1641

1

To whom correspondence should be addressed.

Received September 25, 1995.
Accepted February 7, 1996.

Nutrient Digestion by Ileal Cannulated Dogs as Affected by Dietary

Fibers with Various Fermentation Characteristics

H. E. Muir*, S. M. Murray

†

, G. C. Fahey, Jr.*

,†,1

, N. R. Merchen*

,†

,

and G. A. Reinhart

‡

†

Department of Animal Sciences and *Division of Nutritional Sciences, University of Illinois,

Urbana 61801 and

‡

The Iams Company, Lewisburg, OH

ABSTRACT:

We studied the effects of dietary

fibers with various fermentation characteristics on
nutrient digestion at the distal ileum and in the total
tract of dogs. The following high-protein (34%), high-
fat (23%) diets were fed: 1 ) a control treatment
(CON) with 0% supplemental fiber; 2 ) beet pulp
(BP), 7.5%; 3 ) low-cellulose mixture (LCM), 2.5%
cellulose + 5.0% pectin; 4 ) high-cellulose mixture
(HCM), 5.0% cellulose + 2.5% pectin; or 5 ) Solka
Floc



(SF), 7.5% cellulose. Nutrient intakes by fiber-

supplemented dogs were similar among treatment
groups but greater ( P < .05) than for dogs fed the
control diet. Digestion of nutrients at the distal ileum
was similar among groups except for fat: the dogs fed
BP digested less fat than those fed the other sources of
dietary fiber. Digestion of amino acids at the distal

ileum was similar for all groups, except for lysine,
which increased ( P < .05) in digestibility as dietary
cellulose concentration increased. Dogs consuming
LCM had lower apparent ileal digestibility values for
all nutrients, including most amino acids, than dogs
consuming HCM or SF. Total tract digestion of DM
and OM by dogs fed supplemental fiber was less ( P <
.05) than for dogs fed the control diet. The BP
treatment was higher than other fiber treatments in
total tract digestion of OM ( P < .10) and total dietary
fiber ( P < .05). Total tract digestibilities of all
nutrients

exhibited

either

linear

or

quadratic

responses to dietary cellulose concentrations. Appar-
ent ileal and total tract nutrient digestion was
influenced by the source of dietary fiber consumed.

Key Words: Dog, Fiber, Digestion, Ileum

J. Anim. Sci. 1996. 74:1641–1648

Introduction

Research conducted in our laboratory showed that

an increase in the percentage of dietary beet pulp, a
moderately fermentable fiber source, leads to a
decrease in apparent N digestibility by dogs (Fahey et
al., 1990b). Also, selected fiber sources fed to dogs
resulted in different apparent N digestibilities (Fahey
et al., 1990a). Sunvold et al. (1995) showed that
poorly fermentable fiber sources resulted in higher
apparent N digestibilities than did moderately fer-
mentable fiber sources in dogs. From these data, one
could infer that moderately fermentable fibers act to
inhibit N digestion.

Microbial growth in the large bowel adds to the

quantity of N present at that site; much of this N is
subsequently excreted as feces. Fermentable fibers
encourage microbial growth and thus could contribute

to the production of greater quantities of nitrogenous
constituents. A precise estimate of N and amino acid
digestibility can be obtained using dogs cannulated at
the distal ileum. Therefore, the objectives of this study
were to investigate the effects of dietary fibers of
various fermentation capacities on nutrient and
energy intake, digestion before the distal ileum, total
tract digestibility, and pH and SCFA concentrations in
ileal contents.

Experimental Procedures

Animals and Diets.

Five diets (Table 1 ) containing

either 0% supplemental fiber (control), 7.5% Solka
Floc



( SF; Fiber Sales and Development Corporation,

St. Louis, MO), 7.5% beet pulp ( BP; Michigan Sugar,
Saginaw, MI), a blend of 5.0% cellulose and 2.5%
pectin (high-cellulose mixture, HCM; TIC Gums,
Belcamp, MD), or a blend of 2.5% cellulose and 5.0%
pectin (low cellulose mixture, LCM) were tested in a
5

×

5 Latin square design with periods lasting 11 d.

All diets were extruded. Five female dogs with hound

MUIR ET AL.

1642

Table 1. Ingredient composition of the basal diet fed

to ileal-cannulated dogs

a

Combination of chicken and chicken by-product meal.

b

Provided the following (per kilogram of diet): vitamin A, 26,400

IU; vitamin E, 136 IU; vitamin D

3

, 1,760 IU; thiamine, 16.5 mg;

riboflavin, 29.0 mg; niacin, 58.0 mg; d-pantothenic acid, 35.3 mg;
biotin, .52 mg; folic acid, 1.4 mg; choline, 2,295 mg; vitamin B

12

, .25

mg; monosodium phosphate, 6 g; potassium chloride, 5 g; choline
chloride, 3 g; Mn, 42.2 mg; Zn, 203 mg; Cu, 29.2 mg; Co, .5 mg; Se,
.26 mg.

c

0% supplemental fiber control; 7.5% beet pulp; 7.5% Solka Floc;

a blend of 5% Solka Floc and 2.5% pectin (high-cellulose mixture;
HCM); a blend of 2.5% Solka Floc and 5% pectin (low-cellulose
mixture; LCM). Fiber sources were added to diets at the expense of
the gelatinized cornstarch.

Ingredient

% DM basis

Gelatinized cornstarch

to 100

Chicken protein source

a

40.26

Chicken fat

6.22

Egg

3.25

Vitamin-mineral premix

b

1.90

Herring meal

1.00

Brewer’s dried yeast

1.00

Chicken liver meal

.50

DL-Methionine

.45

Fiber source

c

7.50

bloodlines and an average BW of 31 kg were fitted
with simple T-type ileal cannulas according to the
method of Walker et al. (1994). Surgical and animal
care procedures for the experiment were conducted
under a research protocol approved by the Institu-
tional Animal Care Advisory Committee, University of
Illinois, Urbana-Champaign. Dogs were allowed a
minimum of 2 wk recovery before experiment initia-
tion. Dogs were housed individually in clean floor pens
in a temperature-controlled room with a 12-h dark:
12-h light cycle. Dogs were adjusted to their respective
diets during a 7-d adaptation phase followed by a
4-d collection period.

All dogs were offered 250 g (as-fed basis) of their

respective diet each day at 0700 and 1900, for a total
of 500 g/d for the first period. Because some dogs were
losing weight by the end of Period 1, diet offerings
were increased to 300 g per feeding for a total of 600 g/
d for the remaining four periods. Diets were balanced
to meet or exceed nutrient requirements of dogs at
their physiological state (NRC, 1974).

Chromic oxide was used as a digestion marker.

Beginning on d 3 of each period, dogs were dosed
orally with a capsule containing .5 g of chromic oxide
at 0700 and 1900, before feeding, for a total of 1 g of
marker per day for the duration of the period. Water
was available ad libitum. Throughout the trial, all orts
were collected at the time of each feeding (i.e., at each
12-h period) for subsequent analyses.

Small abscesses around the cannulas were treated

topically with Panalog cream (SOLVAY Animal
Health, Mendota Heights, MN) and were washed
daily with Betadine solution (Becton Dickinson Acute-
Care Division, Franklin Lakes, NJ) and warm water.

Larger abscesses required subcutaneous injections of
antibiotics (Polyflex, G. C. Hanford Manufacturing,
Syracuse, NY) twice daily.

Sampling Procedures.

During the collection phase,

ileal digesta and feces were collected. A 4-d collection
phase was used with three collection times for ileal
digesta daily. Each collection lasted for 1 h. For
example, on d 1, sampling took place at 0700, 1100,
and 1500. The sampling times advanced 1 h for the
three remaining days. Total feces excreted on each of
the 4 d were collected from the floor of the pen,
weighed, composited, and frozen at

−

4

°

C. Ileal digesta

was collected by attaching a Whirlpak bag (Pioneer
Container, Cedarburg, WI) to the cannula hose clamp
with a rubber band. Before attachment of the bag, the
inside of the cannulas was scraped clean with a
spatula and initial digesta discarded. Dogs were
encouraged to move around freely during ileal collec-
tions. Elizabethan collars were utilized at collection
times so that dogs would not pull the bag from the
cannula. Immediately after collection of ileal digesta,
pH was recorded. Samples then were frozen in their
individual bags at

−

4

°

C. After completion of the trial,

all of the digesta collected was composited for each dog
in each period and refrozen at

−

4

°

C. A portion of the

composited ileal digesta was frozen separately for
analysis of short-chain fatty acids ( SCFA) .

Ileal digesta and feces were freeze-dried in a Tri-

Philizer



MP microprocessor-controlled lyophilizer

(FTS Systems, Stone Ridge, NY). After drying, foods,
orts, ileal digesta, and feces were ground through a
2-mm screen in a Wiley mill.

Chemical Analyses.

Foods, orts, ileal contents, and

feces were analyzed for DM, OM, and ash content
using AOAC (1984) procedures. Crude protein was
calculated from Kjeldahl N values ( N

×

6.25) for all

samples (AOAC, 1984). The total lipid content of
diets, orts, ileal digesta, and feces was determined by
acid hydrolysis followed by ether extraction according
to the procedures of AACC (1983) and Budde (1952).
The total dietary fiber ( TDF) content of diets, orts,
ileal digesta, and feces was determined according to
the method of Prosky et al. (1985). The ileal digesta
pH was measured with a flat-glass electrode. Gross
energy content of diets, orts, ileal digesta, and feces
was determined by bomb calorimetry (model 1261,
Parr Instrument, Moline, IL). Ileal and fecal samples
were prepared for Cr analysis according to the method
of Williams et al. (1962), and Cr concentrations were
measured using an atomic absorption spectrophotome-
ter (model 2380, Perkin-Elmer, Norwalk, CT). For
amino acid analysis, approximately 100 mg of food
and 150 mg of ileal contents were hydrolyzed in 15 mL
of 6 N HCl for 22 h at 105

°

C according to the

procedure of Spitz (1973). The amino acid composi-
tion of the resulting hydrolysate was measured on an
amino acid analyzer (model 126, Beckman Instru-
ments, Palo Alto, CA) using sodium citrate buffers
and a ninhydrin detector. Short-chain fatty acids were

VARYING FIBER SOURCES IN DOG FOOD

1643

Table 2. Chemical composition of diets fed to ileal-cannulated dogs

a

CON = 0% supplemental fiber control; BP = 7.5% beet pulp; LCM (low-cellulose mixture) = a blend of

5% pectin and 2.5% Solka Floc; HCM (high-cellulose mixture) = a blend of 5% Solka Floc and 2.5% pectin;
SF = 7.5% Solka Floc.

Diet

a

Item

CON

BP

LCM

HCM

SF

Dry matter, %

91.5

92.8

92.2

93.1

93.3

% DM

Organic matter

93.0

92.2

92.8

92.8

92.6

Crude protein

34.2

34.7

33.7

33.8

34.3

Fat

23.6

23.1

24.2

23.2

22.5

Total dietary fiber

2.6

8.6

9.7

9.7

8.7

Gross energy, kcal/g

5.6

5.5

5.6

5.5

5.5

Amino acids

Essential

Arginine

2.4

2.4

2.2

2.3

2.3

Histidine

.81

.84

.75

.76

.80

Isoleucine

1.5

1.5

1.4

1.4

1.4

Leucine

2.6

2.7

2.4

2.5

2.5

Lysine

2.4

2.5

2.1

2.2

2.3

Methionine

.80

.71

.56

.68

.76

Phenylalanine

1.5

1.5

1.4

1.4

1.4

Threonine

1.4

1.4

1.3

1.3

1.3

Valine

1.8

1.9

1.7

1.7

1.7

Non-essential

Alanine

2.3

2.4

2.2

2.2

2.3

Aspartate

3.3

3.4

3.1

3.2

3.2

Glutamate

5.1

5.2

4.7

4.9

5.0

Glycine

3.2

3.3

3.0

3.1

3.1

Proline

2.2

2.3

2.0

2.1

2.1

Serine

1.5

1.5

1.4

1.4

1.4

Tyrosine

1.0

1.1

.93

.98

.99

analyzed by gas-liquid chromatography. Samples were
prepared according to the method of Erwin et al.
(1961). Concentrations of individual and total SCFA
in the diluted supernatants were determined with a
gas chromatograph (model 5890A, Hewlett-Packard,
Avondale, PA)

equipped with a flame-ionization

detector. The column used was packed with GP 10%
SP1200/1% H

3

PO

4

on 80/100 ChromasorbW AW (Su-

pelco, Bellefonte, PA). The column was 1.83 m in
length and had an internal diameter of 4 mm.
Nitrogen was used as a carrier gas with a flow rate of
75 mL/min. Oven temperature was 125

°

C, and detec-

tor and injector temperatures were 180

°

C and 175

°

C,

respectively. For all procedures, samples were ana-
lyzed in duplicate.

Calculations.

Dry matter (g/d) excreted as feces

was calculated by dividing the Cr intake (mg/d) by
fecal Cr concentration (mg Cr/g feces). Nutrient flows
at the ileum and nutrients in feces were calculated by
multiplying the DM flow by the concentration of the
nutrient in the ileal or fecal DM. Ileal and apparent
total tract nutrient digestibilities were calculated as
nutrient intake (g/d) minus the ileal or fecal (respec-
tively) nutrient flow (the quantity) divided by
nutrient intake (g/d).

Statistical Analyses.

Data were analyzed as a 5

×

5

Latin square design by the General Linear Models

procedure of SAS (1989). Model sums of squares were
separated into treatment, period, and dog effects.
Sums of squares for diet effects were separated further
into orthogonal contrasts. Orthogonal contrasts used
were 1 ) control vs. supplemental fiber treatments; 2 )
BP vs. LCM, HCM, and SF; 3 ) linear cellulose effect,
and 4 ) quadratic cellulose effect. Least squares means
(because of occasional missing data points) were
calculated for nutrient and energy intakes, ileal and
apparent total tract nutrient digestibilities, ileal pH,
and ileal SCFA. Level of probability for statistical
significance was defined as P < .05 unless otherwise
stated.

Results and Discussion

Chemical composition.

The chemical composition of

the diets is presented in Table 2. Diets contained
similar concentrations of DM (92.6% on average), OM
(92.7% of DM), fat (23.3% of DM), CP (34.1% of
DM), and gross energy (5.5 kcal/g DM). All sup-
plemental fiber-containing diets had similar levels of
TDF (range, 8.6% for the diet containing BP to 9.7%
for the diets containing the LCM and the HCM).
Fahey et al. (1990a) fed 30 English pointers meat-
based diets with beet pulp added at levels of 0, 2.5,

MUIR ET AL.

1644

Table 3. Nutrient intakes and digestibilities by ileal-cannulated dogs

a

CON = 0% supplemental fiber control; BP = 7.5% beet pulp; LCM (low cellulose mixture) = a blend of

5% pectin and 2.5% Solka Floc



; HCM (high cellulose mixture) = a blend of 5% Solka Floc



and 2.5%

pectin; SF = 7.5% Solka Floc



.

b

CON vs BP, LCM, HCM, and SF ( P < .05).

c

BP vs LCM, HCM, and SF ( P < .10).

d

Quadratic cellulose effect ( P < .10).

e

Linear cellulose effect ( P < .10).

f

Linear cellulose effect ( P < .05).

g

BP vs. LCM, HCM, and SF ( P < .05).

Diet

a

Item

CON

BP

LCM

HCM

SF

SEM

Intake, g/d

Dry matter

b

368

421

423

447

459

20.4

Organic matter

b

373

418

425

445

455

20.7

Crude protein

b

126

146

143

154

157

7.3

Fat

b

87

96

105

105

103

5.1

Total dietary fiber

b

10

36

40

43

39

2.7

Gross energy,

b

kcal/d

2,042

2,324

2,353

2,500

2,528

120.0

Digestion at ileum, %

Dry matter

76.6

67.8

64.1

74.0

73.4

5.0

Organic matter

83.6

74.9

71.5

79.2

78.7

3.8

Crude protein

73.4

70.9

66.1

76.7

77.8

4.4

Fat

c

95.0

93.2

93.8

96.1

95.7

.93

Total dietary fiber

−

12.4

−

23.4

−

22.3

−

8.1

−

9.8

24.2

Gross energy

85.6

79.2

76.3

82.8

82.5

3.2

Total tract digestion, %

Dry matter

bd

85.3

81.5

82.4

77.1

78.5

1.3

Organic matter

bcd

90.9

86.3

86.7

82.2

83.1

1.0

Crude protein

e

85.1

83.9

83.2

82.4

86.7

1.2

Fat

f

95.1

94.3

94.0

94.9

95.3

.36

Total dietary fiber

fg

23.8

35.0

47.8

5.0

−

12.5

7.1

Gross energy

bd

91.1

87.4

87.7

84.8

85.8

.80

5.0, 7.5, 10.0, and 12.5%. They found that inclusion of
dietary beet pulp at levels up to 7.5% resulted in no
severe reductions in total tract nutrient digestibility
or energy utilization and seemed to be an acceptable
source of dietary fiber in a meat-based dog diet.
Similar TDF concentrations across treatments allow
comparisons of digestive responses to different sources
of dietary fiber. Diets contained similar concentrations
of individual amino acids, with essential amino acids
ranging, on average, from a high of 2.5% for lysine to a
low of .70% for methionine, and with non-essential
amino acids ranging, on average, from 1 to 5% for
tyrosine and glutamate, respectively.

Intake and digestibility.

Intakes of DM, OM, TDF,

fat, GE, and CP did not differ among fiber-sup-
plemented treatment groups (Table 3). Dogs ingest-
ing the control diet consumed less ( P < .05) food than
dogs consuming the other treatments. Fahey et al.
(1990a) fed dogs meat-based diets with increasing
levels of added BP and noted a linear increase ( P <
.05) in DM intake as level of dietary BP increased.
This was attributed to a dilution in nutrient supply
and slightly increased DM levels in diets sup-
plemented with the higher concentrations of fiber.
Thus, as dietary energy content was diluted by the
presence of DF, dogs consumed a greater amount of

diet. Intake of nutrients was highest usually for dogs
fed SF and HCM diets.

No differences among diets were noted in apparent

ileal digestibilities of DM, OM, CP, TDF, or GE (Table
3). However, dogs fed the LCM diet had numerically
lower ( P > .10) ileal digestibilities of all these
constituents, except TDF, than did dogs fed the other
diets. In addition, as regards the supplemental fiber
treatments, both the HCM and the SF treatments
resulted in numerically higher ( P > .10) ileal digesti-
bilities of DM, OM, CP, fat, TDF, and GE compared
with the LCM treatment. Atallah and Melnik (1982)
fed growing rats purified diets containing various
pectins added at the 10% level. These pectins differed
in molecular weight ( MW) and degrees of esterifica-
tion. These researchers noted that pectin-containing
diets led to a decrease of eight percentage units, on
average, in apparent total tract digestion of N;
digestibilities ranged from 79.4% for the pectin with
the highest MW and degree of esterification to 87.4%
for the pectin with the lowest degree of esterification.
Their control diet, which contained no pectin, had an
apparent total tract N digestibility of 92%, thus
indicating that pectin has the ability to significantly
depress N digestibility. Li et al. (1994) fed pigs
isonitrogenous diets with Solka Floc included at levels
of 4.3, 7.3, 10.3, or 13.3% in cornstarch-based soybean

VARYING FIBER SOURCES IN DOG FOOD

1645

meal-containing diets. Apparent ileal digestibilities of
N averaged approximately 73% across treatments.
Apparent ileal and total tract digestibilities were not
affected by the inclusion of Solka Floc at levels up to
13.3%. The trend ( P > .10) for decreased digestibili-
ties by dogs fed LCM, as well as the numerically
higher ( P > .10) digestibility values for dogs fed HCM
or SF, agrees with the results of these two studies.

Apparent total tract digestibilities of DM, OM, and

GE by dogs fed fiber-containing diets were lower ( P <
.05) than values for dogs consuming the control diet.
Apparent total tract DM and GE digestibilities
decreased quadratically ( P < .10) as the level of
dietary cellulose increased. Burrows et al. (1982)
noted a linear decrease in apparent total tract
digestibility of DM when dogs were fed a meat-based
diet with Solka Floc added at increasing levels (0, 3,
6, and 9%). Apparent total tract digestion of OM
followed a similar pattern. In our study, digestibility
of OM in BP-containing diets was higher than the
mean value for the other supplemental fiber-contain-
ing diets. Fahey et al. (1990a) reported a DM
digestibility of 86.2% and an OM digestibility of 89.0%
when apparent total tract digestibilities were meas-
ured in dogs fed a meat-based diet with 7.5%
supplemental BP. The DM and OM apparent total
tract digestibilities observed in this trial (81.5 and
86.3%, respectively) for dogs fed the BP treatment
were slightly lower. This difference could be attributed
to age and(or) breed of dog, housing arrangements
(metabolism cage vs run), marker usage, or cannula-
tion of the dog. Apparent total tract digestibility of GE
was 87.7% for dogs consuming the LCM, whereas dogs
consuming the HCM and SF had an average GE total
tract digestibility of 85.3%. Data indicate that diets
containing higher concentrations of soluble fiber have
two to four percentage units greater total tract DM
and OM digestibility than diets with higher concentra-
tions of insoluble fiber.

Apparent total tract digestibility of TDF was higher

( P < .05) for dogs fed BP compared with the other
fiber treatments. However, this was largely due to the
low TDF digestibility values for the HCM and SF
treatments. Also a negative linear effect of cellulose
concentration was noted ( P < .05). The negative
digestibility for the SF-containing diet indicates that
none of this fiber source was digested by the dogs.
Apparent total tract digestion of fat ( P < .05) and CP
( P < .10) exhibited positive linear responses to dietary
cellulose concentrations. Mosenthin et al. (1994)
reported apparent ileal digestibilities of 74.1 and 69%
for OM and CP digestion, respectively, for a diet
containing 7.5 g pectin/100 g cornstarch-based diet fed
to ileal-cannulated pigs. This agrees well with the
apparent ileal digestion values for OM (71.5%) and
CP (66.1%) when dogs were fed the LCM, which
contained 5% pectin and 2.5% cellulose. In the same
study, Mosenthin et al. (1994) reported apparent
total tract digestibilities of 94.7 and 85.8% for OM and

CP, respectively, by pigs fed pectin. Again, this is in
agreement with apparent total tract OM (86.7%) and
CP (83.2%) digestibility values obtained for dogs fed
the LCM. Total dietary fiber digestibilities indicate
that soluble fibers are better energy substrates for
gastrointestinal microorganisms than are insoluble
fibers. Another aspect of digestion important in dog
nutrition is the moisture content of fecal material and
the amount of feces excreted by the animal. In this
study, dogs fed the control, BP, LCM, HCM, and SF
treatments had average fecal DM concentrations of 45,
29, 39, 45, and 47%, respectively. Average wet fecal
outputs ( g wet feces excreted/d) were 118, 267, 191,
238, and 203, respectively. Inclusion of BP in diets
resulted in the highest fecal moisture content as well
as the greatest fecal volume. Treatments high in
cellulose also resulted in high fecal volumes. The
results of our study agree with the conclusion drawn
by Eggum (1995) that the inclusion of dietary fiber,
in general, decreases apparent protein digestibility;
insoluble fiber increases fecal bulk and N excretion
due to increased excretion of cell wall-bound protein,
and soluble fiber increases fecal bulk and N excretion
due to increased microbial N excretion.

Amino acid intakes and digestibilities.

To our

knowledge, this is the only study in which amino acid
ileal digestibility has been determined in dogs. Amino
acid intakes were similar among supplemental fiber
treatment groups, but greater than intakes of dogs
consuming the control diet for all amino acids
measured except methionine (Table 4). A positive
linear cellulose effect was noted for intakes of
methionine ( P < .05), lysine, and tyrosine ( P < .10),
perhaps reflecting OM and CP intake patterns. Amino
acid intake data generally followed the pattern noted
for CP intake.

Amino acid digestion at the distal ileum was

similar among treatments, and was not affected by
treatment for all amino acids except lysine, for which
a positive linear effect ( P < .05) of cellulose concentra-
tion was noted (Table 5). A trend ( P > .10) for SF
having the highest ileal amino acid digestibilities and
the LCM having the lowest ileal digestibilities for all
amino acids was noted. These results agree with those
of the study by Mosenthin et al. (1994), in which pigs
fed 7.5% pectin had significantly lower ileal amino
acid digestibilities than the control. Those researchers
noted an average decrease in apparent ileal digestibil-
ity of 14.1 percentage units for essential amino acids
and 17.6 percentage units for non-essential amino
acids when pectin was included in the diet. The
depression in apparent ileal digestibility of amino
acids noted for dogs fed the LCM was 5.9 percentage
units, on average, for essential amino acids and 7.5
percentage units, on average, for non-essential amino
acids. When Li et al. (1994) included Solka Floc at
levels of 4.3, 7.3, 10.3, and 13.3% in an isonitrogenous
cornstarch-based soybean meal-containing diet for
pigs, no differences ( P > .05) were noted among

MUIR ET AL.

1646

Table 4. Amino acid intakes (g/d) by ileal-cannulated dogs

a

CON = 0% supplemental fiber control; BP = 7.5% beet pulp; LCM (low-cellulose mixture) = a blend of

5% pectin and 2.5% Solka Floc; HCM (high-cellulose mixture) = a blend of 5% Solka Floc and 2.5% pectin;
SF = 7.5% Solka Floc.

b

CON vs. BP, LCM, HCM, and SF ( P < .05).

c

Linear cellulose effect ( P < .10).

d

Linear cellulose effect ( P < .05).

e

CON vs. BP, LCM, HCM, and SF ( P < .10).

Diet

a

Item

CON

BP

LCM

HCM

SF

SEM

Essential amino acids

Arginine

b

8.7

10.4

9.4

10.3

10.6

.5

Histidine

b

3.0

3.6

3.2

3.4

3.6

.2

Isoleucine

b

5.4

6.5

5.7

6.2

6.6

.3

Leucine

b

9.6

11.6

10.4

11.2

11.7

.6

Lysine

bc

8.7

10.7

9.1

9.9

10.8

.6

Methionine

d

2.9

3.0

2.4

3.0

3.5

.2

Phenylalanine

b

5.3

6.5

5.8

6.2

6.4

.3

Threonine

b

5.4

6.5

5.9

6.3

6.6

.3

Valine

b

6.6

8.0

7.0

7.6

8.0

.4

Non-essential amino acids

Alanine

b

8.4

10.1

9.1

9.9

10.4

.5

Aspartate

b

12.1

14.6

13.1

14.2

14.9

.8

Glutamate

b

18.5

22.2

20.0

21.7

22.7

1.2

Glycine

b

11.6

13.9

12.7

13.9

14.3

.7

Proline

b

7.9

9.7

8.6

9.5

9.7

.5

Serine

b

5.4

6.6

6.0

6.4

6.6

.4

Tyrosine

ce

3.8

4.6

3.9

4.4

4.5

.2

Table 5. Amino acid digestibilities (%) at the distal ileum of cannulated dogs

a

CON = 0% supplemental fiber control; BP = 7.5% beet pulp; LCM (low-cellulose mixture) = a blend of

5% pectin and 2.5% Solka Floc; HCM (high-cellulose mixture) = a blend of 5% Solka Floc and 2.5% pectin;
SF = 7.5% Solka Floc.

b

Linear cellulose effect ( P < .05).

c

TEAA = total essential amino acids.

d

TNEAA = total non-essential amino acids.

e

TAA = total amino acids.

Diet

a

Item

CON

BP

LCM

HCM

SF

SEM

Essential amino acids

Arginine

86.8

87.3

83.4

87.9

88.7

2.8

Histidine

76.2

75.4

68.7

77.6

80.0

4.9

Isoleucine

77.9

78.3

71.1

79.1

81.5

4.3

Leucine

78.9

79.1

74.1

81.0

82.6

4.0

Lysine

b

80.3

80.0

68.2

78.6

83.5

4.6

Methionine

86.0

87.2

86.2

86.7

87.7

3.3

Phenylalanine

75.2

72.8

69.0

77.4

78.0

5.4

Threonine

69.0

67.2

62.7

72.0

73.6

6.0

Valine

74.7

74.7

68.9

77.2

79.0

4.7

Non-essential amino acids

Alanine

80.1

79.6

74.4

81.6

82.7

4.0

Aspartate

66.1

60.0

53.3

65.0

68.1

7.9

Glutamate

79.1

78.3

71.9

80.2

81.8

4.4

Glycine

76.6

74.9

68.2

77.3

77.7

5.2

Proline

75.8

75.2

69.6

78.0

78.4

4.8

Serine

68.6

66.5

62.2

71.7

71.7

6.5

Tyrosine

72.9

72.2

67.0

76.4

77.3

5.8

TEAA

c

78.7

78.3

72.3

80.0

82.0

4.3

TNEAA

d

74.6

72.9

66.9

76.0

77.3

5.4

TAA

e

76.4

75.3

69.3

77.8

79.4

4.9

VARYING FIBER SOURCES IN DOG FOOD

1647

Table 6. Short-chain fatty acid (SCFA) concentrations and molar proportions in

digesta from the distal ileum and pH at the ileum of cannulated dogs

a

CON = 0% supplemental fiber control; BP = 7.5% beet pulp; LCM (low-cellulose mixture) = a blend of

5% pectin and 2.5% Solka Floc; HCM (high-cellulose mixture) = a blend of 5% Solka Floc and 2.5% pectin;
SF = 7.5% Solka Floc.

b

BP vs. LCM, HCM, and SF ( P < .10).

Diet

a

Item

CON

BP

LCM

HCM

SF

SEM

Ileal pH

7.15

7.43

7.16

7.19

7.22

.09

Total ileal SCFA, mM

b

2.3

3.2

1.8

2.4

2.0

.53

SCFA molar proportions,

mol/100 mol

Acetate

76.7

72.7

77.7

76.3

77.8

2.4

Propionate

b

14.6

17.7

15.7

14.8

16.1

.9

Isobutyrate

0

.6

0

.5

0

.3

Butyrate

7.7

7.7

5.5

7.4

5.5

1.4

Isovalerate

.9

1.3

1.1

1.1

.5

.6

treatments in apparent ileal amino acid digestibilities.
These workers noted average apparent ileal amino
acid digestibility values of 78.9 and 77.9% for essential
and non-essential amino aids, respectively, for those
animals fed 7.3% Solka Floc. In our study, dogs fed
7.5% Solka Floc had ileal digestibility values of 82.0
and 77.3% for the essential and non-essential amino
acids, respectively. Data from the two studies are in
general agreement. Total essential amino acid digesti-
bility ( TEAA) at the ileum ranged from 72.3% for the
LCM to 82% for SF; total non-essential amino acid
( TNEAA) apparent ileal digestibility ranged from
66.9% for the LCM to 77.3% for SF; total amino acid
( TAA) digestibility at the ileum ranged from 69.3%
for the LCM to 79.4% for SF. The TEAA, TNEAA, and
TAA digestibilities were not affected by supplemental
fiber treatment, but the trend ( P > .10) indicated that
SF inclusion in the diet resulted in the highest ileal
digestibilities of amino acids, whereas the LCM
treatment resulted in the lowest ileal digestibilities.
Perhaps this was due to the soluble-viscous-fermenta-
ble nature of the pectin, which could alter rate of
passage of digesta through the small intestine, as well
as the viscosity of the intraluminal contents (as
previously described), or to small intestinal fermenta-
tion. In addition, the viscous nature of pectin limits
access of digestive enzymes to substrates, and this
could have a bearing on our results as well.

Short-chain fatty acids and pH.

Averaged across

treatments, ileal pH (7.23) was not affected by
inclusion of fiber in the diets (Table 6). Total ileal
SCFA ranged from 1.8 mM for the LCM to 3.2 mM for
BP; a difference ( P < .10) between BP and the other
treatments was noted. These values indicate a limited
amount of microbial fermentation occurring in the
small intestine. Acetate was present in the highest
molar proportion (average 76.2 mol/100 mol), fol-
lowed by propionate (average 15.8 mol/100 mol) and
butyrate (average 6.8 mol/100 mol). Isobutyrate,

isovalerate, and valerate were not present in any
significant amounts. Propionate molar proportion was
lower ( P < .10) for cellulose treatments than for the
BP treatment.

In conclusion, incorporation of dietary fiber at a

level of 7.5% did not adversely affect apparent ileal
digestibilities of DM, OM, TDF, fat, GE, CP, or amino
acids. Specifically, apparent ileal digestibilities of CP
and amino acids were not affected by fiber inclusion,
regardless of its solubility, viscosity, or fermentability.
Greater variability in data obtained with ileal digesta
and use of marker techniques compared with total
fecal collections may have contributed to this lack of
effect; however, interesting biological trends were
noted in the data. Indeed, much of the CP and amino
acid intake and digestibility data showed significant
effects among treatments if a P value between .10 and
.20 was accepted. These effects were expressed
primarily as a negative influence of soluble, fermenta-
ble fiber (pectin) on ileal amino acid and CP
digestibilities.

Apparent

total

tract

digestion

of

nutrients was influenced by the presence of fiber as
well as by the mixtures of dietary fibers fed.

Implications

Inclusion of pectin in meat-based dog diets tended

to depress apparent nutrient digestibilities at the
distal ileum but had little effect on apparent total
tract nutrient digestibilities, apparently as a result of
active microbial fermentation occurring in the large
bowel of the dog. Cellulose incorporation into diets had
little effect on apparent nutrient digestibilities at the
ileum but resulted in lower apparent total tract
digestibility values for nutrients due to the refractory
nature of cellulose and its general lack of susceptibil-
ity to microbial fermentation in the large bowel.
Amino acid nutrition of dogs could potentially be

MUIR ET AL.

1648

compromised by the presence of a dietary fiber that is
both soluble and viscous.

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