©2012 Poultry Science Association, Inc.
Effects of particle size and feed form
on broiler performance
C. G. Chewning, C. R. Stark,1 and J. Brake
Department of Poultry Science, North Carolina State University, Raleigh 27695-7608
Primary Audience: Feed Manufacturers, Nutritionists, Researchers
SUMMARY
A study was conducted to evaluate the effect of feed form and corn particle size on broiler
performance. Previously, broilers had an improvement in feed conversion when fed pelleted
(P) diets as compared with mash (M) diets, but results for the effects of particle size were not
as clear. This experiment was a 2 × 2 factorial design of feed form (P and M) and corn particle
size (300 and 600 μm). Each of 8 replicate pens had 16 males and 16 females for each of the 4
interactions. The corn and soybean meal starter P diet was crumbled, whereas the grower and
finisher P diets were fed as pellets. The average corn particle size in the 300 and 600 treatment
diets was 267 and 570 μm, respectively. Pellet durability index of the P300 diets and P600 diets,
produced with a hammermill equipped with either a 1.6- or 7.9-mm screen, averaged 88 and
84%, respectively. The chicks fed the P300 diet exhibited a significantly higher BW to 21 d, but
the difference diminished thereafter. The 44-d BW of broilers in the P treatment was higher and
FCR was better than for those fed M diets, as expected. No significant difference was observed
in the FCR of birds fed the P300 (1.88) or P600 (1.85) diets at 44 d. On the basis of these results,
broilers performed better when fed the P diets, and they demonstrated a positive BW response
to feeding finer particles up to 21 d.
Key words: broiler, gizzard, mash, particle size, pellet
2012 J. Appl. Poult. Res. 21:830–837
http://dx.doi.org/10.3382/japr.2012-00553
DESCRIPTION OF PROBLEM
Researchers and nutritionists continually explore options to reduce broiler production costs.
Particle size reduction and pelleting have been
shown to improve feed conversion and reduce
feed cost in both swine and poultry [1, 2]. Broilers fed pelleted (P) feed have higher BW and
improved feed conversion relative to those fed
mash (M) feed [3, 4]. Pelleted feed also has the
benefits of decreased feed ingredient separation,
decreased feed wastage, starch gelatinization,
1
Corresponding author: [email protected]
and improved palatability [5]. Skoch et al. [6]
reported no difference in gelatinization because
of the steam conditioning process; however,
starch gelatinization occurred when the feed was
pressed through the hole in the die. Similarly,
Buchanan et al. [7] demonstrated that a thicker
pellet die relative to the hole diameter increased
starch gelatinization. However, these benefits
tended to decrease when birds were fed lowquality pellets or a high percentage of fines [3].
Briggs et al. [8] reported that a poor-quality pellet resulted in a high percentage of fines, which
Chewning et al.: PARTICLE SIZE AND FEED FORM
were not consumed well by birds. One means
to improve pellet quality has been to reduce the
particle size of the cereal grain. Particle size
reduction also allows for a greater interaction
with digestive enzymes because of an increased
amount of surface area on the grain particle [1,
9]. A potential negative effect of reduced particle size is poor gizzard development, which
has been found to be important for feed utilization and intestinal health [10]. However, results
of studies concerning the effect that particle size
has on gizzard development and feed utilization
have been inconclusive. Nir et al. [11] stated
that a greater coarseness of feed increased the
relative gizzard weight, whereas Amerah et al.
[2] suggested gizzard stimulation was due to the
length of time that the coarse particles resided in
the gizzard. In addition to particle size reduction
as a method to improve broiler performance and
reduce cost, the effect of feed form must be considered in combination with particle size. The
purpose of this study was to determine whether
corn particle size, feed form, and the interaction
between corn particle size and feed form would
have an effect on broiler performance.
MATERIALS AND METHODS
Broiler Management
The experiment was conducted at the North
Carolina State University Chicken Educational Unit. The care of the birds used in the trial
conformed to the Guide for the Care and Use
of Agricultural Animals in Agriculture Research
and Teaching [12]. A total of 512 male and 512
female 1-d-old chicks (Ross 344 × 708 SF) [13]
were weighed and placed on the day of hatching in a curtain-sided, heated, and fan-ventilated
broiler house for 44 d. Thirty-two birds were
placed per pen (16 of each sex), with 32 pens in
total. Each pen was 1.2 m wide × 3.8 m long and
contained 1 bell-type waterer and 2 plastic tube
feeders. Birds were raised on used litter that was
top-dressed with new shavings at the start of the
study. Birds had ad libitum access to water and
feed throughout the study. Feeders were shaken
once per day until 14 d, 3 times per day until 35
d, and 4 times per day from 35 d until the termination of the experiment. The lighting program
provided 23 h of light from 1 to 7 d, 22 h of light
831
to 14 d, 20 h of light to 21 d, and natural light
afterward. The temperature from hatching was
kept at 34 to 32°C to 7 d, at 29°C to 14 d, at
27°C to 21 d, and ambient thereafter.
Feed Preparation and Experimental Design
Corn and soybean meal basal diets were formulated and manufactured for starter, grower,
and finisher feeds (Table 1). The basal starter
diet was formulated to contain 23% CP, 1.26%
total Lys, and 0.96% total Met + Cys. The grower basal diet contained 20% CP, 1.10% Lys, and
0.83% Met + Cys. The finisher basal diet contained 18.5% CP, 1.10% Lys, and 0.75% Met +
Cys. Each diet was isonutritive, and all diets met
or exceeded the NRC suggested requirements
[14]. To create the experimental treatments, corn
was ground with a hammermill [15] equipped
with 1.6-mm screens to achieve an average particle size of 300 μm or with 7.9-mm screens
to achieve an average particle size of 600 μm
for the starter, grower, and finisher basal diets.
These were termed the 300 and 600 corn particle size treatments. A portion of the diets was
pelleted at 82°C using a 4.4 × 35 mm die [16].
Thus, 2 feed forms, crumble or P and M, were
created from each basal diet to create the P and
M treatments, and there were 4 interactions
cells, designated M300, M600, P300, and P600.
The birds were fed 0.7 kg/bird of starter diet, 2.7
kg/bird of grower diet, and 2.7 kg/bird of finisher diet. There were 8 replicates per interaction in
the 2 × 2 design.
Data Collection
Initial pen BW by sex was collected at 1 d of
age. Feed consumption by pen and BW by sex
within pen were also determined at 14, 21, 35,
and 44 d of age. Dead birds were removed and
weighed daily to calculate mortality. The FCR
was adjusted for mortality by adding the weight
of the dead birds to the weight of the live birds
in each pen.
Analytical Methods
Ground corn samples were analyzed for particle size [17] with the addition of sieve agitators and 0.5 g of a dispersing agent [18]. The
JAPR: Research Report
832
Table 1. The composition of the broiler starter, grower,
and finisher diet
Item
Ingredient, %
Corn
Soybean meal (48% CP)
Limestone
Dicalcium phosphate
dl-Met
l-Lys
Thr
NaCl
Vitamin premix1
Choline chloride (60%)
Trace mineral premix2
Se premix3
Coban4
Poultry fat
Calculated analysis
ME, kcal/kg
Protein, %
Ca, %
Available P, %
Total Lys, %
Total Met + Cys, %
Starter
59.30
35.80
2.09
0.97
0.00
0.19
0.05
0.50
0.05
0.20
0.20
0.10
0.05
0.50
Grower
Finisher
67.19
28.15
1.85
1.02
0.06
0.13
0.00
0.50
0.05
0.20
0.20
0.10
0.05
0.50
71.47
23.90
1.57
1.07
0.21
0.10
0.08
0.50
0.05
0.20
0.20
0.10
0.05
0.50
2,935
3,016
3,068
23.00
20.00
18.50
0.90
0.85
0.80
0.45
0.40
0.35
1.26
1.10
1.10
0.96
0.83
0.75
1
The vitamin premix supplied the following per kilogram of
feed: vitamin A, 6,601; cholecalciferol, 1,980 IU; niacin, 55
mg; α-tocopherol, 33 mg; pantothenic acid, 11 mg; riboflavin, 6.6 mg; pyridoxine, 4 mg; menadione, 2 mg; thiamine,
2 mg; folic acid, 1.1 mg; biotin, 0.13 mg; and vitamin B12,
0.02 mg.
2
The mineral premix supplied the following per kilogram of
feed: Zn, 120 mg; Mn, 120 mg; Fe, 80 mg; Cu, 10 mg; I, 2.5
mg; Co, 1.0 mg.
3
The Se premix provided 0.2 ppm of Se.
4
Monensin was included at 99 mg/kg (Elanco Animal
Health, Greenfield, IN).
percentage fines in the diets were determined by
sieving a sample of the cooled P feed through
a US No. 5 sieve. The percentage of fines was
then calculated by dividing the amount of fines
by the total quantity of each sample. Pellet quality, as measured by the pellet durability index
(PDI) [19], was determined on samples collected at the pellet mill die.
Data Analysis
The experiment was analyzed as a 2 × 2
factorial randomized complete block design involving feed form (P vs. M) and corn particle
size (300 vs. 600) as the main effects. Data were
analyzed with the GLM procedure of SAS [20].
Means were partitioned by least squares means,
with significance set at P < 0.05.
RESULTS AND DISCUSSION
Particle size of the ground corn in the P300
treatment averaged 269, 263, and 269 μm,
whereas the P600 treatment averaged 615, 536,
and 519 μm for the starter, grower, and finisher
diets, respectively. Pellet quality values, as determined by the PDI test, for the starter, grower,
and finisher P300 diets were 90, 85, and 87%
compared with 86, 82, and 84% for the P600
diets, respectively. These data were consistent
with previous research demonstrating that a
smaller feed particle size created a more durable
pellet [21, 22]. Wondra et al. [22] reported that
as the particle size of the grain in diets decreased
from 1,020 to 450 µm, there was an improvement in PDI from 79 to 86%, respectively. The
P diet that contained finely ground corn (P300)
contained fewer fines: 15, 22, and 6% compared
with 17, 27, and 8% fines for the starter, grower,
and finisher P600 diets, respectively. A reduction in particle size for both the grain and protein
sources in a diet will improve the pellet quality
and result in fewer fines at the feeder, which is a
primary reason for reducing the particle size of
grain when pellet quality is a key performance
indicator within a feed mill.
On the basis of the results of this experiment,
feed form affected BW of both male and female
broilers at all ages (Table 2). Broilers fed the P
diets had consistently higher BW throughout
the study. Nir et al. [4] reported similar effects
because of feed form, with male broilers fed P
diets exhibiting significantly higher BW (2,298
g) compared with those fed M diets (2,236 g) at
35 d of age [4]. Female broilers in their study
also had a positive response to P feed at 35 and
42 d, but the overall advantage of P feed was
only 20 g [4]. McKinney and Teeter [3] demonstrated that broilers consuming a P vs. M diet
gained 82 g more BW during a 7-d period from
38 to 45 d of age. In a cage study, Lemme et al.
[23] evaluated the difference between coarse M,
poor-quality P feed, and good-quality P feed on
broiler performance and indicated that P diets of
good quality had the highest overall BW gain.
The BW results attributable to particle size
reduction and improved PDI in the P diets observed in the current study were similar to results reported by others. Particle size reduction
resulted in an improvement in BW up to 21 d, but
412A
395B
3
429A
406B
4
16
16
0.0329
0.0001
0.0001
360B
447A
3
373B
462A
4
16
16
0.1557
0.0001
0.0001
373b
347c
452a
442a
4
Female
388
358
470
454
5
Male
8
8
8
8
n
0.1504
0.0001
0.0149
851a
824b
7
751B
925A
7
772
730
931
919
10
Male
0.0524
0.0001
0.0025
785a
761b
5
701B
845A
5
720
682
850
840
7
Female
21-d BW, g
P-value
0.4693
0.0001
0.2413
2,038
2,004
20
1,827B
2,215A
20
1,854
1,799
2,222
2,209
28
Male
A,B
0.0375
0.0001
0.7242
1,718
1,713
12
1,567B
1,864A
12
1,588b
1,546b
1,849a
1,879a
17
Female
35-d BW, g
Means within a column for n pens of 32 broilers with different superscripts differ significantly (P ≤ 0.05).
Means within a column for n pens of 32 broilers with different superscripts differ significantly (P ≤ 0.01).
1
Treatments consisted of mash diets with corn of 300- and 600-μm particle sizes or pelleted diets with corn of 300- and 600-μm particle sizes.
a–c
Source of variation
Feed form × corn particle size
Feed form
Corn particle size
Interaction effect, feed form and particle size
Mash, 300 μm
Mash, 600 μm
Pellet, 300 μm
Pellet, 600 μm
SEM
Main effect
Feed form
Mash
Pellet
SEM
Corn particle size
300 μm
600 μm
SEM
Item
14-d BW, g
Table 2. Effect of feed form, corn particle size, and their interaction on BW of male and female broilers1
0.7835
0.0001
0.9452
2,981
2,979
26
2,733B
3,227A
26
2,739
2,726
3,224
3,231
38
Male
0.9701
0.0001
0.3585
2,440
2,415
19
2,239B
2,616A
19
2,252
2,227
2,629
2,603
27
Female
44-d BW, g
Chewning et al.: PARTICLE SIZE AND FEED FORM
833
JAPR: Research Report
834
feed intake when birds were fed M vs. P to 42
and 21 d, respectively, whereas McKinney and
Teeter [3] did not observe a difference from 38
to 45 d. Parsons et al. [26] reported no difference
in feed intake when birds were fed M vs. P diets
from 21 to 42 d. On the basis of the results of the
present study, when birds were fed extremely
finely ground corn (265 μm), feed intake was
depressed unless the feed was fed in the P form.
This lower feed intake resulted in a lower BW
when birds consumed the M300 diet.
The FCR results attributable to feed form observed in the present study were similar to the
effects on BW (Table 4). The P diets resulted
in better bird performance than did the M diets.
Birds fed the P diets had an FCR of 1.85, compared with an FCR of 2.02 for birds fed the M
diets. Amerah et al. [24] reported a similar trend,
in which birds fed P diets exhibited an FCR of
1.52, whereas birds fed M diets achieved an
FCR of 1.67 at 21 d of age. McKinney and Teeter [3] compared the percentages of P vs. fines
in a P broiler diet for 7 d and found that as the
the overall effect of particle size on BW at 44 d
was not different. The lack of difference in BW
observed in our study was similar to the results
of Amerah et al. [2], who reported no significant difference in BW gain because of fine and
coarse particle sizes. The birds that consumed
the M300 diet had the lowest feed intake of all
interactions from 14 to 44 d (Table 3). However,
the BW of the broilers fed the M300 and M600
diets at 44 d was similar, possibly resulting from
better nutrient utilization or less feed wastage
associated with the M300 vs. M600 diets, which
was also suggested by the improved FCR.
There was a feed form × particle size interaction for feed intake at 44 d. The overall feed intake of the birds fed the M600, P300, and P600
diets were similar and were higher than intakes
of the birds fed the M300 diet. Amerah et al.
[24] found a similar interaction when birds were
fed a diet that contained finely ground wheat.
The results of research on the effect of feeding
birds M vs. P diets had been mixed. Corzo et
al. [25] and Amerah et al. [2] reported decreased
Table 3. Effect of feed form, corn particle size, and their interaction on feed intake of broilers1
Feed intake, g
Item
Interaction effect, feed form and particle size
Mash, 300 μm
Mash, 600 μm
Pellet, 300 μm
Pellet, 600 μm
SEM
Main effect
Feed form
Mash
Pellet
SEM
Particle size
300 μm
600 μm
SEM
n
0 to 14 d
0 to 21 d
0 to 35 d
0 to 44 d
8
8
8
8
572
607
593
590
11
1,196B
1,334A
1,297A
1,289A
20
3,023B
3,376A
3,442A
3,406A
46
4,776B
5,149AC
5,423AD
5,320A
62
16
16
590
592
8
1,265
1,293
14
3,199B
3,424A
32
4,964B
5,372A
43
16
16
582
599
8
1,246B
1,312A
14
3,232B
3,391A
32
5,098b
5,235a
43
P-value
Source of variation
Feed form × corn particle size
Feed form
Corn particle size
A–D
0.0944
0.8523
0.1356
0.0010
0.1581
0.0027
0.0002
0.0001
0.0017
0.0007
0.0001
0.0400
Means within a column for n pens of 32 broilers with different superscripts differ significantly (P ≤ 0.01).
Treatments consisted of mash diets with corn at a 300- and 600-μm particle size or pelleted diets with corn at a 300- and 600μm particle size.
1
Chewning et al.: PARTICLE SIZE AND FEED FORM
835
Table 4. Effect of broilers feed form, particle size, and their interaction on the FCR of broilers
FCR, g/g
Item
Interaction effect, feed form and particle size
Mash, 300 μm
Mash, 600 μm
Pellet, 300 μm
Pellet, 600 μm
SEM
Feed form
Mash
Pellet
SEM
Particle size
300 μm
600 μm
SEM
n
0 to 14 d
0 to 21 d
0 to 35 d
0 to 44 d
8
8
8
8
1.69B
1.96A
1.42C
1.45C
0.03
1.70B
2.01A
1.53C
1.54C
0.03
1.80B
2.07A
1.73C
1.70C
0.02
1.94B
2.11A
1.87C
1.84C
0.02
16
16
1.83A
1.43B
0.02
1.86A
1.54B
0.02
1.93A
1.71B
0.01
2.02A
1.85B
0.01
16
16
1.55B
1.70A
0.02
1.62B
1.78A
0.02
1.76B
1.88A
0.01
1.90B
1.97A
0.01
0.0001
0.0001
0.0001
0.0001
0.0001
0.0007
P-value
Source of variation
Form × particle size
Feed form
Corn particle size
0.0014
0.0001
0.0001
0.0001
0.0001
0.0001
A–C
Means within a column for n pens of 32 broilers with different superscripts differ significantly (P ≤ 0.01).
Treatments consisted each of mash diets with corn at a 300- and 600-μm particle size and pelleted diets with corn at a 300- and
600-μm particle size.
1
percentage fines increased, the FCR worsened
such that the P diets produced an FCR of 1.87
compared with 2.02 for the M diets [3].
Particle size also had an effect on the FCR. In
the present study, an improvement in FCR was
observed when birds were fed the M diets that
contained a corn particle size of 300 vs. 600 μm.
In contrast to these results, others have reported
an improved FCR of 1.58 vs. 1.62 when caged
birds were fed a coarse (1,164 μm) vs. medium
(839 μm) particle size, respectively [24]. In a
follow-up study in cages, Amerah et al. [2] reported an FCR of 1.41 vs. 1.49 for coarse-particle (528 μm) vs. fine-particle (297 μm) grain, respectively. In contrast to the research by Amerah
et al., in the present study we compared male
and female broilers, whereas the studies by Amerah et al. [2, 24] used only male broilers. The
difference in results could be due to the large
particle size that was used in their studies or the
fact that the birds were raised in cages without
access to litter.
The combination of corn ground to 300 or 600
μm and P feed produced similar FCR throughout
the present study. However, birds fed the M300
diet had a better FCR overall as compared with
those fed the M600 diet. The smaller particle
size of corn in the P diet also produced a slightly
better quality pellet, as indicated by the PDI and
percentage of fines, which were consistent with
the observation that pellets made with coarse
grain particles tended to deteriorate as the pellet
moved through the manufacturing process and
feed delivery system to the broiler feeder.
The performance of broilers fed the P diets
was not changed because of the particle size of
the grain in the present study. The 44-d BW and
FCR of the males and females fed the P300 and
P600 diets were similar. It has been suggested
that pellets containing coarser material dissolve
more slowly in the crop, which increases the
time needed to digest, thereby improving feed
utilization [4]. However, in the present study,
birds fed a finely ground M diet had lower feed
intake and improved FCR. The differences attributable to the particle size in M feed vs. P feed
may have been be due in part to the final size
of the particles in a pellet, the rate of feed passage because of the feed form and particle size,
the distribution of particles within the ground
JAPR: Research Report
836
grain, and access to litter because the trial was
conducted in floor pens. Therefore, during the
last 14 to 21 d of growth, when the ability of the
bird to consume sufficient feed may be limited
because of feeder space or pen density, the broiler may respond differently based on the particle
size of the corn and the form of the diet. Pacheco
et al. [27] reported that stimulating the birds to
consume feed by walking the pens 3 times vs.
once a day increased feed intake by 4% and BW
by 6%, respectively.
In the present study, birds fed the M diets
had slightly larger gizzard weights and gizzard
weights relative to BW (g/100 g) as compared
with the birds that received the P feed (Table 5).
The coarser grain particle size resulted in the
highest gizzard weights, 38.1 and 33.6 g, in both
the M and P feed forms, respectively. Parsons
et al. [26] observed a positive broiler growth
response with increased M feed particle size,
with birds fed the coarser diet having the largest gizzard weight. The birds fed the coarse corn
M diets exhibited greater absolute and relative
gizzard weights compared with the birds fed
the fine corn M diets [26]. Data from the present study were similar. Research supports this
finding because the coarser grain results in increased gizzard size and gizzard activity to grind
the particles [28].
Table 5. Effect of feed form, corn particle size, and
their interaction on gizzard weight (g) and percentage
of gizzard of broilers at 44 d1
Gizzard weight
Item
n
Feed form, corn particle size
Mash, 300 μm
Mash, 600 μm
Pellet, 300 μm
Pellet, 600 μm
24
24
24
24
g/100 g
of BW
g
35.8a
38.1a
26.7b
33.6b
1.45b
1.56a
1.05d
1.30c
P-value
Source of variation
a–d
0.0108
0.0387
Means within a column for n pens of 32 broilers with different superscripts differ significantly (P ≤ 0.05).
1
Treatments consisted of mash diets with corn at a 300- and
600-μm particle size and pelleted diets with corn at a 300and 600-μm particle size.
CONCLUSIONS AND APPLICATIONS
1. The P feed form resulted in a higher BW
and improved FCR compared with the M
feed form.
2. The interaction between feed form and
particle size was not apparent in the P diets because the digestibility of the P feed
was apparently the same at both particle
sizes.
3. Broilers fed the M feed that contained
more finely ground corn had better overall FCR.
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