The relationship of body composition, feed intake, and metabolic hormones for broiler breeder females.

Abstract

Three hundred twenty Cobb 500 broiler breeder pullets at 21 wk of age were selected from a flock fed according to Cobb Breeder Management Guide specifications. One hundred sixty pullets at 21 wk of age were switched to ad libitum feeding, and the remaining 160 pullets continued to be control-fed. The pullets were photostimulated at 22 wk and maintained until 36.5 wk. Plasma samples were obtained, BW was determined, and hens were killed for determination of body composition at the following periods: 24 h prior to photostimulation, 2.5 wk after photostimulation, 24 h after first egg, and 36.5 wk following peak egg production. Compared with ad libitum-fed breeders, the restricted breeders had a higher percentage carcass protein and lower percentage carcass fat at all sampling periods. Total egg numbers were greater, and abnormal eggs were less for the restricted pullets compared with the ad libitum-fed pullets at 36.5 wk. Carcass percentage fat of ad libitum-fed pullets was positively related to plasma glucagon, insulin-like growth factor-II (IGF-II), and 17beta-estradiol but negatively related to plasma insulin, insulin/glucagon M ratio, insulin-like growth factor-I (IGF-I), thyroxine (T4), and triiodothyronine (T3). Carcass percentage fat of feed-restricted pullets was negatively related to IGF-I, IGF-II, and T4. The T4 was the most important hormone for predicting the percentage carcass fat in ad libitum-fed pullets, and IGF-I was the most important hormone for predicting the percentage carcass fat in feed-restricted pullets. The percentage carcass protein for ad libitum-fed breeders was positively correlated to IGF-I, T4, T3, insulin/glucagon M ratio, and insulin. Carcass percentage protein for feed-restricted breeders was positively correlated to IGF-I, IGF-II, T4, and glucagon. Stepwise regressions for predicting percentage carcass protein for breeders fed by both systems shows that T3 and IGF-I concentrations were the most important for ad libitum-fed breeders, whereas IGF-II and T4 were best for feed-restricted breeders. The hormone status of breeders may be a key indicator to help predict the body composition and thus support management decisions for maintaining optimum production.

Full text

Page 1

METABOLISM AND NUTRITION
The Relationship of Body Composition, Feed Intake, and Metabolic
Hormones for Broiler Breeder Females
J. M. Sun,‡ M. P. Richards,* R. W. Rosebrough,* C. M. Ashwell,† J. P. McMurtry,* and C. N. Coon‡1
*USDA, ARS, Growth Biology Laboratory, Beltsville, MD 20705-2350, †Department of Poultry Science, North Carolina
State University, Raleigh 27695; and ‡University of Arkansas, Center of Excellence for Poultry Science, Fayetteville 72701
ABSTRACT
breeder pullets at 21 wk of age were selected from a
flock fed according to Cobb Breeder Management Guide
specifications. One hundred sixty pullets at 21 wk of age
were switched to ad libitum feeding, and the remaining
160 pullets continued to be control-fed. The pullets were
photostimulated at 22 wk and maintained until 36.5 wk.
Plasma samples were obtained, BW was determined, and
hens were killed for determination of body composition
at the following periods: 24 h prior to photostimulation,
2.5 wk after photostimulation, 24 h after first egg, and
36.5 wk following peak egg production. Compared with
ad libitum-fed breeders, the restricted breeders had a
higher percentage carcass protein and lower percentage
carcass fat at all sampling periods. Total egg numbers
were greater, and abnormal eggs were less for the re-
stricted pullets compared with the ad libitum-fed pullets
at36.5wk.Carcasspercentagefatofadlibitum-fedpullets
was positively related to plasma glucagon, insulin-like
growth factor-II (IGF-II), and 17β-estradiol but negatively
Three hundred twenty Cobb 500 broiler
Key words: body composition, feed intake, metabolic hormone, broiler breeder
2006 Poultry Science 85:1173–1184
INTRODUCTION
There have been many reports comparing ad libitum
vs. restricted feeding of different type diets on various
aspects of welfare, growth, body composition, and egg
production in broiler breeders (Robbins et al., 1988; Lil-
burn and Myers-Miller, 1990; Joseph et al., 2000; Hock-
ing et al., 2002). A key problem associated with the
feeding and management of modern breeder strains is
theearlyfeedrestrictionrequiredtocontroltheirBW.To
successfully produce sexual maturity and cause breeder
pullets to come into persistent production with photo-
stimulation, breeder pullets need to reach a physiologi-
cal threshold and have adequate fleshing with optimum
levels of protein mass and fat tissue available. There is
2006 Poultry Science Association Inc.
Received April 20, 2005.
Accepted February 11, 2006.
1Corresponding author: ccoon@uark.edu
1173
related to plasma insulin, insulin/glucagon M ratio, insu-
lin-likegrowthfactor-I(IGF-I),thyroxine(T4),andtriiodo-
thyronine (T3). Carcass percentage fat of feed-restricted
pullets was negatively related to IGF-I, IGF-II, and T4.
The T4was the most important hormone for predicting
the percentage carcass fat in ad libitum-fed pullets, and
IGF-I was the most important hormone for predicting
the percentage carcass fat in feed-restricted pullets. The
percentage carcass protein for ad libitum-fed breeders
was positively correlated to IGF-I, T4, T3, insulin/gluca-
gon M ratio, and insulin. Carcass percentage protein for
feed-restricted breeders was positively correlated to IGF-
I, IGF-II, T4, and glucagon. Stepwise regressions for pre-
dicting percentage carcass protein for breeders fed by
bothsystemsshowsthatT3andIGF-Iconcentrationswere
the most important for ad libitum-fed breeders, whereas
IGF-II and T4were best for feed-restricted breeders. The
hormone status of breeders may be a key indicator to
helppredictthebodycompositionandthussupportman-
agement decisions for maintaining optimum production.
evidence to suggest that a minimum amount of body
fat may be required for sexual maturity in broiler
breeder hens (Bornstein et al., 1984). The relationship
of body composition of breeder pullets and plasma hor-
mone levels may be a key indicator for determining
the needed physiological threshold of pullets. In ducks,
turkeys, and broiler breeders, a rapid weight gain at
sexualmaturity hasbeenshowntodecreaseegg produc-
tion and is associated with the ovulation of 2 or more
ova on the same day (Hocking, 1990). Hocking (1993)
showed that multiple ovulations in breeders cause the
release of ova into their body cavity, resulting in no
oviposition. The incidence of multiple ovulations can be
decreased by controlling BW gain with feed restriction
during the period before sexual maturity (Hocking et
al., 1989).
Nutritional status and the subsequent responses of
key plasma metabolic hormones [insulin, glucagon, and
triiodothyronine (T3)] are important factors that deter-
mine the level of hepatic lipogenesis in birds (Hill-
gartner et al., 1995). Fasting and feeding low dietary

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SUN ET AL.
1174
protein concentrations have been shown to increase
plasma growth hormone (GH) concentrations and de-
crease plasma insulin-like growth factor-I (IGF-I; Lau-
terio and Scanes, 1987) in different strains of chickens.
McGuinnessandCogburn(1990)foundastrongpositive
correlation (0.97) between the proportional change in
plasma IGF-I concentrations and relative growth rate.
Decuypere and Kuhn (1984) reported that T3was sup-
pressed during feed restriction in growing birds but
returned to normal levels following realimentation.
McMurtry et al. (1988) also observed feed restriction
significantly suppressed circulating T3levels in broilers.
In mammals, several studies have indicated that feed
intake, and its associated effects on metabolic rate, may
be the triggering mechanism for changes in reproduc-
tive function (Renaville et al., 1993). Fluctuations in
plasma hormones and substrates may provide signals
that link metabolic status to the activation of the repro-
ductive system. The overall goals of the research are to
provideapotentialindicatorofwhenaflockhasreached
a mature BW and physiological threshold needed to
successfully produce sexual maturity and to determine
the hormones associated with carcass composition
changes to better coordinate feed management during
production.
The present study was conducted to observe how
hormones might relate to fat deposition and carcass
traits as a means to evaluate reproductive status prior
to sexual maturity and during egg production and to
observe the hormone status of the breeders fed ad libi-
tum to determine the relationship of hormones to feed
intake. The hormone level of ad libitum-fed breeders
may be a valuable tool in selecting breeding stock to
change progeny’s feed intake.
MATERIALS AND METHODS
Stock and Management
One thousand Cobb 500 breeder pullets were reared
in floor pens and fed restricted amounts of feed using
a combination of controlled daily feeding and skip-a-
day feeding to provide pullets of a standard BW ac-
cording to the Cobb Breeder Management Guide (Cobb-
Vantress, 2002) until 21 wk of age. Three hundred
twenty breeder pullets of similar BW were selected from
this group of 21-wk-old pullets to conduct the research.
Breeder pullets with a mean BW of 1.90 kg ± 0.18 were
allotted to the feed restriction treatment, and breeder
pullets with a mean BW of 1.91 kg ± 0.13 were utilized
for the ad libitum-fed treatment. The breeder pullets
were separated into 4 groups of 40 pullets per treatment
and were housed in individual cages. Four groups of
40pulletseach(160pullets)werefedarestrictedamount
of breeder I diet (2,860 kcal of ME/kg; 16.0% CP) similar
to levels recommended by the Cobb Breeder Manage-
ment Guide (Cobb-Vantress, 2002) from 21 wk through
the laying cycle (Table 1). Four groups of 40 pullets each
(160 pullets) were fed the same breeder I diet ad libitum
Table 1. Feed allocation program for broiler breeders1
Feed allotment
(g/bird per d)Week of age Notes
21
22
23
24
25
26
27
28
113
118
127
132
139
151
160
165
Light stimulation
5% egg production, 397 kcal of ME
60% egg production, peak feed,
472 kcal of ME
29
30
31
32
33
34
35
36
165
165
164
163
162
161
160
159
Peak egg production
1Based on recommendations of the Cobb 500 Breeder Management
Guide (2002).
starting at 21 wk of age through termination of the ex-
periment at 36.5 wk of age. Within the 2 feeding
schemes, feed-restricted breeders and breeders fed ad
libitum were divided into 4 physiological time groups
for data collection. Twenty-one breeder pullets from
each feeding regimen were killed by CO2asphyxiation
onthedaypriortophotostimulationat22wk;21breeder
pullets from each feeding regimen were killed 2.5 wk
after photostimulation; 40 of the breeder pullets from
each feeding regimen were killed within 24 h after lay-
ing their first egg; and a final group of 40 breeders from
each feeding regimen was killed at 36.5 wk of age. The
control-fed breeder hens were fed a daily amount of
feed according to the Cobb Breeder Management Guide
regardless of BW. To evaluate the plasma hormone sta-
tus and the correlation to daily feed intake, the grams
of feed consumed per day per kilogram of metabolic
body weight (MBW) were utilized for both ad libitum
and feed-restricted breeders. The MBW was determined
for each breeder by the equation MBW = kg of BW0.75.
Because the feed intake was controlled in the feed-re-
stricted pullets, the main separation of hormones per
MBW was the range of BW instead of differences in
feed consumption. The breeders fed ad libitum were
evaluated to show individual feed intake and hormone
differences correlated to MBW.
Each pullet’s BW, egg weights, and feed consumption
were determined weekly through 36.5 wk of age or until
thepulletwaskilled.Mortalityandeggproductionwere
determined on a daily basis during the experiment. The
data collected when breeders were killed were BW, ab-
dominal fat pad weight, number and weight of ovarian
follicles, and weight of ovaries without follicles. All
breeder pullets and hens were killed and bled within 4
h of feeding in the morning. Animal use protocol No.
03008 for the experiment was approved by the Univer-
sity of Arkansas Institutional Animal Care and Use
Committee.

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METABOLIC HORMONE STATUS OF BROILER BREEDERS
1175
Each breeder carcass was frozen at −20°C before auto-
claving. The carcasses were placed in trays covered with
foil and autoclaved at 120°C for 15 h in an AMSCO
3053 sterilizer (Steris Corporation, Mentor, OH). The
carcasses were homogenized after autoclaving using a
Waring 4 L blender (Waring products division, Dynam-
ics Corporation of America, New Hartford, CT). Sub-
samples were collected after grinding and freeze-dried
in a Genesis SQ 12 EL Freeze drier (The Virtis Company,
Gardiner, NY). Carcass protein and fat were analyzed
according to AOAC (1990) to correlate the body mass
with hormone levels. The percentage carcass fat and
protein were reported on a dry matter basis. Five millili-
ters of blood were collected using EDTA as anticoagu-
lant from the wing vein from each breeder prior to being
killed. The blood samples were centrifuged with TJ-6
centrifuge (Beckman Coulter Inc., Fullerton, CA) for 10
min at 3,000 rpm, and the plasma was separated and
stored frozen at −20°C. The frozen plasma was analyzed
for leptin, glucagon, insulin, T3, thyroxine (T4), IGF-I,
insulin-like growth factor-II (IGF-II), and 17β-estradiol.
Hormone Assays
Specific radioimmunoassays were used to determine
plasma hormone concentrations. All samples were ana-
lyzedwithin1assay toavoid interassayvariations.Dou-
ble antibody radioimmunoassays were used to deter-
mine plasma concentrations of IGF-I with an intraassay
CV of 2.8% (McMurtry et al., 1994), chicken IGF-II with
intraassay CV of 3.7% (McMurtry et al., 1998), insulin
with intraassay CV of 2.2%, (McMurtry et al., 1983), and
leptin with intraassay CV of 3.9% (Evock-Clover et al.,
2002). The T3and T4were determined as previously
described (McMurtry et al., 1988) and had CV of 2.5 and
2.8%, respectively. Plasma glucagon (Linco Research
Inc., St. Charles, MO) and estradiol-17B (Diagnostics
Products Corporation, Los Angeles, CA) were deter-
mined using commercial kits with an intraassay CV of
1.9 and 3.7%, respectively. For glucagon analysis, an
aliquot of plasma was stored in the presence of 1,000
KIU of aprotinin.
Statistical Analysis
The experimental birds were housed in individual
cages. The experimental design was completely ran-
domized using individual pullets as the experimental
unit. There were 2 feed levels and 4 periods of observa-
tions. All the data were subjected to ANOVA analysis
of SAS (SAS Institute, Cary, NC). Differences between
means were evaluated using Fisher’s protectedleast sig-
nificant difference procedure. The correlation coeffi-
cients between percentage carcass fat, percentage car-
cass protein, and feed consumption per day per meta-
bolic BW (FCPDMBW) with blood hormones within
each feed level were determined by the SAS Corr proce-
dure. The equations using blood hormones to predict
percentage carcass fat, percentage carcass protein, and
FCPDMBW within each feed level were determined by
multiple regression analysis with SAS software. The
stepwise technique was used for variable selection for
the multiple regression equation of percentage carcass
fat, percentage carcass protein, and FCPDMBW, respec-
tively.
RESULTS
Body Composition
Body composition of restricted and ad libitum-fed
breeders at prestimulation, poststimulation, first egg,
and 36.5 wk are shown in Table 2. The results indicated
that BW was increased with breeder age (an exception
was a lack of BW change between the first egg and
36.5 wk for the feed-restricted breeders) in both feeding
systems. The ad libitum-fed pullets gained 423, 685, 741,
and 1,290 g more BW during prestimulation, poststimu-
lation, first egg, and overall 36.5-wk period, respec-
tively, compared with the feed-restricted breeders. Both
absolute fat pad weight and fat pad percentage of BW
were increased with breeder age for both feeding sys-
tems. The ad libitum-fed breeders had 58, 68, and 107
g more fat pad weight at poststimulation, first egg, and
36.5-wk period, respectively, and 1.3, 1.2, and 1.4%
higher fat pad percentage of BW at poststimulation,
first egg, and 36.5-wk period than restricted breeders.
Carcass percentage fat increased with breeder age,
whereas carcass percentage protein decreased with
breeder age in both restricted and ad libitum-fed breed-
ers. Compared with ad libitum-fed breeders, the re-
stricted breeders had 9.8, 9, 8, and 7.4% more carcass
protein at prestimulation, poststimulation, firstegg, and
36.5-wk period and 4.4, 13.3, 14.3, and 7.9% less carcass
fat at prestimulation, poststimulation, first egg, and
36.5-wk period, respectively.
Feed Intake
The FCPDMBW is shown in Table 2. The results indi-
cated that ad libitum-fed breeders consumed 27.3, 33.3,
40.2, and 8.6 g more feed at prestimulation, poststimula-
tion, first egg, and 36.5-wk period than feed-restricted
breeders, respectively.
Egg Production
The average total egg production per hen and the
percentage of abnormal eggs are shown in Table 2. The
results showed the feed-restricted breeders produced
14.9 more eggs per breeder through 36.5 wk, and the
percentage of abnormal eggs was 9.2% lower compared
with the ad libitum-fed breeders.
Ovary Weight and Follicles
The ovary parameters at different physiological peri-
ods are shown in Table 3. The results showed that the

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SUN ET AL.
1176
Table 2. Body composition and performance data1
Prelight stimulation
(22 wk)
Postlight stimulation
(24.5 wk)
Plateau
(36.5 wk)First egg
Variable Ad libitum RestrictedAd libitum Restricted Ad libitumRestrictedAd libitum Restricted
BW (g)
Fat pad (g)
Fat pad (%)2
Total eggs
Abnormal eggs (%)3
FCPDMBW (g)4
Carcass fat (%)5
Carcass protein (%)5
2,567 ± 138e
17.1 ± 4.7f
0.7 ± 0.2f
—
—
91.3 ± 20.5a
25.6 ± 3.7e
53.4 ± 5.2b
2,144 ± 166f
13.0 ± 9.1f
0.6 ± 0.4f
—
—
64 ± 3.7bc
21.2 ± 5.7f
63.2 ± 4.2a
3,637 ± 281c
99.4 ± 39.1c
2.7 ± 0.9c
—
—
87.6 ± 9.5a
43.0 ± 4.3b
43.7 ± 3.0e
2,952 ± 282d
41.3 ± 9.3e
1.4 ± 0.3e
—
—
54.3 ± 5.1de
29.7 ± 4.3d
52.7 ± 3.4b
4,255 ± 328b
139.2 ± 43.5b
3.2 ± 0.8b
—
—
90.5 ± 27.0a
46.3 ± 4.1a
42.1 ± 2.8ef
3,513 ± 207c
71.0 ± 17.8d
2.0 ± 0.5d
—
—
50.3 ± 1.9e
32.0 ± 4.1d
50.1 ± 2.6c
4,809 ± 378a
212.2 ± 56.8a
4.4 ± 1.1a
42.1 ± 12.4b
12.9 ± 2.9a
67.2 ± 10.8b
47.9 ± 6.3a
40.3 ± 4.5f
3,519 ± 229c
105.1 ± 24.4c
3.0 ± 0. 7bc
57 ± 12.9a
3.7 ± 0.7b
58.6 ± 2.6cd
40 ± 4.4c
47.7 ± 3.6d
a–fMeans within rows for same parameter for breeders fed ad libitum and restricted with different superscripts were significantly different (P
< 0.05).
1All values represent the mean ± SEM of 21 (pre- and postlight stimulation) or 40 (first egg and plateau) observations.
2Fat pad weight expressed as a percentage of BW.
3Includes soft shell or shell-less, multiple eggs, and multiple soft shell eggs.
4Feed consumption per day per metabolic BW.
5Percentages of carcass fat and protein are on a dry matter basis.
pullets fed ad libitum had 31.55 and 13.53 g heavier
ovary weight compared with the feed-restricted pullets
at first egg and the 36.5-wk period, respectively. The
ovary weights were heavier when the pullets laid their
first egg and following peak egg production (36.5 wk)
than for ovary weights from the pullets before and after
light stimulation for both restricted and ad libitum-fed
pullets. The number of small atretic ovarian follicles
was 0.68 more in ad libitum-fed pullets compared with
restricted pullets. The ovarian stroma weight at first egg
was 7.35 g heavier in ad libitum-fed pullets than in
restricted pullets. The total large yellow follicles (LYF)
weight followed the same trend as the LYF number and
showed that ad libitum-fed breeders had 24.57 g heavier
total LYF weight than restricted breeders at first egg and
numericallyheaviertotalLYFthanrestrictedbreedersat
the postlight stimulation and 36.5 wk period. The num-
ber of LYF and the total weight of LYF decreased by
5.55 and 19.69 g and by 3.55 and 11.08 g at the 36.5-wk
period compared with first egg in ad libitum-fed and
feed-restricted breeders, respectively. The number of
LYF and the total weight of LYF were 2.84 and 45.76 g
and 3.17 and 34.92 g more at the 36.5-wk period than at
Table 3. Ovarian parameters1
Prelight stimulation
(22 wk)
Postlight stimulation
(24.5 wk)
Plateau
(36.5 wk) First egg
VariableAd libitumRestrictedAd libitumRestrictedAd libitumRestricted Ad libitumRestricted
Ovary weight (g)
Stroma weight (g)
Postovulatory follicles
Atretic ovarian follicles
Number of LYF2
Total LYF weight (g)
0.69 ± 0.24d
—
—
—
—
—
0.49 ± 0.14d
—
—
—
—
—
6.7 ± 3.9d
—
—
—
4.25 ± 2.66c
15.02 ± 9.06c
1.48 ± 0.61d
3.55 ± 0.07c
—
—
1.75 ± 0.95d
9.9 ± 4.75c
96.29 ± 21.64a
14.62 ± 7.28a
3.79 ± 2.72a
0.79 ± 0.48a
12.64 ± 3.44a
80.47 ± 23.67a
64.74 ± 12.6c
7.27 ± 2.75bc
3.08 ± 2.23a
0.11 ± 0.52b
8.47 ± 1.79b
55.9 ± 12.3b
73.87 ± 15.35b
11.37 ± 3.84ab
—
—
7.09 ± 2.08b
60.78 ± 17.72b
60.34 ± 8.6c
10.67 ± 3.22ab
—
—
4.92 ± 1.4c
44.82 ± 16.9b
a–dMeans within rows for same parameter for breeders fed ad libitum and restricted with different superscripts were significantly different ( P
< 0.05).
1All values represent the mean ± SEM of 21 (pre- and postlight stimulation) or 40 (first egg and plateau) observations.
2Large yellow follicles.
postlight stimulation for ad libitum and feed-restricted
breeders, respectively.
Hormone Levels
The different feeding systems had significant effects
on circulating levels of key metabolic hormones prior
to the onset of egg production (Table 4). Circulating
insulin and T3levels were 2.16 and 1.13 ng/mL higher,
and glucagon levels were 626.18 pg/mL lower in the
ad libitum-fed pullets compared with restricted pullets
just prior to light stimulation at 22 wk. There was a
significant decline in insulin levels after first egg for
breeder hens fed by both feeding systems. The highest
insulin levels appeared at postlight stimulation and first
egg for restricted breeders and at postlight stimulation
and prelight stimulation for ad libitum-fed breeders.
Insulin levels for ad libitum-fed breeders were 2.16 and
1.49 ng/mL higher than restricted breeders during the
pre- and postlight stimulation period. In contrast, the
glucagon levels were 626 and 241 pg/mL higher in re-
stricted breeders compared with ad libitum-fed breed-
ers at prelight stimulation and the 36.5-wk period, but

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METABOLIC HORMONE STATUS OF BROILER BREEDERS
1177
Table 4. Plasma hormone levels1
Prelight stimulation
Postlight stimulation
Plateau
(22 wk)
(24.5 wk)
First egg
(36.5 wk)
Variable2
Ad libitum
Restricted
Ad libitum
Restricted
Ad libitum
Restricted
Ad libitum
Restricted
Insulin (ng/mL)
3.76 ± 0.46a
1.6 ± 0.32f
4.05 ± 0.79a
2.56 ± 0.51cd
3.01 ± 0.34b
2.86 ± 0.62bc
2.4 ± 0.41de
2.04 ± 0.26e
Glucagon (pg/mL)
104.92 ± 14.6d
731.1 ± 28.44a
110.4 ± 36.23d
167.09 ± 34.6d
276.82 ± 10.43c
166.09 ± 51.48d
337.66 ± 24.00c
579.10 ± 135.42b
Intogl2
24.08 ± 8.48a
1.42 ± 0.38f
20.50 ± 7.74b
9.49 ± 2.31cd
8.61 ± 5.56d
12.06 ± 3.89c
5.90 ± 3.93e
2.81 ± 1.77f
T3(ng/mL)
1.50 ± 0.58a
0.37 ± 0.17d
1.23 ± 0.63b
1.21 ± 0.39b
0.67 ± 0.33c
0.59 ± 0.33c
0.59 ± 0.26c
0.51 ± 0.29cd
17β-Estradiol (pg/mL)
164.26 ± 65.35b
77.53 ± 34.48c
414.82 ± 205.97a
359.32 ± 153.95a
383.79 ± 170.05a
351.13 ± 104.61a
185.01 ± 90.56b
234.85 ± 155.52b
T4(ng/mL)
9.43 ± 3.2a
8.68 ± 2.37a
4.77 ± 1.99c
6.24 ± 1.38b
5.44 ± 1.6b
5.59 ± 1.72b
5.77 ± 1.86b
6.11 ± 2.01b
Leptin (ng/mL)
13.28 ± 1.98a
10.86 ± 1.56d
12.93 ± 1.99ab
11.50 ± 1.74cd
12.31 ± 2.46abc
10.85 ± 2.41d
12.03 ± 3.73abcd
11.55 ± 2.94bcd
IGF-I (ng/mL)
15.3 ± 6.33de
56.95 ± 22.1a
9.16 ± 4.64ef
37.44 ± 8.12b
7.19 ± 3.7f
19.09 ± 9.37d
8.76 ± 4.07ef
26.09 ± 16.47c
IGF-II (ng/mL)
58.64 ± 7.94d
197.74 ± 45.3a
71.45 ± 10.66d
87.85 ± 14.27c
90.44 ± 7.89c
88.92 ± 12.59c
98.64 ± 16.12c
116.94 ± 35.75b
a–fMeans within rows for same parameter for breeders fed ad libitum and restricted with different superscripts were significantly different (P < 0.05).
1All values represent the mean ± SEM of 21 (pre- and postlight stimulation) or 40 (first egg and plateau) observations.
2Intogl = M ratio of plasma insulin/glucagon; T3= triiodothyronine; T4= thyroxine; IGF = insulin-like growth factor.
glucagon was 110.73 pg/mL lower than ad libitum-fed
breeders at first egg. The changes for the insulin/gluca-
gonMratio(intogl)weresimilartothetrendinglucagon
during different physiological periods. The intogl was
24.08 ± 8.48 vs. 1.42 ± 0.38 for the ad libitum-fed and
feed-restricted pullets,respectively, prior tolight stimu-
lation. This ratio increased in the restricted group to
12.06 ± 3.89 as the pullets began to lay eggs, whereas it
declinedintheadlibitum-fedgroupto8.61 ±5.56during
this same time. As egg production progressed to 36.5
wk, both groups exhibited a decline in the intogl (Table
4). The T3levels were higher in ad libitum-fed breeders
than in restricted breeders at the prelight stimulation
period, but there were no significant differences thereaf-
ter for breeders from the 2 feeding systems. The T4level
was 1.47 ng/mL higher in restricted pullets than in ad
libitum-fed breeder pullets at postlight stimulation pe-
riod. The T4levels were not significantly different for
the 2 feeding systems at other physiological periods.
The 17β-estradiol level was 87 pg/mL higher in ad libi-
tum-fed breeders than in restricted breeders at the pre-
light stimulation period. There were no differences in
17β-estradiol between breeders from the 2 feeding sys-
tems for other periods. The leptin levels were 2.42, 1.43,
and 1.46 ng/mL lower in feed-restricted pullets com-
paredwiththeadlibitum-fedpulletsatprelightstimula-
tion, postlight stimulation, and first egg periods, respec-
tively. There was no significant difference in the leptin
level at the 36.5-wk period for the breeders fed by the
2 feeding systems. The plasma levels of IGF-I and IGF-
II were 41.65, 139.1; 28.28, 16.4; 11.9, 1.52; and 17.33,
18.3 ng/mL higher in feed-restricted pullets compared
with the ad libitum-fed pullets at prelight stimulation,
postlight stimulation, first egg, and at the 36.5-wk pe-
riod, respectively. There was a significant decline in
IGF-I in the feed-restricted group at first egg compared
with the feed-restricted pullets at the other periods. The
ad libitum-fed breeders also had the lowest IGF-I level
at first egg, but the level was not significantly lower
than the IGF-I levels from the ad libitum-fed breeders
at postlight stimulation and the 36.5-wk period.
Correlation Between Hormones, Feed
Intake, and Carcass Composition
The correlation coefficients between the plasma hor-
mone levels and feed intake for ad libitum-fed pullets
are shown in Table 5. The results indicated that
FCPDMBW was positively related with insulin (P =
0.0205), intogl (P = 0.0397), leptin (P = 0.021), and T3(P =
0.0446) but negatively related with IGF-II (P = 0.0102). A
stepwise regression for predicting FCPDMBW for ad
libitum-fed pullets from hormone levels (Table 6)
showed that an index consisting of IGF-I + IGF-II pro-
duced an R2of 0.087 (P = 0.0567). The correlation coeffi-
cients between the plasma hormone levels and percent-
age carcass fat for ad libitum-fed pullets are shown in
Table 5. The results indicated that percentage carcass
fat of ad libitum-fed pullets was positively related with