©2012 Poultry Science Association, Inc.
Performance and carcass characteristics of Cobb
× Cobb 500 slow-feathering male broilers
fed on dietary programs having stepwise
increases in ideal protein density
S. L. Vieira,*1 D. Taschetto,* C. R. Angel,† A. Favero,* N. C. Mascharello,*
and E. T. Nogueira‡
*Departamento de Zootecnia, Universidade Federal do Rio Grande do Sul,
Av. Bento Gonçalves, 7712, Porto Alegre, Rio Grande do Sul, 91540-000, Brazil;
†Department of Animal and Avian Sciences, University of Maryland, College Park 20742;
and ‡Ajinomoto Biolatina–Ajinomoto Animal Nutrition, Rua Joaquim Távora,
541, São Paulo, São Paulo, 04015-901, Brazil
Primary Audience: Nutritionists
SUMMARY
The Cobb × Cobb 500 slow-feathering male is a fast early-growth broiler grown under variable feeding programs and amino acid (AA) densities. An experiment was conducted using
diets with increased ideal protein densities in a feeding program of 1 to 7 d, 8 to 21 d, 22 to 35d,
and 36 to 42 d. Diets had ratios between essential digestible (D) AA and DLys (DAA:DLys) as
follows: TSAA, 75%; DThr, 65%; DVal, 75% (from 1 to 7 d) and 77% (from 8 to 42 d); DIle,
67%; DArg, 104%; and DTrp, 17%. A completely randomized experimental design in a 3 ×
3 factorial arrangement of 3 AA densities (low, moderate, and high) from 1 to 21 d (phase I)
and 3 AA densities from 22 to 42 d (phase II) was used. The moderate dietary program was set
with DLys at 1.26, 1.15, 1.05, and 0.95% from the prestarter to finisher phase. Replications per
treatment were 30 from 1 to 21 d and 10 from 22 to 42 d. Birds fed the high-AA-density diets
in phase I had the best BW gain at 35 and 42 d (P < 0.05) and the lowest FCR (P < 0.05) when
combined with the high- or moderate-AA-density diets in phase II. The high- and moderateAA-density diets in phase I maximized BW gain at 42 d when combined with either the high- or
moderate-AA-density diet in phase II (P < 0.05). Percentages of breast fillets, breast tenders,
and thighs were not affected by treatment in phase I; however, breast fillet percentage was
maximized with when the moderate- or high-AA-density diets (P < 0.05) were fed in phase II,
whereas breast tenders and thighs were maximized only when the high-AA-density diets (P <
0.01) were fed in phase II. Commercial application will depend on ingredient costs and meat
market prices at decision time based on the program that results in the lowest cost per sellable
product.
Key words: broiler, amino acid density, digestible lysine, ideal protein
2012 J. Appl. Poult. Res. 21:797–805
http://dx.doi.org/10.3382/japr.2012-00523
1
Corresponding author: [email protected]
JAPR: Research Report
798
DESCRIPTION OF PROBLEM
Broiler feeding programs should maximize
income per sellable product by optimizing FCR
and BW gain (BWG), depending on the product mix and breast meat yield (BMY). Research
on responses to increases in dietary amino acids
(AA) has been motivated by the dilemma routinely encountered by broiler integrators, whose
target is feeding low-cost (low-density) diets to
broilers that are continuously being selected for
greater growth and meat yields.
Supporting increasing amounts of body protein of the broilers resulting from this selection
pressure is expected to require higher dietary
AA needs. A higher feed intake associated with
the greater growth potential of modern broilers
can partially deliver some of these greater AA
demands. However, changes in nutrient ratios
may be needed because of the greater proportion
of breast muscle in modern breeds as compared
with earlier ones [1]. In addition, evidence exists that the demands of AA required for growth
have increased proportionately faster than those
for energy; thus, a higher AA-to-energy ratio
may be required in faster growing strains of
broilers [2].
When AA requirements for BWG, FCR, and
BMY are evaluated individually, the results
show that requirements are greatest for BMY,
followed by FCR, and finally BWG [3, 4]. This
means that the daily AA supply that leads to the
best economic returns should have an adequate
balance for the end product desired, to avoid
waste caused by excess inclusion of essential
AA. The evaluation of broiler responses to increases in dietary AA has been done through
different approaches: by increasing AA individually and maintaining or not maintaining
the balance between them. Therefore, research
outcomes are frequently difficult to compare.
Increasing the proportion of digestible (D) Lys
under commercial situations has led to improvements in BWG, FCR, and BMY [5, 6]. In these
studies, however, the overall essential AA balance was changed through an increase in DLys
only; therefore, further improvements might
have occurred if other AA had also been increased to maintain optimal ratios [7–9].
Benefits in performance obtained with increased AA density diets have been shown when
applied early in life as well as only in the later
phases [10, 11]. However, in work in which different combinations of AA densities have been
used through the different growth phases, live
performance responses have tended to be better
when broilers were fed high-AA-density diets
in all feeding phases [12, 13]. Matching broiler
performance improvements from feeding highAA-density diets with the best economic returns depends on the market price for meat as
well as ingredient costs, variables that change
frequently. Estimations of broiler responses to
increased AA density diets would allow nutritionists to simulate outcomes based on ingredient costs and meat prices. However, to provide
comparable results, ratios of DAA to DLys (as
in the ideal protein concept) should be maintained. Thus, the objective of this study was to
investigate the effect of feeding programs with
increasing AA densities while ideal AA ratios on
the growth and body composition responses of
broiler males are maintained.
MATERIALS AND METHODS
Broilers in the present study were managed
according to the directives of the Committee of
Ethics and Use of Animals of the Universidade
Federal do Rio Grande do Sul, Porto Alegre,
Brazil. A total of 2,250 one-day-old Cobb ×
Cobb 500 slow-feathering male broiler chickens, obtained from 38-wk-old breeder hens,
were used. Birds were vaccinated for Marek’s
disease and infectious bronchitis at the hatchery [14]. Chickens were placed in 90 floor pens
(2.62 m2 each) with 25 birds each, with unused
rice hulls as litter. Each pen was equipped with
1 tube feeder (18 kg) and 1 bell drinker. Temperature was provided to maintain bird comfort
throughout the study, which was accomplished
through the use of heaters, fans, and foggers.
The lighting program was continuous in the first
week, and 14L:10D was provided thereafter.
Experimental diets were formulated using
energy and nutrient data as minimum restrictions in linear feed formulation, which included
DAA-to-DLys ratios obtained from a representative number of Brazilian nutritionists responding to a survey on dietary programs used in their
commercial operations [15]. These values were
averaged and used to formulate the moderate-
Vieira et al.: Amino acid densities in broilers
AA-density diets. High- and low-AA-density
diets were formulated to be 13% above or below the AA concentrations of the moderate-AAdensity diet within each feeding phase, as shown
in Tables 1 and 2. This percentage value (13%)
was the average difference between the highest
and lowest DLys values reported in the survey.
With the exception of CP and AA, all nutrients
and AME remained the same for the high‑, low‑,
and moderate-AA-density diets. Feeds were
formulated using corn and soybean meal after
the ingredients were analyzed for AA [16, 17].
Digestibility coefficients [18] were applied to
the analyzed AA to obtain linear least-cost feed
formulation solutions for all experimental diets,
and AME and nutrient content for each feed
ingredient were obtained from the recommendations of Rostagno et al. [18]. A feeding program with 4 phases was used: prestarter (1 to 7
d), starter (8 to 21 d), grower (22 to 34 d), and
withdrawal (36 to 42 d; Tables 1 and 2). Diets
were mixed in a 400-kg mixer and were fed as
mash in the prestarter, crumbled in the starter,
and pelleted (3.5 mm) in the grower and withdrawal phases.
Ideal DAA:DLys ratios were as follows:
TSAA (DTSAA), 75%; DThr, 65%; DVal, 75%
(in the prestarter) and 77% (in the phases thereafter); DIle, 67%; DArg, 104%; and DTrp, 17%.
After feed mixing, a sample of each experimental diet was sent for AA analysis. Feeding
programs with 3 AA densities (low, moderate,
and high) were provided from 1 to 21 d (phase
I), which were then further divided into 3 other
treatments (low, moderate, and high) from 22
to 42 d of age (phase II). Therefore, 9 treatments in total were used after 22 d of age (highhigh, high-moderate, high-low, moderate-high,
moderate-moderate, moderate-low, low-high,
low-moderate, low-low). Diets were formulated
without a CP minimum restriction.
Performance was evaluated at the end of each
feeding phase for BWG, FCR corrected for the
weight of dead birds, and feed intake. At 42 d
of age, 6 birds from each replication were randomly selected, individually indentified, and
processed for evaluation of the carcass yield,
and weight and yield of abdominal fat, breast fillets (pectoralis major), breast tenders (pectoralis
minor), thighs, and drumsticks. Bird processing
followed 8 h fasting and was done with the use
799
of electrical stunning (minimum of 45 mA per
bird), bleeding through a jugular vein cut, scalding at 58°C for 1 min, defeathering, and manual
evisceration. Carcasses were then immersed in
chilled water (2°C) for 3 H. Carcasses without viscera, necks, and feet were hung to draw
water excesses for 3 min and then individually
weighed. Carcass yield was expressed as a percentage of the live broiler weight, and commercial cuts were expressed as percentage of the
eviscerated carcass.
A completely randomized experimental design was used in a 3 × 3 factorial arrangement
of 3 AA densities from 1 to 21 d (low, moderate, and high) and 3 AA densities from 22 to 42
d (low, moderate, and high). Thirty replications
per treatment were used in phase I, whereas 10
were used in phase II. The results were submitted to an ANOVA using the GLM procedure
of SAS [19]. Differences were considered significant when P ≤ 0.05 and separated using the
Tukey honest significant differences test [20].
For statistical analysis, mortality and carcass
data were arcsine square root transformed [(%
mortality/100) + 0.05)0.5] [21].
RESULTS AND DISCUSSION
Formulated and analyzed CP and AA concentrations were similar (Tables 1 and 2). Live
performance responses are presented in cumulative periods based on feed phase changes that
also corresponded to weighing periods (Tables
3 and 4).
No effect of treatments was observed on percentage of mortality throughout the study (grand
mean = 1.55%; SEM = 0.09). Differences were
found for BWG, FCR, and feed intake in the
periods from 1 to 7 d and 1 to 21 d. In these 2
cumulative periods, birds fed the moderate- and
high-AA-density diets had greater BWG when
compared with those fed the low-AA-density diets, whereas feed intake was lowest for birds fed
the high-AA-density diets. However, a stepwise
improvement in FCR was observed when broilers were fed diets varying from low to medium
and then to high AA density (Table 3).
Responses measured from 1 to 35 d and 1 to
42 d of age showed that BWG and FCR were
affected by the interaction between treatments
fed in the 2 phases. Broilers fed the high-AA-
61.08
32.96
1.37
2.12
1.00
0.10
0.63
0.25
0.18
0.06
0.08
0.17
Corn
Soybean meal
Soybean oil
Dicalcium phosphate
Limestone
Common salt
Sodium bicarbonate
dl-Met (99%)
l-Lys hydrochloride (78%)
l-Thr (98.5%)
Choline chloride
Premix2
51.58
41.03
2.93
2.08
0.98
0.30
0.34
0.31
0.16
0.06
0.06
0.17
Moderate
40.67
50.32
4.71
2.04
0.96
0.53
—
0.37
0.14
0.07
0.02
0.17
High
63.53
29.67
2.45
2.00
0.96
0.14
0.58
0.21
0.16
0.04
0.09
0.17
Low
54.64
37.25
3.91
1.969
0.94
0.33
0.30
0.26
0.13
0.04
0.06
0.17
Moderate
Starter
45.30
45.22
5.44
1.93
0.92
0.53
0.01
0.31
0.10
0.04
0.03
0.17
High
70.75
22.41
2.69
1.91
0.93
0.01
0.65
0.16
0.18
0.05
0.11
0.15
Low
58.97
32.45
4.62
1.86
0.91
0.27
0.28
0.22
0.14
0.06
0.07
0.15
Moderate
Grower
50.08
39.98
6.07
1.83
0.89
0.45
0.01
0.27
0.16
0.07
0.04
0.15
High
75.24
17.63
3.35
1.66
0.85
0.01
0.65
0.13
0.19
0.03
0.11
0.15
Low
63.44
27.67
5.28
1.62
0.83
0.27
0.28
0.19
0.16
0.04
0.07
0.15
Moderate
Withdrawal
54.62
35.20
6.73
1.58
0.81
0.45
0.01
0.24
0.13
0.04
0.04
0.15
High
2
The prestarter was fed from 1 to 7 d, the starter was fed from 8 to 21 d, the grower was fed from 22 to 35 d, and feed was withdrawn from 36 to 42 d.
Composition (per kg of feed): vitamin A, 8,000 IU; vitamin D3, 2,000 UI; vitamin E, 30 IU; vitamin K3, 2 mg; thiamine, 2 mg; riboflavin, 6 mg; pyridoxine, 2.5 mg; cyanocobalamin, 0.012 mg,
pantothenic acid, 15 mg; niacin, 35 mg; folic acid, 1 mg; biotin, 0.08 mg; iron, 40 mg; zinc, 80 mg; manganese, 80 mg; copper, 10 mg; iodine, 0.7 mg; selenium, 0.3 mg. Surmax 200 (avilamycin,
20 mg/kg; Elanco, São Paulo, São Paulo, Brazil), Maxiban (narasin, 80 g/kg, and nicarbazin 80 g/kg; Elanco), or Coban 400 (monensin sodium, 40%; Elanco).
1
Low
Ingredient, %
Prestarter
Table 1. Composition of the experimental diets1
800
JAPR: Research Report
2,950
19.7
(19.6)
1.10
0.82
0.71
0.82
0.77
1.19
(1.16)
0.90
(0.84)
0.80
(0.78)
0.93
(0.89)
0.85
(0.81)
1.00
0.50
0.77
0.23
254
1,725
Low
2,950
22.6
(23.0)
1.26
0.95
0.82
0.95
0.90
1.34
(1.39)
1.03
(0.96)
0.92
(0.93)
1.06
(1.05)
0.99
(0.98)
1.00
0.50
0.89
0.23
254
1,725
Moderate
2,950
26.0
(26.0)
1.45
1.09
0.95
1.09
1.05
1.58
(1.59)
1.19
(1.10)
1.06
(1.04)
1.22
(1.20)
1.15
(1.20)
1.00
0.50
1.03
0.23
254
1,725
High
3,050
18.4
(19.0)
1.00
0.75
0.65
0.77
0.72
1.08
(1.19)
0.82
(0.72)
0.73
(0.75)
0.86
(0.92)
0.79
(0.81)
0.95
0.47
0.72
0.23
236
1,650
Low
3,050
21.1
(21.8)
1.15
0.86
0.75
0.89
0.84
1.25
(1.35)
0.94
(0.82)
0.83
(0.87)
0.99
(1.04)
0.92
(0.94)
0.95
0.47
0.83
0.23
236
1,650
Moderate
Starter
3,050
23.9
(24.2)
1.32
0.98
0.85
1.01
0.97
1.43
(1.46)
1.07
(0.94)
0.96
(0.96)
1.13
(1.10)
1.06
(1.06)
0.95
0.47
0.95
0.23
236
1,650
High
3,150
15.7
(15.9)
0.91
0.64
0.57
0.65
0.60
1.00
(1.02)
0.69
(0.72)
0.63
(0.64)
0.74
(0.75)
0.65
(0.68)
0.90
0.45
0.61
0.20
213
1,600
Low
3,150
19.3
(19.0)
1.05
0.79
0.70
0.81
0.76
1.14
(1.14)
0.86
(0.82)
0.79
(0.75)
0.91
(0.83)
0.83
(0.77)
0.90
0.45
0.76
0.20
213
1,600
Moderate
Grower
3,150
22.0
(21.9)
1.21
0.90
0.80
0.92
0.88
1.32
(1.38)
0.98
(0.91)
0.90
(0.89)
1.03
(1.00)
0.96
(0.91)
0.90
0.45
0.87
0.20
213
1,600
High
3,250
13.9
(13.9)
0.83
0.56
0.49
0.58
0.52
0.91
(0.90)
0.61
(0.60)
0.55
(0.59)
0.65
(0.65)
0.57
(0.56)
0.80
0.40
0.53
0.20
193
1,500
Low
3,250
17.4
(17.6)
0.95
0.71
0.62
0.73
0.68
1.03
(0.98)
0.78
(0.73)
0.69
(0.67)
0.82
(0.74)
0.74
(0.63)
0.80
0.40
0.68
0.20
193
1,500
Moderate
Withdrawal
2
High
3,250
20.2
(20.3)
1.09
0.82
0.71
0.85
0.80
1.18
(1.20)
0.90
(0.78)
0.80
(0.78)
0.95
(0.90)
0.88
(0.83)
0.80
0.40
0.80
0.20
193
1,500
Ideal ratios between digestible amino acids and digestible Lys: TSAA, 75%; Thr, 65%; Val, 75% (in the prestarter, and 77% in the other diets); Ile, 67%; Arg, 104%; and Trp, 17%.
Formulated nutrient content; values in parentheses are analyzed.
3
Dietary electrolyte balance (Na + K − Cl, mEq/kg of diet).
1
Ca, %
Available P, %
K, %
Na, %
DEB3
Choline, mg/kg
Ile, %
Val, %
Thr, %
TSAA, %
Digestible Lys, %
Digestible TSAA, %
Digestible Thr, %
Digestible Val, %
Digestible Ile, %
Lys, %
AMEn, kcal/kg
CP, %
Energy and nutrient
Prestarter
Table 2. Nutritional composition of the experimental diets1,2
Vieira et al.: Amino acid densities in broilers
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JAPR: Research Report
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Table 3. Live performance of broilers fed diets with increased amino acid (AA) densities from 1 to 21 d
1 to 7 d
AA density
High
Moderate
Low
Mean
SEM
P-value
BW gain, g
a
154
155a
140b
150
1.00
0.001
1 to 21 d
Feed intake, g
b
FCR1
BW gain, g
a
162
169a
170a
167
1.30
0.001
1.051
1.092b
1.217c
1.120
0.005
0.001
Feed intake, g
a
 
 
 
 
 
 
FCR
b
1,090
1,104a
1,057b
1,084
4.71
0.001
1.235a
1.265b
1.329c
1.276
0.003
0.001
1,346
1,397a
1,404a
1,382
6.09
0.001
a–c
Means within the same column with different superscript letters differ (P < 0.05) based on the Tukey test [20]; n = 30 replications of 25 birds at the beginning of the experiment per treatment.
1
Corrected for the weight of dead birds.
density diet in phase I combined with the highor moderate-AA-density diets in phase II had
the best BWG and FCR from 1 to 35 d as well
as FCR from 1 to 42 d. However, BWG from
1 to 42 d was highest when birds were fed the
high- or moderate-AA-density diet in phase I
combined with high- and moderate-AA-density
diets in phase II. Feeding the low-AA-density
diet in phase I led to the lowest BWG from 1 to
35 d and 1 to 42 d when combined with either
Table 4. Live performance of broilers fed diets with increased amino acid (AA) densities from 1 to 42 d
1 to 35 d
Source of variation
Item
Main effect
Phase I, 1 to 21 d
High
Moderate
Low
Phase II, 22 to 42 d
High
Moderate
Low
Pooled SEM4
Interaction
Phase I, 1 to 21 d
 
High
 
 
Moderate
 
 
Low
 
SEM
P-value
Phase I
Phase II
Phase I vs. phase II
 
 
 
 
 
 
 
 
 
 
 
Phase II, 22 to 42 d
High
Moderate
Low
High
Moderate
Low
High
Moderate
Low
 
 
 
 
 
BW
gain, g
 
 
2,664a
2,641a
2,564b
 
2,660a
2,629b
2,579c
11
 
 
2,713a
2,657ab
2,622bc
2,667bc
2,663bc
2,593c
2,599c
2,567cd
2,525d
13.16
 
0.001
0.001
0.046
1 to 42 d
Feed
intake, g
 
 
3,897b
3,952a
3,950a
 
3,900b
3,911b
3,988a
21
 
 
3,867c
3,877c
3,947abc
3,925abc
3,935abc
3,995ab
3,904bc
3,924abc
4,022a
23.78
 
0.015
0.001
0.865
BW
gain, g
FCR1
 
 
1.462c
1.497b
1.541a
 
1.467c
1.489b
1.546a
0.01
 
 
1.426a
1.458ab
1.506cd
1.471bc
1.477bc
1.541e
1.502cd
1.528de
1.593f
0.008
 
0.001
0.001
0.034
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
3,540a
3,505a
3,409b
 
3,533a
3,488b
3,431c
15
 
 
3,604a
3,530abc
3,488bcd
3,542ab
3,526abc
3,446d
3,452cd
3,415de
3,359e
17.36
 
0.001
0.001
0.031
Feed
intake, g
 
 
5,525b
5,593a
5,579a
 
5,492b
5,530b
5,674a
28
 
 
5,480c
5,474c
5,605abc
5,508c
5,565bc
5,707ab
5,485c
5,541c
5,710a
31.88
 
0.028
0.001
0.640
FCR
 
 
1.563c
1.597b
1.637a
 
1.555c
1.585b
1.654a
0.01
 
 
1.521a
1.551ab
1.607cd
1.555b
1.578bc
1.656e
1.589c
1.622d
1.700f
0.007
 
0.001
0.001
0.014
a–f
Means within the same column with different superscript letters differ (P < 0.05) based on the Tukey test [20]; n = 10 replications of 25 birds at the beginning of the experiment per treatment.
1
Corrected for the weight of dead birds.
Vieira et al.: Amino acid densities in broilers
803
Table 5. Main effects on carcass, abdominal fat, and commercial cut yields (%) of broilers fed diets with different
densities of amino acids (AA) and processed at 42 d1
Source of variation
AA density
Phase I, 1 to 21 d
High
Moderate
Low
Phase II, 22 to 42 d
High
Moderate
Low
Pooled SEM
P-value
Phase I
Phase II
Phase I vs. phase II
Carcass
Abdominal
fat
Breast
fillets2
Breast
tenders3
Thighs
Drumsticks
79.70
79.65
79.17
 
79.43
79.38
79.71
0.41
 
0.387
0.673
0.336
1.55b
1.63ab
1.80a
 
1.43b
1.62b
1.92a
0.10
 
0.047
0.001
0.925
29.42
29.22
28.99
 
29.38a
29.33a
28.93b
0.19
 
0.091
0.031
0.935
5.28
5.24
5.20
 
5.38a
5.20b
5.07c
0.05
 
0.687
0.002
0.984
12.24
12.52
12.48
 
12.67a
12.33b
12.25b
0.13
 
0.096
0.008
0.771
18.41
18.44
18.47
 
18.45
18.42
18.44
0.15
 
0.915
0.985
0.644
a–c
Means within the same column with different letters are different (P < 0.05) using the Tukey test [20]; n = 10 replications
of 6 birds each treatment.
1
Eviscerated carcass is expressed as a percentage of live BW, whereas cuts are proportions of the eviscerated carcass.
2
Deboned pectoralis major.
3
Deboned pectoralis minor.
the low- or moderate-AA-density diet in phase
II; FCR was impaired when birds were fed the
low-AA-density diet in phase I, regardless of the
treatment fed in phase II, when compared with
all other combinations. All other combinations
between treatments fed in phases I and II led to
intermediate responses.
Effects of the treatments fed in phases I and II
were independent of feed intake. The high-AAdensity diets fed in phase I led to a reduction in
feed intake measured from both 1 to 35 d and
1 to 42 d, whereas the high- or moderate-AAdensity diets fed in phase II led to a reduction in
feed intake at both ages.
Carcass yield, as a percentage of live BW, as
well as drumsticks, as a percentage of the eviscerated carcass weight, were not affected by any
of the feeding programs studied. Effects of the
treatments fed in the 2 phases on the percentages of abdominal fat, breast fillets, and breast
tenders were independent. Feeding the low-AAdensity diets led to an increase in the percentage of abdominal fat, regardless of whether it
was fed in phase I or in phase II. Percentages
of breast fillets, breast tenders, and thighs were
affected only by treatments fed in phase II; however, although the percentage of breast fillets
was maximized in birds fed the moderate- and
high-AA-density diets, breast tenders had a step-
wise reduction in yields with the high- to moderate-AA-density diets and then to the low-AAdensity diet. Percentages of thighs were greatest
when birds were fed the high-AA-density diet
in comparison with those fed the moderate- and
low-AA-density diets (Table 5).
The high-yield broiler has to be fed sufficient nutrients and energy to fulfill its genetic
potential. It is generally accepted that the modern broiler has had a constant increase in AA
requirements as genetic selection has continuously produced new generations of broilers with
higher potential for BWG, FCR, and BMY [2].
Feeding programs that improve broiler performance and in parallel increase economic returns
are of great interest to producers because feeding
costs account for almost two-thirds of the overall broiler production costs. To optimize returns,
gains obtained in broiler performance have to be
balanced for the increased cost of using dietary
programs with higher AA densities. Increases
in feed costs with graded supplementation of
AA are linear, whereas improvements in performance are not. Dozier et al. [22] evaluated
the economic returns under a variety of market
scenarios and concluded that high-AA-density
diets led to increased profits. In general, returns
from increased dietary AA density depend on
the proportional improvement in FCR and BMY
JAPR: Research Report
804
balanced with the market price of the product
sold. The objective of the present study was not
to conduct a cost-benefit analysis of broiler responses to increased dietary AA, but to generate live performance and BMY response data
to changing AA concentrations with Cobb 500
slow-feathering males. Such data could then be
used under different market conditions to help
nutritionists decide what the best AA density is
under current product and ingredient prices.
Several papers have been published in the
last few years on the topic of diet AA density
and broiler performance. In general, improvements in FCR and BMY are seen when the daily
dietary supply of AA is increased, but comparisons among results have to be done among those
studies that applied similar feed formulation
concepts such that the increase in AA concentrations had similar effects on all essential AA.
In the past, an increase in AA density was frequently referred to as one AA being increased,
or to increases in AA without maintaining the
same balance of essential AA throughout all the
feeding phases [5, 23]. More recent research
has been taking these inconsistencies in design
into consideration and, therefore, has produced
results to changes in AA programs that can be
compared [12, 13, 22]. In the current research,
improvements obtained between the low-low
and moderate-moderate, and the moderate-moderate and high-high feeding programs were 7.0
and 9.8% in BWG and 9.0 and 3.5% in FCR at
35 d, whereas at 42 d, the improvements were
9.3 and 2.2% in BWG and 8.8 and 3.6% in FCR.
Improvements in BMY at 42 d were seen with
the change in AA density only in phase II from
low- to either moderate- or high-AA-density diets and were 1.5%. Changing from the low- to
high-AA-density diets in phase II has also led to
an increase in the percentage of thighs of 1.5%.
Similar results were seen in a study conducted
with the same Cobb 500 slow-feathering broiler
fed dietary programs with graded increases in
AA density. When diets were increased from
low to moderate and then to high AA densities,
improvements of 5.1 and 3.3% were observed in
BWG and improvements of 5.0 and 2.0% were
observed in FCR with birds grown to 40 d, and
increases in BMY were 2.3% from the low- to
moderate-AA-density diets without further
gains when compared with the high-AA-density
feeding program [13]. Improvements were also
seen in a study using Cobb 500 fast-feathering
males grown to 42 d. Improvements between the
low- to moderate- and moderate- to high-AAdensity feeding programs were 9.1 and 2.0%
for BWG and of 3.9 and 1.7% for FCR, and for
BMY, improvements were 5.2 and 3.5%, respectively [12].
In the present study, feeding high-AA-density
diets from placement to processing was needed
to maximize FCR at 35 and 42 d and BWG at 35
d, but BWG at 42 d was maximized when birds
were fed either the high- or moderate-AA-density diets in phase I as long as they were also fed
high- and moderate-AA-density diets in phase
II. However, breast meat data were dependent
only on the diets fed in phase II, which, therefore, present an opportunity for the use of less
costly starter feeding programs combined with
either high- or moderate-AA-density diets fed
from 22 d on when breast meat market prices
become more attractive.
The decision regarding which AA density
leads to the best economic returns is dependent
on dynamic variables, such as feed ingredient costs and market prices of the meat. These
variables are difficult to predict at the start of
the fiscal year, but can be somewhat predicted
when a flock is being started. This means that
data such as those presented in this study and
others with similar designs [12, 13] can be used
to determine the effect of AA density on productive parameters and can thus be factored into the
multifactorial equation needed for determining
the best economic returns at a specific time.
CONCLUSIONS AND APPLICATIONS
1. Feeding diets with high concentrations
of AA from 1 to 21 d of age can result
in improved overall broiler live performance at 35 d (individual broiler weights
averaging 2.6 kg) when high- or moderate-AA-density diets are fed from 22 d to
processing; however, BWG at 42 d can
also be maximized as long as the diets
fed from 22 d on are of high or moderate
AA concentrations.
2. The best performance and breast yields
were obtained when high AA concentrations were fed from 22 to 42 d of age.
Vieira et al.: Amino acid densities in broilers
3. Whether the high-high or high-moderate
diet combinations optimize economic
returns will depend primarily on ingredient costs, the product mix being produced, and the price of products being
sold.
4. Data from work such as this can be used
in the decision-making process to determine the optimal diet AA concentrations
that optimize economic returns at a specific point in time.
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