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Effect of dietary fiber levels on performance, gizzard development, intestinal
morphology, and nutrient utilization in meat ducks from 1 to 21 days of age
H. Y. Han, K. Y. Zhang, X. M. Ding, S. P. Bai, Y. H. Luo, J. P. Wang, and Q. F. Zeng1
Institute of Animal Nutrition, Key Laboratory for Animal Disease-Resistance Nutrition of China, Ministry of
Education, Sichuan Agricultural University, Chengdu, Sichuan, China, 611130
ABSTRACT The objective of this experiment was to
determine the effects of dietary fiber levels on growth
performance, gizzard development, intestinal morphol-
ogy, and nutrient utilization in Cherry Valley meat
ducks. In total, 720 1-day-old ducklings were fed with
starter diets (120 ducklings, 8 pens of 15 ducklings, on
each diet) containing 6 levels of crude fiber (CF, 1.46,
3.09, 4.15, 6.18, 7.52, and 9.03%, based on analysis) for
21 d. Then, on d 22, ducks fed all of the starter di-
ets were transferred to a grower diet (containing 4%
CF) to examine the residual effect of starter dietary
fiber levels until 35 d. Body weight (BW), body weight
gain (BWG), feed intake (FI), feed to gain ratio (F:G)
were recorded/calculated weekly. Ducks were sampled
for gizzard development and intestinal morphology de-
termination on d 7, 14, and 21. Nutrient utilization
was assessed using 25- to 27-day-old ducks. The re-
sults showed that BW (d 21), BWG (d 15 to 21, d
1 to 21), and F:G (d 15 to 21, d 1 to 21, and d 1 to 35)
were increased quadratically (P<0.01), and FI (all
periods except for d 22 to 35) was increased linearly
(P<0.01), when starter dietary CF levels increased
from 1.46 to 9.03%. Ducks under 3.09% and 4.15% CF
starter diets had decreased 1 to 35 d FI and F:G when
compared to ducks under other starter diets. When
compared to ducks fed 1.46% and 3.09% CF starter
diets, ducks fed starter diet containing 7.52% CF had
increased gizzard development, jejunal morphology, en-
ergy retention, excreta nutrients availability, and stan-
dardized ileal digestibility (SID) of Arg, Ile, Leu, Thr,
Val, Asp, Ala, Glu, Gly, Pro, Ser, and total amino acids.
In conclusion, meat ducks from 1 to 21 d of age could
adapt to a wide range (3.09% to 7.52%) of dietary fiber
levels.
Key words: dietary fiber, gizzard, meat ducks, performance, nutrients utilization
2017 Poultry Science 96:4333–4341
http://dx.doi.org/10.3382/ps/pex268
INTRODUCTION
China is the largest duck-producing country, account-
ing for more than 75% of the global duck market
(Zeng et al., 2015a). Dietary regimens that would in-
crease duck production efficiency are of great interest
for China’s duck nutritionists. Recently, many studies
reported that the dietary inclusion of insoluble fiber
products improved digestive physiology of broilers and
laying hens (Mateos et al., 2012; Lim et al., 2013). Of
particular note is the observation that dietary insol-
uble fiber increases the weight and length of poultry
gastrointestinal tract (GIT), which are important eco-
nomic traits in China (Jim´enez-Moreno et al., 2009a;
Sacranie et al., 2012; Ling et al., 2014). In the study
of Han et al. (2016), dietary inclusion of 1,500 mg/kg
nanocrystalline cellulose dramatically improved growth
performance of ducks. While no specific research in
ducks has been conducted, these mentioned studies
C
2017 Poultry Science Association Inc.
Received July 20, 2016.
1Corresponding author: zqf@sicau.edu.cn
suggest that an appropriate dietary fiber regimen may
benefit the duck industry.
The type and level of dietary fiber were directly con-
cerned with GIT development and growth performance
of broilers (Jim´enez-Moreno et al., 2009a). Reports
have indicated that both soluble and insoluble non-
starch polysaccharides (NSP) affect digestive organs
development (Banfield et al., 2002;Jim´enez-Moreno
et al., 2009b) and intestinal morphology (Iji et al., 2001;
Jim´enez-Moreno et al., 2013) of broilers. In recent years,
studies have noted the positive effects of dietary insol-
uble fiber (e.g., rice husk) on gizzard activity and GIT
reflux, which might promote nutrient digestibility (Het-
land et al., 2004). In the study of Rezaei et al. (2011),
dietary supplementation of micronized insoluble fiber
particles increased growth performance, the ileal villus
height to crypt depth ratio, and the number of gob-
let cells in broilers. In addition, dietary fiber (10% oat
hulls) stimulates HCl and jejunal bile acid concentra-
tion and improves jejunal amylase activity, which re-
sults in increased nutrient utilization (Hetland et al.,
2003). However, very limited information is available in
meat ducks. Thus, the aim of this study is to investigate
the influence of dietary insoluble fiber levels coming
4333
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4334 HAN ET AL.
Table 1 . Ingredients and compositions of the experimental diets (%, dry matter basis).
Ingredients Diet 1 Diet 2 Diet 3 Diet 4 Diet 5 Diet 6
Corn 0.00 6.30 12.60 18.90 25.20 31.50
Soybean meal 26.20 25.89 25.59 25.29 24.98 25.19
Wheat husk 0.00 3.00 6.00 9.00 12.00 15.00
Rice husk 0.00 3.00 6.00 9.00 12.00 15.00
Wheat middling 10.00 8.00 6.00 4.00 2.00 0.00
Corn starch 46.50 37.20 27.90 18.60 9.30 0.00
Corn protein meal 9.52 8.55 7.58 6.61 5.64 4.66
Rapeseed oil 0.60 1.42 2.25 3.07 3.90 4.72
Limestone 0.95 0.98 1.01 1.04 1.07 1.10
Dicalcium phosphate 1.85 1.80 1.75 1.70 1.65 1.59
L-Lysine, HCL 0.23 0.23 0.23 0.23 0.23 0.23
DL-Methionine 0.16 0.17 0.17 0.18 0.18 0.19
Threonine 0.01 0.02 0.02 0.03 0.04 0.05
Tryptophan 0.08 0.08 0.08 0.08 0.08 0.08
Bentonite 2.87 2.33 1.79 1.24 0.70 0.16
Sodium chloride 0.35 0.35 0.35 0.35 0.35 0.35
Choline chloride 0.15 0.15 0.15 0.15 0.15 0.15
Vitamin premix10.03 0.03 0.03 0.03 0.03 0.03
Mineral premix20.50 0.50 0.50 0.50 0.50 0.50
Total 100.0 100.00 100.00 100.00 100.00 100.00
Calculated value
ME MJ/kg 12.12 12.12 12.12 12.12 12.12 12.12
Crude protein % 19.50 19.50 19.50 19.50 19.50 19.50
Calcium % 0.90 0.90 0.90 0.90 0.90 0.90
Available P % 0.42 0.42 0.42 0.42 0.42 0.42
Digestible Lys % 0.96 0.96 0.96 0.96 0.96 0.96
Digestible Met % 0.46 0.46 0.46 0.46 0.46 0.46
Digestible Thr % 0.63 0.63 0.63 0.63 0.63 0.63
Digestible Trp % 0.26 0.26 0.26 0.26 0.26 0.26
Analyzed value
CF3% 1.46 3.09 4.15 6.18 7.52 9.03
NDF3% 5.47 7.97 10.50 13.07 15.88 18.69
ADF3% 3.24 4.71 5.59 6.68 7.75 9.12
1Provided per kilogram of diet: vitamin A, 8,000 IU; cholecalciferol, 2,000 IU; vitamin E, 5 IU; vitamin K, 1 mg; thiamine,
0.4 mg; riboflavin, 3.2 mg; pyridoxine, 1.2 mg; vitamin B12,6μg; folic acid, 100 μg; niacin, 7 mg; calcium pantothenate, 5 mg.
2Provided per kilogram of diets: Fe (FeSO4·H2O) 80 mg, Cu (CuSO4·5H2O) 8 mg, Mn (MnSO4·H2O) 70 mg, Zn (ZnSO4·H2O)
90 mg, I (KI) 0.4 mg, Se (Na2SeO3)0.3mg.
3CF = crude fiber; NDF = neutral detergent fiber; ADF = acid detergent fiber.
from rice husk and wheat husk on growth performance,
gizzard and intestinal characteristics, and nutrient uti-
lization of meat ducks age 1 to 21 d as well as determine
the residual effect of initial dietary fiber levels in grow-
ing ducks (22 to 35 d).
MATERIALS AND METHODS
The Institutional Animal Care and Use Committee
of Sichuan Agricultural University approved all proce-
dures used in the study.
Birds, Diets, and Management
A total of 720 1-day-old meat ducks (Cherry Valley)
were obtained from a commercial hatchery (Mianyin
duck breeding farm, Sichuan Province, P. R. China),
weighed on arrival, and randomly allotted to 6 treat-
ments (each had 8 replicates of 15 birds) in a completely
randomized manner based on mean body weight. Six
isonitrogenous and isocaloric starter (1 to 21 d) di-
ets (Table 1, 2-mm-diameter pellet, containing 1.46%,
3.09%, 4.15%, 6.18%, 7.52%, and 9.03% crude fiber
(CF), respectively, based on analysis) were formulated
under digestible amino acid basis to meet nutrient re-
quirements of Pekin ducks suggested in NRC (1994). On
d 22, ducks fed all of the starter diets were transferred
to the same grower (22 to 35 d) diet (CF = 4.0%, ME
= 12.12 MJ/kg, CP = 16.5%, 3-mm-diameter pellet)
to examine the residual effect of starter dietary fiber
levels until 35 d. Ducks were reared in pens (2.2 ×1.2
×0.9 m) in a temperature- and humidity-controlled
room with 24-h constant light schedule and free access
to water and feed.
Data Collection and Sampling
Body weight (BW) and feed consumption of ducks
were recorded weekly on pen basis, and BW gain
(BWG), feed intake (FI), and feed to gain ratio (F:G)
were calculated accordingly at the following intervals: 1
to 7 d, 8 to 14 d, 15 to 21 d, and 22 to 35 d, as well as ag-
gregated data for 1 to 21 d and 1 to 35 d). Feed wastage
was recorded daily and the data were used in the cal-
culations of feed consumption. Birds that died during
the experiment were weighed, and the data were used
in the calculations of F:G.
On d 7, 14, and 21, one bird close to the mean BW of
each replicate was individually weighed and euthanized
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DIETARY FIBER LEVELS FOR PEKIN DUCKS 4335
by cervical dislocation (n = 8/treatment). Immediately
after dressing, the gizzard, small intestine, and ceca
were removed. The gizzard, intestine, and ceca were
cleaned of contents and were weighed. Gizzard char-
acteristics included the absolute weight (g) and per-
centage (g/100 g BW) of gizzard. The relative weight
(g/100 g BW) and length (cm/100 g BW) of intestinal
segments including duodenum (from the gizzard to the
bile duct), jejunum (from the bile duct to the Meckel’s
diverticulum), ileum (from the Meckel’s diverticulum
to the ileocecal junction), and cecum were measured
(Sadeghi et al., 2015; Han et al., 2016; Kimiaeitalab
et al., 2017).
Jejunum segments 1.5 cm in length (midway between
the point of entry of the bile ducts and Meckel’s di-
verticulum) were flushed with saline (0.9% NaCl) and
fixed in 100 g/L buffered formalin (pH = 7.0). The fixed
intestinal samples were embedded in paraffin, then sec-
tioned (5 μm) and stained with hematoxylin and eosin
(H&E), and examined by light microscope (Olympus
CX31, Tokyo, Japan). The villus height, crypt depth,
villus height-to-crypt-depth ratio (V/C), mucous mem-
brane layer thickness, and muscle layer thickness were
determined according to Sadeghi et al. (2015).
Digestibility Study
On d 22, 2 birds per pen were randomly selected (12
ducks per treatment, 72 ducks in total) and transferred
to metabolic cages (2 ducks per cage) and fed with the
original starter diets mixed with chromic oxide (0.3%).
Another 12 ducks from the 3.09% CF group were ran-
domly selected based on BW, allotted to 6 cages of 2
ducks, and fed with a nitrogen- (N-) free diet mixed
with chromic oxide (0.3%) (Table 2) in order to de-
termine the basal endogenous amino acid (AA) losses.
After a 3-d adaptive period (d 22, 23, and 24), the
total excreta samples from each cage were collected
for 72 hours (d 25, 26, and 27). Fecal samples were
weighed and then were stored at –20◦C immediately.
These fecal samples were dried at 65 ±5◦C for 24 h, and
then weighed and crushed to pass through a 40-mesh
sieve for dry matter (DM), Cr, N, ether extract (EE),
and energy to calculate apparent metabolizable energy
(AME) and nitrogen-corrected AME (AMEn) accord-
ingtoAdeolaetal.(2006) and Zeng et al. (2015b).
On d 27, when the 72-h excreta collection was finished,
ducks were fed 4 h, and then were euthanized by cervi-
cal dislocation, and the ileal digesta was gently rinsed
with distilled water into plastic containers (Qin et al.,
2017). The collected ileal samples from 2 birds within
a cage were pooled and stored in a freezer at −20◦C
for subsequent analyses of DM, Cr, AA. Ileal digesta
were thawed and dried in an oven at 65◦Cfor3d.
Samples of diets and ileal digesta were ground through
a 0.425-mm screen and thoroughly mixed for analysis.
The standardized ileal digestibility (SID, %) and basal
ileal endogenous losses (BEL) of AA in the assay diets
Table 2 . Ingredient and composition of the nitrogen-free diets
(%, dry matter basis).
Ingredient (%) Content (%)
Corn starch 71.00
Glucose 21.24
Carboxymethyl cellulose 3.00
Limestone 0.51
Dicalcium phosphate 2.33
Sodium bicarbonate 0.54
Potassium chloride 0.25
Potassium sulphate 0.20
Choline chloride 0.10
1Vitamin premix 0.03
2Mineral premix 0.50
Cr2O30.30
Total 100.00
Calculated value
ME MJ/kg 12.12
Crude protein % 0.28
Crude fiber % 3.00
Calcium % 0.74
Available P % 0.42
1Provided per kilogram of diet: vitamin A, 8000 IU; cholecalciferol,
2000 IU; vitamin E, 5 IU; vitamin K3, 1 mg; thiamine, 0.4 mg; riboflavin,
3.2 mg; pyridoxine, 1.2 mg; vitamin B12, 6 μg; folic acid, 100 μg; niacin,
7 mg; calcium pantothenate, 5 mg.
2Provided per kilogram of diets: Fe (FeSO4·H2O) 80 mg, Cu
(CuSO4·5H2O) 8 mg, Mn (MnSO4·H2O) 70 mg, Zn (ZnSO4·H2O) 90 mg,
I (KI) 0.4 mg, Se (Na2SeO3)0.3mg.
were calculated according to Kong and Adeola (2013)
and Qin et al. (2017).
Analytical Evaluation of Feeds, Excreta, and
Ileal Digesta
Dietary neutral (NDF) and acid detergent fiber
(ADF), and CF were determined using method as de-
scribedinVanSoestetal.(1991). Duplicate proximate
analyses were performed on diets, excreta, and ileal di-
gesta samples. DM content of samples was conducted
by drying the samples in an oven at 105◦C for 24 h.
Energy content of the samples was determined by the
adiabatic oxygen bomb calorimeter. Nitrogen, EE, AA,
and Cr contents of the samples were determined accord-
ingtoAOAC(2000) and Zeng et al. (2015b).
Statistical Analysis
All data were analyzed using SAS statistical soft-
ware (version 9.2, SAS Institute Inc., 2004). The ex-
perimental unit was replicate pen (n = 8) for growth
performance, and individual duck for gizzard and in-
testinal characteristics (n = 8) measurements. The ef-
fect of diet fiber level was determined as one-way anal-
ysis of variance (ANOVA) using the GLM procedure
in SAS software (SAS Institute Inc., Cary, NC). When
dietary effect was significant (P<0.05), polynomial
contrasts and the linearity of response to analyzed di-
etary fiber levels were examined using linear, quadratic
regression. The R2was provided to compare these re-
gressions when linear or quadratic effect was significant
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4336 HAN ET AL.
(P<0.05) (Pesti et al., 2009). Probability values ≤0.05
were considered significant.
RESULTS
Dietary CF contents were analyzed to be 1.46%,
3.09%, 4.15%, 6.18%, 7.52%, and 9.03% (Table 1). In
the following results and regressions, all the data were
expressed on an analyzed dietary fiber basis.
Growth Performance
Dietary fiber linearly decreased (P<0.05, Table 3)
BW (d 14), BWG (d 8 to 14), and quadratically affected
(P<0.05) BW (d 21) and BWG (d 1 to 21). When
compared to the 7.52% and 9.03% CF groups, birds fed
diets containing 1.46%, 3.09%, 4.15%, and 6.18% CF
had higher (P<0.05) BW at 14 d of age. However, at 21
d of age, birds fed 1.46% CF and 9.03% CF of diets had
lower (P<0.05) BW than birds fed other experimental
diets. Increasing of dietary fiber levels linearly increased
(P<0.05) FI (all intervals except for 22 to 35 d) and
F:G (all intervals except for 15 to 21 d and 22 to 35
d) of ducks. From 15 to 21 d of age, feeding 1.46% and
9.03% CF of diet significantly increased (P<0.05) F:G
of ducks when compared to the 3.09%, 4.15%, 6.18%,
and 7.52% CF diets.
Starter dietary fiber levels (from 1 to 21 d) had no
effect (P>0.05) on grower (from 22 to 35 d) BW and
BWG of meat ducks. However, the increase of dietary
CF level quadratically affected the 1 to 35 d FI and
F:G. Ducks fed 3.09% and 4.15% CF diets had lower 1
to 35 d FI and F:G than ducks fed with the other diets.
Digestive Organs
Data for gizzard and intestine characteristics are pre-
sented in Table 4. In general, the increase of dietary CF
level linearly increased (P<0.05) gizzard weight and
percentage at 7, 14, and 21 d of age. At 21 d of age,
ducks fed 7.52% CF had the higher gizzard weight and
percentage (P<0.05) when compared to ducks fed with
1.46%, 3.09%, 4.15%, and 6.18% CF diets. The relative
length of the duodenum (d 14), cecum (d 14) and ileum
(d 7), and the relative weight of duodenum (d 21) and
cecum (d 21) were increased linearly (P<0.05) with
the increase of dietary fiber levels.
Jejunal Morphology
Dietary fiber levels presented a quadratically effect
(P<0.05, Table 5) on villi height, crypt depth, mu-
cous membrane layer thickness, and muscle layer thick-
ness at 7 d of age, and birds subjected to 7.52% group
Table 3 . Effect of dietary fiber levels on growth performance of ducks.
Dietary fiber level (%, based on analyzed) P-value
Item 1.46 3.09 4.15 6.18 7.52 9.03 SEM ANOVA Linear Quadratic
Body weight, BW, g
1d 57.8
157.8 57.8 57.8 57.8 57.7 0.05 0.939 0.427 0.712
7 d 2881290 289 292 292 290 3.04 0.905 0.432 0.481
14 d 7832,a 782a787a773a743b727b8.35 <0.0001 <0.0001 0.009
21 d 13953,c 1443a1432a,b 1448a1443a1398b,c 12.4 0.008 0.710 <0.0001
35 d 267042690 2688 2690 2701 2665 37.8 0.986 0.973 0.515
Body weight gain, BWG, g
1–7 d 230 233 232 234 235 232 3.03 0.906 0.426 0.488
8–14 d 495a492a497a481a451b437b7.51 <0.0001 <0.0001 0.009
15–21 d 612c660b645b676a,b 699a671a,b 10.9 <0.0001 <0.0001 0.021
1–21 d 1337c1385a1374a,b 1391a1385a1340b,c 12.4 0.007 0.707 <0.0001
22–35 d 1276 1247 1256 1242 1258 1267 35.4 0.986 0.925 0.496
1–35 d 2613 2632 2630 2632 2643 2608 37.8 0.986 0.972 0.515
Feed intake, FI, g
1–7 d 274d282c,d 289b,c 294a,b 297a,b 302a3.83 <0.0001 <0.0001 0.366
8–14 d 726 743 752 762 752 769 9.90 0.059 0.004 0.416
15–21 d 1147b1095d1101c,d 1140b,c 1189a1223a14.2 <0.0001 <0.0001 <0.0001
1–21 d 2128c2108c2126c2185b2226b2282a18.4 <0.0001 <0.0001 0.009
22–35 d 3080 3022 3001 3053 3061 3072 39.9 0.706 0.665 0.215
1–35 d 5136b,c 5052c5043c5162a–c 5210a,b 5282a47.5 0.007 0.002 0.026
Feed to gain ratio, F:G
1–7 d 1.19c1.21c1.25b1.26b1.26b1.30a0.01 <0.0001 <0.0001 0.686
8–14 d 1.47 d 1.51d1.51d1.59c1.67b1.76a0.03 <0.0001 <0.0001 0.029
15–21 d 1.88a1.66b1.71b1.69b1.71b1.82a0.03 <0.0001 0.512 <0.0001
1–21 d 1.59b,c 1.52e1.55d,e 1.57c,d 1.61b1.70a0.01 <0.0001 <0.0001 <0.0001
22–35 d 2.43 2.44 2.40 2.47 2.45 2.43 0.07 0.989 0.823 0.950
1–35 d 1.97a,b 1.92b1.92b1.96a,b 1.97a,b 2.03a0.02 0.030 0.016 0.015
a–eMeans in the same low with no common superscript are significantly different (P<0.05).
1Means represent 8 pens of 15 ducks per pen.
2Means represent 8 pens of 14 ducks per pen.
3Means represent 8 pens of 13 ducks per pen.
4Means represent 8 pens of 10 ducks per pen.
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DIETARY FIBER LEVELS FOR PEKIN DUCKS 4337
Table 4 . Effect of dietary fiber levels on gizzard and intestine characteristics in ducks at 7, 14 and 21 d of age.
Dietary fiber level (%, based on analyzed) P-value
Item 1.46 3.09 4.15 6.18 7.52 9.03 SEM ANOVA Linear Quadratic
Absolute gizzard weight, g
7 d 9.491,d 12.5c13.4b,c 13.2b,c 14.0a,b 14.8a0.33 <0.0001 <0.0001 <0.0001
14 d 19.5c26.2b28.9a,b 31.4a29.7a30.2a1.05 <0.0001 <0.0001 <0.0001
21 d 28.7 d 39.9c43.8b,c 44.7b,c 51.6a48.3a,b 1.99 <0.0001 <0.0001 0.001
Relative gizzard weight, g/100 g of live BW
7 d 3.31d4.28c4.60b,c 4.57b,c 4.78a,b 5.10a0.12 <0.0001 <0.0001 0.002
14 d 2.50d3.35c3.69b,c 4.06a,b 4.01a,b 4.14a0.14 <0.0001 <0.0001 <0.0001
21 d 2.05c2.77b3.04b3.08b3.60a3.47a0.13 <0.0001 <0.0001 0.007
Relative intestinal length, cm/100 g of live BW
Duodenum
7 d 6.27 6.41 6.49 6.85 6.99 6.56 0.25 0.312 0.086 0.245
14 d 3.04 3.04 3.15 3.37 3.37 3.43 0.12 0.084 0.004 0.921
21 d 2.06 2.01 2.01 2.00 2.10 2.14 0.07 0.698 0.266 0.241
Jejunum
7 d 16.4 17.2 18.0 16.3 18.2 18.3 0.68 0.140 0.085 0.943
14 d 8.12 8.29 8.34 8.37 8.40 8.49 0.20 0.855 0.195 0.776
21 d 5.34 5.12 5.22 5.48 5.51 5.42 0.16 0.445 0.153 0.794
Ileum
7 d 16.3 15.8 16.6 17.3 17.5 17.6 0.62 0.245 0.023 0.910
14 d 8.04 7.72 8.11 7.92 8.51 8.30 0.24 0.262 0.102 0.519
21 d 5.30 4.78 5.37 5.37 5.53 5.38 0.25 0.390 0.235 0.903
Cecum
7 d 5.73 5.80 6.03 6.44 6.45 6.31 0.32 0.423 0.053 0.501
14 d 3.05 3.30 3.21 3.24 3.39 3.45 0.11 0.122 0.011 0.913
21 d 2.37 2.18 2.36 2.50 2.25 2.38 0.10 0.338 0.642 0.954
Relative intestinal weight, g/100 g of live BW
Duodenum, %
7 d 0.57 0.58 0.68 0.62 0.69 0.61 0.05 0.430 0.309 0.232
14 d 0.50 0.54 0.55 0.49 0.53 0.48 0.03 0.452 0.373 0.201
21 d 0.37 0.37 0.35 0.38 0.42 0.40 0.02 0.086 0.018 0.435
Jejunum, %
7 d 1.80 1.67 1.76 1.75 1.89 1.78 0.10 0.736 0.488 0.705
14 d 1.42 1.41 1.47 1.40 1.39 1.32 0.06 0.719 0.231 0.354
21 d 1.05 1.07 1.05 1.11 1.15 1.11 0.04 0.537 0.111 0.792
Ileum, %
7 d 1.63 1.40 1.66 1.65 1.71 1.70 0.12 0.422 0.206 0.764
14 d 1.39 1.21 1.39 1.38 1.40 1.38 0.06 0.222 0.344 0.678
21 d 1.12 1.09 1.08 1.12 1.19 1.15 0.05 0.615 0.195 0.600
Cecum, %
7 d 0.26 0.19 0.22 0.21 0.24 0.22 0.02 0.188 0.581 0.099
14 d 0.23 0.27 0.25 0.25 0.26 0.25 0.02 0.669 0.709 0.377
21 d 0.21 0.23 0.23 0.25 0.25 0.24 0.02 0.312 0.043 0.228
a–dMeans in the same low with no common superscript are significantly different (P<0.05).
1Means represent 8 pens of 1 ducks per pen.
had improved jejunum morphology when compared to
ducks fed the other diets. At 14 d of age, there were
no difference in jejunal morphology among all treat-
ments (P>0.05). However, at 21 d of age, dietary
fiber levels also presented a quadratic effect (P<0.05,
Table 5) on crypt depth and mucous membrane layer
thickness. Birds fed 7.52% CF diet had increased mus-
cle layer thickness (P<0.05) when compared to ducks
fed 1.46%, 3.09%, and 9.03% CF diets.
Nutrients Utilization and SID of Amino Acids
The effects of dietary fiber levels on excreta nutrients
utilization and energy retention are shown in Table 6.
The increase of dietary CF levels linearly decreased
(P<0.05) on excreta DM and energy utilization, yet
linearly increased (P<0.05) excreta N and EE avail-
ability. In general, the diet containing 7.52% CF had
better excreta nutrient utilization and higher AME and
AMEn compared with other dietary treatments. Stan-
dardized ileal digestibility of Arg, Ile, Leu, Thr, Val,
Asp, Ala, Glu, Gly, Pro, Ser, and total AA were lin-
early increased (P<0.05, Table 7) with the increase of
dietary fiber levels, and 7.52% CF group had the higher
SID AA value when compared to 1.46% and 3.09% CF
groups.
DISCUSSION
Performance
The results of current study showed that 1.46% or
9.03% CF diet suppressed the growth performance of
ducks from 1 to 21 d of age, but starter dietary fiber
level had no residual effect on the growth performance
of grower ducks from 22 to 35 d of age. Dietary CF lev-
els had no effect on 35-d BW. These results indicated
that meat duck could adapt a wide range of dietary CF
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4338 HAN ET AL.
Table 5 . Effect of dietary fiber levels on jejunal morphology of ducks at 7, 14, and 21 d of age.
Dietary fiber level (%, based on analyzed) P-value
Item 1.46 3.09 4.15 6.18 7.52 9.03 SEM ANOVA Linear Quadratic
Villus height, μm
7 d 4701630 659 584 685 544 58.1 0.135 0.381 0.029
14 d 1069 932 770 849 710 990 127 0.362 0.388 0.074
21 d 828 842 997 1090 1053 799 114 0.321 0.555 0.058
Crypt depth, μm
7 d 122c139b,c 128b,c 164a,b 179a109c12.5 0.005 0.347 0.007
14 d 189 202 164 181 188 179 17.8 0.783 0.693 0.730
21 d 160b154b240a236a231a139b18.1 0.001 0.509 <0.0001
Villus height/Crypt depth
7 d 4.04b,c 4.63a–c 5.35a3.61c3.85c5.13a,b 0.44 0.047 0.839 0.675
14 d 5.81 4.84 5.39 5.05 3.97 5.89 0.84 0.620 0.707 0.291
21 d 5.37 5.65 4.22 4.61 4.93 5.93 0.67 0.478 0.810 0.111
Mucous membrane layer thickness, μm
7 d 599 768 757 709 848 658 62.6 0.120 0.372 0.042
14 d 1272 1145 918 1022 877 1183 146 0.365 0.388 0.077
21 d 977 1001 1209 1330 1265 964 130 0.209 0.449 0.034
Muscle layer thickness, μm
7 d 101b,c 102b,c 111a,b 111a,b 122a84.2c5.99 0.005 0.607 0.003
14 d 146 182 158 140 145 136 16.5 0.430 0.223 0.450
21 d 171 211 185 186 154 193 21.1 0.531 0.766 0.836
a–cMeans in the same low with no common superscript are significantly different (P<0.05).
1Means represent 8 pens of 1 ducks per pen.
Table 6 . Effect of dietary fiber levels on excreta nutrient utilization and energy retention of ducks.
Dietary fiber level (%, based on analyzed) P-value
Item 1.46 3.09 4.15 6.18 7.52 9.03 SEM ANOVA Linear Quadratic
Dry Matter, % 74.69a70.72b72.04a,b 65.11c73.20a,b 65.78c1.37 <0.0001 <0.0001 0.407
Energy, % 80.49a76.54b77.19a,b 71.67c77.70a,b 70.72c1.18 <0.0001 <0.0001 0.518
Crude Protein, % 50.93b,c 46.18c55.51a,b 46.13c64.44a61.80a3.16 0.001 0.001 0.111
EE1, % 56.52d74.78c82.32b84.70b92.45a92.35a2.00 <0.0001 <0.0001 <0.0001
AME(MJ/Kg) 12.87a,b 12.33b,c 12.48a–c 12.00c13.02a12.02c0.20 0.003 0.102 0.510
AMEn(MJ/Kg) 12.17a11.76a,b 11.81a,b 11.46b12.25a11.36b0.17 0.005 0.049 0.693
a–dMeans in the same low with no common superscript are significantly different (P<0.05).
1EE = ether extract.
content (from 1.46% to 9.03%), and CF in uncommon
feedstuffs was not an anti-nutritional factor for ducks.
One reason may be due to the insoluble fiber compo-
sition of rice husk and wheat husk. Rice husk was the
byproduct of rice, which contains 3.46% crude protein
(CP), 80.8% NDF, 65.5% ADF, 15.4% hemicellulose
(HC), and 43.5% CF; wheat husk was the byprod-
uct of flour, which contained the bran of the wheat
kernel and a very small part of the wheat straw, and
contained 4.48% CP, 75.4% NDF, 50.7% ADF, 24.7%
HC, and 34.9% CF (Zhang et al., 2013). Dietary in-
soluble fiber such as whole rice hulls (60 g/kg) could
be used to enhance growth and uniformity of pullets
(Incharoen and Maneechote, 2013). Dietary inclusion
of oat hulls insoluble fiber, at levels between 2 to 3%,
improved the growth performance of broilers fed low-
fiber diets (Mateos et al., 2012), and dietary inclusion of
3% inulin or cellulose (insoluble fiber source) has been
shown to reduce FI and improved egg production of
broiler breeder hens from 43 to 55 wk of age (Mohiti-
Asli et al., 2012). Hetland and Svihus (2001)reported
that birds were able to maintain adequate BWG when
fed diets containing high levels of insoluble fiber (10%
oat hulls), probably because fiber increases the rate of
passage of the digesta through the digestive system as
well as the physical capacity of the GIT. The other
reason may relate to the duck’s own gastrointestinal
structures and digestive physiology. Ducks can move
their tongue rapidly up and down, which encourages a
pumping action, sucking in a mixture of food and wa-
ter through the open tip of their bill and then squirting
the mixture through fine comb-like structures (lamel-
lae) located evenly about 1 mm apart along the sides of
the bill (Cherry and Morris, 2008). Mallard can swallow
slugs and snails of more than about 1 cm diameter. For
this reason, producers use a large amount of uncommon
feedstuffs in the complete feed for duck in China.
After 14 d of age, feeding diets with 1.46% CF re-
sulted in the increase of F:G in our study. This result
is in line with broilers have been shown to consume lit-
ter material when it is available, presumably to com-
pensate for a lack of structural material in the diet
(Hetland et al., 2004,2005). Jim´enez-Moreno et al.
(2009b) reported that the inclusion of fiber improved
BWG and feed efficiency of broilers from 1 to 21 d
of age, suggesting that young broilers require a min-
imal amount of fiber in the diet when using growth
performance as response. In this study, a 9.03% CF
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DIETARY FIBER LEVELS FOR PEKIN DUCKS 4339
Table 7 . Effect of dietary fiber levels on standardized ileal amino acid digestibility of ducks.
Dietary fiber level (%, based on analyzed) P-value
Item 1.46 3.09 4.15 6.18 7.52 9.03 SEM ANOVA Linear Quadratic
Standardized ileal amino acid digestibility, SID, %
Indispensable amino acids
Arginine 88.91c90.48b,c 94.73a93.95a,b 94.74a92.76a–c 1.39 0.025 0.014 0.021
Isoleucine 78.86b,c 76.35c85.61a,b 83.54a–c 87.30a84.95a,b 2.63 0.044 0.012 0.430
Leucine 86.50a,b 82.08b91.13a90.49a91.59a90.03a2.09 0.023 0.019 0.438
Lysine 87.06 83.63 89.03 90.44 90.11 88.49 2.01 0.200 0.115 0.509
Methionine 91.37 88.28 93.52 94.20 94.02 92.20 1.61 0.117 0.125 0.357
Threonine 72.99b,c 71.13c82.98a81.68a82.31a79.47a,b 2.89 0.022 0.016 0.085
Valine 78.42b,c 76.10c86.10a,b 86.57a88.18a84.44a,b 2.73 0.020 0.008 0.134
Dispensable amino acids
Aspartic acid 76.67b75.74b85.16a85.59a86.50a84.53a2.51 0.010 0.002 0.115
Alanine 83.61 78.49 87.91 87.52 88.83 87.39 2.65 0.081 0.040 0.640
Cysteine 80.40 73.34 84.30 77.80 83.32 83.81 3.35 0.180 0.198 0.537
Glutamic acid 84.63b,c 82.71c90.92a90.73a91.51a89.84a,b 2.06 0.017 0.006 0.170
Glycine 72.59b,c 69.47c82.13a81.94a83.68a80.96a,b 2.95 0.007 0.003 0.161
Proline 81.51b,c 77.89c89.79a87.79a,b 88.81a86.12a,b 2.30 0.006 0.013 0.100
Serine 80.60b,c 78.50c87.97a87.95a88.23a86.04a,b 2.46 0.026 0.013 0.132
Tot a l AA 82.5 2 b,c 79.90c88.76a,b 88.28a,b 89.27a87.37a,b 2.20 0.023 0.011 0.211
a–cMeans in the same low with no common superscript are significantly different (P<0.05).
(18.69% NDF) diet also suppressed growth performance
of starter duck. Walugembe et al. (2014) found that
high dietary fiber content (15% NDF) decreased FI of
broilers (by 9.3%). On the contrary, 10.3% NDF diets
had no adverse effect on FI in broilers and pullets in
the study of Kimiaeitalab et al. (2017). This discrep-
ancy indicates that different species may have differ-
ent gastrointestinal structures and digestive physiology,
and there is a great difference in the digestive physiol-
ogy between ducks and chickens (Jamroz et al., 2001,
2004).
Gastrointestinal Tract Traits
In agreement with Gracia et al. (2009)andJim´enez-
Moreno et al. (2009b), in this study, the absolute and
relative weight of gizzard, and the relative weight and
length of the different segments of the intestine de-
creased as the ducks age. Ducks fed with 7.52% CF
had improved gizzard and intestine development when
compared to ducks under other diets. Similarly, in
Gon´zalez-Alvarado et al. (2008), the inclusion of 3%
oat hulls in diet increased gizzard weight of broiler by
32% (on d 22). Hetland et al. (2003) also reported a sig-
nificant increase in gizzards relative weights in 29-wk-
old Leghorn pullets when dietary supplemented with
insoluble fiber for 14 wk. In addition, the supplemen-
tation of pea fiber, wheat bran and oat bran in broiler
diets caused a significant increase in the weight of the
GIT tract (Jørgensen et al., 1996). Gonz´alez-Alvarado
et al. (2007) found that inclusion of 3% oat hulls or 3%
soy hulls in low-fiber diets (crude fiber 2.5%), oat hulls
caused a significant increase in gizzard weight. However,
Starck (1999) observed that the development of quail
gizzard reached an asymptote when diets contained
30 to 45% NDF; when above 45% NDF, no further
mass increased could be elicited. Similarly, in our study,
increasing dietary CF levels from 7.52% (15.88% NDF)
to 9.02% (18.69% NDF) did not increase the weight and
percentage of gizzard.
Nutrients Utilization and Intestinal
Morphology
In our study, we found that nitrogen and EE avail-
ability, and SID of AA increased with the increase
of dietary CF levels, and ducks fed diets with 7.52%
CF had the highest nitrogen and EE utilization, and
SIDAA. The current results agree with Kimiaeitalab
et al. (2017), who observed that the AMEn of the diet in
broilers increased significantly with 3% sunflower hulls
inclusion. Jim´enez-Moreno et al. (2013) and Gonz´alez-
Alvarado et al. (2010) reported that the supplementa-
tion of 2.5 and 3.0% oat hulls in diets of broilers, energy
content of diets increased by 2.1% and 4.4%, respec-
tively. At the same time, Kalmendal et al. (2011) found
increased EE digestibility when 20% sunflower meal was
included in broiler diet. Transit time of ingested food
from the crop to the gizzard, as well as the gizzard ac-
tivity, could be increased by insoluble fiber, and these
physiological effects could improve mixing of feed parti-
cles with digestive secretions and hence improve diges-
tion and absorption of nutrients (Mateos et al., 2012).
Dietary fiber improved the total tract apparent reten-
tion of feed (Gonz´alez-Alvarado et al., 2007). Mateos
and Sell (1980) reported that a longer retention time
of the digesta might result in an improvement in nu-
trient digestibility. In addition, Hetland et al. (2003)
observed a higher total amount of bile acids in the giz-
zards of birds with access to wood shavings, indicating
that digesta reflux between the gizzard and duodenum
is increased by access to insoluble fiber. The activities
of pepsin and pancreatic general proteolytic activity,
and the mRNA expression for pepsinogens A and C
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4340 HAN ET AL.
were greater in pullets or broilers fed diet with insoluble
fiber (Boguslawska-Tryk, 2005; Yokhana et al., 2016).
The above reports could partly explain why ducks fed
7.52% CF of diet had a better nutrition utilization, and
higher AME or AMEn in the present study.
Furthermore, in the current study, dietary fiber
quadratically affected the villus height, crypt depth,
mucous membrane layer thickness and muscle layer
thickness of duck, in agreement with the results of
Jim´enez-Moreno et al. (2011), who reported that the
inclusion of 2.5% pea hulls in the diet tended to in-
crease VH in the jejunum mucosa but that a further
increase to 7.5% had an opposite effect. Sklan et al.
(2003) reported that the surface area of the small in-
testine of turkeys increased as the level of dietary fiber
increased. In contrast, Kalmendal et al. (2011)reported
a linear decrease in VH as the crude fiber content of the
diet increased from 2.3 to 11.0% with sunflower meal
inclusion. This discrepancy further indicated that meat
duck and broiler have different gastrointestinal struc-
tures and digestible physiology, and duck can adapt a
wide range of fiber in diets in compared with broiler.
CONCLUSIONS
Based on the current observations on growth perfor-
mance, GIT development, nutrients utilization and je-
junal morphology, we concluded that the optimum di-
etary crude fiber level in diet for meat duck from 1 to
21 d of age is 7.52%.
ACKNOWLEDGMENTS
This research was supported by grants from the
National Scientific and Technical Supporting Pro-
gram (2014BAD13B02), Meat Duck Industry Chain
in Sichuan Province (2014NZ0030), Academy of
Kechuang Feed Industry in Sichuan and Sichuan Agri-
cultural University 211 Foundation of China.
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