feeding

1. Effects of restricted feeding, low-energy diet, and implantation of trenbolone
acetate plus estradiol on growth, carcass traits, and circulating concentrations
of insulin-like growth factor (IGF)-I and IGF-binding protein-3
in finishing barrows1
C. Y. Lee*2
, H. P. Lee*3
, J. H. Jeong*, K. H. Baik†, S. K. Jin*, J. H. Lee‡, and S. H. Sohn†
Departments of *International Livestock Industry and †Animal Science and Biotechnology, Chinju National
University, Chinju 660-758 and ‡Pusan and Kyungnam Cooperative Swine Farms Feed Mill,
Kimhae 621-010, South Korea
ABSTRACT: Effects of restricted feeding (80% ad li-
bitum), feeding a low-energy diet containing 84% DE
(2.95 Mcal/kg) of the control diet, and implantation of
Revalor H (140 mg trenbolone acetate plus 14 mg estra-
diol-17β) on growth, carcass traits, and serum concen-
trations of insulin-like growth factor (IGF)-I and IGF-
binding protein-3 (IGFBP-3) were studied in crossbred
finishing barrows beginning from 59 ± 0.9 kg of body
weight. Blood samples were taken every 3 wk and the
animals were slaughtered at approximately 105 kg
body weight. Restricted feeding caused a decrease (P <
0.01) in ADG; feeding the low-energy diet was effective
in reducing backfat thickness but decreased gain:feed;
the implantation caused a decrease in ADG, feed intake,
and backfat thickness and increased gain:feed. Overall
pork quality based on pH, drip loss, and the lightness
in color of longissimus muscle was not affected by any
of the treatments. Serum IGF-I concentration increased
Key Words: Anabolics, Diet, Insulin-like Growth Factor, Pigs, Restricted Feeding
2002 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2002. 80:84–93
Introduction
When pigs are fed to appetite, barrows eat excessively
more feed than boars and gilts, and because of this
their carcass leanness and feed efficiency are reduced
compared with that of boars and gilts (Field, 1971).
Restricted feeding is known to be effective for improving
the reduced production efficiency of barrows (Leymas-
1
This study was supported by Research Grant 297047-3 (CYL) of
the Ministry of Agriculture and Forestry, South Korea.
2
Correspondence: phone: +82 55-751-3285; fax: +82 55-753-4422;
E-mail: cylee@cjcc.chinju.ac.kr.
3
Present address: Department of Anatomy and Neurobiology, Col-
lege of Medicine, Gyungsang National University, Chinju 660-702,
South Korea.
Received April 14, 2001.
Accepted August 22, 2001.
84
following the implantation but did not change (P > 0.05)
due to other treatments. Immunoreactive IGFBP-3 con-
centration was not changed by any of the treatments.
Overall ADG was positively correlated with early-stage
(d 21) IGF-I and IGFBP-3 concentrations only in unim-
planted barrows, whereas backfat thickness was nega-
tively correlated with d-42 IGF-I concentration in all
but unimplanted barrows with ad libitum intake. A
strong positive correlation (P < 0.01) between IGF-I and
IGFBP-3 concentrations was apparent with increasing
age of the animals. Results suggest that growth rate
and backfat thickness are decreased by a moderate re-
striction of feed or energy intake with no accompanying
changes in circulating IGF-I and IGFBP-3 concentra-
tions and that the beneficial effect of Revalor H implan-
tation on feed efficiency may be mediated, in part, by
IGF-I. Moreover, both IGF-I and IGFBP-3 concentra-
tions may be useful as growth indices in pigs.
ter and Mersmann, 1991), although this practice re-
quires additional labor for weighing the feed. Alterna-
tively, use of a low-energy diet (Coffey et al., 1982;
Hale et al., 1986) or an anabolic implant (Galbraith and
Topps, 1981) also is known to be effective in reducing fat
deposition. Moreover, feed efficiency is also improved by
the anabolic implant. An increase in growth rate with
no change in feed intake (Grandadam et al., 1975; van
Weerden and Grandadam, 1976), as well as a decrease
in both of these (De Wilde and Lauwers, 1984), has
been reported as an effect of a combined trenbolone/
estradiol implant in barrows.
Insulin-like growth factor (IGF)-I is a 7.5-kDa endo-
crine as well as autocrine/paracrine peptide that medi-
ates the growth-stimulating action of GH (Jones and
Clemmons, 1995; Simmen et al., 1998; Liu and LeRoith,
1999). As such, circulating IGF-I concentration is re-
flective of endogenous GH status in well-nourished hu-

2. Nutrition, steroids and IGF system in barrows 85
Table 1. Composition of experiment diets (as-fed basis)
fed to growing pigs
Item Control diet Low-energy diet
Ingredient, %
Corn 62.68 30.48
Wheat 5.38 13.44
Wheat mill run — 35.00
Rice bran (13% fat) 3.00 3.00
Soybean meal (44% CP) 17.76 9.64
Limestone 0.48 0.88
Rapeseed meal 2.00 2.00
Dicalcium phosphate 1.80 1.62
Salt 0.30 0.30
Vitamin premixa
0.30 0.30
Mineral premixb
0.26 0.26
Tallow 3.04 —
Molasses 3.00 3.00
Lysine-HCl — 0.08
Calculated chemical composition
DE, Mcal/kg 3.50 2.95
Crude protein, % 15.0 15.0
Lysine, % 0.75 0.75
Crude fat, % 6.2 3.2
Crude fiber, % 3.4 5.2
Crude ash, % 5.0 5.9
Ca, % 0.85 0.98
P, % 0.67 0.83
a
Provided per kg of diet: 8,100 IU vitamin A, 1,200 IU vitamin D3,
45 IU vitamin E, 2.55 mg vitamin K, 1.5 mg thiamin, 0.6 mg riboflavin,
2.55 mg pyridoxine, 0.03 mg vitamin B12, 19.5 mg pantothenic acid,
39 mg niacin, 0.09 mg biotin, and 0.75 mg folic acid.
b
Provided per kg of diet: 102.7 mg FeSO4, 0.442 mg CoSO4, 174.2
mg CuSO4, 54.18 mg MnSO4, 106.6 mg ZnSO4, 0.546 mg CaIO3, and
0.338 mg Na2SeO3.
mans and animals (Blum et al., 1993; Simmen et al.,
1998). Moreover, the majority of circulating IGF is
bound to 40- to 45-kDa IGF-binding protein-3 (IGFBP-
3), which also is GH-dependent (Jones and Clemmons,
1995; Bell et al., 1998; Baxter, 2000). Besides GH, nutri-
tion and gonadal steroids also are known to regulate
the expression of IGF-I and IGFBP-3 (Lee et al., 1990;
Ketelslegers et al., 1996; Hall et al., 1999).
The present study was undertaken to further investi-
gate the effect of trenbolone-plus-estradiol implant on
production efficiency and to find whether effects of mod-
erately restricted nutrition and the anabolic implant
on growth are associated with a change in the circulat-
ing IGF-I system in finishing barrows.
Materials and Methods
Animals
Sixty-four 104 ± 7-d-old barrows weighing approxi-
mately 50 kg, which were progenies of Landrace × York-
shire dams and Duroc sires, were randomly divided into
eight groups under a 2 × 2 × 2 factorial arrangement
of treatments in such a way that each group had eight
animals in one pen. Main effects included feeding (ad
libitum intake vs 80% ad libitum intake), diet (control
vs low-energy), and anabolic implant. The low-energy
and control diets (Table 1) were formulated to contain
87 and 103% DE requirement for barrows (NRC, 1998);
the relative energy level of the former was low enough
to bring about a reduction in backfat thickness, as could
be expected from previously reported results (Coffey
et al., 1982; Hale et al., 1986). Crude protein, lysine,
vitamin, and mineral contents of the two diets were
similar. The animals, which were group-fed, were pro-
vided with 2.4 m2
space and 30 cm feeder length per
pig and free access to water. On d 0 of the experiment
after 2 wk of adaptation to the respective diet and new
environment, half of the animals weighing 59 ± 0.9
kg received an implantation of Revalor H (Hoechst-
Roussel, Warren, NJ) containing 140 mg trenbolone
acetate and 14 mg estradiol-17β at the base of an ear.
Each restricted feeding group of each diet × implant
combination received 80% of the average daily feed in-
take of the corresponding ad libitum group during the
previous week. The amount of feed given to the re-
stricted feeding group was adjusted every 7th d. A 10-
mL jugular blood sample was taken from each animal
every 3 wk for the analysis of hormones and glucose.
The sixteen heaviest animals, irrespective of the pen,
that had reached approximately 105 kg body weight
were slaughtered at one time at the abattoir of Pusan
and Kyungnam Cooperative Swine Farms Association;
this was repeated four times once a week to minimize
a difference in slaughter weight among groups. Loin-
muscle cross-sectional area (LMA) was estimated at
the 10th rib using a real-time ultrasonic scanner (model
SSD-500V, Aloka, Tokyo, Japan) on the day before
slaughter. The estimated LMA was adjusted for 105-
kg live weight using the following equation suggested
by National Swine Improvement Federation (NSIF;
1997) for barrows weighing 113.4 ± 13.6 kg: adjusted
LMA = actual LMA + [(desired wt − actual wt) × actual
LMA ÷ (actual wt + 70.31)], where weight is in kilo-
grams. Backfat thickness was measured after overnight
chilling of the carcass at 4°C at the last rib and between
the 11th and 12th ribs. The average of the two measure-
ments was adjusted for 105-kg live weight using the
following equation that was suggested for the adjust-
ment of the 10th-rib backfat thickness for barrows
weighing 113.4 ± 13.6 kg (NSIF, 1997): adjusted backfat
= actual backfat + [(desired wt − actual wt) × actual
backfat ÷ (actual wt − 13.608)], where weight is in ki-
lograms.
Physicochemical Analysis
of Longissimus Muscle Section
For the analysis of pork quality traits and chemical
composition of the longissimus dorsi muscle, a midsec-
tion was prepared by slicing the whole muscle, includ-
ing the attached backfat layer, between the 7th and
8th ribs and between the 11th and 12th ribs. Backfat
and muscle color of the longissimus muscle section was
measured on the caudal cut by the Commission Interna-
tionale de l’Eclairage (CIE; 1978) L* (lightness), a* (red-
ness), and b* (yellowness) standards using a chromome-

3. Lee et al.86
ter (model CR 300, Minolta Camera Co., Osaka, Japan),
after which the fat layer was removed for the physico-
chemical analysis of the muscle. Drip loss was deter-
mined by measuring the percentage weight loss of a 7-
cm sample of the muscle section from the caudal end
during 48-h suspension at 4°C in a closed plastic con-
tainer, basically as described by Joo et al. (1999). An-
other 7-cm sample at the cranial end of the muscle
section was ground and used for the determination of
pH and chemical composition. The pH of the ground
muscle was measured after homogenization with dis-
tilled water at a 1:10 (wt/vol) ratio as described by Za-
nardi et al. (2000). Moisture and fat contents of the
longissimus muscle were determined by freeze-drying
and Soxhlet extraction, respectively, following the pro-
cedure of AOAC (1990). Fatty acid composition was
determined by gas chromatography on total lipids ex-
tracted according to the method of Folch et al. (1957)
as described by Zanardi et al. (2000).
Determination of Serum Glucose
and Hormone Concentrations
Blood samples were clotted overnight at 4°C and se-
rum was harvested by centrifugation for 30 min at 1,660
× g. Glucose concentration was determined using a
blood analyzer Dri-Chem 3000 (Fuji Film, Tokyo, Ja-
pan) following manufacturer’s instructions.
Radioimmunoassay of IGF-I was performed using a
commercial IGF-I antiserum (Gropep, Adelaide, Aus-
tralia) following removal of serum IGFBP by acidic C18
Sep-Pak (Waters, Milford, MA) chromatography as pre-
viously described and validated (Lee et al., 1991; Lee
and Chung, 2000). Nonspecific binding (NSB) and B0
of the present assays were 2.3 ± 0.3% and 36 ± 1.8%,
respectively. Intra- and interassay coefficients of varia-
tion were 15.3% and 19.3%, respectively.
Serum IGFBP-3 concentration was determined by a
homologous RIA in which unlabeled pIGFBP-3 stan-
dard and its antiserum had been prepared by Lee and
Chung (2000), according to a standard double-antibody
procedure (Walton and Etherton, 1989). Briefly, whole
serum (10 ␮L) was incubated for 16 h at 4°C in a total
volume of 0.3 mL, with 1:1,500 antiserum and 15,000
cpm [125
I]pIGFBP-3 that had been radiolabeled to ap-
proximately 100 ␮Ci/␮g by using chloramine-T. Anti-
gen-antibody complexes were precipitated by addition
of 0.1 mL of each of 1:10 goat anti-rabbit IgG (Gropep)
serum and 1:30 normal rabbit serum followed by 1 h
of incubation at room temperature, further addition
of 1 mL of ice-cold PEG-8000 (Amresco, Solon, OH),
centrifugation for 30 min at 4°C at 1,660 × g, and aspira-
tion. The NSB and B0 were 5.3 ± 0.3% and 36.8 ± 2.8%,
respectively; intra- and interassay coefficients of varia-
tion were 13.5% and 10.6%, respectively. It has been
previously reported that the half-maximal binding of
[125
I]pIGFBP-3 was observed at approximately 50 ng
of unlabeled pIGFBP-3 standard and that cross-reactiv-
ities of the pIGFBP-3 antiserum to human, bovine, and
rat IGFBP-3 were less than 5% (Lee and Chung, 2000).
Estradiol-17β concentration in unextracted, raw se-
rum was determined in a single assay using a RIA kit
manufactured for human serum (Diagnostic Products,
Los Angeles, CA). The intra-assay coefficient of varia-
tion was 4.4%. Testosterone concentration also was
measured using a RIA kit (Diagnostic Products) in the
last blood sample from each animal only to confirm the
success of castration.
Statistical Analysis
Measurements of the live animal and carcass and
hormone concentrations were analyzed using the GLM
procedure of SAS (SAS Inst. Inc., Cary, NC). The model
included main effects of feeding, diet, and implant, two-
way interactions of these, and a three-way interaction.
Additionally included in the model for the analysis of
repeated hormone and glucose measurements were
blood sampling day and corresponding interactions as-
sociated with it. The animal nested within feeding ×
diet × implant was used as the error term for the test
of main effects and their interactions. In the analysis
of feed intake and gain:feed in which pen was the exper-
imental unit, only main effects and two-way interac-
tions of them were included in the model.
Results
Growth and Carcass Traits
Growth performance and carcass traits of the animals
are shown in Table 2. Average daily gain was reduced
(P < 0.01) by restricted feeding by 18% (0.86 and 0.70
kg for ad libitum vs restricted intake, respectively) as
well as by implantation of Revalor H by 14% (0.84 and
0.72 kg for unimplanted vs implanted groups, respec-
tively). The low-energy diet only tended to cause a de-
crease in ADG (0.81 and 0.76 kg for the control vs low-
energy diet group; P = 0.06). The ADFI was 21% less
(P < 0.01) in the restricted feeding group than in the ad
libitum group (2.48 vs 3.14 kg). Feed intake increased (P
< 0.05) when the barrows were fed the low-energy diet
(3.00 kg) vs the control diet (2.62 kg) but decreased (P
< 0.01) by as much as 24% following implantation (3.19
vs 2.43 kg for the unimplanted and implanted groups,
respectively). The gain:feed did not change (P = 0.48)
due to restricted feeding (0.285) vs ad libitum intake
(0.278). It was decreased (P < 0.01) by feeding the low-
energy diet (0.309 vs 0.254 for the control and low-
energy diets, respectively) but increased (P < 0.05) by
the implant (0.267 vs 0.297 for unimplanted and im-
planted groups, respectively). Carcass weight was re-
duced (P < 0.01) in the restricted feeding group com-
pared with its counterpart, which was attributable to
the reduced final weight (P < 0.01) in the former. Simi-
larly, the decreased carcass weight (P < 0.05) in the
low-energy diet group (74.0 ± 0.9 kg) vs control diet

4. Nutrition, steroids and IGF system in barrows 87
Table2.Effectsofrestrictedfeeding,low-energydiet,andtrenboloneacetateplusestradiol-17βimplantationon
growthperformanceandcarcasstraits
incrossbredfinishingbarrows
AdlibitumintakeRestrictedfeedinga
ControldietLow-energydietb
ControldietLow-energydiet
Pooled
ItemNoneImplantc
NoneImplantNoneImplantNoneImplantSEP-value
Initialwt,kg58.059.960.060.161.060.657.056.92.5
Finalwt,kg112.7107.5108.5110.0105.7102.4102.998.22.3Feeding**
ADG,kg0.970.810.860.800.790.670.740.610.04Feeding**,implant**
ADFI,kgd
3.252.523.942.842.592.102.972.250.09Feeding**,diet*,implant**
Gain:feedd
0.2970.3180.2170.2790.3040.3170.2480.2720.007Diet**,implant*
Carcasswt,kg82.7±1.978.4±1.878.1±1.879.4±1.876.9±1.874.6±1.972.3±1.870.1±1.8Feeding**,diet*
Dressing,%75±1.072±0.972±0.971±0.972±0.972±1.070±0.971±0.9Diet**
Backfat,measured,mme
23.1±1.717.1±1.619.6±1.618.1±1.621.8±1.617.1±1.714.5±1.613.8±1.6Feeding*,diet**,implant**
Backfat,adjusted,mmf
21.2±1.516.6±1.419.0±1.417.1±1.421.6±1.417.4±1.514.9±1.414.7±1.4Diet**,implant**
LMA,cm2g
38.837.338.238.937.836.336.336.11.0Feeding*
a
80%adlibitumintake.
b
Contained84%DE(2.95Mcal/kg)ofthecontroldiet(3.50McalDE/kg;15%CP;0.75%lysine).
c
ImplantedwithRevalorH(140mgtrenboloneacetate+14mgestradiol−17β).
d
Penwastheexperimentalunit.Onlymaineffectswereincludedinthemodelafterconfirmingnon-significance(P>0.05)ofallthethreetwo-wayinteractions.
e
Averagethicknessatslaughterbetweenthe11thand12thribsandatthelastrib.
f
105-kgliveweight-adjustedaveragethicknessbetweenthe11thand12thribsandatthelastrib.
g
Loinmuslcearea(adjustedfor105-kgliveweight)estimatedatthe10thribusingareal-timeultrasonicscanner.
*P<0.05.
**P<0.01.

5. Lee et al.88
group (78.1 ± 0.9 kg) may have been related to the
smaller final weight of the former group (107.1 kg vs
104.9 kg for the control and low-energy diet groups,
respectively; P = 0.18). Of note, dressing percentage
was reduced (P < 0.01) in the low-energy diet group vs
the control diet group. Backfat thickness at slaughter
was less in the restricted feeding (P < 0.05), low-energy
diet (P < 0.01) and implanted (P < 0.01) groups than
in their respective counterparts. However, when the
measurements were adjusted to 105 kg live weight,
significant effects (P < 0.01) were detected only for the
diet and implant (19.2 ± 0.73 and 16.5 ± 0.70 mm for
the control diet group vs low-energy diet group, respec-
tively; 19.2 ± 0.71 and 16.5 ± 0.71 mm for the unim-
planted group vs implanted group, respectively).
Whereas adjusted backfat thickness did not change (P
= 0.19) due to restricted feeding (18.5 and 17.2 mm for
ad libitum intake vs restricted feeding), LMA at the
10th rib was affected (P < 0.05) only by restricted feed-
ing (38.3 and 36.5 cm2
for ad libitum intake vs restricted
feeding, respectively). The LMA and backfat thickness
were also analyzed by including the live weight as a
covariate in the statistical model; results (data not
shown) were very similar to those described above.
Longissimus muscle color was affected by the implant
(Table 3). The lightness (L*) tended to decrease (P =
0.07) due to implantation when pigs were restrictively
fed but not when they had ad libitum access to feed (P
= 0.35). Both the redness (a*) and the yellowness (b*)
also decreased (P < 0.05) in response to the implant
(8.1 ± 0.41 vs 6.8 ± 0.38 for a* and 5.5 ± 0.29 vs 4.5 ±
0.27 for b* for unimplanted vs implanted groups, re-
spectively). Moreover, the yellowness decreased in the
implanted group vs the unimplanted group only when
the barrows were restrictively fed (P < 0.01). Drip loss,
which was less than 5% across all the treatments, did
not differ between groups. The pH was greater in the
restricted feeding (P < 0.05) and the implanted (P <
0.01) groups than in their corresponding counterparts,
but numerical effects were less than 0.15 unit. Moisture
content was greater (P < 0.05) in the implanted group
(74.4 ± 0.23%) than in the unimplanted group (73.5 ±
0.25%). In contrast, live weight-adjusted fat content did
not change (P = 0.23) due to implantation (3.0 ± 0.18
and 2.79 ± 0.16% for unimplanted vs implanted groups,
respectively), although unadjusted fat content (data not
shown) was less (P < 0.05) in the implanted (2.68 ±
0.17%) vs the unimplanted group (3.22 ± 0.18%). In
fatty acid composition, main effects for stearic acid
(18:0) content and a three-way interaction with or with-
out two-way interactions for palmitic (16:0) and total
saturated and unsaturated fatty acids were detected,
but numerical differences between groups were rather
small. Neither the L* nor the b* value for color of the
backfat attached to longissimus muscle changed in re-
sponse to any treatment (P > 0.05).
Serum Glucose and Hormone Concentrations
Serum glucose concentration was not affected by any
of the treatments (Table 4). Mean estradiol-17β concen-
tration, as expected, increased (P < 0.01) following im-
plantation. Although not shown in the table, testoster-
one concentrations were less than 0.02 ng/mL in all the
animals, which confirms that they had been success-
fully castrated. Serum IGF-I concentration increased
(P < 0.01) in response to the implant (187 and 226 ng/
mL for the unimplanted vs implanted group) and also
linearly with increasing days of the experiment (P <
0.01; Figure 1). Moreover, IGF-I concentration in-
creased (P < 0.01) during the first 3 wk of the experiment
in implanted animals, whereas in unimplanted animals
it increased (P < 0.01) during the second 3 wk. However,
IGF-I concentration was not changed by restricted feed-
ing (213 and 200 ng/mL for ad libitum intake vs re-
stricted feeding; P = 0.16) or by feeding the low-energy
diet (210 and 202 ng/mL for the control vs low-energy
diet; P = 0.39). Serum IGFBP-3 concentration did not
change in response to any treatment. Instead, IGFBP-
3 concentration increased (P < 0.01) during the first 3
wk of the experiment, albeit to a small extent numeri-
cally (3.0, 3.3, and 3.4 ␮g/mL on d 0, 21, and 42, respec-
tively; data not shown).
Correlations between the growth-related variables
and serum IGF-I and IGFBP-3 concentrations are
shown in Table 5. Interestingly, overall ADG was corre-
lated with LMA in all barrows and unimplanted bar-
rows. The ADG was not significantly correlated with
either IGF-I or IGFBP-3 concentration across all the
treatments. However, in all unimplanted animals, ADG
was positively correlated (P < 0.01) with IGF-I and
IGFBP-3 concentrations on d 21 of the experiment.
Backfat thickness, by contrast, was negatively corre-
lated (P < 0.01) with d-42 IGF-I concentration in all
barrows and in unimplanted barrows; the correlation
was not significant in unimplanted barrows with ad
libitum access to feed. Moreover, IGFBP-3 concentra-
tion was correlated (P < 0.01) with IGF-I, especially on
d 42.
Discussion
It has been decisively proven recently, by GH injec-
tion studies in mice with various disruptions of the IGF-
I gene (Liu and LeRoith, 1999), that IGF-I mediates
the growth-stimulating action of GH. It also has been
well documented that systemically administered IGF-
I stimulates growth in GH-deficient as well as pituitary-
intact animals and humans (Froesch et al., 1996). Al-
though there are instances in which systemic IGF-I
level has no relation to growth (e.g., in cases of GH-
injected rats [Orlowski and Chernausek, 1988] and
liver-specific IGF-I knock-out mice [Sjogren et al.,
1999]), these are more exceptional rather than typical.
Moreover, numerous studies have shown that circulat-
ing IGF-I concentration, as a whole, reflects the status
of GH secretion and accordingly overall body growth in
well-nourished humans and animals (Jones and Clem-
mons, 1995; Simmen et al., 1998).

6. Nutrition, steroids and IGF system in barrows 89
Table3.Effectsofrestrictedfeeding,lowenergy-diet,andimplantationofanabolicsteroidsonphysicochemicalcharacteristics
ofthelongissimusmuscleinfinishingbarrows
AdlibitumintakeRestrictedfeedinga
ControldietLow-energydietb
ControldietLow-energydiet
ItemNoneImplantc
NoneImplantNoneImplantNoneImplantP<0.05
Colordef
CIEL*48.1±2.251.2±1.945.6±2.146.2±1.751.7±2.048.7±2.153.4±1.948.7±2.2Feeding×implant
CIEa*8.91±0.927.25±0.776.75±0.866.85±0.697.77±0.856.47±0.859.28±0.786.30±0.89Implant
CIEb*5.52±0.654.88±0.544.51±0.614.85±0.485.69±0.604.00±0.606.43±0.554.20±0.63Implant,feeding×implant
Driplosse
3.79±0.783.71±0.712.70±0.784.38±0.784.30±0.782.67±0.784.73±0.713.76±0.71
pHe
5.48±0.085.56±0.075.52±0.085.53±0.065.57±0.085.86±0.085.47±0.075.69±0.07Feeding,implant**
Moisture,%f
73.0±0.5574.1±0.4673.5±0.5174.5±0.4174.1±0.5074.5±0.5073.5±0.4674.5±0.53Implant
Crudefat,%f
3.45±0.383.21±0.322.92±0.352.87±0.282.86±0.352.51±0.353.15±0.322.58±0.37
Fattyacidcomposition
14:01.01±0.100.98±0.081.33±0.090.93±0.070.92±0.090.90±0.101.00±0.080.99±0.08
16:021.70±0.4520.90±0.3722.00±0.4121.70±0.3420.90±0.4121.90±0.4521.50±0.3720.50±0.37Feeding×diet×implant
18:013.46±0.4814.02±0.3913.22±0.4313.87±0.3613.73±0.4315.12±0.4814.40±0.3914.79±0.39Feeding**,implant
Totalsaturated36.21±0.5535.91±0.4536.59±0.4936.28±0.4535.54±0.4938.68±0.7836.89±0.4536.25±0.45Feeding×implant,diet×implant,
fattyacidsfeeding×diet×implant
16:11.73±0.141.82±0.111.97±0.121.83±0.101.81±0.121.93±0.141.63±0.111.95±0.11
18:140.50±1.0340.53±0.8440.82±0.9240.85±0.7840.77±0.9237.40±1.0339.51±0.8439.88±0.84
18:217.09±0.6716.61±0.5516.55±0.6016.32±0.5117.14±0.6017.75±0.6717.30±0.5517.22±0.55
18:30.56±0.070.62±0.060.61±0.060.75±0.050.73±0.060.56±0.070.63±0.060.70±0.06
20:43.91±0.384.52±0.313.47±0.343.76±0.294.01±0.344.38±0.384.04±0.314.01±0.31
Totalunsaturated63.79±0.5564.09±0.4563.41±0.4963.72±0.4564.46±0.4961.32±0.7863.11±0.4563.75±0.45Feeding×implant,diet×implant,
fattyacidsfeeding×diet×implant
Attachedbackfatcolordf
CIEL*75.0±0.8775.6±0.7374.5±0.8175.2±0.6575.6±0.8074.6±0.8174.6±0.7474.1±0.84
CIEb*4.80±0.505.01±0.424.59±0.464.83±0.375.36±0.465.66±0.465.59±0.425.17±0.48
a
80%adlibitumintake.
b
Contained84%DE(2.95Mcal/kg)ofthecontroldiet(3.50McalDE/kg;15%CP;0.75%lysine).
c
ImplantedwithRevalorH(140mgtrenboloneacetate+14mgestradiol-17β).
d
Measuredonthecross-sectionalslicebetweenthe11thand12thribs.GreaterL*,a*,andb*valuesindicatemorelightcolor,moreredcolor,andmoreyellowcolor,respectively.CIE=
CommissionInternationaledel’Eclairage.
e
L*>50,42≤L*≤50andL*<42areclassifiedas“pale,”“reddish-pink”and“dark,”respectively;driploss>5%is“exudative”;dark,firmanddry(DFD)porkhaspH≥6.0(Warneret
al.,1997).
f
Liveweightwasincludedinthestatisticalanalysismodelasacovariate.
**P<0.01.

7. Lee et al.90
Table 4. Effects of restricted feeding, low-energy diet, and anabolic steroids on serum glucose and
hormone concentrations in crossbred finishing barrows
Ad libitum intake Restricted feedinga
Control diet Low-energy dietb
Control diet Low-energy diet
Item None Implantc
None Implant None Implant None Implant P < 0.01
Glucose, mg/dL 91 ± 3.0 93 ± 2.7 90 ± 2.7 92 ± 2.7 88 ± 2.7 90 ± 2.7 91 ± 2.7 87 ± 2.7
E2-17β, pg/mLd
DLe
47.1 ± 10.5 DL 23.8 ± 10.5 DL 35.0 ± 10.5 DL 15.5 ± 10.5 Implant
IGF-I, ng/mL 201 ± 15 247 ± 13 179 ± 13 226 ± 13 177 ± 13 217 ± 13 191 ± 13 213 ± 14 Implant
IGFBP-3, ␮g/mL 3.3 ± 0.15 3.4 ± 0.14 3.1 ± 0.14 3.3 ± 0.14 3.0 ± 0.14 3.3 ± 0.14 3.3 ± 0.14 3.1 ± 0.15
a
Fed 80% ad libitum intake.
b
Contained 84% DE (2.95 Mcal/kg) of the control diet (3.50 Mcal DE/kg; 15% CP; 0.75% lysine).
c
Implanted with Revalor H (140 mg trenbolone acetate + 14 mg estradiol-17β).
d
Determined using a RIA kit for human serum; values may represent relative concentrations, because estradiol was not extracted prior to assay.
e
Detection limit (3.3 pg/mL).
The present study was undertaken to investigate the
effects of restricted feeding, low-energy diet, and ana-
bolic steroids on growth, carcass traits, and serum IGF-
I and IGFBP-3 concentrations and thereby to find rela-
tionships among these variables in finishing barrows.
All the experimental treatments independently caused
or tended to cause a decrease in ADG and backfat thick-
ness, which was consistent with previous reports (De
Wilde and Lauwers, 1984; Hale et al., 1986; Leymaster
and Mersmann, 1991). Moreover, the trenbolone-plus-
estradiol implant, Revalor H, caused a decrease in feed
intake and increased gain:feed, presumably resulting
from the anabolic actions of the implanted steroids.
These results are consistent with those of De Wilde and
Figure 1. Serum IGF-I concentrations in Revalor H-
implanted and unimplanted finishing barrows. Revalor
H contains 140 mg trenbolone acetate and 14 mg estradiol-
17β. Data are means ± SE of 32 animals. The effect of day
was significant (P < 0.01).
Lauwers (1984) but only partially consistent with those
of Grandadam et al. (1975) and van Weerden and Gran-
dadam (1976), who reported that ADG as well as feed
efficiency was increased by trenbolone-plus-estradiol
implantation with no significant change in feed intake.
It is not clear, however, why feed intake was variable
following the combined implantation in different stud-
ies, although there are many unexplained instances
of variable effects for other anabolic implants as well
(Galbraith and Topps, 1981).
From the practical point of view, Revalor H seemed
to have a few undesirable effects in pigs. Implanted
barrows frequently mounted each other and were mis-
judged as boars at the slaughterhouse where sex was
determined according to the appearance of the genital
tract of the carcass. It is thus presumed that, although
the trenbolone contained in Revalor or Finaplix pellets
has been reported to cause little androgenization of
steers (Heitzman et al., 1977), the dose of this steroid
contained in the Revalor H pellet was probably high
enough to elicit a development of external genitalia in
barrows in the presence of coimplanted estrogen, which
is known to inhibit penis development to some extent
in cattle (Greathouse et al., 1983).
Results of muscle pH, drip loss, and lightness (L*)
fell within the range for the normal RFN (reddish-pink,
firm, and non-exudative) pork in all the groups when
the pork quality was classified as RFN, DFD (dark,
firm, and dry), PSE (pale, soft, and exudative), or RSE
(reddish-pink, soft, and exudative) based on these qual-
ity traits (Warner et al., 1997; Joo et al., 1999). Although
pH, moisture content, and fatty acid composition of lon-
gissimus muscle were changed due to the treatments
or a two- or three-way interaction of them, differences
among groups were more numerically than qualita-
tively significant. Moreover, textural properties of fresh
and cooked longissimus muscle (data not shown) also
did not change (P > 0.05) in response to any treatment.
It was noteworthy, however, that the redness (a*) and
the yellowness (b*) of longissimus muscle decreased
due to the implant, although there is no plausible expla-
nation for this at present.

8. Nutrition, steroids and IGF system in barrows 91
Table 5. Pearson’s correlations between ADG, backfat thickness, LMA, and serum
concentrations of IGF-I and IGFBP-3 in crossbred finishing barrows
ADG Backfata
LMAb
IGFBP-3c
Item r P r P r P r P
Total barrows (n = 63)
Backfat 0.24 0.06 — — — — — —
LMA 0.33 <0.01 0.31 <0.05 — — — —
d-0 IFG-I 0.21 0.10 0.02 0.85 0.21 0.09 0.19 0.13
d-0 IGFBP-3 −0.07 0.55 0.01 0.92 −0.08 0.51 — —
d-21 IGF-I 0.16 0.20 −0.25 <0.05 −0.05 0.72 0.44 <0.01
d-21 IGFBP-3 0.22 0.09 −0.04 0.78 −0.06 0.66 — —
d-42 IGF-I −0.02 0.88 −0.48 <0.01 −0.17 0.18 0.57 <0.01
d-42 IGFBP-3 −0.01 0.93 −0.17 0.20 −0.25 <0.05 — —
Unimplanted barrows (n = 31)
Backfat 0.06 0.74 — — — — — —
LMA 0.38 <0.05 0.32 0.08 — — — —
d-0 IGF-I 0.17 0.36 −0.05 0.77 0.17 0.37 0.17 0.34
d-0 IGFBP-3 −0.08 0.66 −0.08 0.67 −0.06 0.75 — —
d-21 IGF-I 0.69 <0.01 −0.15 0.43 0.11 0.54 0.40 <0.05
d-21 IGFBP-3 0.50 <0.01 −0.07 0.71 0.30 0.11 — —
d-42 IGF-I 0.12 0.52 −0.46 <0.01 −0.06 0.76 0.54 <0.01
d-42 IGFBP-3 −0.01 0.96 −0.27 0.15 −0.27 0.15 — —
Unimplanted barrows with ad libitum access to feed (n = 15)
Backfat −0.19 0.49 — — — — — —
LMA 0.21 0.46 0.21 0.46 — — — —
d-0 IGF-I 0.25 0.37 −0.19 0.50 0.13 0.64 0.21 0.43
d-0 IGFBP-3 0.21 0.43 0.26 0.35 −0.33 0.23 — —
d-21 IGF-I 0.68 <0.01 −0.12 0.66 −0.16 0.56 0.21 0.44
d-21 IGFBP-3 0.24 0.39 −0.39 0.14 −0.32 0.25 — —
d-42 IGF-I 0.41 0.13 −0.25 0.38 −0.13 0.64 0.70 <0.01
d-42 IGFBP-3 0.23 0.41 0.03 0.90 −0.50 0.06 — —
a
Average thickness adjusted for 105-kg live weight between the 11th and 12th ribs and at the last rib.
b
Loin muscle area at the 10th rib adjusted for 105-kg live weight.
c
Concentration in serum on the corresponding day.
It is known that circulating IGF-I and IGFBP-3 con-
centrations are reduced under conditions of restricted
energy or feed intake (Booth et al., 1996; Ketelslegers
et al., 1996; Hall et al., 1999). However, the lack of
any significant change in serum IGF-I and IGFBP-3
concentrations in response to the restricted feed intake
or the low-energy diet in the present study indicates
that restriction of feed or energy intake by 20% or less
was not enough to cause a change in concentrations of
these IGF system components. It has also been reported
that a 25% restriction of feed intake (2.8 [control] vs
2.1 [restricted] times maintenance level) did not affect
plasma IGF-I concentrations in gilts (Almeida et al.,
2001). By contrast, IGF-I concentration increased fol-
lowing Revalor H implantation, suggesting that the an-
abolic effects of the implanted steroids may have been
mediated, in part, by increased IGF-I. It also can be
speculated that part of the effects of Revalor H may be
mediated by GH independently of IGF-I, but, based on
previously reported studies in steers, this seems to be
only a small possibility. Enright et al. (1990) have re-
ported that implantation of estradiol increased GH and
IGF-I concentrations but that this steroid had a GH-
independent anabolic effect in steers. Moreover, Hunt
et al. (1991) reported that, although serum IGF-I con-
centration was additively increased by trenbolone and
estradiol, GH concentration did not change in response
to either trenbolone or trenbolone-plus-estradiol im-
plantation.
The lack of effect of the Revalor H implant on serum
IGFBP-3 concentration somewhat contrasts with a re-
ported 30 to 50% increase in implanted steers (Johnson
et al., 1996). However, the present result cannot be
directly compared with the previous report, because
total IGFBP-3, including ≤ 31-kDa truncated IGFBP-3
(Lee et al., 1991), was determined by RIA in the present
study, whereas in the previous study only the 43- and
39-kDa intact IGFBP-3 was measured by Western li-
gand blot analysis. Further studies are therefore neces-
sary to determine whether the effect of trenbolone-plus-
estradiol implantation on circulating IGFBP-3 concen-
tration is species- and(or) possibly dose-dependent.
Relationships between growth-related variables and
serum IGF-I and IGFBP-3 concentrations were ana-
lyzed in the three strata of all barrows, unimplanted
barrows, and unimplanted barrows that had ad libitum
access to feed because of possible confounding effects
of the treatments on these variables. For instance, the
opposing effects of the implant on ADG and IGF-I con-
centration resulted in a positive correlation between
these variables only in unimplanted animals. Neverthe-
less, the positive correlations between IGF-I, IGFBP-

9. Lee et al.92
3, and ADG in all barrows or in unimplanted barrows
were similar to previously reported relationships be-
tween the growth variables and these peptides in grow-
ing-finishing pigs (Lamberson et al., 1995; Owens et al.,
1999), growing rats (Fukuda et al., 1998), and children
(Jaruratanasirikul et al., 1999; Park et al., 1999). These
results are thus thought to reflect the fact that both of
these peptides are GH-dependent (Walton and
Etherton, 1989; Bell et al., 1998). In summary, the in-
creased feed efficiency in Revalor H-implanted barrows
was associated with an increase in serum IGF-I concen-
tration. However, the moderately restricted nutritional
status in unimplanted barrows was not reflected by
either IGF-I or IGFBP-3 serum concentration.
Implications
In finishing barrows, a low-energy diet may be useful
for reducing backfat thickness in exchange for a de-
crease in feed efficiency and growth rate. Revalor H
implantation is effective in increasing gain:feed as well
as decreasing backfat thickness, but it causes a de-
crease in feed intake resulting in a decreased growth
rate. Circulating IGF-I and IGFBP-3 concentrations do
not decrease in proportion to a reduced growth rate due
to a moderately restricted feed or energy intake or the
anabolic implant. Nevertheless, growth rate is corre-
lated with serum concentrations of these peptide hor-
mones in unimplanted finishing barrows, suggesting
that these hormones are adequate measures of growth
indices in unimplanted, castrated pigs.
Literature Cited
Almeida, F. R. C. L, J. Mao, S. Novak, J. R. Cosgrove, and G. R.
Foxcroft. 2001. Effects of different patterns of feed restriction
and insulin treatment during the luteal phase on reproductive,
metabolic, and endocrine parameters in cyclic gilts. J. Anim.
Sci. 79:200–212.
AOAC. 1990. Official Methods of Analysis. 15th ed. Association of
Official Analytical Chemists, Arlington, VA.
Baxter, R. C. 2000. Insulin-like growth factor (IGF)-binding proteins:
Interactions with IGFs and intrinsic bioactivities. Am. J. Phys-
iol. 278:E967–E976.
Bell, A. W., D. E. Bauman, D. H. Beermann, and R. J. Harrell. 1998.
Nutrition, development and efficacy of growth modifiers in live-
stock species. J. Nutr. 128:360S–363S.
Blum, W. F., K. Albertsson-Wikland, S. Rosberg, and M. B. Ranke.
1993. Serum levels of insulin-like growth factor I (IGF-I) and
IGF binding protein 3 reflect spontaneous growth hormone secre-
tion. J. Clin. Endocrinol. Metab. 76:1610–1616.
Booth, P. J., J. R. Cosgrove, and G. R. Foxcroft. 1996. Endocrine and
metabolic responses to realimentation in feed-restricted prepu-
bertal gilts: associations among gonadotropins, metabolic hor-
mones, glucose, and uteroovarian development. J. Anim. Sci.
74:840–848.
CIE. 1978. Recommendations on uniform color spaces-color difference
equations, psychometric color terms. Supplement no. 2 to CIE
Publication No. 15 (E-1.3.1) 1971/(TC-1-3). Commission Interna-
tionale de l’Eclairage, Paris.
Coffey, M. T., R. W. Seerley, D. W. Funderburke, and H. C. McCamp-
bell. 1982. Effect of heat increment and level of dietary energy
and environmental temperature on the performance of growing-
finishing swine. J. Anim. Sci. 54:95–105.
De Wilde, R. O., and H. Lauwers. 1984. The effect of parenteral use
of estradiol, progesterone, testosterone and trenbolone on growth
and carcass composition in pigs. J. Anim. Sci. 59:1501–1509.
Enright, W. J., J. F. Quirke, P. D. Gluckman, B. H. Breier, L. G.
Kennedy, I. C. Hart, J. F. Roche, A. Coert, and P. Allen. 1990.
Effects of long-term administration of pituitary-derived bovine
growth hormone and estradiol on growth in steers. J. Anim. Sci.
68:2345–2356.
Field, R. A. 1971. Effect of castration on meat quality and quantity.
J. Anim. Sci. 32:849–858.
Folch, J., M. Lees, and G. H. Sloane-Stanley. 1957. A simple method
for the isolation and purification of total lipids from animal
tissues. J. Biol. Chem. 226:497–500.
Froesch, E. R., M. A. Hussain, C. Schmid, and J. Zapf. 1996. Insulin-
like growth factor I: physiology, metabolic effects and clinical
uses. Diabetes Metab. Rev. 12:195–215.
Fukuda, R., S. Usuki, N. Mukai, H. Amagai, K. Hayashi, and K.
Takamatsu. 1998. Serum insulin-like growth factor-I, insulin-
like growth factor binding protein-3, sex steroids, osteocalcin
and bone mineral density in male and female rats. Gynecol.
Endocrinol. 12:297–305.
Galbraith, H., and J. H. Topps. 1981. Effect of hormones on the growth
and body composition of animals. Nutr. Abst. Rev. 51:521–540.
Grandadam, J. A., J. P. Scheid, A. Jobard, H. Breux, and J. M.
Boisson. 1975. Results obtained with trenbolone acetate in con-
junction with estradiol 17β in veal calves, feedlot bulls, lambs
and pigs. J. Anim. Sci. 41:969–977.
Greathouse, J. R., M. C. Hunt, M. E. Dikeman, L. R. Corah, C. L.
Kastner, and D. H. Kropf. 1983. Ralgro-implanted bulls: perfor-
mance, carcass characteristics, longissimus palatability and car-
cass electrical stimulation. J. Anim. Sci. 57:355–363.
Hale, O. M., G. L. Newton, and K. D. Haydon. 1986. Effect of diet
and exercise on performance, carcass traits and plasma compo-
nents of growing-finishing barrows. J. Anim. Sci. 62:665–671.
Hall, K., A. Hilding, and M. Thoren. 1999. Determinants of circulating
insulin-like growth factor-I. J. Endocrinol. Invest. 22:48S–57S.
Heitzman, R. J., K. H. Chan, and I. C. Hart. 1977. Liveweight gains,
blood levels of metabolites, proteins and hormones following
implantation of anabolic agents in steers. Br. Vet. J. 133:62–70.
Hunt, D. W., D. M. Henricks, G. C. Skelley, and L. W. Grimes. 1991.
Use of trenbolone acetate and estradiol in intact and castrate
male cattle: effects on growth, serum hormones, and carcass
characteristics. J. Anim. Sci. 69:2452–2462.
Jaruratanasirikul, S., H. Sriplung, and K. Leethanaporn. 1999. Se-
rum insulin-like growth factor-1 (IGF-I) and insulin-like growth
factor binding protein-3 (IGFBP-3) in healthy Thai children and
adolescents: relation to height, weight, and body mass index. J.
Med. Assoc. Thailand 82:984–990.
Johnson, B. J., M. R. Hathaway, P. T. Anderson, J. C. Meiske, and W.
R. Dayton. 1996. Stimulation of circulating insulin-like growth
factor I (IGF-I) and insulin-like growth factor binding proteins
(IGFBP) due to administration of a combined trenbolone acetate
and estradiol implant in feedlot cattle. J. Anim. Sci. 74:372–379.
Jones, J. I., and D. R. Clemmons. 1995. Insulin-like growth factors
and their binding proteins: Biological actions. Endocrinol. Rev.
16:3–34.
Joo, S. T., R. G. Kauffman, B. C. Kim, and G. B. Park. 1999. The
relationship of sarcoplasmic and myofibrillar protein solubility
to colour and water-holding capacity in porcine longissimus mus-
cle. Meat Sci. 52:291–297.
Ketelslegers, J. M., D. Maiter, M. Maes, L. E. Underwood, and J. P.
Thissen. 1996. Nutritional regulation of the growth hormone
and insulin-like growth factor-binding proteins. Horm. Res.
45:252–257.
Lamberson, W. R., T. J. Safranski, R. O. Bates, D. H. Keisler, and
R. L. Matteri. 1995. Relationships of serum insulin-like growth
factor I concentrations to growth, composition, and reproductive
traits of swine. J. Anim. Sci. 73:3241–3245.
Lee, C. Y., F. W. Bazer, T. D. Etherton, and F. A. Simmen. 1991.
Ontogeny of insulin-like growth factors (IGF-I and IGF-II) and

10. Nutrition, steroids and IGF system in barrows 93
IGF-binding proteins in porcine serum during fetal and postna-
tal development. Endocrinology 128:2336–2344.
Lee, C. Y., and C. S. Chung. 2000. Developmental patterns of circulat-
ing concentrations of insulin-like growth factor-I(IGF-I) and
IGF-binding protein-3(IGFBP-3) in growing gilts and barrows:
purification of porcine IGFBP-3, development of IGFBP-3 and
IGF-I RIAs and their utilization. J. Anim. Sci. Technol. (Korea)
46:817–826.
Lee, C. Y., D. M. Henricks, G. C. Skelley, and L. W. Grimes. 1990.
Growth and hormonal response of intact and castrate male cattle
to trenbolone acetate and estradiol. J. Anim. Sci. 68:2682–2689.
Leymaster, K. A., and H. J. Mersmann. 1991. Effect of limited feed
intake on growth of subcutaneous adipose tissue layers and on
carcass composition in swine. J. Anim. Sci. 69:2837–2843.
Liu, J. L., and D. LeRoith. 1999. Insulin-like growth factor I is essen-
tial for postnatal growth in response to growth hormone. Endo-
crinology 140:5178–5184.
NRC. 1998. Nutrient Requirements of Swine. 10th ed. National Acad-
emy Press, Washington, DC.
NSIF. 1997. Guidelines for Uniform Swine Improvement Programs.
On-farm Programs. National Swine Improvement Federation,
Raleigh, NC.
Orlowski, P. C., and S. D. Chernausek. 1988. Discordance of serum
and tissue somatomedin levels in growth hormone-stimulated
growth in the rat. Endocrinology 123:44–49.
Owens, P. C., K. L. Gatford, P. E. Walton, W. Morley, and R. G.
Campbell. 1999. The relationship between endogenous insulin-
like growth factors and growth in pigs. J. Anim. Sci. 77:2098–
2103.
Park, M. J., H. S. Kim, J. H. Kang, D. H. Kim, and C. Y. Chung.
1999. Serum levels of insulin-like growth factor (IGF)-I, free
IGF-I, IGF binding protein (IGFBP)-1, IGFBP-3 and insulin in
obese children. J. Pediatr. Endocrinol. Metab. 12:139–144.
Simmen, F. A., L. Badinga, M. L. Green, I. Kwak, S. Song, and
R. C. M. Simmen. 1998. The porcine insulin-like growth factor
system: at the interface of nutrition, growth and reproduction.
J. Nutr. 128:315S–320S.
Sjogren, K., J. L. Liu, K. Blad, S. Skrtic, O. Vidal, V. Wallenius, D.
LeRoith, J. Tornell, O. G. Isaksson, J. O. Jansson, and C. Ohls-
son. 1999. Liver-derived insulin-like growth factor I (IGF-I) is
the principal source of IGF-I in blood but is not required for
postnatal body growth in mice. Proc. Natl. Acad. Sci. USA
96:7088–7092.
van Weerden, E. J., and J. A. Grandadam. 1976. The effect of an
anabolic agent on N deposition, growth, and slaughter quality
in growing castrated male pigs. In: F. C. Lu and J. Rendel (ed.)
Anabolic Agents in Animal Production. Environmental Quality
and Safety. pp 115–122. Georg Thieme Verlag, Stuttgart,
Germany.
Walton, P. E., and T. D. Etherton. 1989. Effects of porcine growth
hormone and insulin-like growth factor-I (IGF-I) on immunore-
active IGF-binding protein concentration in pigs. J. Endocrinol.
120:153–160.
Warner, R. D., R. G. Kauffman, and M. L. Greaser. 1997. Muscle
protein changes post mortem in relation to pork quality traits.
Meat Sci. 45:339–352.
Zanardi, E., E. Novelli, G. P. Ghiretti, and R. Chizzolini. 2000. Oxida-
tive stability of lipids and cholesterol in salame Milano, coppa
and Parma ham: dietary supplementation with vitamin E and
oleic acid. Meat Sci. 55:169–175.