Efficacy of phase-feeding in supporting growth performance of broiler chicks during the starter and finisher phases

Abstract

A feeding regimen has been developed that uses regression equations to predict amino acid requirements over time. Phase-feeding (PF) of broilers was tested to evaluate its efficacy compared with feeding broilers NRC or Illinois ideal chick protein (IICP) recommendations. In Experiment 1, NRC or IICP requirements for lysine, sulfur amino acids, and threonine were fed from 0 to 21 d, whereas PF was tested using a series of three diets (0 to 7, 7 to 14, and 14 to 21 d). No differences (P > 0.05) in weight gain, feed intake, feed efficiency, digestible amino acid intake, or gain per unit digestible amino acid intake were noted among chicks fed NRC, IICP, or PF diets. In Experiment 2, NRC or IICP requirements were fed from 40 to 61 d, whereas PF was tested using a series of three diets (40 to 47, 47 to 54, and 54 to 61 d). No differences (P > 0.05) in weight gain or feed intake were observed, but the feed efficiency of birds fed the IICP diet was decreased (P < 0.05). The IICP and PF diets resulted in decreased (P < 0.05) digestible lysine and threonine intake; gain per unit digestible lysine and threonine intake was increased (P < 0.05) by PF. No differences (P < 0.05) in breast meat, wing, or leg yield were noted among treatments. Economic analysis indicated that PF may facilitate reduced dietary costs without sacrificing growth performance or carcass yield.

Full text

Efficacy of Phase-Feeding in Supporting Growth Performance of Broiler
Chicks During the Starter and Finisher Phases
1
W. A. Warren and J. L. Emmert
2
Department of Poultry Science, University of Arkansas, Fayetteville, Arkansas 72701
ABSTRACT A feeding regimen has been developed
that uses regression equations to predict amino acid re-
quirements over time. Phase-feeding (PF) of broilers was
tested to evaluate its efficacy compared with feeding
broilers NRC or Illinois ideal chick protein (IICP) recom-
mendations. In Experiment 1, NRC or IICP requirements
for lysine, sulfur amino acids, and threonine were fed
from 0 to 21 d, whereas PF was tested using a series of
three diets (0 to 7, 7 to 14, and 14 to 21 d). No differences
(P > 0.05) in weight gain, feed intake, feed efficiency,
digestible amino acid intake, or gain per unit digestible
amino acid intake were noted among chicks fed NRC,
(Key words: phase-feeding, broiler, growth performance, amino acids, feeding programs)
2000 Poultry Science 79:764–770
INTRODUCTION
The poultry industry encompasses production sys-
tems that include grow-out periods of as little as 4 wk
of age, and it is becoming increasingly common for com-
panies to attempt to maximize economic, uniform pro-
duction of breast meat by raising cockerels separately,
in some cases for up to 10 wk of age. The NRC (1994)
provides a single set of recommendations that encom-
passes both pullets and cockerels, and requirements are
segregated into three fixed periods: starter, 0 to 3 wk of
age; grower, 3 to 6 wk of age; and finisher, 6 to 8 wk of
age. This regimen does not correspond with the grow-
out periods used in typical production systems. In addi-
tion, many companies are now rearing cockerels sepa-
rately beyond 8 wk of age to obtain large quantities of
breast meat.
A flexible set of amino acid requirements that can
adapt to various production systems is needed. Amino
acid requirements (% of diet or % of calories) decrease
steadily throughout the grow-out period, and studies
have shown that broilers may be switched to a less nutri-
Received for publication August 30, 1999.
Accepted for publication January 28, 2000.
1
Support by the Arkansas Agricultural Experiment Station, Fayette-
ville, AR 72701.
2
To whom correspondence should be addressed: jemmert@comp.
uark.edu.
764
IICP, or PF diets. In Experiment 2, NRC or IICP require-
ments were fed from 40 to 61 d, whereas PF was tested
using a series of three diets (40 to 47, 47 to 54, and 54 to
61 d). No differences (P > 0.05) in weight gain or feed
intake were observed, but the feed efficiency of birds fed
the IICP diet was decreased (P < 0.05). The IICP and PF
diets resulted in decreased (P < 0.05) digestible lysine
and threonine intake; gain per unit digestible lysine and
threonine intake was increased (P < 0.05) by PF. No differ-
ences (P < 0.05) in breast meat, wing, or leg yield were
noted among treatments. Economic analysis indicated
that PF may facilitate reduced dietary costs without sacri-
ficing growth performance or carcass yield.
ent-dense grower diet earlier than 3 wk of age without
sacrificing growth performance or carcass yield (Wat-
kins et al., 1993; Saleh et al., 1995, 1996a,b). Phase-feeding
(PF) has been used in swine to decrease nitrogen excre-
tion without sacrificing growth performance.
In an attempt to provide a flexible feeding program
that is adaptable and applicable to a wide range of com-
mercial conditions, Emmert and Baker (1997) used the
Illinois ideal chick protein (IICP; Baker and Han, 1994;
Baker, 1997) to develop regression equations that predict
amino acid requirements for use in a PF regimen for
broilers. Because the equations express digestible amino
acid requirement as a function of age, requirement pre-
dictions for any specified period of time may be derived,
including periods beyond 8 wk of age for which few
requirement estimates are available. Moreover, PF may
support the elimination of some excess dietary supple-
mental amino acids, thereby potentially decreasing di-
etary costs. Our objective was to evaluate the efficacy of
PF in supporting growth of broilers during the starter
and finisher periods.
MATERIALS AND METHODS
All procedures were approved by the University of
Arkansas Institutional Animal Care and Use Committee.
Abbreviation Key: IICP = Illinois ideal crude protein, PF = phase-
feeding, SAA = sulfur amino acids, SBM = soybean meal

PHASE-FEEDING 765
TABLE 1. Composition of diets for 0 to 21-d-old chicks (Experiment 1)
NRC
1
IICP
2
PF
3
PF
3
PF
3
Ingredient (d 0 to 21) (d 0 to 21) (d 0 to 7) (d 7 to 14) (d 14 to 21)
(%)
Corn 56.58 53.34 51.12 54.02 56.26
Soybean meal 34.25 37.61 39.77 36.89 34.72
Poultry fat 5.00 5.00 5.00 5.00 5.00
Vitamin mix
4
0.20 0.20 0.20 0.20 0.20
Mineral mix
4
0.15 0.15 0.15 0.15 0.15
Dicalcium phosphate 2.00 2.00 2.00 2.00 2.00
Limestone 1.00 1.00 1.00 1.00 1.00
NaCl 0.40 0.40 0.40 0.40 0.40
Choline Cl (60%) 0.10 0.10 0.10 0.10 0.10
L-LysineⴢHCl 0.1331 0.0235 0.0467 0.0455 0.0226
DL-Methionine 0.1913 0.1733 0.2104 0.1914 0.1431
1
NRC diets contained lysine, sulfur amino acid, and threonine levels recommended by NRC (1994), with the
exception of lysine, which was supplemented to the level recommended by the Illinois ideal chick protein (IICP;
Baker and Han, 1994; Baker, 1997).
2
IICP diets contained lysine, sulfur amino acids, and threonine levels recommended by the IICP profile (Baker
and Han, 1994; Baker, 1997).
3
Levels of amino acids in phase-feeding (PF) diets were predicted by linear regression equations (Table 3).
4
Han and Baker (1993).
Two experiments were conducted utilizing male broiler
chicks of a commercial strain (Cobb × Cobb
3
) that were
purchased from a local hatchery. Chicks were housed
in floor pens containing a litter mixture of new pine
shavings and rice hulls. A 24-h constant light schedule
was maintained, and water and experimental diets were
freely available. In both experiments, dietary treatments
(Tables 1 and 2) consisted of 1) a single diet, formulated
to contain NRC (1994) recommendations for lysine, sul-
fur amino acids (SAA), and threonine, and fed for the
entire 3-wk experiment; 2) a single diet, formulated to
contain IICP (Baker and Han, 1994; Baker, 1997) recom-
mendations for lysine, SAA, and threonine, fed for the
entire 3-wk experiment; and 3) a series of three diets,
formulated to contain lysine, SAA, and threonine re-
quirements predicted by linear regression equations
(Emmert and Baker, 1997); dietary amino acid concentra-
tion was lowered after each week of the experiment.
Regression equations from Emmert and Baker (1997)
were modified to reflect male requirements and were
used to predict PF requirements for the first, second and
third weeks of both trials as follows: digestible lysine,
y = 1.22 − 0.0095x; digestible methionine and cystine, y
= (0.88 − 0.0063x)/2; and digestible threonine, y = 0.8 −
0.0053x, where y = digestible amino acid level, and x =
midpoint (day) of the desired age range (example: x =
3.5 d for the first week of age). These equations are based
on a combination of the best available digestible lysine,
SAA, and threonine requirements for the starter, grower,
and finisher periods. Specifically, digestible amino acid
requirements for the starter period were lysine, 1.07%
(Han and Baker, 1993); SAA, 0.77% (NRC, 1994); and
threonine, 0.70% (NRC, 1994); for the grower period
were lysine, 0.865% (Han and Baker, 1994); SAA, 0.62%
3
Cobb-Vantress Inc., Siloam Springs, AR 72761.
(Baker et al., 1996); and threonine, 0.593% (Webel et al.,
1996); and for the finisher period were lysine, 0.745%
(NRC, 1994); SAA, 0.54% (Baker and Han, 1994; Baker,
1997); and threonine, 0.51% (Webel et al., 1996).
In both experiments, corn and soybean meal (SBM)
were added in sufficient quantities to meet the target
digestible threonine concentration, and crystalline lysine
and methionine were supplemented to meet their re-
quirements. Because NRC (1994) recommendations are
based on total dietary amino acid needs, after we formu-
lated the NRC diet to meet total amino acid recommen-
dations, the digestible lysine, SAA, and threonine con-
tents were calculated by applying digestibility coeffi-
cients for corn and SBM. Corn was analyzed (as fed) to
contain 8.6% CP, 0.28% total lysine, 0.22% total methio-
nine, 0.22% total cystine, and 0.30% total threonine, and
the digestibility of lysine, methionine, cystine and threo-
nine in corn was assumed to be 78, 91, 86, and 84%,
respectively (Parsons, 1991). Soybean meal was analyzed
(as fed) to contain 46.7% CP, 2.91% total lysine, 0.66%
total methionine, 0.71% total cystine, and 1.84% total
threonine, and the digestibility of lysine, methionine,
cystine, and threonine in SBM was assumed to be 90,
92, 83, and 89%, respectively (Parsons, 1991). The energy
contents of corn, SBM, and poultry fat were assumed
to be 3,350, 2,440, and 8,800 kcal ME
n
/kg, respectively
(NRC, 1994).
Experiment 1
Experiment 1 was conducted to assess the efficacy of
PF in supporting growth of chicks during the starter
period (0 to 21 d). It should be noted that the NRC diet
(Treatment 1) was based on NRC (1994) recommenda-
tions for SAA and threonine, but the IICP starter period
lysine recommendation was used for the NRC diet
(Treatment 1) in this experiment because of previous
research suggesting that the NRC (1994) lysine recom-

WARREN AND EMMERT766
TABLE 2. Composition of diets for 40 to 61-d-old chicks (Experiment 2)
NRC
1
IICP
2
PF
3
PF
3
PF
3
Ingredient (d 40 to 61) (d 40 to 61) (d 40 to 47) (d 47 to 54) (d 54 to 61)
(%)
Corn 64.54 69.22 66.35 69.26 71.47
Soybean meal 26.50 21.73 24.62 21.73 19.57
Poultry fat 5.00 5.00 5.00 5.00 5.00
Vitamin mix
4
0.20 0.20 0.20 0.20 0.20
Mineral mix
4
0.15 0.15 0.15 0.15 0.15
Dicalcium phosphate 2.00 2.00 2.00 2.00 2.00
Limestone 1.00 1.00 1.00 1.00 1.00
NaCl 0.40 0.40 0.40 0.40 0.40
Choline Cl (60%) 0.10 0.10 0.10 0.10 0.10
L-LysineⴢHCl . . . 0.0504 0.0258 0.0249 0.0017
DL-Methionine 0.0100 0.0470 0.0545 0.0356 0.0099
Sacox salinomycin
5
0.05 0.05 0.05 0.05 0.05
BMD-50 Bacitracin
6
0.05 0.05 0.05 0.05 0.05
1
NRC diets contained lysine, sulfur amino acid, and threonine levels recommended by NRC (1994).
2
IICP diets contained lysine, sulfur amino acid, and threonine levels recommended by the IICP profile (Baker
and Han, 1994; Baker, 1997).
3
Levels of amino acids in phase-feeding (PF) diets were predicted by linear regression equations (Table 3).
4
Han and Baker (1993).
5
Sacox 60, Hoechst-Roussel Agri-Vet Co., Somerville, NJ 08876. Provides 66 mg/kg salinomycin activity.
6
BMD-50, AlPharma, Inc., Ft. Lee, NJ 07024. Provides 55 mg/kg bacitracin methylene disalicylate activity.
mendation is too low (Han and Baker, 1991; Han and
Baker, 1993). Ten pens of 40 male chicks were assigned
to each of the three experimental feeding regimens. Ex-
perimental diets (Tables 1 and 3) based on NRC (Treat-
ment 1) or IICP (Treatment 2) requirements were fed
from 0 to 21 d, whereas PF (Treatment 3) was tested
using a series of three diets (0 to 7, 7 to 14, and 14 to 21
d). Because PF lysine, SAA, and threonine requirements
are based on digestible amino acid requirements as a
TABLE 3. Calculated digestible amino acid levels in Experiments 1 and 2
Digestible content, % of diet
1
CP, ME
n
,
3
Experiment 1
2
Day Lysine Methionine Cystine Threonine % kcal/kg
NRC
4
0 to 21 1.12
5
0.41 0.38 0.70 20.9 3,173
IICP 0 to 21 1.12 0.41 0.41 0.75 22.2 3,143
PF 0 to 7 1.19 0.43 0.43 0.78 23.0 3,123
7 to 14 1.12 0.41 0.41 0.74 21.9 3,149
14 to 21 1.05 0.38 0.38 0.71 21.1 3,173
Experiment 2
6
NRC
4
40 to 61 0.83
7
0.30 0.28 0.60 17.9 3,247
IICP 40 to 61 0.76 0.29 0.29 0.53 16.1 3,288
PF 40 to 47 0.81 0.30 0.30 0.57 17.2 3,265
47 to 54 0.74 0.28 0.28 0.53 16.1 3,291
54 to 61 0.67 0.26 0.26 0.50 15.3 3,313
1
Digestible amino acid, CP, and dietary ME content calculated from the analytical values for total lysine,
sulfur amino acids, and threonine in corn and soybean meal and published digestibility coefficients (Parsons,
1991; see Materials and Methods).
2
Experiment 1 was conducted from 0 to 21 d posthatching.
3
Metabolizable energy values for corn, soybean meal, and poultry fat were assumed to be 3,350, 2,440, and
8,800 kcal ME
n
/kg, repectively.
4
Although the NRC (1994) provides total dietary amino acid recommendations, digestible amino acid levels
for Experiments 1 and 2 were calculated after formulation of diets to meet total NRC (1994) recommendations
for dietary lysine, sulfur amino acids, and threonine. PF = phase-feeding.
5
The lysine requirement for the NRC treatment in Experiment 1 was based on Illinois ideal chick protein
(IICP) (Baker and Han, 1994; Baker, 1997) recommendations.
6
Experiment 2 was conducted from 40 to 61 d posthatching.
7
Corn and soybean meal were added to the basal diet in sufficient quantities to meet the NRC (1994) recommen-
dation for threonine, resulting in a level of dietary lysine that exceeded NRC (1994) recommendations.
function of age, the levels of dietary lysine, SAA, and
threonine in the PF diets decreased when diets were
switched on Days 7 and 14 (Table 3). Additionally, CP
and ME
n
varied according to the dietary content of corn
and SBM (Table 3). With PF, CP decreased from 23.0 to
21.1% over the course of the experiment, whereas ME
n
increased from 3,123 to 3,173 kcal ME
n
/kg. Chicks and
feed were weighed at 7, 14, and 21 d of age for determina-
tion of weight gain, feed intake, and feed efficiency.

PHASE-FEEDING 767
Experiment 2
Experiment 2 was conducted to assess the efficacy of
PF in supporting growth of chicks during the finisher
period (40 to 61 d). It should be noted that the finisher
period NRC (1994) recommendation for threonine is
high relative to lysine when compared with IICP recom-
mendations. Therefore, the decision to meet the NRC
(1994) dietary threonine recommendation from corn and
SBM led to an excess of dietary lysine in the NRC diet
(Treatment 1). In addition, although NRC (1994) and
IICP recommendations for the finisher period encom-
pass 42 to 56 d of age, no attempt was made to adjust
NRC (1994) or IICP lysine, SAA, and threonine levels
for the extended finisher period used in this experiment.
Experimental diets (Tables 2 and 3) based on NRC (Treat-
ment 1) or IICP (Treatment 2) requirements were fed
from 40 to 61 d, whereas PF (Treatment 3) was tested
using a series of three diets (40 to 47, 47 to 54, and 54
to 61 d). As in Experiment 1, dietary lysine, SAA, and
threonine levels decreased when diets were switched on
Days 47 and 54 (Table 3). Again, CP and ME
n
varied
according to the dietary content of corn and SBM (Table
3). With PF, CP decreased from 17.2 to 15.3% over the
course of the experiment, whereas ME
n
increased from
3,265 to 3,313 kcal ME
n
/kg. Because Experiment 2 was
initiated on Day 40, chicks were fed a common starter
diet from 0 to 21 d and a common grower diet from 21
to 40 d that were formulated to meet or exceed NRC
(1994) requirements for all essential nutrients. Ten pens
of 20 male chicks were assigned to each of the three
experimental feeding regimens. Chicks and feed were
weighed at 47, 54, and 61 d of age for determination of
weight gain, feed intake, and feed efficiency. Feeders
were removed from experimental pens on Day 60, 10 h
prior to experiment termination. After weights were
taken on Day 61, five birds per pen were randomly se-
lected for processing at the University of Arkansas pro-
cessing plant. Part weights were recorded for wings,
legs (drum and thigh), breast, abdominal fat, and rack,
and parts yields were calculated as a percentage of evis-
cerated weight.
Statistical Analysis
Both experiments were analyzed as completely ran-
domized designs, and the general linear models proce-
dure of SAS威 (SAS Institute, 1996) was used to conduct
ANOVA on all data. Differences among treatment means
were established using the least significant difference
multiple-comparison procedure (Carmer and Walker,
1985).
RESULTS AND DISCUSSION
Experiment 1 was conducted to assess the efficacy of
PF in supporting growth performance during the starter
period. No differences (P > 0.05) in weight gain, feed
intake, or feed efficiency were observed among birds fed
NRC, IICP, or PF diets (Table 4). Although PF resulted in
slight numerical improvements, no differences (P >0.05)
among treatments were noted with regard to digestible
lysine, SAA, or threonine intake, weight gain per unit
digestible lysine, SAA, or threonine intake.
During the starter period, only a small amount of feed
is consumed relative to the total feed consumed by a
broiler over a 6 to 9 wk grow-out period. In addition,
IICP requirement recommendations for lysine, SAA, and
threonine are higher than NRC (1994) recommendations
when expressed on a digestible basis (Table 3). Because
PF amino acid requirements are largely based on the
IICP (Emmert and Baker, 1997), the authors were not
expecting an increase in growth performance or effi-
ciency of amino acid utilization. The ability of PF to
support equivalent growth performance to chicks fed
the diet based on NRC (1994) requirements may not be
surprising. This finding is in light of work showing that
broiler chickens may be switched to a less nutrient-dense
grower diet earlier than the recommended 3 wk of age
without sacrificing 6-wk growth performance or carcass
yield (Watkins et al., 1993; Saleh et al., 1995, 1996a,b).
Although the results of Experiment 1 indicate that
amino acid levels may be gradually lowered during the
starter period without negatively impacting growth per-
formance, the impact of PF during the finisher period is
of even more interest. In Experiment 2, no difference (P
> 0.05) in weight gain or feed intake was observed, but
feed efficiency of birds fed the IICP diet was decreased
(P < 0.05) relative to chicks consuming the NRC diet
(Table 5). Both the IICP and PF diets were effective at
decreasing (P < 0.05) digestible lysine and threonine in-
take, and PF also resulted in an increased (P < 0.05)
weight gain per unit digestible lysine and threonine in-
take relative to chicks fed the NRC diet. In contrast, no
differences (P > 0.05) in SAA intake or weight gain per
unit digestible SAA intake were observed between
chicks fed NRC and PF treatments, and chicks fed IICP
diets exhibited the lowest (P < 0.05) weight gain per unit
digestible SAA intake. The IICP diet resulted in a slight
increase (P < 0.05) in abdominal fat relative to birds
consuming the NRC diet, but no differences (P < 0.05)
in breast meat, wing, or leg yield were noted among
treatments.
The chosen age range can play a large role in the
results of studies evaluating PF. Because a single set of
NRC and IICP recommendations is provided for the
finisher period, and no requirement estimates are made
beyond 8 wk of age, it would be expected that PF would
be increasingly economically advantageous as the length
of growout increases beyond the traditional finisher pe-
riod. The authors are planning future studies to evaluate
whether the magnitude of the improvements associated
with PF are magnified when birds are raised beyond the
age used in Experiment 2. It is possible that eventually
PF would result in reductions in digestible SAA intake
as well. Nevertheless, PF was effective in promoting
equivalent growth performance and carcass composition
and improved the efficiency with which lysine and thre-

WARREN AND EMMERT768
TABLE 4. Growth performance of chicks fed NRC, Illinois idel chick protein (IICP), or phase-feeding
(PF)-based diets from 0 to 21 d of age (Experiment 1)
1
Treatment
Parameter NRC
2
IICP
3
PF
4
SEM
Weight gain, g 566 556 566 20
Feed intake, g 855 815 809 31
Gain:feed, g:kg 664 686 700 16
Digestible lysine intake, g 9.6 9.1 9.0 0.4
Digestible SAA
5
intake, g 6.7 6.7 6.4 0.3
Digestible threonine intake, g 6.0 6.1 5.9 0.2
Gain:digestible lysine intake, g:g 59.2 61.3 63.2 1.4
Gain:digestible SAA intake, g:g 85.1 83.7 88.3 2.0
Gain:digestible threonine intake, g:g 94.8 91.5 96.0 2.2
1
Values are means of 10 pens of 40 male chicks fed the experimental diets from 0 to 21 d posthatching; average
initial weight was 46 g.
2
NRC diets contained 20.9% CP, 1.12% digestible Lys, 0.41% digestible Met, 0.38% digestible Cys, and 0.70%
digestible Thr (digestible amino acid levels were calculated after formulation of diets to meet total NRC (1994)
recommendations). Values are based on analysis of total amino acid content of corn and soybean meal combined
with digestibility coefficients from Parsons (1991).
3
IICP diets contained 22.2% CP, 1.12% digestible Lys, 0.41% digestible Met, 0.41% digestible Cys, and 0.75%
digestible Thr. Values are based on analysis of total amino acid content of corn and soybean meal combined
with digestibility coefficients from Parsons (1991).
4
PF diets contained 23.0% CP, 1.19% digestible Lys, 0.43% digestible Met, 0.43% digestible Cys, and 0.78%
digestible Thr from 0 to 7 d posthatching; 21.9% CP, 1.12% digestible Lys, 0.41% digestible Met, 0.41% digestible
Cys, and 0.74% digestible Thr from 7 to 14 d posthatching; and 21.1% CP, 1.05% digestible Lys, 0.38% digestible
Met, 0.38% digestible Cys, and 0.71% digestible Thr from 14 to 21 d posthatching. Values are based on analysis
of total amino acid content of corn and soybean meal combined with digestibility coefficients from Parsons
(1991).
5
Sulfur amino acids.
TABLE 5. Growth performance of chicks fed NRC, Illinois ideal chick protein (IICP) or phase-feeding
(PF)-based diets from 40 to 61 d of age (Experiment 2)
1
Treatment
Parameter NRC
2
IICP
3
PF
4
SEM
Weight gain, g 1,576 1,483 1,514 33
Feed intake, g 3,733 3,852 3,774 75
Gain:feed, g:kg 422
a
386
b
402
ab
7
Digestible Lys intake, g 31.0
a
29.3
b
28.0
b
0.6
Digestible SAA
5
intake, g 21.7 22.3 21.2 0.4
Digestible Thr intake, g 22.4
a
20.4
b
20.2
b
0.4
Gain:digestible Lys intake, g:g 50.9
b
50.7
b
54.2
a
1.0
Gain:digestible SAA intake, g:g 72.8
a
66.5
b
71.6
a
1.3
Gain:digestible Thr intake, g:g 70.4
b
72.8
ab
75.2
a
1.4
Eviscerated carcass, % of live weight
6
70.7 69.2 70.0 0.7
Breast, % of eviscerated carcass 25.9 25.5 26.0 0.3
Wing, % of eviscerated carcass 11.5 11.5 11.6 0.1
Leg, % of eviscerated carcass 33.4 33.2 33.1 0.2
Abdominal fat, % of eviscerated carcass 2.7
b
3.1
a
2.9
ab
0.1
a–b
Means within a row lacking a common superscript differ (P < 0.05).
1
Values are means of 10 pens of 20 male chicks fed the experimental diets from 40 to 61 d posthatching;
average initial weight was 1.82 kg.
2
NRC diets contained 17.9% CP, 0.83% digestible Lys, 0.30% digestible Met, 0.28% digestible Cys, and 0.60%
digestible Thr (digestible amino acid levels were calculated after formulation of diets to meet total NRC (1994)
recommendations). Values are based on analysis of total amino acid content of corn and SBM combined with
digestibility coefficients from Parsons (1991).
3
IICP diets contained 16.1% CP, 0.76% digestible Lys, 0.29% digestible Met, 0.29% digestible Cys, and 0.53%
digestible Thr. Values are based on analysis of total amino acid content of corn and SBM combined with
digestibility coefficients from Parsons (1991).
4
PF diets contained 17.2% CP, 0.81% digestible Lys, 0.30% digestible Met, 0.30% digestible Cys, and 0.57%
digestible Thr from 40 to 47 d posthatching; 16.1% CP, 0.74% digestible Lys, 0.28% digestible Met, 0.28% digestible
Cys, and 0.53% digestible Thr from 47 to 54 d posthatching; and 15.3% CP, 0.67% digestible Lys, 0.26% digestible
Met, 0.26% digestible Cys, and 0.50% digestible Thr from 54 to 61 d posthatching. Values are based on analysis
of total amino acid content of corn and SBM combined with digestibility coefficients from Parsons (1991).
5
Sulfur amino acids.
6
Live weights for birds fed NRC, IICP, and PF diets were 3.46, 3.49, and 3.48 kg, respectively.

PHASE-FEEDING 769
TABLE 6. Impact of phase-feeding (PF) on dietary costs (Experiment 2)
Finisher period, days
NRC IICP
1
PF PF PF
(40 to 61) (40 to 61) (40 to 47) (47 to 54) (54 to 61)
Dietary cost ($/kg)
2
0.1105 0.1089 0.1105 0.1082 0.1063
Feed cost ($/bird)
3
0.4114 0.4188 0.4087
Difference from
NRC
4
($/bird) . . . −0.0074 0.0027
1
Illinois ideal chick protein.
2
Dietary costs based on prices of $0.1036/kg for corn, $0.1631/kg for soybean meal, $1.1023/kg for L-lysineⴢHCl,
and $2.4251/kg for DL- methionine.
3
Feed cost per bird determined by multiplying the dietary cost by the total feed consumed per bird.
4
Calculated by subtracting the feed cost of the IICP and PF programs from the NRC feed cost.
onine were used for weight gain during the finisher
phase.
A potential concern associated with formulating diets
to match the requirements predicted by PF equations is
the substantial decrease in dietary CP that occurs (Table
3), bringing into question whether dietary indispensable
nitrogen levels are sufficient to support dispensable
amino acid synthesis. Our results suggest that despite
substantial CP reductions associated with the latter
phases of PF, indispensable nitrogen levels were suffi-
cient to support growth performance and meat yield.
No differences in growth performance were detected
with the exception of the feed efficiency of birds fed the
IICP diet in Experiment 2, and it is possible that the
decreased feed efficiency (relative to the NRC diet) was
the result of a combination of low CP and increased
ME
n
. Previous research also suggests that growth perfor-
mance may be maintained when dietary protein levels
are slightly to moderately decreased, provided diets are
supplemented with essential amino acids such as lysine
and methionine (Daghir, 1983; Han et al., 1992; Morris
et al., 1992; Deschepper and De Groote, 1995). However,
other researchers (Fancher and Jensen, 1989a,b) have
been unable to maintain growth performance and pro-
tein accretion when feeding CP levels at which other
researchers have noted no impact on performance,
which may reflect differences in experimental protocols
such as assay length and age of chick. Fancher and Jensen
(1989a,b) included supplemental amino acids in their
calculation of dietary CP calculations, whereas other re-
searchers reported the dietary CP level from only intact-
protein sources, without regard to the nitrogen fur-
nished by supplemental amino acids.
The lower CP levels associated with PF may also be
a concern because of the potential impact on carcass
composition. Carcass fat has been shown to be elevated
in birds consuming low-protein diets for a period of
weeks (Fancher and Jensen, 1989a,b; Deschepper and De
Groote, 1995). Low-protein diets contain fewer excess
amino acids that require energy expenditure for catabo-
lism, thereby likely increasing the net energy of the diet
and the dietary energy available for fat synthesis. The
increased abdominal fat percentage associated with the
IICP and PF treatments in Experiment 2 seem to support
this conclusion, but the observed increase was slight,
and the relative economic importance may be minor. Of
greater economic importance is breast muscle accretion
under PF conditions. Although previous research has
suggested that the level of dietary lysine and methionine
needed to maximize breast yield may exceed the amount
needed to maximize weight gain and feed efficiency (Sib-
bald and Wolynetz, 1986; Hickling et al., 1990; Moran
and Bilgili, 1990; Bilgili et al., 1992; Han and Baker, 1993),
we observed no negative impact of PF on breast, wing,
or leg yield in Experiment 2.
Economic analysis of amino acid-containing ingredi-
ents (Table 6) indicates that the cost of feeding broilers
during the finisher period may be reduced by PF. Al-
though seemingly small on an individual basis, the re-
duction in dietary cost associated with PF in Experiment
2 would be substantial when applied to the billions of
birds processed annually in the US. Other potential bene-
fits of PF have yet to be explored. We did not analyze
litter, but it is possible that PF may reduce nitrogen
excretion due to elimination of excess nitrogen from the
diet. Phase-feeding has been evaluated in swine as a
means of reducing nitrogen excretion (Boisen et al.,
1991). Pigs fed under PF conditions maintained a rate
of gain and feed efficiency that was similar to pigs fed
diets containing higher crude protein levels. Conversely,
pigs given the PF regimen excreted significantly less
nitrogen, indicating an increased efficiency of dietary
nitrogen utilization.
Clearly, PF would not be economically feasible if six
or more diets are fed during the grow-out period, due
to the increased cost associated with diet preparation,
transport, and storage. Rather, it may be possible to
accomplish PF by initially delivering a nutrient-dense
starter-type diet and a less-dense finisher-type diet,
which could be blended at a desired rate to achieve
gradual decreases in dietary amino acid levels. This pro-
cedure is similar to the approach used in parts of Europe,
where diets are diluted by one or few relatively inert
dietary ingredients as broiler chickens advance in age
and weight. However, that system is functional because
the basal diet is over-fortified, whereas PF would closely
meet dietary amino acid requirements over the entire
grow-out period.

WARREN AND EMMERT770
Further investigation is needed to verify the efficacy
of PF over the entire grow-out period, with particular
emphasis on the impact of PF during the starter period
on growth performance and carcass composition of
broiler chickens marketed between 6 and 10 wk of age.
In addition, the impact of factors such as dietary energy
level and bird density should be investigated. However,
early indications suggest the PF may offer nutritionists
a flexible alternative that facilitates application to com-
mercial poultry nutrition programs. Substantial savings
in the cost of production may be possible should PF be
proven feasible under commercial conditions.
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