Directory UMM :Data Elmu:jurnal:A:Animal Feed Science and Technology:Vol81.Issue3-4.Oct1999:
Animal Feed Science and Technology
81 (1999) 205±219
Hydrothermal and b-glucanase effects on the
nutritional and physical properties of starch
in normal and waxy hull-less barley
N.O. Ankraha, G.L. Campbellb,*, R.T. Tylerc,
B.G. Rossnageld, S.R.T. Sokhansanje
a
Department of Animal Sciences, Washington State University, P.O. Box 646351, Pullman, WA 99164-6351, USA
b
Department of Animal and Poultry Science, University of Saskatchewan, 72 Campus Drive,
Saskatoon, SK S7N 5B5, Canada
c
Department of Food Science and Microbiology, 51 Campus Drive, University of Saskatchewan,
Saskatoon, SK S7N 5A8, Canada
d
Crop Development Centre, 51 Campus Drive, University of Saskatchewan, Saskatoon, SK S7N 5A8, Canada
e
Department of Agricultural and Bioresource Engineering, 57 Campus Drive, University of Saskatchewan,
Saskatoon, SK S7N 5A9, Canada
Received 9 November 1998; received in revised form 5 March 1999; accepted 22 June 1999
Abstract
Cereals having a waxy (high amylopectin) starch type may offer advantages for animal feed
associated with heat processing characteristics and/or starch digestibility. Nutritional and physical
characteristics of starch were evaluated in hull-less barley cultivars having a normal or waxy starch
type (228 and 55 g kgÿ1 amylose, respectively). Broiler chicks (192) were fed one of eight diets in a
2 2 2 factorial arrangement from 3 to 21 days of age. The dietary factors included: (1) normal
or waxy starch type barley; (2) pelleted (758C, 160 g kgÿ1 total moisture) or meal form; and (3)
with or without addition of b-glucanase. The pelleted diets were reground to remove any physical
aspect of feeding pellets. There were no differences in body weight gain (BWG), feed intake (FI),
feed-to-gain ratio (F/G) or intestinal starch digestibility due to starch type, nor were treatment
interactions significant (p > 0.05). Feeding waxy starch barley resulted in higher digesta viscosity
than normal starch barley, which was attributed to its higher b-glucan content. Fecal digestibility of
waxy starch was 10% higher (p < 0.05) than that of normal starch. Pelleting did not affect BWG, FI,
or F/G, but reduced (p < 0.05) digesta viscosity by 45% and increased starch digestibility by 17% in
non-enzyme supplemented diets. b-Glucanase addition improved BWG, FI, F/G, and starch
*
Corresponding author. Tel.: +1-306-9664128; fax: +1-306-9664151
E-mail address: leigh.campbell@usask.ca (G.L. Campbell)
0377-8401/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 9 9 ) 0 0 0 8 4 - X
206
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
digestibility (p < 0.01), and eliminated the high digesta viscosity otherwise associated with feeding
the waxy starch diets in meal form.
Starch characteristics during heating were examined with 11 hull-less barley samples (5 waxy
and 6 normal starch types) using a Brabender Viscoamylograph. Waxy starch hull-less barley
exhibited peak viscosity 10oC lower than did normal starch, exhibited a higher peak viscosity,
paste instability and a lower cold-paste viscosity (negative set-back). Waxy barley may offer
advantages in feed processing associated with lower gelatinization temperature, as indicated by
superior pellet hardness in a model pelleting system over a range of added moisture levels and
temperatures. The waxy trait did not compromise chick performance when diets were supplemented
with b-glucanase. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Hull-less barley; Starch; Feed; Pelleting; b-Glucanase
1. Introduction
Barley has historically been considered a less desirable cereal grain for poultry due to
its low energy content. Recent developments that have increased acceptance of barley as a
poultry feed have been the widespread use of dietary enzymes (b-glucanase; Campbell
and Bedford, 1992), and the development of hull-less cultivars. Dietary b-glucanase
relieves the viscous state that arises in the intestine (Salih et al., 1991) with solubilization
of b-glucan originating from the endospermal cell wall in barley. Nutrient digestibility
and absorption, as well as feed intake are reduced, and in the case of starch, its digestion
is shifted distally in the small intestine (Hesselman and Aman, 1986). The production of
`sticky feces' in poultry due to b-glucan also poses litter handling problems and adverse
effects on the environment of intensively housed poultry.
A second development has been the introduction of hull-less barley genotypes, in
which the hull is shed during harvesting. This increases the metabolizable energy
content by removing the dilution effect of the fibrous hull. While b-glucan levels
are affected by both genetics and environment, early hull-less barley cultivars were
notorious for containing high b-glucan, and this occurrence likely prevented their
adoption prior to widespread application of dietary enzymes (Campbell et al., 1993).
With enzyme supplementation the effect of varying b-glucan level is minimal, although
plant breeders have purposely selected for moderate levels in current hull-less barley
varieties.
Both hull-less and conventional barley genotypes occur as waxy types, in which the
starch consists almost entirely of amylopectin (970±1000 g kgÿ1), as opposed to normal
types containing 750±850 g kgÿ1 amylopectin with 150±250 g kgÿ1 amylose (Ullrich
et al., 1986). Amylopectin is more susceptible to a-amylase than amylose suggesting that
waxy starch may be more digestible than the normal starch type. High amylopectin/waxy
starch gelatinizes at a lower temperature compared to normal starch, which could have
obvious benefits in the production of pelleted feeds, since the benefit of cooking could
potentially be achieved with lower temperatures with reduced destructive effects on other
nutrients (e.g. lysine).
The objectives of these experiments were to determine the effects of heat and moisture
on the physical properties of starch in waxy and normal starch type hull-less barley, the
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
207
effects of limited heat and moisture treatment (pelleting) on site and extent of starch
digestion, and to determine the relative response to dietary b-glucanase addition in broiler
chicks.
2. Materials and methods
2.1. Hull-less barley samples
Eleven hull-less barley cultivars were used in the study (Dr. B.G. Rossnagel; Crop
Development Centre, University of Saskatchewan, Saskatoon, SK, Canada) representing
normal (six cultivars: 025; 032; 034; 035; 036; and 038) and waxy (five cultivars: 026;
027; 028; 029; and 037) starch types.
2.2. Broiler chick feeding trial
Two hull-less barley cultivars representing a normal (034) and waxy (037) starch type
were available in sufficient quantity for evaluation in broiler chick diets. The effect of
pelleting or meal form of barley based diets, with or without b-glucanase addition was
examined in broiler chicks. Variables examined were body weight, body weight gain,
feed conversion, digesta viscosity and intestinal starch digestibility.
2.3. Experimental allocation and management
Commercial strain day old broiler chicks were fed a commercial diet for three days.
The chicks were weighed after the third day and randomly allocated to eight dietary
treatments. Each treatment was replicated (cages) six times with four birds per replication
(two males and two females, 192 chicks total). The broiler chicks were housed in battery
brooders and given feed and water ad libitum throughout the experimental period (3±21
days).
2.4. Diets and feeding
A broiler starter diet (Table 1) was formulated based on two hull-less barley cultivars,
containing normal (278 g kgÿ1 amylose, 58 g kgÿ1 b-glucan) or waxy starch (55 g kgÿ1
amylose, 73 g kgÿ1 b-glucan) type. Each of the normal or waxy starch hull-less barley
diets was divided into two portions. One portion was steam (160 g kgÿ1 total moisture)
pelleted through a 5 mm matrix at 75oC (Superior Separator, Process Machine Div.,
Hopkins, Minnesota). The other portion was not pelleted (meal form). The pelleted diets
were reground to a meal form using a hammermill without a screen to remove any effect
due to form differences between the normal and waxy type hull-less barleys. The pelleted
or intact portion was fed with (+) or without (ÿ) a commercial b-glucanase enzyme
addition (derived from Aspergillus niger). The enzyme was added to the meal or reground
pelleted diets. The enzyme preparation was added after pelleting to avoid any potential
confounding attributable to partial enzyme inactivation with heat.
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N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
Table 1
Composition of basal diets (g kgÿ1 air dry basis)
Ingredient
hull-less barleya
soybean meal (480 g/kg CP)
canola oil
limestone
dicalcium phosphate
salt (iodized)
DL-methionine
L-lysine±HCL
Vitamin±mineral premixb
610.0
313.0
40.0
15.0
14.8
2.5
1.2
0.5
3.0
Calculated analysesc
metabolizable energy (MJ/kg)
crude protein
calcium
available phosphorous
lysine
methionine
11.96
240.0
10.3
6.9
13.0
5.5
a
Waxy or normal cultivar. Hull-less barley diets were given with or without enzyme supplementation at
1.0 g kgÿ1. Aspergillus niger, GNC Bioferm, Saskatoon, SK; to provide 1000 b-glucanase units per kg
manufacturer's specification; unit is total reducing sugars (glucose equivalent) released per 10 min at 308C and
pH 4.0.
b
Vitamin±mineral premix provided the following per kilogram of diet: vitamin A, 9000 IU; vitamin D3,
1500 IU; vitamin E, 20 IU; vitamin K, 1.5 mg; riboflavin, 5 mg; pantothenic acid, 11 mg; niacin, 24 mg; folic
acid, 0.75 mg; biotin, 0.1 mg; choline, 500 mg; vitamin B12. 0.012 mg; zinc, 60 mg; copper, 5 mg; manganese,
60 mg; selenium, 0.1 mg.
c
Crude protein calculations based on analysed value; other values were calculated.
2.5. Response criteria
During the experimental period, weekly data collection and calculation included body
weight gain, feed-to-gain ratio. At the termination of the experiment, starch digestibility
was determined at the proximal small intestine (PSI), distal small intestine (DSI) and
feces. PSI was defined as the region from the gizzard to Meckel's diverticulum and DSI,
from Meckel's diverticulum to the ileo±ceco±colic junction.
2.6. Intestinal digesta collection
All the chicks were starved for 14 h (overnight) prior to trial termination and fed again
early the next morning in order to ensure the presence of sufficient digesta for analytical
purposes. Two hours after feeding, broilers from each treatment were sacrificed by
cervical dislocation, dissected, and the digesta collected. Following thorough mixing, one
portion of the pooled digesta sample (4 birds per replication) was taken for viscosity
determination immediately, and the remainder transferred into sealable polythene bags
and immediately frozen in liquid nitrogen (ÿ208C ) for later determination of starch
digestibility. The birds were taken sequentially by treatment replication in order to assure
treatment differences were not confounded by differing time periods after feeding.
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
209
2.7. Measuring viscosity of intestinal contents
A portion of the pooled digesta of intestinal digesta from chicks on each treatment
was centrifuged for 10 min using a micro-centrifuge (1200 g rpm at 25oC)
immediately after collection. The viscosity (centipoise, cps = 0.01 dynes s cmÿ2) of
the supernatant solution was determined using a Brookfield digital viscometer (Model
LVTD VCP-II, Brookfield Engineering Laboratory, Soughton, MA) at 24oC and a shear
rate of 5±22 sÿ1.
2.8. Measuring starch digestion
Chromic oxide (5 g kgÿ1) was added to all the diets for the determination of starch
digestibility at PSI, DSI and excreta regions. The marked diets were fed throughout the
experimental period. Prior to digesta collection, excreta samples were collected daily
from each pen, frozen (ÿ10oC), and the daily collections pooled.
The pooled, frozen excreta samples were dried (60oC for 24 h), and the digesta samples
lyophilized. Feed and the dried excreta and digesta samples were ground (1 mm screen).
Chromic oxide concentration in feed, digesta and fecal samples was measured (Fenton
and Fenton, 1979). Dry matter (DM) of digesta was determined as difference in weight
between fresh and lyophilized samples and DM of feed and feces was determined
according to AOAC procedures (AOAC, 1990). Starch determination was according to
the procedure of Bjorck et al. (1987), in which starch is solubilized, digested using
a-amylase followed by amyloglucosidase, and quantified as glucose released (glucose
oxidase method).
2.9. Starch characteristics during heating
The cooking and pasting characteristics of starch in waxy (5 types) and normal (6
types) hull-less barleys were evaluated using the Brabender viscoamylograph (C.W.
Brabender Instruments, South Hackensack, NJ, USA). Characteristics measured were
gelatinization temperature, peak viscosity in Brabender units (BU), viscosity at 958C
(BU), viscosity at 958C for 30 min, and viscosity on cooling to 508C. The
viscoamylograph (700 cm/g sensitivity cartridge) was equipped with a 500 cm3 bowl
rotating at 75 rpm. The samples were weighed on a moisture-free basis and mixed with
distilled water to form a slurry (80 g kgÿ1w/w). Mercuric oxide was added to the slurry to
inhibit all enzymatic activities. The slurry was equilibrated in the viscoamylograph at
308C for 30 min, and then heated to 958C, at the rate of 1.58C per minute, with constant
stirring. At 958C the paste was held for 30 min with continuous stirring (holding period),
then cooled (setback period) for 30 min (508C). The consistency profile of the entire
pasting cycle was traced on a chart recorder (amylogram).
2.10. Pellet hardness
A model pellet die was constructed to measure pelletability of small samples at
variable moisture and temperature levels (Department of Agricultural and Bioresource
210
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
Engineering, University of Saskatchewan). The pelleting unit consisted of a single bore
die (130 mm effective length) with an internal diameter of 6.4 mm. The unit was
insulated and temperature controlled. The pre-heated, conditioned ground grain samples
were placed in the pre-heated die (708, 808, or 908C) and forced against the die end
(plunger diameter 0.60 cm) at 772 kg load. The conditioning process consisted of placing
the ground sample (0.5 g) in a test tube (16 100 mm), adding the appropriate moisture
(0, 30, or 60 g kgÿ1) as distilled water with a 25 ml pipette, mixing, sealing with rubber
stoppers, and allowing equilibration (30 min) in a hot oil bath set at the desired
temperature.
Six pellets were produced per treatment combination. These were cooled and
stored until pellet hardness determination. Pellet hardness (vertical orientation) was
measured using an Instron 1011 Automated Material Testing System (Instron, Canton,
MA).
2.11. Statistical analysis
The general linear model (GLM) procedure for SAS (SAS, 1989) was used to analyze
body weight gain (BWG), feed intake (FI), feed efficiency (F/G), intestinal and excreta
starch digestibility in a completely randomized design with 2 2 2 factorial
arrangement. Pens were used as experimental units, with six pens per treatment.
Student-Newman Keuls (SNK) test was used to detect differences among treatment
means. Only interaction means were presented because of the strong interactions present
in much of the data. Pellet hardness in response to moisture, temperature, and starch type
were analyzed using multiple regression procedures (REG).
3. Results
3.1. Composition of waxy and normal starch hull-less barley
The composition of normal and waxy starch hull-less barley genotypes, with reference
to b-glucan, starch, viscosity, amylose (per cent of total starch), and crude protein, are
presented in Table 2. Total starch and crude protein did not differ appreciably between the
two barley types, whereas b-glucan and extract viscosity were generally higher with the
waxy barley. The samples of waxy and normal hull-less barley used for the feeding trial
were, in general, representative of the two groups.
3.2. Broiler chick performance
The dominant effect in terms of broiler chick performance was the response to dietary
enzyme supplementation, which increased body weight gain and feed intake, and lowered
feed conversion (p < 0.01; Table 3) for both waxy and normal hull-less barley diets,
whether fed as mash or pelleted (reground) diets. There were no significant differences
(p > 0.05) in body weight gain, feed intake, or feed conversion (F/G) of broiler chicks in
response to feeding waxy or normal starch hull-less barley. Higher numerical mean values
Composition
Hull-less barley genotypes
normal starch
b-Glucan (g kgÿ1, as fed)
Starch (g kgÿ1, as fed)
Amylose (g kgÿ1 starch)
Crude protein (g kgÿ1, as fed)
Viscosity (cps)a
a
Barley cultivar coding.
waxy starch
025
032
034
035
036
038
X, SD
026
027
028
029
037
X, SD
54
620
254
151
103
73
640
220
140
269
60
624
280
144
762
40
564
260
143
22
40
642
220
140
76
50
631
250
150
501
52 13
619 28
247 23
144 5
289 290
80
571
60
160
179
73
592
60
141
818
72
600
62
142
171
70
620
60
152
446
73
632
60
150
845
73 2
603 24
57 3
148 06
492 330
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
Table 2
Chemical composition and viscosity of hull-less barley genotypes with normal or waxy starch type
211
212
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
Table 3
Effect of feeding normal or waxy hull-less barley as pellets (reground +) or mash (ÿ), with (+) or without (ÿ)
b-glucanase supplementation on broiler chick (21days) body weight gain, feed intake, and feed conversion
Starch
type
Pellet
Enzyme
Body weight
gaina (g)
Feed
intakea(g)
Feed conversion
(F/G)a
Normal
Normal
Normal
Normal
Waxy
Waxy
Waxy
Waxy
SEMb
+
+
ÿ
ÿ
+
+
ÿ
ÿ
+
ÿ
+
ÿ
+
ÿ
+
ÿ
615ac
447bc
677ac
438bc
650ac
429bc
596ac
414bc
29.9
1017abc
963abc
1065ac
900bc
1083ac
907bc
959abc
893bc
32.3
1.69bc
2.19ac
1.58bc
2.08ac
1.67bc
2.12ac
1.63bc
2.19ac
0.08
a
Analysis of variance (2 2 2) indicated treatment effects as follows: body weight gain, enzyme
(p < 0.01); feed intake, enzyme (p < 0.01), starch type pelleting enzyme (p < 0.05); feed conversion,
enzyme (p < 0.01).
b
Standard error of mean.
c
Means in the same column followed by different letters differ significantly (p < 0.05).
for body weight gain and feed intake were observed for chicks fed the normal starch hullless barley in the absence of dietary enzyme, but no consistent effect was evident in the
presence of dietary enzyme. Feeding the pelleted feeds (reground) did not significantly
affect body weight gain, feed intake, or feed conversion in comparison to the mash feeds.
The treatment yielding the best performance results (body weight gain, F/G) was the
normal starch hull-less barley diet fed to broiler chicks as mash with enzyme
supplementation.
3.3. Digesta viscosity
Initial statistical analysis indicated that the magnitude of the effect of dietary enzyme
was overwhelming (p < 0.01) in reducing digesta viscosity in relation to any effect of
starch type or processing. Digesta viscosity was 10±30-fold higher for both the waxy and
normal starch hull-less barley in the absence of dietary enzyme, and differences in
variability within treatments indicated a similar range. To delineate the effects of starch
type and pelleting the data were separately analyzed for treatments with and without
enzyme supplementation (Table 4).
Digesta extract viscosity generally increased from the proximal to the distal small
intestine in the chicks fed diets without enzyme supplementation, reflecting b-glucan
solubilization and/or b-glucan concentration with assimilation of digestible nutrients (i.e.
starch, protein). With enzyme supplementation digesta viscosity was uniformly low in the
proximal and distal small intestine. Among the non-supplemented treatment groups,
digesta from chicks fed waxy starch hull-less barley diets was more (p < 0.01) viscous in
the proximal small intestine (PSI) compared to the normal hull-less barley isotype.
Pelleting reduced (p < 0.01) viscosity of digesta in the PSI by 45% in both hull-less
barley types.
213
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
Table 4
Viscosity of digesta from small intestine of broiler chicks fed normal and waxy hull-less barley pelleted
(reground +) or mash (ÿ) with (+) or without (ÿ) b-glucanase supplementation
Starch type
Normal
Normal
Waxy
Waxy
SEMd
Pellet
+
ÿ
+
ÿ
Enzyme
ÿ
ÿ
ÿ
ÿ
Viscosity (cps)a
PSIb,c
DSIb,c
102be
254be
276be
475ae
53.1
390
316
376
504
140.6
Enzyme
+
+
+
+
Viscosity (cps)a
PSIc
DSIc
10.3
8.9
8.7
9.0
0.8
9.1
11.8
10.3
9.9
1.2
a
Centipoise.
Proximal (PSI) and distal (DSI) small intestine.
c
Analyses of variance (2 2 2) indicated response to dietary enzyme was highly significant (p < 0.01).
Because of large error differences among treatments with and without enzyme addition the data was re-analyzed
(2 2). Viscosity in the PSI was affected by starch type (p < 0.01) and pelleting (p < 0.01); other treatment
effects were not significant (p > 0.05).
d
Standard error of mean.
e
Means in the same column followed by different letters differ significantly (p < 0.05).
b
3.4. Intestinal starch digestibility
Overall, starch digestion as reflected by the excreta analysis was high, with a
sequential progression noted from the proximal to the distal small intestine, to the fecal
content (Table 5). The major factor affecting starch digestion was enzyme supplementation, which increased starch digestion throughout the PSI and DSI (p < 0.01), and to a
lesser extent, in the fecal analysis. The region of starch digestion was affected more so
than the overall level; with enzyme supplemented groups achieving equivalent or better
starch digestion in the PSI than non-supplemented groups did in the DSI. Normal or
waxy hull-less starch barley (non-pelleted) did not influence starch digestibility in the
PSI and feces (Table 5). However, normal starch was more digestible (p < 0.01) than
waxy starch in the DSI, largely as a result of the low starch digestibility of the
non-pelleted waxy barley without enzyme addition. This was primarily due to b-glucan
differences rather than starch type, since there were no significant differences in starch
digestion (DSI) in the presence of b-glucanase. Pelleting increased starch digestion
(p < 0.01) in both the PSI and DSI, irrespective of starch type. The pelleting effect was
not evident in the excreta, indicating that the overall effort of pelleting was to shift
starch digestion anteriorly. Waxy hull-less barley was numerically more digestible at
the excreta level.
b-Glucanase supplementation significantly (p < 0.01) increased starch digestibility in
the PSI, DSI and feces. The greatest response was seen when diets were pelleted and
supplemented with enzymes. The effect of pelleting and enzyme supplementation on
starch digestibility was more pronounced in waxy starch than normal starch. Since all
barley diets would normally be enzyme supplemented, it is noteworthy that there were
virtually no differences in starch digestibility among treatments at the DSI and feces
(Table 5).
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N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
Table 5
Intestinal and excreta starch digestibility of broiler chicks fed normal and waxy hull-less barley pelleted
(reground +) or mash (ÿ) with (+) or without (ÿ) b-glucanase supplementation
Starch type
Normal
Normal
Normal
Normal
Waxy
Waxy
Waxy
Waxy
SEMc
Coefficient of starch digestibility
pellet
enzyme
PSIa,b
DSIa,b
excretab
+
+
ÿ
ÿ
+
+
ÿ
ÿ
+
ÿ
+
ÿ
+
ÿ
+
ÿ
0.793abd
0.558bd
0.763ad
0.360cd
0.866ad
0.540bd
0.752ad
0.370cd
0.031
0.951ad
0.734bd
0.969ad
0.636cd
0.963ad
0.794bd
0.972ad
0.519dd
0.023
0.963ad
0.857abd
0.990ad
0.791bd
0.985ad
0.943ad
0.992ad
0.881abd
0.033
a
Proximal (PSI) or distal (DSI) small intestine.
Analysis of variance (2 2 2) indicated treatment effects as folloes: PSI, enzyme (p < 0.01), pelleting
(p < 0.01), enzyme starch type (p < 0.05); DSI, enzyme (p < 0.01), pelleting (p < 0.01), enzyme starch type
(p < 0.05); DSI, enzyme (p < 0.01), pelleting (p < 0.01), starch type pelleting (p < 0.05), starch type pelleting enzyme (p < 0.05); excreta, enzyme (p < 0.01), starch type (p < 0.05).
c
Standard error of mean.
d
Means in the same column followed by different letter differ significantly (p < 0.05).
b
3.5. Cooking and pasting characteristics of barley starch
The characteristics of normal and waxy starch in barley in response to heating as a
barley flour slurry, as measured by the viscoamylograph are presented in Table 6. The
results for a typical normal and waxy starch hull-less barley as an amylogram are
depicted in Fig. 1. The viscosity units in this case refers to resistance of the hull-less
barley slurries encountered by a central stirring device as the slurry progresses through
pasting and ultimately gel stages. The viscosity is reflective of starch granular and
molecular changes occurring during heating and subsequent cooling. There was
Table 6
Mean Brabender pasting characteristics of starch in waxy and normal hull-less barley flours (with mercuric
oxide)
Hull-less barley
starch typea
Temperature
at peak (BU)b
Normal
SDc
Waxy
SDc
95.0
0.0
86
4.3
a
Viscosity
peak
(8C)
594
150.8
1061
154.1
at 958C
(BU)b
595
152.1
747
78.7
30 min. at
958C (BU)b
348
48.2
570
42.9
Normal barley (n = 6), Waxy barley (n = 5). Mean values presented.
Brabender units.
c
Standard deviation.
b
cooled to
508C (BU)b
718
97.5
712
38.7
set-back
(BU)b
+123
95.7
ÿ346
ÿ164
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
215
Fig. 1. Viscoamylograms of normal and waxy hull-less barley flours (with mercuric oxide).
essentially no change in slurry viscosity as the temperature was increased from 308 to
808C, after which the slurry viscosity of the waxy barley increased rapidly, peaking
(gelatinization temperature) at 868C in comparison to 958C for barley with normal starch.
The peak viscosity attained with the waxy hull-less barley was higher than that attained
with the normal starch hull-less barley. With continued stirring at 958C, the viscosities of
both barleys declined, ultimately reaching a plateau. In proportion to peak height, the
decline for the waxy starch samples was much greater than the normal starch samples.
However, the viscosity in the plateau region continued to be higher for the waxy starch.
Upon cooling, the plateau regions were initially maintained, after which only the normal
starch elicited higher paste viscosity, eventually higher than the peak height attained
during gelatinization. This is conventionally expressed as `set-back', which is calculated
as the difference between the endpoint viscosity and the gelatinization peak. Thus,
normal starch hull-less barley exhibited positive set-back, whereas the waxy starch hullless barley exhibited negative set-back.
3.6. Pellet hardness
Pellet hardness for normal and waxy starch hull-less barley was assessed at three
moisture and temperature combinations, as depicted in Fig. 2. Waxy barley pellets were
significantly (p < 0.01) harder than normal starch barley, as described by the equation
y = ÿ6.43 + 1.99 (barley type) + 1.76 (moisture) + 0.14 (temperature) (r = 0.66**).
Barley type was represented by waxy (1) or normal (0) starch. Both moisture level
(p < 0.01) and temperature (p < 0.01) positively affected pellet hardness. More complex
models incorporating curvilinear and interactive elements either did not improve hardness
prediction significantly, or the magnitude of the improvement was small. It was
noteworthy that pellet hardness differences were most apparent at low moisture
conditions.
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Fig. 2. Pellet hardness of normal and waxy hull-less barley pellets at various added moisture (M, g/kg) and
temperature (T) levels (treatments 1, 2, 3 M = 0; T = 708; 808 and 908C, respectively; 5, 6, 7, M = 30; T = 708,
808, and 908C, respectively; 7, 8, 9, M = 50; T = 708, 808, and 908C, respectively.
4. Discussion
The development of hull-less barley has resulted in a crop that is more compatible than
conventional barley with the nutrient-dense feeds preferred in monogastric feeds,
especially by the poultry industry. A second possibility in the refinement of hull-less
barley for feed may be the incorporation of the waxy starch trait for improvement of feed
processing characteristics, and possibly the rate or extent of starch digestion. Changes in
starch physical properties in response to heat and moisture are conventionally measured
for baking and industrial applications using a viscoamylograph, although the specific
relation between such results and the feed pelleting process have not been established. In
the present study, waxy starch hull-less barley underwent gelatinization (i.e. achieved
peak viscosity) at 98C lower than did conventional barley. Although the difference in
gelatinization temperature was somewhat less than previously reported (12% vs. 20%;
Goering et al., 1973), the results were comparable. The higher peak viscosity (`pasting
peak') for waxy barley is indicative of swollen starch granules, which resist movement
due to physical contact among adjacent granules in the starch paste and is reflected as a
higher paste viscosity (Schoch, 1969). Since the molecular weight of amylopectin is
greater in waxy than in normal starch (DeHaas and Goering, 1972; Zobel, 1984), granular
expansion may be greater as well. Similar results have been reported previously
comparing normal and waxy barley (cv. Compana) starches (DeHaas and Goering, 1972;
Goering et al., 1973).
The lower gelatinization temperature of waxy starch potentially offers several
advantages in feed processing. Greater plasticity of waxy starch could reduce energy
input, lower mechanical effort in pellet production, and higher gelatinization (at an
equivalent temperature) could improve adhesion and pellet hardness. Although starch
does not undergo gelatinization during conditioning prior to pelleting in the true sense, it
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
217
seems reasonable to expect that the general relationship between waxy and normal starch
would hold true during the initial stages of starch gelatinization, or starch `melting'
(Thomas and Van der Poel, 1996). This interpretation was supported by the model
pelleting system employed, in that there was a linear relationship between pellet hardness
and temperature at all moisture levels, and equivalent pellet hardness with the waxy hullless barley (calculated from pellet hardness prediction equation) was achieved at 14.28C
lower than the normal starch hull-less barley.
Achieving equivalent pellet hardness at lower temperature would also reduce damage
to heat-sensitive dietary components, for example dietary protein or feed additives.
Although the present study only considered conventional pelleting, it is anticipated that
expansion or extrusion systems would react similarly. In the latter case, the temperatures
are sufficient for the formation of resistant starch, which is a function of amylose content
and would presumably be less with the waxy starch type. In the model pellet system waxy
barleys provided significantly harder pellets than normal starch barley at a range of
temperatures and added moisture levels encountered in feed processing. Whether or not
this can be attained commercially remains to be determined. In related studies (Ankrah,
1994) normal starch hull-less barley resulted in pellets that were significantly harder
than pellets from corn (p < 0.01) and not significantly different than pellets from wheat.
Corn starch also had a higher gelatinization temperature range (62±728C) than barley
(51±608C) or wheat (56±648C) starches (Biliaderis, 1980).
The total b-glucan content is consistently and significantly higher in waxy hull-less
barley than in normal isotype (Ullrich et al., 1986; Xue et al., 1991). In the present study,
the high extract viscosity associated with hull-less barley (without b-glucanase) was
evident in both the PSI and DSI. Waxy barley in general had higher extract viscosity than
the normal hull-less barley in the absence of enzyme supplementation, and pelleting
alone tended to reduce viscosity. This latter effect may be due to a shearing effect on
b-glucan during pelleting, or, more likely, the pelleting procedure that was used provided
some opportunity for b-glucan degradation due to endogenous b-glucanase during the
conditioning process, which allowed a longer period of exposure than normal pelleting.
Clearly, however, the dominant effect in terms of intestinal viscosity reduction was
b-glucanase supplementation, which greatly reduced viscosity levels. As observed
previously with high and low viscosity barleys (Campbell et al., 1989, Campbell et al.,
1993), there were no differences among barleys attributable to viscosity differences when
supplemented with dietary enzymes.
Extract viscosity provides a uniform measure of intestinal viscosity, however, it is
reasonable to expect that in vivo there is a concentration gradient with viscosity
increasing with proximity to the cell surface, reflecting gradual dissolution of the cell
wall during digestion. The similarity in extract viscosity between the proximal and distal
small intestine indicate that this process was virtually complete in the proximal region.
High b-glucan induced viscosity has a pronounced effect on digestibility of most
nutrients, but especially fat (Campbell and Bedford, 1992). Starch digestion is affected as
well, but in this case the effect was to shift starch digestion posteriorly, rather than affect
total digestibility. In the present study, overall starch digestibility was reduced as well in
the case of the normal starch hull-less barley without enzyme supplementation. The
granule surfaces of raw waxy starch are covered with natural fissures, which, along with
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N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
higher solubility of amylopectin, has been suggested to enhance susceptibility to aamylase. There was no indication of higher starch digestion in the PSI with waxy starch
type in enzyme-supplemented, non-pelleted diet compared to the normal starch type,
indicating that any granular surface differences had no effect. The effect of heat on starch
digestion can also be explained in terms of partial granule disruption increasing the rate
of degradation by a-amylase. The effect of heat treatment imparted by the conditioning/
pelleting process on starch digestion was most apparent in the proximal small intestine,
where starch digestion was considerably greater in the pelleted as opposed to the
untreated hull-less barley, in the absence of dietary enzyme. The waxy hull-less barley
was numerically, but not statistically higher in starch digestion than the normal hull-less
barley in the pelleted feed supplemented with enzyme. The most consistent factor
affecting starch digestion was the inclusion of dietary b-glucanase, followed by heat
treatment and finally, starch type. Waxy starch only offered an apparent advantage in the
enzyme-supplemented, pelleted diets which may relate to its lower gelatinization
temperature.
While starch digestion in poultry is virtually complete, Hesselman and Aman
(1986) considered starch digestion in the lower regions of the small intestine as
less efficient than anterior regions because of the presence of indigenous microflora,
which compete with the host for digested products. Greater starch digestion in the
proximal small intestine, whether accomplished by enzyme supplementation, heat
processing, or starch type differences, may be interpreted as a higher rate of starch
digestion, which introduces other potential metabolic savings. Nutrient assimilation
may be higher within a given time period, which would ultimately be reflected in higher
feed consumption, and faster growth. Anterior digestion of starch may also be indicative
of reduced enzyme protein required to digest starch, protein which could then be
channeled for growth and development. Heat and moisture treatment as it occurs
during pelleting may obliterate differences in starch digestibility attributable to granular
surfaces.
Chick performance, as reflected by body weight gain, feed intake, and feed conversion,
did tend to correspond to starch digestibility in the proximal small intestine. As observed
previously, with waxy and normal starch barley, starch type influenced body weight gain
and feed efficiency (Newman and Newman, 1987). The major response was to enzyme
addition, where body weight gain improvement approached 50%. Among the enzyme
supplemented groups there were no significant differences attributable to heat treatment
(pelleting) or starch type, indicating that the digestibility differences attributable to these
factors were insufficient to affect performance parameters, or the response magnitude was
below detectable levels under the conditions of the assay.
It may be concluded from this study that high amylopectin hull-less barley may offer
advantages in feed processing associated with its lower gelatinization temperature. The
higher b-glucan affiliated with the waxy trait would seriously confound the analysis of
nutritional value in diets which did not include an enzyme supplement. Although
experimental results have indicated that the effect due to high b-glucan is not a major
concern in enzyme-supplemented diets (Campbell et al., 1989, Campbell et al., 1993),
barley breeders should strive to lower b-glucan genetically to at least moderate levels if
waxy starch-type barleys are developed for feed applications.
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
219
References
Ankrah, 1994. Heat and moisture effects on the nutritional and physical characteristics of starch in normal and
waxy hull-less barley. M. Sc. Thesis. University of Saskatchewan.
Association of Official Analytical Chemists, 1990. Official method of analysis, fifteenth ed., pp. 152±169.
Biliaderis, 1980. Physiochemical studies on legume starches. Ph.D. thesis. University of Saskatchewan.
Bjorck, I., Nyman, M., Pederson, B., Siljesstromm, M., Asp, N-G., Eggum, B.O., 1987. Formation of enzyme
resistant starch during autoclaving of wheat starch: studies in vitro and in vivo. J. Cereal Sci. 6, 159±172.
Campbell, G.L., Bedford, M.R., 1992. Enzyme applications for monogastric feed: a review. Can J. Anim. Sci.
72, 449±466.
Campbell, G.L., Rossnagel, B.G., Bhatty, R.S., 1993. Evaluation of hull-less barley genotypes varying in extract
viscosity in broiler chick diets. Anim. Feed Sci. Technol. 41, 191±197.
Campbell, G.L., Rossnagel, B.G., Classen, H.L., Thacker, P.A., 1989. Genotypic and environmental differences
in extract viscosity of barley and its relationship to its nutritive value for broiler chickens. Anim. Feed Sci.
Technol. 26, 221±230.
DeHaas, B.W., Goering, K., 1972. Chemical structure of barley starches. 1. A study of the properties of the
amylose and amylopectin from barley starches showing a wide variation in Brabender viscosity curves.
Starke 24, 145±149.
Fenton, T.W., Fenton, M., 1979. An improved procedure for the determination of chromic oxide in feed and
feces. Can. J. Anim. Sci. 59, 631±634.
Goering, K., Eslick, R., DeHaas, B.W., 1973. Barley Starch. V. Comparison of the properties of waxy compana
barley starch with the starches of its parents. Cereal Chem. 50, 322.
Hesselman, K., Aman, P., 1986. The effect of b-glucanase on the utilization of starch and nitrogen by broiler
chickens fed barley of low or high viscosity. Anim. Feed Sci. Technol. 15, 83±93.
Newman, R.K., Newman, C.W., 1987. Beta-glucanase effect on the performance of broiler chicks fed covered
and hulless barley isotypes having normal and waxy starch. Nutr. Rep. Int. 36, 693±697.
Salih, M.E., Classen, H.L., Campbell, G.L., 1991. Response of chicken fed on hull-less barley dietary bglucanase at different ages. Anim. Feed Sci. Technol. 33, 139±149.
SAS, 1989. SAS Institute, Box 8000, Cary, NC, USA 27512-8000.
Schoch, 1969. Mechano-chemistry of starch. Wallerstan Lab. Commun. 32, 149±159.
Thomas, M., Van der Poel, A.F.B., 1996. Physical quality of pelleted animal feed. 1. Criteria for pellet quality.
Anim. Feed Sci. Technol. 61, 89±112.
Ullrich, S.E., Clancy, J.A., Eslick, R.F., Lance, R., 1986. b-glucan content and viscosity of extract from barley. J.
Cereal Sc. 4, 279±285.
Xue, Q., Newman, R.K., Newman, C.W., 1991. Waxy gene effects on b-glucan, dietary fiber content, and
viscosity of barleys. Cereal Res. Comm. 19, 339±404.
Zobel, H.F., 1984. Gelatinization of starch and mechanical properties of starch pastes. In: Whistler, R.L., Pascall,
E.F. (Eds.), Starch: Chemistry and Technology, second ed., Academic Press Inc. Orlando, pp. 285±309.
81 (1999) 205±219
Hydrothermal and b-glucanase effects on the
nutritional and physical properties of starch
in normal and waxy hull-less barley
N.O. Ankraha, G.L. Campbellb,*, R.T. Tylerc,
B.G. Rossnageld, S.R.T. Sokhansanje
a
Department of Animal Sciences, Washington State University, P.O. Box 646351, Pullman, WA 99164-6351, USA
b
Department of Animal and Poultry Science, University of Saskatchewan, 72 Campus Drive,
Saskatoon, SK S7N 5B5, Canada
c
Department of Food Science and Microbiology, 51 Campus Drive, University of Saskatchewan,
Saskatoon, SK S7N 5A8, Canada
d
Crop Development Centre, 51 Campus Drive, University of Saskatchewan, Saskatoon, SK S7N 5A8, Canada
e
Department of Agricultural and Bioresource Engineering, 57 Campus Drive, University of Saskatchewan,
Saskatoon, SK S7N 5A9, Canada
Received 9 November 1998; received in revised form 5 March 1999; accepted 22 June 1999
Abstract
Cereals having a waxy (high amylopectin) starch type may offer advantages for animal feed
associated with heat processing characteristics and/or starch digestibility. Nutritional and physical
characteristics of starch were evaluated in hull-less barley cultivars having a normal or waxy starch
type (228 and 55 g kgÿ1 amylose, respectively). Broiler chicks (192) were fed one of eight diets in a
2 2 2 factorial arrangement from 3 to 21 days of age. The dietary factors included: (1) normal
or waxy starch type barley; (2) pelleted (758C, 160 g kgÿ1 total moisture) or meal form; and (3)
with or without addition of b-glucanase. The pelleted diets were reground to remove any physical
aspect of feeding pellets. There were no differences in body weight gain (BWG), feed intake (FI),
feed-to-gain ratio (F/G) or intestinal starch digestibility due to starch type, nor were treatment
interactions significant (p > 0.05). Feeding waxy starch barley resulted in higher digesta viscosity
than normal starch barley, which was attributed to its higher b-glucan content. Fecal digestibility of
waxy starch was 10% higher (p < 0.05) than that of normal starch. Pelleting did not affect BWG, FI,
or F/G, but reduced (p < 0.05) digesta viscosity by 45% and increased starch digestibility by 17% in
non-enzyme supplemented diets. b-Glucanase addition improved BWG, FI, F/G, and starch
*
Corresponding author. Tel.: +1-306-9664128; fax: +1-306-9664151
E-mail address: leigh.campbell@usask.ca (G.L. Campbell)
0377-8401/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 9 9 ) 0 0 0 8 4 - X
206
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
digestibility (p < 0.01), and eliminated the high digesta viscosity otherwise associated with feeding
the waxy starch diets in meal form.
Starch characteristics during heating were examined with 11 hull-less barley samples (5 waxy
and 6 normal starch types) using a Brabender Viscoamylograph. Waxy starch hull-less barley
exhibited peak viscosity 10oC lower than did normal starch, exhibited a higher peak viscosity,
paste instability and a lower cold-paste viscosity (negative set-back). Waxy barley may offer
advantages in feed processing associated with lower gelatinization temperature, as indicated by
superior pellet hardness in a model pelleting system over a range of added moisture levels and
temperatures. The waxy trait did not compromise chick performance when diets were supplemented
with b-glucanase. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Hull-less barley; Starch; Feed; Pelleting; b-Glucanase
1. Introduction
Barley has historically been considered a less desirable cereal grain for poultry due to
its low energy content. Recent developments that have increased acceptance of barley as a
poultry feed have been the widespread use of dietary enzymes (b-glucanase; Campbell
and Bedford, 1992), and the development of hull-less cultivars. Dietary b-glucanase
relieves the viscous state that arises in the intestine (Salih et al., 1991) with solubilization
of b-glucan originating from the endospermal cell wall in barley. Nutrient digestibility
and absorption, as well as feed intake are reduced, and in the case of starch, its digestion
is shifted distally in the small intestine (Hesselman and Aman, 1986). The production of
`sticky feces' in poultry due to b-glucan also poses litter handling problems and adverse
effects on the environment of intensively housed poultry.
A second development has been the introduction of hull-less barley genotypes, in
which the hull is shed during harvesting. This increases the metabolizable energy
content by removing the dilution effect of the fibrous hull. While b-glucan levels
are affected by both genetics and environment, early hull-less barley cultivars were
notorious for containing high b-glucan, and this occurrence likely prevented their
adoption prior to widespread application of dietary enzymes (Campbell et al., 1993).
With enzyme supplementation the effect of varying b-glucan level is minimal, although
plant breeders have purposely selected for moderate levels in current hull-less barley
varieties.
Both hull-less and conventional barley genotypes occur as waxy types, in which the
starch consists almost entirely of amylopectin (970±1000 g kgÿ1), as opposed to normal
types containing 750±850 g kgÿ1 amylopectin with 150±250 g kgÿ1 amylose (Ullrich
et al., 1986). Amylopectin is more susceptible to a-amylase than amylose suggesting that
waxy starch may be more digestible than the normal starch type. High amylopectin/waxy
starch gelatinizes at a lower temperature compared to normal starch, which could have
obvious benefits in the production of pelleted feeds, since the benefit of cooking could
potentially be achieved with lower temperatures with reduced destructive effects on other
nutrients (e.g. lysine).
The objectives of these experiments were to determine the effects of heat and moisture
on the physical properties of starch in waxy and normal starch type hull-less barley, the
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
207
effects of limited heat and moisture treatment (pelleting) on site and extent of starch
digestion, and to determine the relative response to dietary b-glucanase addition in broiler
chicks.
2. Materials and methods
2.1. Hull-less barley samples
Eleven hull-less barley cultivars were used in the study (Dr. B.G. Rossnagel; Crop
Development Centre, University of Saskatchewan, Saskatoon, SK, Canada) representing
normal (six cultivars: 025; 032; 034; 035; 036; and 038) and waxy (five cultivars: 026;
027; 028; 029; and 037) starch types.
2.2. Broiler chick feeding trial
Two hull-less barley cultivars representing a normal (034) and waxy (037) starch type
were available in sufficient quantity for evaluation in broiler chick diets. The effect of
pelleting or meal form of barley based diets, with or without b-glucanase addition was
examined in broiler chicks. Variables examined were body weight, body weight gain,
feed conversion, digesta viscosity and intestinal starch digestibility.
2.3. Experimental allocation and management
Commercial strain day old broiler chicks were fed a commercial diet for three days.
The chicks were weighed after the third day and randomly allocated to eight dietary
treatments. Each treatment was replicated (cages) six times with four birds per replication
(two males and two females, 192 chicks total). The broiler chicks were housed in battery
brooders and given feed and water ad libitum throughout the experimental period (3±21
days).
2.4. Diets and feeding
A broiler starter diet (Table 1) was formulated based on two hull-less barley cultivars,
containing normal (278 g kgÿ1 amylose, 58 g kgÿ1 b-glucan) or waxy starch (55 g kgÿ1
amylose, 73 g kgÿ1 b-glucan) type. Each of the normal or waxy starch hull-less barley
diets was divided into two portions. One portion was steam (160 g kgÿ1 total moisture)
pelleted through a 5 mm matrix at 75oC (Superior Separator, Process Machine Div.,
Hopkins, Minnesota). The other portion was not pelleted (meal form). The pelleted diets
were reground to a meal form using a hammermill without a screen to remove any effect
due to form differences between the normal and waxy type hull-less barleys. The pelleted
or intact portion was fed with (+) or without (ÿ) a commercial b-glucanase enzyme
addition (derived from Aspergillus niger). The enzyme was added to the meal or reground
pelleted diets. The enzyme preparation was added after pelleting to avoid any potential
confounding attributable to partial enzyme inactivation with heat.
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Table 1
Composition of basal diets (g kgÿ1 air dry basis)
Ingredient
hull-less barleya
soybean meal (480 g/kg CP)
canola oil
limestone
dicalcium phosphate
salt (iodized)
DL-methionine
L-lysine±HCL
Vitamin±mineral premixb
610.0
313.0
40.0
15.0
14.8
2.5
1.2
0.5
3.0
Calculated analysesc
metabolizable energy (MJ/kg)
crude protein
calcium
available phosphorous
lysine
methionine
11.96
240.0
10.3
6.9
13.0
5.5
a
Waxy or normal cultivar. Hull-less barley diets were given with or without enzyme supplementation at
1.0 g kgÿ1. Aspergillus niger, GNC Bioferm, Saskatoon, SK; to provide 1000 b-glucanase units per kg
manufacturer's specification; unit is total reducing sugars (glucose equivalent) released per 10 min at 308C and
pH 4.0.
b
Vitamin±mineral premix provided the following per kilogram of diet: vitamin A, 9000 IU; vitamin D3,
1500 IU; vitamin E, 20 IU; vitamin K, 1.5 mg; riboflavin, 5 mg; pantothenic acid, 11 mg; niacin, 24 mg; folic
acid, 0.75 mg; biotin, 0.1 mg; choline, 500 mg; vitamin B12. 0.012 mg; zinc, 60 mg; copper, 5 mg; manganese,
60 mg; selenium, 0.1 mg.
c
Crude protein calculations based on analysed value; other values were calculated.
2.5. Response criteria
During the experimental period, weekly data collection and calculation included body
weight gain, feed-to-gain ratio. At the termination of the experiment, starch digestibility
was determined at the proximal small intestine (PSI), distal small intestine (DSI) and
feces. PSI was defined as the region from the gizzard to Meckel's diverticulum and DSI,
from Meckel's diverticulum to the ileo±ceco±colic junction.
2.6. Intestinal digesta collection
All the chicks were starved for 14 h (overnight) prior to trial termination and fed again
early the next morning in order to ensure the presence of sufficient digesta for analytical
purposes. Two hours after feeding, broilers from each treatment were sacrificed by
cervical dislocation, dissected, and the digesta collected. Following thorough mixing, one
portion of the pooled digesta sample (4 birds per replication) was taken for viscosity
determination immediately, and the remainder transferred into sealable polythene bags
and immediately frozen in liquid nitrogen (ÿ208C ) for later determination of starch
digestibility. The birds were taken sequentially by treatment replication in order to assure
treatment differences were not confounded by differing time periods after feeding.
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
209
2.7. Measuring viscosity of intestinal contents
A portion of the pooled digesta of intestinal digesta from chicks on each treatment
was centrifuged for 10 min using a micro-centrifuge (1200 g rpm at 25oC)
immediately after collection. The viscosity (centipoise, cps = 0.01 dynes s cmÿ2) of
the supernatant solution was determined using a Brookfield digital viscometer (Model
LVTD VCP-II, Brookfield Engineering Laboratory, Soughton, MA) at 24oC and a shear
rate of 5±22 sÿ1.
2.8. Measuring starch digestion
Chromic oxide (5 g kgÿ1) was added to all the diets for the determination of starch
digestibility at PSI, DSI and excreta regions. The marked diets were fed throughout the
experimental period. Prior to digesta collection, excreta samples were collected daily
from each pen, frozen (ÿ10oC), and the daily collections pooled.
The pooled, frozen excreta samples were dried (60oC for 24 h), and the digesta samples
lyophilized. Feed and the dried excreta and digesta samples were ground (1 mm screen).
Chromic oxide concentration in feed, digesta and fecal samples was measured (Fenton
and Fenton, 1979). Dry matter (DM) of digesta was determined as difference in weight
between fresh and lyophilized samples and DM of feed and feces was determined
according to AOAC procedures (AOAC, 1990). Starch determination was according to
the procedure of Bjorck et al. (1987), in which starch is solubilized, digested using
a-amylase followed by amyloglucosidase, and quantified as glucose released (glucose
oxidase method).
2.9. Starch characteristics during heating
The cooking and pasting characteristics of starch in waxy (5 types) and normal (6
types) hull-less barleys were evaluated using the Brabender viscoamylograph (C.W.
Brabender Instruments, South Hackensack, NJ, USA). Characteristics measured were
gelatinization temperature, peak viscosity in Brabender units (BU), viscosity at 958C
(BU), viscosity at 958C for 30 min, and viscosity on cooling to 508C. The
viscoamylograph (700 cm/g sensitivity cartridge) was equipped with a 500 cm3 bowl
rotating at 75 rpm. The samples were weighed on a moisture-free basis and mixed with
distilled water to form a slurry (80 g kgÿ1w/w). Mercuric oxide was added to the slurry to
inhibit all enzymatic activities. The slurry was equilibrated in the viscoamylograph at
308C for 30 min, and then heated to 958C, at the rate of 1.58C per minute, with constant
stirring. At 958C the paste was held for 30 min with continuous stirring (holding period),
then cooled (setback period) for 30 min (508C). The consistency profile of the entire
pasting cycle was traced on a chart recorder (amylogram).
2.10. Pellet hardness
A model pellet die was constructed to measure pelletability of small samples at
variable moisture and temperature levels (Department of Agricultural and Bioresource
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Engineering, University of Saskatchewan). The pelleting unit consisted of a single bore
die (130 mm effective length) with an internal diameter of 6.4 mm. The unit was
insulated and temperature controlled. The pre-heated, conditioned ground grain samples
were placed in the pre-heated die (708, 808, or 908C) and forced against the die end
(plunger diameter 0.60 cm) at 772 kg load. The conditioning process consisted of placing
the ground sample (0.5 g) in a test tube (16 100 mm), adding the appropriate moisture
(0, 30, or 60 g kgÿ1) as distilled water with a 25 ml pipette, mixing, sealing with rubber
stoppers, and allowing equilibration (30 min) in a hot oil bath set at the desired
temperature.
Six pellets were produced per treatment combination. These were cooled and
stored until pellet hardness determination. Pellet hardness (vertical orientation) was
measured using an Instron 1011 Automated Material Testing System (Instron, Canton,
MA).
2.11. Statistical analysis
The general linear model (GLM) procedure for SAS (SAS, 1989) was used to analyze
body weight gain (BWG), feed intake (FI), feed efficiency (F/G), intestinal and excreta
starch digestibility in a completely randomized design with 2 2 2 factorial
arrangement. Pens were used as experimental units, with six pens per treatment.
Student-Newman Keuls (SNK) test was used to detect differences among treatment
means. Only interaction means were presented because of the strong interactions present
in much of the data. Pellet hardness in response to moisture, temperature, and starch type
were analyzed using multiple regression procedures (REG).
3. Results
3.1. Composition of waxy and normal starch hull-less barley
The composition of normal and waxy starch hull-less barley genotypes, with reference
to b-glucan, starch, viscosity, amylose (per cent of total starch), and crude protein, are
presented in Table 2. Total starch and crude protein did not differ appreciably between the
two barley types, whereas b-glucan and extract viscosity were generally higher with the
waxy barley. The samples of waxy and normal hull-less barley used for the feeding trial
were, in general, representative of the two groups.
3.2. Broiler chick performance
The dominant effect in terms of broiler chick performance was the response to dietary
enzyme supplementation, which increased body weight gain and feed intake, and lowered
feed conversion (p < 0.01; Table 3) for both waxy and normal hull-less barley diets,
whether fed as mash or pelleted (reground) diets. There were no significant differences
(p > 0.05) in body weight gain, feed intake, or feed conversion (F/G) of broiler chicks in
response to feeding waxy or normal starch hull-less barley. Higher numerical mean values
Composition
Hull-less barley genotypes
normal starch
b-Glucan (g kgÿ1, as fed)
Starch (g kgÿ1, as fed)
Amylose (g kgÿ1 starch)
Crude protein (g kgÿ1, as fed)
Viscosity (cps)a
a
Barley cultivar coding.
waxy starch
025
032
034
035
036
038
X, SD
026
027
028
029
037
X, SD
54
620
254
151
103
73
640
220
140
269
60
624
280
144
762
40
564
260
143
22
40
642
220
140
76
50
631
250
150
501
52 13
619 28
247 23
144 5
289 290
80
571
60
160
179
73
592
60
141
818
72
600
62
142
171
70
620
60
152
446
73
632
60
150
845
73 2
603 24
57 3
148 06
492 330
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
Table 2
Chemical composition and viscosity of hull-less barley genotypes with normal or waxy starch type
211
212
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
Table 3
Effect of feeding normal or waxy hull-less barley as pellets (reground +) or mash (ÿ), with (+) or without (ÿ)
b-glucanase supplementation on broiler chick (21days) body weight gain, feed intake, and feed conversion
Starch
type
Pellet
Enzyme
Body weight
gaina (g)
Feed
intakea(g)
Feed conversion
(F/G)a
Normal
Normal
Normal
Normal
Waxy
Waxy
Waxy
Waxy
SEMb
+
+
ÿ
ÿ
+
+
ÿ
ÿ
+
ÿ
+
ÿ
+
ÿ
+
ÿ
615ac
447bc
677ac
438bc
650ac
429bc
596ac
414bc
29.9
1017abc
963abc
1065ac
900bc
1083ac
907bc
959abc
893bc
32.3
1.69bc
2.19ac
1.58bc
2.08ac
1.67bc
2.12ac
1.63bc
2.19ac
0.08
a
Analysis of variance (2 2 2) indicated treatment effects as follows: body weight gain, enzyme
(p < 0.01); feed intake, enzyme (p < 0.01), starch type pelleting enzyme (p < 0.05); feed conversion,
enzyme (p < 0.01).
b
Standard error of mean.
c
Means in the same column followed by different letters differ significantly (p < 0.05).
for body weight gain and feed intake were observed for chicks fed the normal starch hullless barley in the absence of dietary enzyme, but no consistent effect was evident in the
presence of dietary enzyme. Feeding the pelleted feeds (reground) did not significantly
affect body weight gain, feed intake, or feed conversion in comparison to the mash feeds.
The treatment yielding the best performance results (body weight gain, F/G) was the
normal starch hull-less barley diet fed to broiler chicks as mash with enzyme
supplementation.
3.3. Digesta viscosity
Initial statistical analysis indicated that the magnitude of the effect of dietary enzyme
was overwhelming (p < 0.01) in reducing digesta viscosity in relation to any effect of
starch type or processing. Digesta viscosity was 10±30-fold higher for both the waxy and
normal starch hull-less barley in the absence of dietary enzyme, and differences in
variability within treatments indicated a similar range. To delineate the effects of starch
type and pelleting the data were separately analyzed for treatments with and without
enzyme supplementation (Table 4).
Digesta extract viscosity generally increased from the proximal to the distal small
intestine in the chicks fed diets without enzyme supplementation, reflecting b-glucan
solubilization and/or b-glucan concentration with assimilation of digestible nutrients (i.e.
starch, protein). With enzyme supplementation digesta viscosity was uniformly low in the
proximal and distal small intestine. Among the non-supplemented treatment groups,
digesta from chicks fed waxy starch hull-less barley diets was more (p < 0.01) viscous in
the proximal small intestine (PSI) compared to the normal hull-less barley isotype.
Pelleting reduced (p < 0.01) viscosity of digesta in the PSI by 45% in both hull-less
barley types.
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N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
Table 4
Viscosity of digesta from small intestine of broiler chicks fed normal and waxy hull-less barley pelleted
(reground +) or mash (ÿ) with (+) or without (ÿ) b-glucanase supplementation
Starch type
Normal
Normal
Waxy
Waxy
SEMd
Pellet
+
ÿ
+
ÿ
Enzyme
ÿ
ÿ
ÿ
ÿ
Viscosity (cps)a
PSIb,c
DSIb,c
102be
254be
276be
475ae
53.1
390
316
376
504
140.6
Enzyme
+
+
+
+
Viscosity (cps)a
PSIc
DSIc
10.3
8.9
8.7
9.0
0.8
9.1
11.8
10.3
9.9
1.2
a
Centipoise.
Proximal (PSI) and distal (DSI) small intestine.
c
Analyses of variance (2 2 2) indicated response to dietary enzyme was highly significant (p < 0.01).
Because of large error differences among treatments with and without enzyme addition the data was re-analyzed
(2 2). Viscosity in the PSI was affected by starch type (p < 0.01) and pelleting (p < 0.01); other treatment
effects were not significant (p > 0.05).
d
Standard error of mean.
e
Means in the same column followed by different letters differ significantly (p < 0.05).
b
3.4. Intestinal starch digestibility
Overall, starch digestion as reflected by the excreta analysis was high, with a
sequential progression noted from the proximal to the distal small intestine, to the fecal
content (Table 5). The major factor affecting starch digestion was enzyme supplementation, which increased starch digestion throughout the PSI and DSI (p < 0.01), and to a
lesser extent, in the fecal analysis. The region of starch digestion was affected more so
than the overall level; with enzyme supplemented groups achieving equivalent or better
starch digestion in the PSI than non-supplemented groups did in the DSI. Normal or
waxy hull-less starch barley (non-pelleted) did not influence starch digestibility in the
PSI and feces (Table 5). However, normal starch was more digestible (p < 0.01) than
waxy starch in the DSI, largely as a result of the low starch digestibility of the
non-pelleted waxy barley without enzyme addition. This was primarily due to b-glucan
differences rather than starch type, since there were no significant differences in starch
digestion (DSI) in the presence of b-glucanase. Pelleting increased starch digestion
(p < 0.01) in both the PSI and DSI, irrespective of starch type. The pelleting effect was
not evident in the excreta, indicating that the overall effort of pelleting was to shift
starch digestion anteriorly. Waxy hull-less barley was numerically more digestible at
the excreta level.
b-Glucanase supplementation significantly (p < 0.01) increased starch digestibility in
the PSI, DSI and feces. The greatest response was seen when diets were pelleted and
supplemented with enzymes. The effect of pelleting and enzyme supplementation on
starch digestibility was more pronounced in waxy starch than normal starch. Since all
barley diets would normally be enzyme supplemented, it is noteworthy that there were
virtually no differences in starch digestibility among treatments at the DSI and feces
(Table 5).
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N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
Table 5
Intestinal and excreta starch digestibility of broiler chicks fed normal and waxy hull-less barley pelleted
(reground +) or mash (ÿ) with (+) or without (ÿ) b-glucanase supplementation
Starch type
Normal
Normal
Normal
Normal
Waxy
Waxy
Waxy
Waxy
SEMc
Coefficient of starch digestibility
pellet
enzyme
PSIa,b
DSIa,b
excretab
+
+
ÿ
ÿ
+
+
ÿ
ÿ
+
ÿ
+
ÿ
+
ÿ
+
ÿ
0.793abd
0.558bd
0.763ad
0.360cd
0.866ad
0.540bd
0.752ad
0.370cd
0.031
0.951ad
0.734bd
0.969ad
0.636cd
0.963ad
0.794bd
0.972ad
0.519dd
0.023
0.963ad
0.857abd
0.990ad
0.791bd
0.985ad
0.943ad
0.992ad
0.881abd
0.033
a
Proximal (PSI) or distal (DSI) small intestine.
Analysis of variance (2 2 2) indicated treatment effects as folloes: PSI, enzyme (p < 0.01), pelleting
(p < 0.01), enzyme starch type (p < 0.05); DSI, enzyme (p < 0.01), pelleting (p < 0.01), enzyme starch type
(p < 0.05); DSI, enzyme (p < 0.01), pelleting (p < 0.01), starch type pelleting (p < 0.05), starch type pelleting enzyme (p < 0.05); excreta, enzyme (p < 0.01), starch type (p < 0.05).
c
Standard error of mean.
d
Means in the same column followed by different letter differ significantly (p < 0.05).
b
3.5. Cooking and pasting characteristics of barley starch
The characteristics of normal and waxy starch in barley in response to heating as a
barley flour slurry, as measured by the viscoamylograph are presented in Table 6. The
results for a typical normal and waxy starch hull-less barley as an amylogram are
depicted in Fig. 1. The viscosity units in this case refers to resistance of the hull-less
barley slurries encountered by a central stirring device as the slurry progresses through
pasting and ultimately gel stages. The viscosity is reflective of starch granular and
molecular changes occurring during heating and subsequent cooling. There was
Table 6
Mean Brabender pasting characteristics of starch in waxy and normal hull-less barley flours (with mercuric
oxide)
Hull-less barley
starch typea
Temperature
at peak (BU)b
Normal
SDc
Waxy
SDc
95.0
0.0
86
4.3
a
Viscosity
peak
(8C)
594
150.8
1061
154.1
at 958C
(BU)b
595
152.1
747
78.7
30 min. at
958C (BU)b
348
48.2
570
42.9
Normal barley (n = 6), Waxy barley (n = 5). Mean values presented.
Brabender units.
c
Standard deviation.
b
cooled to
508C (BU)b
718
97.5
712
38.7
set-back
(BU)b
+123
95.7
ÿ346
ÿ164
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
215
Fig. 1. Viscoamylograms of normal and waxy hull-less barley flours (with mercuric oxide).
essentially no change in slurry viscosity as the temperature was increased from 308 to
808C, after which the slurry viscosity of the waxy barley increased rapidly, peaking
(gelatinization temperature) at 868C in comparison to 958C for barley with normal starch.
The peak viscosity attained with the waxy hull-less barley was higher than that attained
with the normal starch hull-less barley. With continued stirring at 958C, the viscosities of
both barleys declined, ultimately reaching a plateau. In proportion to peak height, the
decline for the waxy starch samples was much greater than the normal starch samples.
However, the viscosity in the plateau region continued to be higher for the waxy starch.
Upon cooling, the plateau regions were initially maintained, after which only the normal
starch elicited higher paste viscosity, eventually higher than the peak height attained
during gelatinization. This is conventionally expressed as `set-back', which is calculated
as the difference between the endpoint viscosity and the gelatinization peak. Thus,
normal starch hull-less barley exhibited positive set-back, whereas the waxy starch hullless barley exhibited negative set-back.
3.6. Pellet hardness
Pellet hardness for normal and waxy starch hull-less barley was assessed at three
moisture and temperature combinations, as depicted in Fig. 2. Waxy barley pellets were
significantly (p < 0.01) harder than normal starch barley, as described by the equation
y = ÿ6.43 + 1.99 (barley type) + 1.76 (moisture) + 0.14 (temperature) (r = 0.66**).
Barley type was represented by waxy (1) or normal (0) starch. Both moisture level
(p < 0.01) and temperature (p < 0.01) positively affected pellet hardness. More complex
models incorporating curvilinear and interactive elements either did not improve hardness
prediction significantly, or the magnitude of the improvement was small. It was
noteworthy that pellet hardness differences were most apparent at low moisture
conditions.
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N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
Fig. 2. Pellet hardness of normal and waxy hull-less barley pellets at various added moisture (M, g/kg) and
temperature (T) levels (treatments 1, 2, 3 M = 0; T = 708; 808 and 908C, respectively; 5, 6, 7, M = 30; T = 708,
808, and 908C, respectively; 7, 8, 9, M = 50; T = 708, 808, and 908C, respectively.
4. Discussion
The development of hull-less barley has resulted in a crop that is more compatible than
conventional barley with the nutrient-dense feeds preferred in monogastric feeds,
especially by the poultry industry. A second possibility in the refinement of hull-less
barley for feed may be the incorporation of the waxy starch trait for improvement of feed
processing characteristics, and possibly the rate or extent of starch digestion. Changes in
starch physical properties in response to heat and moisture are conventionally measured
for baking and industrial applications using a viscoamylograph, although the specific
relation between such results and the feed pelleting process have not been established. In
the present study, waxy starch hull-less barley underwent gelatinization (i.e. achieved
peak viscosity) at 98C lower than did conventional barley. Although the difference in
gelatinization temperature was somewhat less than previously reported (12% vs. 20%;
Goering et al., 1973), the results were comparable. The higher peak viscosity (`pasting
peak') for waxy barley is indicative of swollen starch granules, which resist movement
due to physical contact among adjacent granules in the starch paste and is reflected as a
higher paste viscosity (Schoch, 1969). Since the molecular weight of amylopectin is
greater in waxy than in normal starch (DeHaas and Goering, 1972; Zobel, 1984), granular
expansion may be greater as well. Similar results have been reported previously
comparing normal and waxy barley (cv. Compana) starches (DeHaas and Goering, 1972;
Goering et al., 1973).
The lower gelatinization temperature of waxy starch potentially offers several
advantages in feed processing. Greater plasticity of waxy starch could reduce energy
input, lower mechanical effort in pellet production, and higher gelatinization (at an
equivalent temperature) could improve adhesion and pellet hardness. Although starch
does not undergo gelatinization during conditioning prior to pelleting in the true sense, it
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
217
seems reasonable to expect that the general relationship between waxy and normal starch
would hold true during the initial stages of starch gelatinization, or starch `melting'
(Thomas and Van der Poel, 1996). This interpretation was supported by the model
pelleting system employed, in that there was a linear relationship between pellet hardness
and temperature at all moisture levels, and equivalent pellet hardness with the waxy hullless barley (calculated from pellet hardness prediction equation) was achieved at 14.28C
lower than the normal starch hull-less barley.
Achieving equivalent pellet hardness at lower temperature would also reduce damage
to heat-sensitive dietary components, for example dietary protein or feed additives.
Although the present study only considered conventional pelleting, it is anticipated that
expansion or extrusion systems would react similarly. In the latter case, the temperatures
are sufficient for the formation of resistant starch, which is a function of amylose content
and would presumably be less with the waxy starch type. In the model pellet system waxy
barleys provided significantly harder pellets than normal starch barley at a range of
temperatures and added moisture levels encountered in feed processing. Whether or not
this can be attained commercially remains to be determined. In related studies (Ankrah,
1994) normal starch hull-less barley resulted in pellets that were significantly harder
than pellets from corn (p < 0.01) and not significantly different than pellets from wheat.
Corn starch also had a higher gelatinization temperature range (62±728C) than barley
(51±608C) or wheat (56±648C) starches (Biliaderis, 1980).
The total b-glucan content is consistently and significantly higher in waxy hull-less
barley than in normal isotype (Ullrich et al., 1986; Xue et al., 1991). In the present study,
the high extract viscosity associated with hull-less barley (without b-glucanase) was
evident in both the PSI and DSI. Waxy barley in general had higher extract viscosity than
the normal hull-less barley in the absence of enzyme supplementation, and pelleting
alone tended to reduce viscosity. This latter effect may be due to a shearing effect on
b-glucan during pelleting, or, more likely, the pelleting procedure that was used provided
some opportunity for b-glucan degradation due to endogenous b-glucanase during the
conditioning process, which allowed a longer period of exposure than normal pelleting.
Clearly, however, the dominant effect in terms of intestinal viscosity reduction was
b-glucanase supplementation, which greatly reduced viscosity levels. As observed
previously with high and low viscosity barleys (Campbell et al., 1989, Campbell et al.,
1993), there were no differences among barleys attributable to viscosity differences when
supplemented with dietary enzymes.
Extract viscosity provides a uniform measure of intestinal viscosity, however, it is
reasonable to expect that in vivo there is a concentration gradient with viscosity
increasing with proximity to the cell surface, reflecting gradual dissolution of the cell
wall during digestion. The similarity in extract viscosity between the proximal and distal
small intestine indicate that this process was virtually complete in the proximal region.
High b-glucan induced viscosity has a pronounced effect on digestibility of most
nutrients, but especially fat (Campbell and Bedford, 1992). Starch digestion is affected as
well, but in this case the effect was to shift starch digestion posteriorly, rather than affect
total digestibility. In the present study, overall starch digestibility was reduced as well in
the case of the normal starch hull-less barley without enzyme supplementation. The
granule surfaces of raw waxy starch are covered with natural fissures, which, along with
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N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
higher solubility of amylopectin, has been suggested to enhance susceptibility to aamylase. There was no indication of higher starch digestion in the PSI with waxy starch
type in enzyme-supplemented, non-pelleted diet compared to the normal starch type,
indicating that any granular surface differences had no effect. The effect of heat on starch
digestion can also be explained in terms of partial granule disruption increasing the rate
of degradation by a-amylase. The effect of heat treatment imparted by the conditioning/
pelleting process on starch digestion was most apparent in the proximal small intestine,
where starch digestion was considerably greater in the pelleted as opposed to the
untreated hull-less barley, in the absence of dietary enzyme. The waxy hull-less barley
was numerically, but not statistically higher in starch digestion than the normal hull-less
barley in the pelleted feed supplemented with enzyme. The most consistent factor
affecting starch digestion was the inclusion of dietary b-glucanase, followed by heat
treatment and finally, starch type. Waxy starch only offered an apparent advantage in the
enzyme-supplemented, pelleted diets which may relate to its lower gelatinization
temperature.
While starch digestion in poultry is virtually complete, Hesselman and Aman
(1986) considered starch digestion in the lower regions of the small intestine as
less efficient than anterior regions because of the presence of indigenous microflora,
which compete with the host for digested products. Greater starch digestion in the
proximal small intestine, whether accomplished by enzyme supplementation, heat
processing, or starch type differences, may be interpreted as a higher rate of starch
digestion, which introduces other potential metabolic savings. Nutrient assimilation
may be higher within a given time period, which would ultimately be reflected in higher
feed consumption, and faster growth. Anterior digestion of starch may also be indicative
of reduced enzyme protein required to digest starch, protein which could then be
channeled for growth and development. Heat and moisture treatment as it occurs
during pelleting may obliterate differences in starch digestibility attributable to granular
surfaces.
Chick performance, as reflected by body weight gain, feed intake, and feed conversion,
did tend to correspond to starch digestibility in the proximal small intestine. As observed
previously, with waxy and normal starch barley, starch type influenced body weight gain
and feed efficiency (Newman and Newman, 1987). The major response was to enzyme
addition, where body weight gain improvement approached 50%. Among the enzyme
supplemented groups there were no significant differences attributable to heat treatment
(pelleting) or starch type, indicating that the digestibility differences attributable to these
factors were insufficient to affect performance parameters, or the response magnitude was
below detectable levels under the conditions of the assay.
It may be concluded from this study that high amylopectin hull-less barley may offer
advantages in feed processing associated with its lower gelatinization temperature. The
higher b-glucan affiliated with the waxy trait would seriously confound the analysis of
nutritional value in diets which did not include an enzyme supplement. Although
experimental results have indicated that the effect due to high b-glucan is not a major
concern in enzyme-supplemented diets (Campbell et al., 1989, Campbell et al., 1993),
barley breeders should strive to lower b-glucan genetically to at least moderate levels if
waxy starch-type barleys are developed for feed applications.
N.O. Ankrah et al. / Animal Feed Science and Technology 81 (1999) 205±219
219
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