METABOLISM AND NUTRITION
Apparent metabolizable energy needs of male and female broilers
from 36 to 47 days of age1
W. A. Dozier III,*2 C. k. Gehring,* A. Corzo,† and H. A. Olanrewaju†
*Department of Poultry Science, Auburn University, Auburn, AL 36849; †USDA, Agriculture Research Service,
Poultry Research Unit, Mississippi State, MS 39762; and ‡Department of Poultry Science,
Mississippi State University, Mississippi State 39762
ABSTRACT Two experiments were conducted to examine AMEn responses of Ross × Ross 708 male and
female broilers from 36 to 47 d of age. In each experiment, 1,440 male and female broilers were randomly
distributed into 96 floor pens (15 birds/pen; 8 replicate pens/treatment) sexed separately and were fed 6
levels of AMEn ranging from 3,140 to 3,240 kcal/kg
in increments of 20 kcal of AMEn/kg, resulting in a 6
× 2 factorial arrangement of treatments. Body weight
gain, feed intake, feed conversion, AMEn intake, AMEn
intake per BW gain, plasma 5-triiodothyronine and
thyroxine concentrations, mortality, and meat yields
were evaluated during experimentation. Average temperature and RH were 20.3°C and 49.0% for experiment
1 and 26.1°C and 66.6% for experiment 2. In experiment 1, broilers fed progressive additions of AMEn had
lower (P ≤ 0.02) feed intake, feed conversion, and caloric conversion. Progressive increments of AMEn did
not influence plasma 5-triiodothyronine and thyroxine
concentrations, carcass yield, or breast meat yield. No
AMEn × sex interactions were observed in experiment
1. In experiment 2, AMEn × sex linear interactions (P
≤ 0.04) were observed for BW gain, caloric conversion,
carcass weight, and total breast weight. Male broilers
responded more to higher AMEn levels than did female
broilers. These data indicate that AMEn needed for
growth performance of broilers from 36 to 47 d of age
differed between experiments.
Key words: apparent metabolizable energy, broiler, fat
2011 Poultry Science 90:804–814
doi:10.3382/ps.2010-01132
INTRODUCTION
ningham, 2009). Broilers fed diets low in AMEn have
exhibited higher feed conversion and caloric conversion
compared with birds fed diets with higher energy density to achieve maximum responses (Leeson et al., 1996;
Saleh et al., 2004a,b).
Apparent ME responses in broilers grown to less than
2.0 kg have been well documented (Donaldson et al.,
1956; Farrell et al., 1973; Bartov et al., 1974; Farrell,
1974; Waldroup et al., 1976; Griffiths et al., 1977; Dale
and Fuller, 1980; Mabray and Waldroup, 1981; McNaughton and Reece, 1982; Hidalgo et al., 2004; Zaman
et al., 2008), and information is less available on the
AMEn needs of broilers grown to 3.0 kg or larger (Saleh
et al., 2004a,b, Downs et al., 2006; Dozier et al., 2006a,
2007a,b). Previous research evaluating AMEn responses with broilers grown to 3.0 kg have been conducted
throughout multiple growth periods and have shown
that responses in the finisher phase may be confounded
by responses in previous growth phases (Saleh et al.,
2004a,b; Downs et al., 2006). Data are needed to determine the minimum AMEn used in formulating diets
during the finishing period because approximately 45%
of the cumulative feed intake occurs during the last 2
wk of production for 3.0-kg broilers (Aviagen, 2007).
Energy-contributing ingredients constitute approximately 65% of the dietary cost for broiler chickens
(Donohue and Cunningham, 2009). Defining minimum
dietary energy specifications for broilers is economically important for integrated operations. In the United
States, the amount of corn used as an input for ethanol
production has increased dramatically within the last
several years (Aho, 2007). Consequently, the demand
for corn has reached market highs, translating into unprecedented feed ingredient prices (Donohue and Cunningham, 2009). Increased feed ingredient prices have
escalated live production costs for broilers, and decreasing the energy density of the diet has been practiced
to reduce the live production cost (Donohue and Cun©2011 Poultry Science Association Inc.
Received September 17, 2010.
Accepted December 15, 2010.
1 Mention of trade names or commercial products in this publication
is solely for the purpose of providing specific information and does not
imply recommendation or endorsement by Auburn University, USDA,
or Mississippi State University.
2 Corresponding author: [email protected]
804
DIETARY APPARENT METABOLIZABLE ENERGY NEEDS OF BROILERS
Furthermore, the minimum AMEn specifications used
in diet formulation during the finishing period may be
different between summer and winter growing conditions (Dale and Fuller, 1980; McNaughton and Reece,
1982; Dozier et al., 2006).
Previous research from this laboratory has evaluated the dietary energy needs of broilers from 5 to 8
wk of age (Dozier et al., 2006, 2007a,b). These studies
were designed to evaluate the growth performance and
meat yield of broilers fed diets having AMEn values at
or exceeding the specifications used by the US broiler
industry because feed ingredient prices were relatively
low at the time of experimentation. Because of the increase in feed ingredient prices from 2005 to 2010, lower
AMEn specifications are being used in diet formulation
than the optimal AMEn previously determined in the
literature. Research is needed to evaluate the responses
of modern broilers to lower AMEn, particularly with
broilers grown beyond 2.0 kg in BW. Broilers grown
from 2.0 to 4.0 kg in BW eat to satisfy their energy
needs (Leeson et al., 1996; Downs et al., 2006; Dozier
et al., 2006, 2007a,b). When feeding low-energy diets,
it is important to understand the change in feed intake
so other nutrients can be adjusted to avoid excess nutrient intake. Leeson et al. (1996) evaluated a wide range
of AMEn levels throughout a 49-d production period.
Data interpretation is difficult when studies are conducted to evaluating nutrient responses throughout the
life cycle of the broiler because the results occurring in
the finishing period can be affected by the responses
occurring in the starter and grower periods. Moreover,
this study had a spread of 200 kcal of AMEn/kg between the treatments, which is hard to apply directly
to current broiler formulations.
Information is needed on the responses of modern
broilers to low-energy diets at or above the thermal
neutral zone from 5 to 7 wk of age. This research examined the AMEn responses of male and female broilers
from 36 to 47 d of age within environments simulating
winter and summer temperatures in the southeastern
United States. In addition to growth performance and
processing yields, actual AMEn values were determined
concurrently with growth trials to validate AMEn levels
that were fed, and plasma 5-triiodothyronine (T3) and
thyroxine (T4) concentrations were determined. Protein and energy metabolism are affected by T3 and T4
concentrations, and broilers subjected to temperatures
beyond their thermal neutral zone have lower plasma
T3 and T4 concentrations.
MATERIALS AND METHODS
Experimental Treatments
In each experiment, 6 AMEn concentrations were fed
to male and female broilers from 36 to 47 d of age, resulting in a 6 × 2 factorial arrangement of treatments.
Calculated AMEn concentrations ranged from 3,140
to 3,240 kcal/kg in increments of 20 kcal of AMEn/
805
kg by adding supplemental fat in increments of 0.48%,
from 0.54 to 2.92% (Table 1). Digestible amino acid
and CP concentrations were increased by 0.75% with
each increment in AMEn to minimize differences in the
consumption of amino acids and CP among the dietary
treatments that were due to the reduction in feed intake of broilers fed the high AMEn diets (Dozier et
al., 2007b). Apparent ME values used in formulations
for corn, soybean meal, poultry by-product meal, and
poultry oil were 3,384, 2,380, 3,150 and 8,200 kcal/kg,
respectively.
Poultry oil quality varied among the 2 sources used
in experimentation (Table 2). Oil samples were analyzed by an independent laboratory (Eurofins Scientific
Inc., Des Moines, IA) for 24-h active oxygen method
(AOM), iodine value, moisture, and volatiles by hot
plate, insoluble impurities, titer, initial peroxide value,
unsaponified matter, fatty acid profile, total fatty acids,
and free fatty acids by the official methods of AOCS
(1998): Cd 12-57, Cd 1d-92, Ca 2b-38, Ca 3a-46, Cc
12-59, Cd 8-53, Ca 6a-40, Ce 2-66, G 3-53, and Ca 5a40, respectively. Saponification value was determined
based on USP vs. Twenty method (401) (United States
Pharmacopeial Convention, 1980).
Common Procedures
All procedures relating to the use of live birds were
approved by a USDA-Agricultural Research Service
Animal Care and Use Committee at the Mississippi
State location. The following procedures were identical
for each experiment. Twenty-five hundred Ross × Ross
708 straight-run broiler chicks (Aviagen North America, Huntsville, AL) were obtained from a commercial
hatchery and placed into an open-sided house. Chicks
were vaccinated for Marek’s disease, Newcastle disease,
and infectious bronchitis at the hatchery. Birds were
fed corn-soybean meal diets (0 to 17 d of age = AMEn,
3,040 kcal/kg; digestible TSAA, 0.92%; digestible Lys,
1.22%; Ca, 0.90%; and nonphytate P, 0.45%; 18 to 35 d
of age = AMEn, 3,140 kcal/kg; digestible TSAA, 0.86%;
digestible Lys, 1.13%; Ca, 0.88%; and nonphytate P,
0.45%) with similar management practices until 35 d
of age. The ambient temperature set point consisted
of 33°C at placement and was decreased as the birds
advanced with age, resulting in a final set point of 21°C
at 33 d of age. Photoperiod was a continuous schedule,
with lighting intensities of 30 lx from 0 to 7 d of age,
10 lx from 8 to 22 d of age, and 3 lx from 23 to 35 d
of age. Light intensity settings were verified at the bird
level (30 cm) by using a photometric sensor with National Institute of Standards and Technology-traceable
calibration for each intensity adjustment (403125, Extech Instruments, Waltham, MA). At 36 d of age, 1,440
broilers were moved to a solid-sided facility equipped
with floor pens to initiate a growth assay, and the following day, 240 broilers were placed in battery cages in
an adjacent solid-sided facility to determine AMEn of
the experimental diets fed in the growth assay.
806
Dozier et al.
Table 1. Ingredient and nutrient composition of the experimental diets fed to male and female broilers from 36 to 47 d of age (%,
as-fed basis unless otherwise noted)
Item
Ingredient
Ground yellow corn
Soybean meal (47.5% CP)
Poultry by-product meal (58% CP)
Defluorinated phosphate
Poultry oil
Limestone
Sodium chloride
dl-Met
l-Lys HCl
l-Thr
Vitamin premix1
Mineral premix2
Choline (70%)
Calculated analysis3
AMEn4 (kcal/kg)
CP
Digestible TSAA
Digestible Lys
Digestible Thr
Digestible Val
Digestible Ile
Digestible Arg
Digestible Trp
Ca
Nonphytate P
Na
1
2
75.64
18.22
3.00
1.26
0.54
0.47
0.32
0.16
0.20
0.04
0.06
0.06
0.03
3,140
16.50
0.662
0.882
0.591
0.701
0.600
0.964
0.155
0.760
0.380
0.220
74.87
18.51
3.00
1.26
1.01
0.47
0.32
0.17
0.20
0.04
0.06
0.06
0.03
3,160
16.57
0.666
0.888
0.595
0.704
0.604
0.971
0.156
0.760
0.380
0.220
3
74.06
18.85
3.00
1.26
1.49
0.47
0.32
0.19
0.17
0.04
0.06
0.06
0.03
3,180
16.67
0.671
0.895
0.599
0.708
0.608
0.980
0.158
0.760
0.380
0.220
4
73.28
19.16
3.00
1.26
1.97
0.46
0.32
0.19
0.17
0.04
0.06
0.06
0.03
3,200
16.77
0.676
0.901
0.604
0.712
0.613
0.987
0.159
0.760
0.380
0.220
5
72.50
19.45
3.00
1.26
2.45
0.46
0.32
0.19
0.18
0.04
0.06
0.06
0.03
3,220
16.85
0.680
0.907
0.608
0.715
0.616
0.994
0.160
0.760
0.380
0.220
6
71.76
19.72
3.00
1.26
2.92
0.46
0.32
0.19
0.18
0.04
0.06
0.06
0.03
3,240
16.93
0.684
0.912
0.611
0.718
0.620
1.001
0.161
0.760
0.380
0.220
1Vitamin premix included the following per kilogram of diet: vitamin A (acetate), 7,934 IU; vitamin D (cholecalciferol), 2,645 ICU; vitamin E (dl-α
tocopherol acetate), 35 IU; menadione (menadione sodium bisulfate complex), 1.76 mg; vitamin B12 (cyanocobalamin), 0.014 mg; folic acid, 1.2 mg;
d-pantothenic acid (calcium pantothenate), 15 mg; riboflavin, 7.9 mg; niacin (niacinamide), 34 mg; thiamine (thiamine mononitrate), 1.9 mg; d-biotin
(biotin), 0.15 mg; pyridoxine (pyridoxine hydrochloride), 31 mg.
2Mineral premix included the following per kilogram of diet: manganese (manganous oxide), 106 mg; zinc (zinc oxide), 106 mg; iron (iron sulfate
monohydrate), 121 mg; copper (copper sulfate pentahydrate), 10 mg; iodine (calicum iodate), 1.5 mg; selenium (sodium selenite), 0.3 mg.
3Digestible amino acid values were determined from digestibility coefficients and calculated total amino acid content of the ingredients (Ajinomoto
Heartland LLC, 2004).
4Determined AME concentrations were 3,185, 3,250, 3,282, 3,286, 3,331, and 3,365 for experiment 1 and 3,132, 3,159, 3,180, 3,201, 3,217, and 3,266
n
for experiment 2.
Table 2. Qualitative assessment of the poultry oil used in the experimental diets1
Measurement
Total fatty acids (%)
Free fatty acids (%)
Peroxide value, initial (mEq/kg)
AOM stability at 20 h4 (mEq/kg)
Titer (°C)
Iodine value
Saponification value (mg of KOH/g)
Unsaponifiable matter (%)
Insoluble impurities (%)
Moisture and volatiles by hot plate (%)
MIU5 (%)
Fatty acid (%)
Myristic (C14:0)
Palmitic (C16:0)
Palmitoleic (C16:1)
Stearic (C18:0)
Oleic (C18:1)
Linoleic (C18:2)
Linolenic (C18:3)
Arachidonic (C20:4)
1Values
Experiment 1
Experiment 2
95.3
3.8
2.8
236
34.1
81.5
197
0.52
0.15
0.15
0.82
90.2
1.8
0.6
7
34.7
81.0
194
0.46
1.36
0.21
2.02
0.63
22.99
7.55
5.52
41.07
18.58
1.22
0.38
0.63
23.34
7.46
5.62
40.67
18.73
1.14
0.40
Analytical method2,3
AOCS G 3-53
AOCS Ca 5a-40
AOCS Cd 8-53
AOCS Cd 12-57
AOCS Cc 12-59
AOCS Cd 1d-92
USP vs. Twenty method (401)1
AOCS Ca 6a-40
AOCS Ca 3a-46
AOCS Ca 2b-38
AOCS Ce 2-66
were determined from a 500-g sample by an independent laboratory (Eurofins Scientific Inc., Des Moines, IA).
(1998).
3United States Pharmacopeial Convention (1980).
4AOM = active oxygen method.
5MIU = moisture and volatiles by hot plate and insoluble impurities plus unsaponifiable matter.
2AOCS
DIETARY APPARENT METABOLIZABLE ENERGY NEEDS OF BROILERS
Experiments 1 and 2
The following procedures were identical for experiments 1 and 2, with the exception of temperature set
points. In experiment 1, temperature set points were
decreased from 21 to 18°C as the birds advanced with
age. Previous research from this laboratory has shown
increased BW gain and decreased feed conversion with
a similar step-down temperature program during winter production (Dozier et al., 2007b). In experiment
2, temperature was set at 25°C to emulate a summer
grow-out because average daily house temperatures
have been reported to range from 24.9 to 29.6°C in the
southeastern United States during summer production
(Xin et al., 1994).
At 36 d of age, broilers (720 males and 720 females)
were separated by sex and randomly distributed to 96
floor pens (15 birds/pen; 0.09 m2/bird) of a solid-sided
facility. Ventilation consisted of a single fan producing
positive pressure in the house with still air at brooding and approximately 3.4 m3/h of air flow per bird
approaching market weight. Heating was provided by
a heat exchanger fed with hot water from a boiler system. Each floor pen had fresh pine shavings and was
equipped with a pan feeder and a nipple drinker line.
Birds had free access to feed and water, and feed was
presented in whole pellet form. Temperature was decreased from 21 to 18°C (20.3 ± 1.1°C; 49.01 ± 11.3%
RH) as the birds advanced with age for experiment 1,
whereas it was set at 25°C (26.1 ± 0.3°C; 66.61 ± 3.4%
RH) for experiment 2. Birds were weighed on d 36 and
47 for the determination of growth rate, feed intake,
caloric conversion, and feed conversion. Mortality was
recorded daily.
On d 42, blood was collected from 1 bird from each
pen via the ulnar vein directly into a heparinized (50
IU/mL) monovette syringe. Samples were centrifuged
at 4,000 × g for 20 min at 4°C, and 1 mL of plasma was
obtained and stored at −20°C for later analysis. Shortterm exposure (<2 d) of treatments has been shown to
detect differences in T3 and T4 concentrations (Gärtner
et al., 1980; Wrutniak and Cabello, 1987). Plasma T3
and T4 concentrations were measured by using a universal microplate spectrophotometer (Bio-Tek Instruments Inc., Winooski, VT) with ELISA reagent assay
test kits from Assay Designs (EIA-CS Kit, Assay Designs Inc., Ann Arbor, MI) according to the manufacturer’s instructions. Standards, samples, and controls
were added to the appropriate wells of a microtiter
plate precoated with anti-T3 or anti-T4 antibodies. The
microtiter plate was then incubated for 60 min with T3
conjugated with horseradish peroxidase or T4 conjugated with horseradish peroxidase. Following incubation,
the plate was washed 5 times and then incubated with
the horseradish peroxidase substrate 3,3′,5,5′-tetramethyl benzidine for 20 min. Absorbance was measured at
450 nm following the addition of stop solution to each
well. The concentrations of T3 and T4 were calculated
using standard curves.
807
On d 47, feed was removed 9 h before processing, and
the following day, 5 birds/pen were randomly selected
for processing, weighed, placed in coops, and transported to the Mississippi State University Poultry Processing Plant. Birds were electrically stunned (5 s; 12.5 V),
bled (80 s), scalded (150 s and 53°C) and mechanically
picked (35 s), and eviscerated. Whole carcass (without
abdominal fat) and abdominal fat were weighed. Carcasses were split into front and back halves, and the
front halves were placed on ice for 18 h. Afterward, the
front halves were deboned to obtain weights of the pectoralis major and minor muscles. Carcass, abdominal
fat, and total breast meat (pectoralis major and minor
muscles) yields were determined from 48-d BW (after
feed withdrawal) of the broilers selected for processing.
Energy Balance Assays
At 37 d of age, 240 Ross × Ross 708 male and female
broilers (48 pens; 5 birds per pen) were randomly distributed into grower battery cages (Alternative Design
Mfg., Siloam Springs, AR). Each cage (66 × 66 × 76
cm) was equipped with 1 trough feeder and 1 nipple
waterer. The experimental facility was a solid-sided
house with temperature control. Temperature was decreased from 21 to 18°C as the birds advanced with age
for evaluating AMEn of the experimental diets used in
experiment 1, whereas it was set at 25°C for the assay determining AMEn of the diets fed in experiment
2. A 48 h, a total excreta collection period (42 to 44
d of age) was conducted to evaluate AMEn of the experimental diets. After a 3-d acclimation period, feed
disappearance and total amount of excreta voided at
the end of the collection were weighed (wet basis). Multiple subsamples were collected from the total amount
of excreta and homogenized, and then a 250-g representative sample was placed in a plastic bag for analysis.
Representative samples of feed and excreta were frozen
and subsequently dried at 55°C for 48 h. Dried samples
were then ground using a Thomas-Wiley mill (Arthur
H. Thomas Company, Philadelphia, PA) equipped with
a 1-mm screen to ensure a homogeneous mixture.
Gross energy contents of feed and excreta were determined in duplicate on 1-g samples using an isoperibol
oxygen bomb calorimeter (model 1281, Parr Instruments, Moline, IL) as described by the manufacturer’s
manual (Parr Instruments, 1948). Nitrogen content of
feed and nitrogen content of excreta were determined in
duplicate on a 0.2-g sample with a Combustion N Analyzer (Truspec N Determinator, Leco Corp., St. Joseph,
MI) by using a previously established method (AOAC,
2006; method 968.06). Feed consumption and excreta
weights during the 48-h collection period were used to
calculate energy and nitrogen intake and excretion. Apparent ME was calculated using the following equation:
AMEn = [gross energy intake − gross energy output in
the excreta] − [8.73 × (nitrogen intake from the diet
− nitrogen output from excreta)] ÷ feed intake. A ni-
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Dozier et al.
trogen correction factor of 8.73 was used from previous
research (Titus, 1956).
Statistical Analyses
Data in both experiments were analyzed as a 6 × 2
factorial treatment structure in a randomized complete
block design. Pen location was the blocking factor. Interaction and main effects were evaluated. Each treatment was represented by 8 replicate pens. Analysis was
performed by PROC MIXED (SAS Institute, 2004).
Statistical significance was established at P ≤ 0.05.
RESULTS AND DISCUSSION
AMEn Determination
Experimental diets were formulated to contain AMEn
concentrations ranging from 3,140 to 3,240 kcal/kg in
increments of 20 kcal of AMEn/kg. Determined AMEn
concentrations were 3,185, 3,250, 3,282, 3,286, 3,331,
and 3,365 (linear P ≤ 0.001, SEM = 23) for experiment 1 and 3,132, 3,159, 3,180, 3,201, 3,217, and 3,266
(linear P ≤ 0.001, SEM = 15) for experiment 2. Different batches of corn, soybean meal, poultry by-product
meal, and poultry oil were used in the 2 experiments.
An explanation for the difference in the calculated and
actual values in experiment 1 may be that AMEn of the
energy-contributing ingredients was underestimated.
Fat quality was extensively measured for the sources
used in both experiments (Table 2). Total fatty acid
composition of poultry oil used in experiment 1 was
numerically higher (95 vs. 90%) than the source used
in experiment 2. A higher total fatty acid content may
potentially increase AMEn of the final diet by 10 to 15
kcal/kg. For example, if a pure oil source had 100% total fatty acids, it would contain 10,000 kcal of AMEn/
kg (NRC, 1994). The 2 oil sources used in the current
research had a total fatty acid content of 90 and 95%
and would differ by only 500 kcal of AMEn/kg (9,000
vs. 9,500 kcal of AMEn/kg). In the current research,
experimental diets were formulated to contain supplemental poultry oil ranging from 0.54 to 2.92%. Hence,
AMEn should differ by only 15 kcal of AME/kg between the 2 sources, based on a 2.92% inclusion rate.
Free fatty acids and initial peroxide values were observed to be within acceptable ranges for experiments
1 and 2, whereas 20-h AOM had extensive numerical
differences between the 2 sources of poultry oil. Apparent ME values of the experimental diets used in experiment 1 were higher than those in experiment 2, but the
AOM value of the oil source used for experiment 1 was
numerically higher. Hence, fat quality differences may
not have contributed to the lower AMEn values of the
test diets in experiment 2. Pesti et al. (2002) determined that the 20-h AOM value among 8 fat sources
was highly correlated with AMEn, but initial peroxide
value and free fatty acids were not significantly correlated. Conversely, fatty acids existing as free fatty acids
have decreased absorption compared with triglycerides
(Renner and Hill, 1961a,b; Poling et al., 1962), resulting in lower AMEn (Wiseman et al., 1992). In addition
to chemical analysis of fat, the extracaloric effect of
dietary fat is a factor that may contribute to the higher
than expected AMEn of the diets. Fat supplementation has been reported to elicit a slower rate of passage
that increases the utilization of nutrients (Mateos et
al., 1982).
Growth Performance
Experiment 1. Results were based on calculated values of AMEn. Apparent ME × sex interactions were not
significant for the variables evaluated in experiment 1;
therefore, presentation of results focuses on main effects (Table 3). Broilers fed progressive additions of
AMEn increased BW gain, resulting in a significant
quadratic response (P ≤ 0.003). Broilers fed the lowest
level of AMEn had 50 g lower BW gain compared with
broilers fed diets containing 3,180 AMEn kcal/kg. Feed
and AMEn intakes were not limiting with broilers fed
diets having the lowest AMEn. Diets were formulated
to be adequate in amino acid density, so the difference
in BW gain should not be due to marginal amino acid
levels, although the diets were not analyzed for amino
acid content. In agreement, other research has shown
increased BW gain when feeding increasing higher levels of AMEn (Farrell, 1974; Waldroup et al., 1976), but
it does reach a point of diminishing returns (Farrell,
1974). In experiment 1, BW gain varied by only 29 g
when broilers were diets ranging in AMEn from 3,160
to 3,240 kcal/kg. In agreement, broilers fed diets not
exceeding 3,300 kcal of AMEn/kg had no differences in
BW gain from 25 to 49 d and 30 to 59 d of age (Leeson
et al., 1996; Dozier et al., 2006). Saleh et al. (2004a)
reported no difference in BW throughout 49 d of age
but did report a decline at 63 d of age, when broilers
were fed diets having 3,324 to 3,444 kcal of AMEn/
kg. Skinner et al. (1992) reported a reduction in BW
gain with increasing levels of AMEn. Growth rate was
similar with broilers fed diets ranging in AMEn from
3,080 to 3,245 kcal/kg, but the reduction in BW gain
occurred from 3,300 to 3,435.
Gradient additions of AMEn decreased (P ≤ 0.015)
feed intake, feed conversion, and caloric conversion (kcal
of AMEn/kg of BW gain) linearly (Table 3). Linear regression equations for feed intake and feed conversion
were Y = 5.21 − 0.00096x (slope = P ≤ 0.002) and Y
= 8772.12 − 0.5490x (slope = P ≤ 0.012), respectively.
No dietary treatment differences occurred for AMEn
intake, mortality, and plasma T3 and T4 concentrations
(data not shown; grand means for T3 = 3.09 mg/dL
and for T4 = 1.69 mg/dL). Broilers fed progressive increments of AMEn had decreased feed intakes and feed
conversion ratios (Skinner et al., 1992; Leeson et al.,
1996; Hidalgo et al., 2004; Saleh et al., 2004a; Dozier
et al., 2006, 2007a,b). Moreover, increasing AMEn has
been shown to decrease caloric conversion (Hidalgo et
809
DIETARY APPARENT METABOLIZABLE ENERGY NEEDS OF BROILERS
al., 2004; Dozier et al., 2006, 2007a,b), but other research has documented increased caloric conversion,
particularly when AMEn exceeds 3,300 kcal/kg with
broilers grown beyond 49 d (Skinner et al., 1992) or 63
d of age (Saleh et al., 2004a,b).
The decreased efficiency of feeding diets high in
AMEn may relate to the low pellet quality attributable
to adding high levels of fat in the mixer. Pellet quality
influences caloric conversion of broilers (McKinney and
Teeter, 2004; Skinner-Noble et al., 2005). The reduction
in caloric conversion with broilers fed diets as highquality pellets may relate to less time spent eating and
more time resting compared with birds provided diets
having low-quality pellets or in mash form (Nir et al.,
1994; McKinney and Teeter, 2004). Moreover, feeding
broilers diets as low-quality pellets results in broilers
spilling fines from the sides of the beak, and a reduced
amount of feed is consumed per meal, translating into
additional energy being used for prehension compared
with feeding broilers diets in the form of high-quality pellets (Jensen et al., 1962; McKinney and Teeter,
2004).
The main effect of sex influenced growth performance
variables. Males grew faster, consumed more feed, and
had lower feed conversion and caloric conversion than
females (P ≤ 0.001). It is well documented that the
broiler male grows faster, consumes more feed, and has
better feed and caloric conversion ratios than females
(Han and Baker, 1994; NRC, 1994; Kidd et al., 2004;
Corzo et al., 2005).
Experiment 2. Results were based on calculated
values of AMEn. Significant AMEn interactions were
determined for several response variables; thus, interaction data are provided (Table 4). Increasing AMEn
resulted in higher BW gain with male (but not female)
broilers, translating into an AMEn × sex interaction
(P ≤ 0.010). These results are inconsistent with data
from experiment 1, but environmental conditions may
have limited growth in experiment 2 (26.1°C and 66.6%
RH). Other research has demonstrated that when broilers from 2.0 to 3.0 kg in BW are subjected to ambient
temperatures exceeding 25°C with a dew point of 23°C,
it adversely affects their growth performance (Dozier et
al., 2005, 2006a), and increasing the temperature from
15.6 to 26.7°C has been shown to decrease the 56-d BW
of male broilers by 835 g (Olanrewaju et al., 2010).
It is important to note that the combination of temperature and RH or dew point influences adverse performance with broilers, not just the effect of ambient
temperature alone. In experiment 2, the combination
of temperature and RH was more pronounced than the
combination of the lower temperature and RH (20.3°C
and 49.0%) in experiment 1. We observed that the performance of broilers noted in experiment 1 was similar
to that of broilers subjected to a low temperature and
RH from 2.0 to 4.0 kg (Dozier et al., 2006b). In experiment 2, an explanation for the increased BW gain of
male broilers fed gradient increments of AMEn may
relate to the heat of evaporation, in which AMEn for
maintenance is increased when broilers are exposed to
high temperatures or when they advance in BW (Hurwitz et al., 1980). When broilers are unable to remove
metabolic heat by sensible heat loss, heat loss shifts
to latent heat loss (heat of evaporation) as birds pant
to remove heat (Simmons et al., 1997). Latent heat
loss is an energy-consuming process and less energy is
available for growth (Hurwitz et al., 1980). Male broilers have higher metabolic heat production and heavier
BW than females, which may have resulted in a more
pronounced response to gradient increments of AMEn
in experiment 2. Furthermore, males secrete more testosterone and growth hormone, and the increased en-
Table 3. Growth performance responses of broilers from 36 to 47 d of age (experiment 1)
BW
gain
(kg)
Main effect
Dietary AMEn1
3,140
3,160
3,180
3,200
3,220
3,240
SEM
Sex2
Male
Female
SEM
Source of variation
AMEn linear
AMEn quadratic
Sex
1Values
2Values
1.040
1.074
1.090
1.072
1.077
1.061
0.013
1.158
0.980
0.010
0.269
0.003
0.001
Feed
intake
(kg)
2.311
2.336
2.335
2.262
2.271
2.234
0.019
2.427
2.157
0.013
0.001
0.080
0.001
Feed
conversion
(kg/kg)
2.226
2.190
2.165
2.116
2.118
2.113
0.020
2.109
2.201
0.013
0.001
0.133
0.001
AMEn
intake
(kcal)
7,255
7,390
7,425
7,241
7,314
7,229
61
7,741
6,877
43
P-value
Caloric conversion
(kcal of AMEn intake/
kg of BW gain)
0.978
0.061
0.001
are least squares means of 8 replicate pens, with each pen having 15 broilers at 36 d of age.
are least squares means of 48 replicate pens, with each pen having 15 broilers at 36 d of age.
6,990
6,895
6,834
6,773
6,820
6,828
57
6,693
7,021
38
0.012
0.040
0.001
Mortality
(%)
0.0
0.4
0.4
0.0
0.0
0.8
0.4
0.4
0.2
0.2
0.535
0.732
0.360
810
Dozier et al.
Table 4. Growth performance responses of broilers from 36 to 47 d of age (experiment 2)
BW
gain
(kg)
Treatment
Dietary AMEn × sex1
Males
3,140
3,160
3,180
3,200
3,220
3,240
Females
3,140
3,160
3,180
3,200
3,220
3,240
SEM
Dietary AMEn2
3,140
3,160
3,180
3,200
3,220
3,240
SEM
Sex3
Males
Females
SEM
Feed
intake
(kg)
Feed
conversion
(kg/kg)
AMEn
intake
(kcal)
Caloric conversion
(kcal of AMEn intake/
kg of BW gain)
Mortality
(%)
0.487
0.562
0.614
0.573
0.637
0.653
1.663
1.679
1.708
1.679
1.690
1.689
3.542
2.953
2.790
2.630
2.668
2.670
5,172
5,305
5,431
5,373
5,444
5,472
10,890
9,572
8,874
9,480
8,606
8,615
1.0
0.9
0.0
4.4
0.0
0.0
0.581
0.569
0.599
0.565
0.599
0.596
0.032
0.534
0.566
0.607
0.569
0.618
0.625
0.026
0.587
0.585
0.021
1.588
1.578
1.581
1.547
1.545
1.561
0.037
1.626
1.629
1.646
1.613
1.637
1.625
0.031
1.648
1.574
0.031
2.763
2.697
2.676
2.679
2.547
2.559
0.119
3.044
2.825
2.733
2.655
2.607
2.615
0.088
2.839
2.654
0.119
4,987
4,987
5,040
4,950
5,103
5,060
120
5,104
5,146
5,236
5,161
5,274
5,266
100
5,375
5,021
83
8,678
8,924
8,510
8,800
8,615
8,559
329
9,784
9,248
8,692
9,140
8,611
8,605
253
9,346
8,681
188
0.0
0.0
1.8
0.0
2.8
0.9
0.9
0.5
1.3
0.0
2.6
1.4
0.4
0.7
1.0
1.0
0.4
P-value
Source of variation
AMEn linear
AMEn quadratic
Sex
AMEn linear × sex
AMEn quadratic × sex
0.001
0.007
0.861
0.010
0.420
0.940
0.825
0.001
0.421
0.574
0.001
0.960
0.007
0.052
0.063
0.049
0.830
0.001
0.386
0.580
0.001
0.886
0.001
0.002
0.089
0.641
0.689
0.994
0.361
0.426
1Values
are least squares means of 8 replicate pens with each pen having 15 broilers at 36 d of age.
are least squares means of 16 replicate pens with each pen having 15 broilers at 36 d of age.
3Values are least squares means of 48 replicate pens with each pen having 15 broilers at 36 d of age.
2Values
ergy may have been used by males to accrete more lean
muscle mass than female broilers can (Leenstra et al.,
1991; Kühn et al., 1996; Sakomura et al., 2005).
During heat stress conditions, the reduced growth
rate of broilers is thought to be attributable to decreased feed intake. Dale and Fuller (1980) determined
that approximately 63% of the growth rate depression
with broilers subjected to heat stress conditions was
due to decreased feed intake and 37% of the growth
depression may have been due to metabolic factors. In
experiment 2, treatments did not alter plasma T3 and
T4 concentrations (data not shown; grand means for
T3 = 1.88 mg/dL and for T4 = 1.16 mg/dL). However,
the overall means for T3 and T4 were reduced by 40
and 32%, respectively, in experiment 2 vs. experiment
1. This could partially explain some of the reduced
growth when broilers are subjected to heat-stress conditions because of the roles that T3 and T4 have in
protein metabolism. Thyroxine influences protein metabolism and growth rate in poultry (King and May,
1984) and T3 enhances DNA replication in muscle cells
(King et al., 1987). Plasma T3 and T4 concentrations
may be reduced when birds are subjected to heat stress
conditions (de Andrade et al., 1977), limiting maximum
growth rate regardless of feed intake. If broilers are fed
inadequate amounts of energy, T4 may stimulate protein degradation to meet energy needs (Guyton, 1991).
Growth performance and the responses of AMEn
between the 2 experiments varied, and these differences may be related to environmental conditions and
their influence on the endocrine system of the bird.
Feed intake is inversely related to ambient temperature
(Prince et al., 1961). If ambient temperature exceeds
thermoneutrality, birds will reduce their feed intake to
minimize metabolic heat production (Ferket and Gernat, 2006). Additionally, the inability to dissipate heat
generated via amino acid catabolism, active transport,
and other metabolic events reduces the maintenance
energy requirement (Hurwitz et al., 1980), further suppressing feed intake.
To cope with high environmental temperatures,
broilers regulate heat production and dissipation via
811
DIETARY APPARENT METABOLIZABLE ENERGY NEEDS OF BROILERS
Table 5. Carcass yield responses of broilers from 36 to 47 d of age (experiment 1)
Chilled carcass
Main effect
Dietary AMEn1
3,140
3,160
3,180
3,200
3,220
3,240
SEM
Sex2
Males
Females
SEM
Weight (kg)
2.119
2.160
2.156
2.144
2.165
2.132
0.023
2.349
1.943
0.014
Abdominal fat
Yield (%)
71.9
71.7
71.7
71.9
71.9
71.6
0.2
72.3
71.3
0.1
Weight (kg)
0.068
0.069
0.069
0.061
0.065
0.064
0.001
0.065
0.068
0.001
Total breast meat
Yield (%)
2.36
2.32
2.35
2.12
2.20
2.18
0.06
2.01
2.49
0.04
Weight (kg)
0.640
0.642
0.643
0.647
0.661
0.633
0.008
0.699
0.590
0.005
Yield (%)
21.7
21.4
21.4
22.3
22.0
21.3
0.3
21.7
21.6
0.1
P-value
Source of variation
AMEn linear
AMEn quadratic
Sex
1Values
2Values
0.667
0.160
0.001
0.796
0.410
0.001
0.020
0.785
0.042
0.009
0.603
0.001
0.652
0.179
0.001
0.766
0.647
0.901
are least squares means of 8 replicate pens with each pen having 15 broilers at 36 d of age.
are least squares means of 48 replicate pens with each pen having 15 broilers at 36 d of age.
coordinated neuroendocrine control by involving various hormones and catecholamines (Etches et al., 2008).
In particular, thyroid hormones are of interest because
of their central role in the control of metabolic rate
and thermogenesis in chickens. The avian thyroid gland
responds to environmental temperature by altering the
production and secretion of hormones (Hoffman and
Shaffner, 1950; Joiner and Huston, 1957). As reviewed
by Etches et al. (2008), metabolic rate and heat production are decreased by thyroidectomy and increased
following thyroid hormone administration in birds.
Huston et al. (1962) determined that the thyroid glands
of 12-wk-old White Plymouth Rock cockerels held at
31°C weighed less per unit of BW but had more stored
T4 compared with those from birds held at 19°C, indicating a reduction of T4 secretion. O’Neill et al. (1971)
demonstrated that fasting heat production and the
maintenance ME requirement of feathered and defeathered cockerels decreased with increasing environmental
temperature. Despite an overall reduction in thyroid
activity, heat production is related to circulating levels
of T3, and not T4 (Klandorf et al., 1981). It follows that
reducing circulating T3 levels during exposure to high
ambient temperature increases heat tolerance because
heat acclimatization occurs by reducing heat production rather than by increasing heat loss (Sykes and Salih, 1986). Kühn et al. (1984) reviewed the hormonal
and environmental interactions on thyroid function in
chickens. During heat stress, plasma levels of T3 are
mainly altered by decreasing inner ring deiodination
of T4 by the type 1 and 2 deiodinases and by increasing outer ring deiodination of T3 to produce inactive
reverse T3.
Under thermoneutral conditions, birds tend to consume feed to meet their metabolic energy needs. In
experiment 1, feed intake decreased linearly with in-
creasing AMEn. However, in experiment 2, when ambient temperatures were on average 5.8°C higher than in
experiment 1, the typical feed intake response was not
observed. Body maintenance requirements take precedence over growth, so the need to minimize metabolic
heat production will preclude any dietary energy response on feed intake during heat stress (Ferket and
Gernat, 2006). Thus, during chronic exposure to high
temperatures, feed intake will not respond to energy
and circulating T3 levels will be decreased, as observed
in the current study.
In parallel with growth rate, male broilers minimized
feed conversion (P = 0.052) and caloric conversion (P
= 0.002) with higher AMEn levels than females, resulting in AMEn × sex interactions. Male broilers fed 3,140
kcal of AMEn/kg had the highest feed conversion, which
skewed the response, resulting in an interaction. Male
broilers fed diets having AMEn varying from 3,160 to
3,240 kcal/kg had a 28-point range in feed conversion,
whereas female broilers had a 22-point spread in feed
conversion when fed the experimental diets. High caloric conversion of male broilers fed 3,140 kcal of AMEn/
kg was due primarily to the reduced BW gain. The
main effect of AMEn did not alter feed intake or mortality, but a linear response (P = 0.049) was observed
for AMEn intake. Dozier et al. (2006) evaluated AMEn
responses of mixed-sexed broilers from 30 to 59 d of age
subjected to environmental conditions mimicking summer production (25°C). Four diets were formulated to
range in AMEn from 3,175 to 3,310 kcal/kg. Significant
linear reductions in feed conversion and caloric conversion were observed with increasing AMEn. Decreases
in feed conversion and caloric conversion were due to
a reduction in feed intake, with no change occurring in
BW gain. The diet with the lowest AMEn (3,175 kcal/
kg) did not the limit growth rate of broilers.
812
Dozier et al.
Table 6. Carcass yield responses of broilers from 36 to 47 d of age (experiment 2)
Chilled carcass
Treatment
Dietary AMEn × sex1
3,140, males
3,160, males
3,180, males
3,200, males
3,220, males
3,240, males
3,140, females
3,160, females
3,180, females
3,200, females
3,220, females
3,240, females
SEM
Dietary AMEn2
3,140
3,160
3,180
3,200
3,220
3,240
SEM
Sex3
Males
Females
SEM
Weight (kg)
1.750
1.839
1.847
1.859
1.879
1.937
1.640
1.661
1.609
1.626
1.655
1.629
0.033
1.695
1.750
1.728
1.743
1.767
1.783
0.023
1.852
1.637
0.013
Abdominal fat
Yield (%)
73.1
73.3
73.3
73.4
73.6
73.5
73.1
72.7
72.2
73.2
73.1
73.4
0.3
73.1
73.0
72.8
73.3
73.3
73.4
0.2
73.4
72.9
0.1
Weight (kg)
0.045
0.043
0.042
0.042
0.047
0.044
0.045
0.047
0.049
0.045
0.048
0.048
0.002
0.045
0.045
0.046
0.044
0.048
0.046
0.001
0.044
0.047
0.001
Total breast meat
Yield (%)
1.891
1.691
1.685
1.660
1.831
1.678
2.028
2.068
2.225
2.035
2.130
2.157
0.079
1.959
1.880
1.955
1.848
1.980
1.918
0.056
1.740
2.107
0.032
Weight (kg)
0.510
0.535
0.543
0.549
0.555
0.565
0.480
0.487
0.477
0.476
0.487
0.482
0.139
0.495
0.511
0.510
0.512
0.521
0.524
0.009
0.543
0.482
0.005
Yield (%)
21.2
21.3
21.5
21.6
21.7
21.4
21.4
21.3
21.4
21.4
21.5
21.7
0.3
21.3
21.3
21.5
21.5
21.6
21.6
0.2
21.5
21.4
0.1
P-value
Source of variation
AMEn linear
AMEn quadratic
Sex
AMEn linear × sex
AMEn quadratic × sex
0.010
0.771
0.001
0.004
0.650
0.066
0.072
0.015
0.920
0.144
0.456
0.705
0.004
0.975
0.336
0.980
0.672
0.001
0.173
0.231
0.749
0.835
0.001
0.038
0.553
0.204
0.860
0.874
0.957
0.500
1Values
are least squares means of 8 replicate pens, with each pen having 15 broilers at 36 d of age.
are least squares means of 16 replicate pens, with each pen having 15 broilers at 36 d of age.
3Values are least squares means of 48 replicate pens, with each pen having 15 broilers at 36 d of age.
2Values
Direct comparisons are difficult between the present
research and that of Dozier et al. (2006) because of differences in genetic strain, feed ingredients, AMEn, and
sex. In the present study, male broilers consumed (P
= 0.001) more feed, translating to higher (P = 0.001)
AMEn intake than female broilers (Table 4). These observations are consistent with the results from experiment 1, and other research has shown that males consume more feed than females (Han and Baker, 1994;
NRC, 1994; Kidd et al., 2004; Corzo et al., 2005). Conversely, BW gain was not different between the sexes, translating to higher (P ≤ 0.007) feed and caloric
conversions with male broilers. The low growth rate
displayed when male broilers were fed diets containing
3,140 kcal of AMEn/kg adversely skewed overall BW
gain, feed conversion, and caloric conversion data for
the main effects on males.
Processing Yields
Experiment 1. Increasing dietary AMEn did not significantly increase carcass and total breast meat weight
and yield, but linear responses (P ≤ 0.020) were ob-
served for decreasing abdominal fat weight and percentage (Table 5). Increasing dietary AMEn fed to male
broilers has resulted in a higher percentage of abdominal fat (Leeson et al., 1996). The higher abdominal fat
percentage may have been related to a lower intake of
amino acids when birds consumed diets formulated to
contain higher AMEn. In the present study, abdominal
fat percentage did not increase with broilers fed diets containing higher AMEn. Dietary amino acids were
increased with gradient increments of AMEn to avoid
confounding effects caused by amino acid intake. Moreover, abdominal fat percentage has been shown to be
similar with broilers fed diets differing in AMEn when
diets were formulated to a constant calorie-to-CP ratio
or increased amino acid density (Bartov et al., 1974;
Griffiths et al., 1977; Mabray and Waldroup, 1981;
Saleh et al., 2004a,b). Skinner et al. (1992) reported
that increasing nutrient density levels (AMEn and amino acids) reduced abdominal fat weight and percentage linearly (P ≤ 0.001). Male broilers had heavier (P
≤ 0.001) carcass and total breast meat weights and a
lower (P ≤ 0.05) abdominal fat weight and percentage than female broilers. Other research has noted that
DIETARY APPARENT METABOLIZABLE ENERGY NEEDS OF BROILERS
males have higher carcass and breast weights and lower
abdominal fat percentage (Kidd et al., 2004; Corzo et
al., 2005).
Experiment 2. In parallel with BW gain, AMEn and
sex interacted (P ≤ 0.04) to influence carcass weight
and total breast meat weight (Table 6). These data indicated that male broilers fed diets increasing in AMEn
had higher carcass and breast meat weights but that
female broilers did not respond to progressive AMEn
levels. Abdominal weight and yield, carcass yield, and
total breast meat yield were not altered by the dietary
treatments. Male broilers had greater (P ≤ 0.02) carcass yield and lower (P ≤ 0.01) abdominal fat weight
and yield.
In conclusion, the maximum response of AMEn for
experiment 1 (winter-type conditions) reached a plateau at 3,200 kcal/kg, based on feed conversion and
caloric conversion. In contrast, male broilers responded
to AMEn beyond 3,200 kcal/kg, based on BW gain,
feed conversion, caloric conversion, carcass weight, and
total breast meat weight in experiment 2 (summer-type
conditions), whereas female broilers did not respond to
increasing levels of AMEn. It must be noted that caution should be exercised when making direct comparisons between the 2 studies because different batches
of ingredients were used, even though the experiments
were identical with respect to the facility used, diet
formulation, and genetic strain.
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