 5.4%, P > 0.05). This
indicates that the large intestine does not play a major role in the
absorption of exogenous P. This observation is consistent with previous
reports (10
,31)
. Furthermore, the results from this study
also suggest that 40% of total P in feces was made up of
water-soluble inorganic phosphates. This form of P is readily
available for absorption (Fig. 6
B). Because only 10% of
total P leaving the small intestine was in the form of
water-soluble inorganic phosphates (Fig. 6
B), microbial
fermentation in the large intestine might have played a role in
converting the water-insoluble P, including phytate-P, into
free inorganic phosphates. This is consistent with reports that various
microbes, such as Escherichia coli, secrete phytase that
specifically hydrolyzes phytate-bound phosphates (32)
.
However, at present, it was not clear why a large proportion of
water-soluble inorganic phosphates was not absorbed in the large
intestine. This is the first report of the determination of true P
digestibility in SBM for pigs. The true P digestibility values
determined in this study (49–51%) suggest that 50% of total P in SBM
could be digested and absorbed by postweaned young pigs.
As demonstrated in this study, true P digestibility and the endogenous P output associated with a test feed and/or food ingredient can be conveniently and simultaneously determined by the linear relationship between total P output and dietary input. The key to this methodology is to design a series of diets to contain graded levels (at least three to four) of P from an assay ingredient and then analyze data to obtain true P digestibility and the endogenous P output values according to Equation (2) as described in the Materials and Methods section.
Many studies were conducted to measure apparent P digestibility and
availability values in SBM for pigs (12)
. As summarized in
Table 6
, there was a large variability in apparent P digestibility values
between studies, ranging from 24 to 41%. Furthermore, there was also a
large variability in P availability values between studies, ranging
from 15 to 35%, as determined by the slope-ratio assay. Intrinsic
factors such as differences in phytate-P content and intrinsic
phytase activity in different samples of SBM between studies might have
contributed in part to this variability (12)
. In this
study, a much larger variability in apparent ileal (-24.8 to 37.1%)
and fecal P (18.8–42.5%) digestibility values in SBM was observed
than those reported in the literature as summarized in Table 6
. This is
due to the fact that large differences in P contents between diets were
created in this study to demonstrate principles. These data suggest
that differences in P contents between studies were the largest single
factor responsible for the large variability in the apparent P
digestibility values reported in the literature. This is due to the
fact that the relative contribution of the endogenous P outputs, as a
percentage of total dietary P content, decreases exponentially as
dietary P content increases (Figs. 4
and 5)
. Furthermore, the average
apparent P digestibility and availability values are at 25% in the
literature, whereas true P digestibility is 50% as determined from
this study in SBM. Therefore, the literature data underestimate the
true digestive utilization of P in SBM for pigs by 25%.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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2 Supported by grants from the Natural Sciences
and Engineering Research Council (NSERC) of Canada, Ontario Pork
Producers Marketing Board (OPPMB), Agriculture and Agri-Food Canada
(AAFC) and Canadian Pork Council (CPC) Multi-Partner Hog
Environmental Management Strategy (HEMS) Program and Ontario Ministry
of Agriculture, Food and Rural Affairs (OMAFRA)-University of Guelph
Animal Research Program (to M.Z.F.).
3 In memory of William Douglas Morrison for his
instrumental support in the initiation of the studies. He was born
October 16, 1927, in Provost, Alberta and passed away April 6, 2000, in
Guelph, Ontario, Canada.
5 Abbreviations used: DM, dry matter; P,
phosphorus; SBM, soybean meal.
Manuscript received March 1, 2001. Initial review completed April 30, 2001. Revision accepted June 7, 2001.
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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1. Anderson J.J.B. (1991) Nutritional biochemistry of calcium and phosphorus. J. Nutr. Biochem. 2:300-307.
2. Abelson P. H. (1999) A potential phosphate crisis 1999 Science (Washington DC) 283 2015. .
3. National Research Council (1998) Nutrient Requirements for Swine 10th ed. 1998 National Academy Press Washington, DC. .
4. Mallin M. (2000) Impacts of industrial animal production on rivers and estuaries. Am. Sci. 88:26-37.
5. Jongbloed A. W., Everts H. & Kemme P. A. (1991) Phosphorous availability and requirements in pigs. Heinemann E. R. eds. Recent Advances in Animal Nutrition 1991:65-80 Butterworth London, UK. .
6. Cromwell G. L. & Coffey R. D. (1991) Phosphorus—a key essential nutrient, yet a possible major pollutant—its central role in animal nutrition. Lyons T. P. eds. Biotechnology in the Feed Industry 1991:133-145 Alltech Technical Publications Nicholasville, KY .
7. Cromwell G. L., Stahly T. S., Coffey R. D., Monegue H. J. & Randolph J. H. (1993) Efficacy of phytase in improving the bioavailability of phosphorus in soybean meal and corn-soybean meal diets for pigs. J. Anim. Sci. 71:1831-1840.[Abstract]
8. Danisi G. & Murer H. (1992) Inorganic phosphate absorption in small intestine. Schultz S. G. Field M. eds. Handbook of Physiology. 6: The Gastrointestinal system IV. Intestinal Absorption and Secretion 1992:323-335 Oxford University Press New York, NY .
9. Civitelli R. & Avioli L. V. (1994) Calcium, phosphate, and magnesium absorption. Johnson L. R. eds. Physiology of the Gastrointestinal Tract 3rd ed. 1994:2173-2181 Raven Press New York, NY. .
10. Peerce B. E. (1997) Interaction of substrates with the intestinal brush border membrane Na/phosphate cotransporter. Biochim. Biophys. Acta 1323:45-56.[Medline]
11. Dellaert B. M., Van der Peet G.V.F., Jongbloed A. W. & Beers S. (1990) A comparison of different techniques to assess the biological availability of feed phosphates in pig feeding. Neth. J. Agric. Sci. 38:555-566.
12. Weremko D., Fandrejewski H., Zebrowska T., Han I. K., Kim J. H. & Cho W. T. (1997) Bioavailability of phosphorus in feeds of plant origin for pigs. Asian J. Anim. Sci. 10:551-566.
13. Fan M. Z., Archbold T., Lackeyram D., Rideout T., Gao Y., Squires E. J., Hacker R. R., de Lange C.F.M. & Sauer W. C. (1999) Formulation of swine diets on the basis of true digestible phosphorus supply. Agri-Food Canada (AAFC) Multi-Partner Hog Environmental Management Strategy (HEMS) Program Symposium, Dec. 9–12 1999 Canadian Pork Council (CPC) and Agriculture Ottawa, Ontario, Canada. .
14. Fan M. Z. & Sauer W. C. (2001) Apparent phosphorus digestibility values in single feedstuffs are not always additive in the diet formulation for swine. Can. J. Anim. Sci 81:(abs.) (in press).
15. Whittemore C. T. & Thompson A. (1969) A simplified radioisotopic procedure for the determination of calcium and phosphorus availability. Proc. Nutr. Soc. 28:16A(abs.).[Medline]
16. Carlson K. H. & Bayley H. S. (1970) Nitrogen and amino acids in the feces of young pigs receiving a protein-free diet and diets containing graded levels of soybean meal or casein. J. Nutr. 100:1353-1362.
17. Fan M. Z. & Sauer W. C. (1997) Determination of true ileal amino acid digestibility in feedstuffs for pigs with the linear relationships between distal ileal outputs and dietary inputs of amino acids. J. Sci. Food Agric. 73:189-199.
18. Li S., Sauer W. C. & Fan M. Z. (1993) The effect of dietary crude protein level on amino acid digestibility in early-weaned pigs. J. Anim. Physiol. Anim. Nutr. 70:117-128.
19. Canadian Council on Animal Care (1980) Guide to the Care and Use of Experimental Animals 1 (with addendum) CCAC Ottawa, Canada .
20. Association of Official Analytical Chemists (1993) Official Methods of Analysis 15th ed. 1993 AOAC Washington, DC. .
21. Goering H.K. & Van Soest P. J. (1970) Forage fiber analysis (apparatus, reagents, procedures and some application). Agriculture Handbook no 1970:379 ARS USDA, Washington, DC. .
22. Saha D. C. & Gilbreath R. L. (1991) Analytical recovery of chromium from diet and feces determined by colorimetry and atomic absorption spectrophotometry. J. Sci. Food Agric. 55:433-446.
23. Heinoen J. K. & Lahti R. J. (1981) A new and convenient colorimetric determination of inorganic orthophosphate and its application to the assay of inorganic pyrophosphate Anal. Biochem 133:313-317.
24. Fan M. Z., Archbold T., Mead K. & Gao Y. (2000) Partitioning various forms of phosphorus in the distal ileal digesta and feces. Can. J. Anim. Sci. 80:780(abs.).
25. Steel R.G.D. & Torrie J. H. (1980) Principles and Procedures of Statistics: A Biometrical Approach 2nd ed. 1980 McGraw-Hill New York, NY. .
26. SAS Institute Inc (2000) The SAS System 2000 SAS Institute Cary, NC. .
27. Byrkit D. R. (1987) Statistics Today—A Comprehensive Introduction 1987 Benjamin/Cummings Publishing Company Menlo Park, CA. .
28. Eeckhout W. & Papepe M. (1994) Total phosphorus, phytate phosphorus and phytase activity in plant feedstuffs. Anim. Feed Sci. Technol. 47:19-29.
29. Fan M. Z., Sauer W. C. & McBurney M. I. (1995) Estimation by regression analysis of the endogenous amino acid levels in digesta collected from the distal ileum of pigs. J. Anim. Sci. 73:2319-2328.[Abstract]
30. Souffrant W. B. (1991) Endogenous nitrogen losses during digestion in pigs. Verstegen M.W.A. Huisman J. Den Hartog L. A. eds. Digestive Physiology in Pigs. Proceedings of the 5th International Symposium on Digestive Physiology in Pigs. EAAP Publication no. 54 1991:147-166 Wageningen The Netherlands. .
31. Jongbloed A. W., Mroz Z. & Kemme P. A. (1992) The effect of supplementary Aspergillus niger phytase in diets for pigs on concentration and apparent digestibility of dry matter, total phosphorous, and phytic acid in different sections of the alimentary tract. J. Anim. Sci. 70:1159-1168.[Abstract]
32. Rodriguez E., Mullaney E. J. & Lei X. G. (2000) Expression of the Aspergillus fumigatus phytase gene in Pichia pastoris and characterization of the recombinant enzyme. Biochem. Biophys. Res. Commun. 268:373-378.[Medline]
33. Jongbloed A. W. (1987) Phosphorus in the Feeding Of Pigs: Effect of Diet on the Absorption and Retention of Phosphorus by Growing Pigs 1987 Doctoral thesis Wageningen Agricultural University, Wageningen, The Netherlands. .
34. Jongbloed A. W. & Kemme P. A. (1990) Apparent digestible phosphorus in the feeding of pigs in relation to availability, requirement and environment. 1. Digestible phosphorus in feedstuffs from plant and animal origin. Neth. J. Agric. Sci 38:567-575.
35. Rodehutscord M., Faust M. & Lorenz H. (1996) Digestibility of phosphorus contained in soybean meal, barley and different varieties of wheat, without and with supplemental phytase fed to pigs and additivity of digestibility in a wheat-soybean-meal diet. J. Anim. Physiol. Anim. Nutr. 75:40-48.
36. Coffey R. D., Cromwell G. L. & Stahly T. S. (1992) Bioavailability of phosphorus in monocalcium phosphate, corn, dehulled soybean meal, barley, sorghum and wheat for growing pigs. J. Anim. Sci. 70(suppl. 1):288(abs.).
37. Cromwell G. L. (1992) The biological availability of phosphorus in feedstuffs for pigs. Pig News Inform 13:75N-78N.
38. Ross R. D., Cromwell G. L. & Stahly T. S. (1982) Biological availability of phosphorus in regular and dehulled soybean meal for growing pigs. J. Anim. Sci. 55(suppl. 1):93(abs.).
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