Arch. Geflügelk. 1996, 61 (2), 66 - 71, ISS
0003-9098.
© Verlag Eugen Ul mer GmbH
& Co.,
tuttgart
Effects of the sex-linked dwarf gene on plasma somatotrophic and thyroid
hormone levels and on energy metabolism of Leghorn and brown
egg-type laying hens and their reciprocal crosses
Einfluß des dwarf-Gens auf Plasma-Hormonspiegel und auf den Energie-Metabolismus bei Leghorn und braunen
Legehennen und ihren reziproken Kreuzungen
2
3
3
3
M. Zeman 1 , J. Buyse 2 , F. Minvielle , A. Bo rdas , P. Merat and E. Decuypere
Manuskript eingegangen am 5. August 1996
lntroduclion
The sex-linked dwarf (SLD) gene cause 30- 40% reduction
of adult body weight in chickens and is associated with
decreased egg production, especially in hens of low body
weight strains. Together with other physiological alterations
(see DECUYPERE et al., 1991 for a review), SLD birds express
some modifications in circulating levels of hormones involved in growth regulation in comparison with normalsized chickens.
Hormonal conseguences of the dwarf gene manifestation
in chickens have been intensively studied during the embryonic development (HUYBRECHTS et al, 1989) and the
phase of rapid growth (D ECUYPERE et al., 1991 ). However,
information about concentrations of thyroid hormones and
especially growth hormone (GH) and insulin-like growth
factor-I (IGF-I) in mature hens bearing the dwarf gene is
scanty. Plasma GH concentrations are elevated (ScANES
et al„ 1983) and IGF-I levels are decreased (HOSHINO et al.,
1982; HuYBRECHTS et al., 1985) during the phase of rapid
growth. At the same time, plasma triiodoth yronine levels
(T 3 ) are lower in dwarfs than in normal-sized chickens in
spite of slightly elevated concentrations of thyroxine (ScANES et al., 1983; TrxIER-BorcHARD et al„ 1989). On the basis
of these findings, it was hypothesized that different variants
of GH that lost their biological activity but preserved their
immunological activity are present in SLD chickens (ScA ES
et al„ 1983). However, an observation of a decreased or
absent hepatic GH binding in dwarf chickens (LEUNG et al.,
1987; KüttN et al„ 1989; V ANDERPOOTEN et al., 1991) points
out that an absence or an impaired function of hepatic
growth hormone receptors is the primary cause of sex-linked
dwarfism in the chicken. Cloning of cD A for the GH
receptor (BuRNSIDE et al„ 1991) enabled the analysis of the
structure and expression of the GH receptor gene in the
SLD chicken and proved that aberrations of the GH receptor
gene in dwarf chickens result in symhesis of result GH receptor with a limited or completey missing binding capacity
(BuR SIDE et al„ 1992; D uRIEZ et al„ 1993).
The aim of our experiment was to study the activity of
the thyreotropic and somatotrophic axes in mature normal
and dwarf hens of two different genetic strains as well as
in their reciprocal crosses . In addition, energy metabolism
trials were conducted in order to establish causal links with
the observed genotypic differences in laying performance.
Materials and Methods
Animals and housing
Mature hens, aged 15 months, were used in the present
studies. These hens came from matings of heterozygous sires
(Dwdw) with dwarf females (dw-) in pure lines of White
Leghorn (L x L) or a brown egg layer strain of medium
body weight (BE x BE) and their reciprocal crosses. In this
way hens were of normal growth (Dw) or carrying the
dwarf gene (dw) and were full sisters or half sibs. More
details about the genetic background of all genotypes is
given elsewhere (ME.RAT et al„ 1994). In total, 54 hens from
eight different genotypes were used: L x L Dw, L x L dw,
BExBEDw, BExBEdw, LxBEDw, LxBEdw, BExL
Dw, BE x L dw. Bens were kept in individual cages in an
environmentally-contr olled room. Lighting schedule provided 14 hours lig ht and 10 hours darkness per day and
temperature was set at 22 °C. Water and commercial layer
pellets (18.5% total protein, 2900 kcal ME/ kg) were provided ad libitum.
Energy metabolis111 trials
1
Institute of Animal Biochemistry and Genetics, SASci, l vanka
Dunaji, Slovakia
Laboratory of Ph ysiology and lmmunology ofDomestic Animals.
Department of Anima] Production. K. U. Leuven, Kardinaal
Mercierlaan 92, 3001 He verlee, Belgium
3
Laboratoire de Genetique Factorielle, INRA, J o uy-en-Josas
78350, France
~ri
Six open-circuit respiration chambers (55 x 30 x SOcm) were
used for the energy balance trials. Detailed descriptions of
the respiration system and of the calculations of total heat
production based on 0 2 consumption and C0 2 production
are given elsewhere (ScttELLEKENS et al„ submitted). Energy
metabolism of six hens was followed weekly and the
experimental design was continued for 8 weeks in a comArchiv für Geflügelkunde 2/1997
ZEMAN
et al., Effects of the sex-linked dwarf gene on plasma somatotrophic and thyroid hormone levels
pletely randomized design until all 54 hens were measured .
The same layers pellets and water were provided ad libitium
during the balance trials. Lighting schedule and temperature
were as in the environmentally-controlled room. Hens were
allowed to adapt for 2 days to the respiration chambers.
During the next 3 days, continuous measurements of 0 2
consumption and C0 2 production of each hen were obtained
at 15 min intervals. Body weights, feed intake, and egg
production were monitored daily. Excreta (faeces and urine)
were collected daily, weighed and stored frozen. Gross
energy of feed samples and excreta were determined by using
an isoperibol Parr calorimeter.
Apparent metabolisable energy intake (AME) was calculated as the difference between gross energy (GE) intake and
energy in excreta. Apparent metabolisability was obtained
as the ratio between AME and GE. Net energy for
production (NEP) was calculated by substracting total heat
production (THP) from AME. All calculations were clone
on a metabilic body weight basis (body weight (kg) raised
to the power 0. 75). Notwithstanding the 2-day adaptation
period, some hens of each genotype showed adaptive
problems as reflected in their abnormally low feed intake.
However, due to this broad range in feed and hence AME
intake, it was possible to perform linear regression between
NEP and AME for each genotype: NEP = a + b x AME.
This also allowed to estimate the net efficiency of utilisation
of metabolisable energy for production (egg formation and
body weight gain) ( =slope b) and AME for maintenance
when NEP equals zero ( = -a/b).
Results
Plasma hormone concentrations
Normal-sized hens of all four genotypes exhibited very low
plasma GH concentrations as indicated by a significant effect
(P < 0.01) of size (Figure 1). Dwarf hens of the Leghorn
genotype and both crossed showed higher GH levels in
comparison with their normal-sized counterparts. However,
in brown-egg layers bearing the dwarf gene, GH concentrations were lower than in other dwarfs and were similar to
those of normal-size BE x BE hens (size x line interaction:
P < 0.01 ). Plasma IGF-I concentrations were lower in
dwarfs than in non-dwarfs (size effect: P < 0.001) (Figure
2). A nearly significant line effect (P < 0.1) for IGF-I was
calculated as BE x L hens had on average lower plasma
IGF-levels than their normal-sized counterparts, irrespective
of size.
,.-._
~60
5
6 40
«l
E
~
ö..
20
0
LxL
LxBE
BExL
BExBE
Genotypes
Blood sampling and hormonal ana(ysis
At 15 months of age, a blood sample from each hen was
taken from a wing vein using a heparinized syringe. Plasma
was separated after centrifucation at 3000 rpm, aliquoted
and stored at -20 °C until assayed for hormone content.
Plasma T 3 , and T 4 levels were measured by radioimmunoassay (RIA) using antisera from Byk-Sangtec, 125 1T 3 and -T 4 from Amersham, and standard solutions prepared in hormone-free · human serum. Intra-assay variabilities were 4.5%, and 5.4% for T 3 , T 4 respectively. Chicken
growth hormone (GH) was measured with a homologous
RIA as developed and validated by BERGHMAN et al. (1988).
The intra-assay coefficient of variation was 4.0%. Plasma
insulin-like growth factor-I(IGF-I) levels were measured
with a heterologus radioimmunoassay (HuYBRECHTS et al.,
1985). The intra-assay coefficient of variation was 6.9% . All
measurements of a given hormone were clone in a single
assay.
67
•
m
normal
dwarf
Fig. 1. Plasma growth hormone concentrations (GH, ng/m1) on
15-month-old, normal-sized (black bar) or dwarf (hatched bar)
Leghorn (L) and medium body weight, brown egg-type (BE) laying
hens and their reciprocal crosses
Wachstumshormon ( GH, ng/ml) im Plasma von norma/Jvüchsigen
( sch1varz) oder verz wergten (weiß) 1veißen L eghorn und B ra11nlegerH ennen und ihren reziproken F1 -K reuzungen
Fig. 2. Plasma insulin -like g rowth factor-I concentration s (IGF1, ng/ml) of 15-month-old , normal-sized (black bar) or dwarf
(hatched bar) Leghorn (L) and medium body weig ht, brown
egg-type (BE) la ying hens and their reciprocal crosses
Insulin-ähnlicher Wachstumsfaktor-! ( IGF-1, ng/ml) im Plasma von
normalwüchsigen ( sch1varz) oder verz wergten ( weiß) weißen L eghorn
und Braunleger-H ennen und ihren reziproken F1 -Kreuz ungen
200.--~~~~~~~~~~~~~~~
Statistical ana(yses
For plasma hormone concentrations, overall analysis of
variance (GLM procedure; SAS, 1986) was performed on
Log transformed data with size (normal or dwarf size) and
line (L, BE, L x BE and BE x L) as classification variables.
The data were used also to estimate heterosis within size
dass, both overall, as difference between crossbreds and
purebreds, and for each reciprocal cross, and to compare
heterosis in normal and dwarf hens, from appropriate linear
combinations of least squares means. Energy balance data
were analyzed by two-way analysis of variance. Linear
regression between NEP and AME was performed by using
the REG procedure (SAS, 1986).
Archi v für Geflü gelkunde 2/ 1997
~160
s::
;::::' 120
~
8
80
~
40
«l
«l
ö..
0
LxL
LxBE
BExL
Genotypes
•
normal
m
dwarf
BExBE
68
Z EMAN
et al„ Effects of the sex-linked dwarf gene on plasma somatotrophic and thyroid hormone levels
1.50
15
ä
12
~l.20
9
~0.90
Oll
i::
'--'
'<!"
i::
E-<
E-<
«S
8
~---------------------,
,.......
,.......
60.60
6
"'
"'
ö. 3
«S
«S
ö.0.30
0.00
0
LxL
BExL
LxBE
LxL
BExBE
normal
•
BExBE
Genotypes
Genotypes
•
BExL
LxBE
•
dwarf
•
normal
dwarf
Fig . 3. Plasma thyroxine concemrations (T 4 , ng/ml) of 15month-old, normal-sized (black bar) or dwarf (hatched bar)
Leghorn (L) and medium bod y weight, brown egg-type (BE)
la ying hens and their reciprocal crosses
Thy roxin Konzentrationen ( T 4 , ngfml) im Plasma von normal1vüchsigen, ( schwarz) oder verz wergten, (1veiß) weißen Leghorn und
Braunleger-Hennen und ihre reziproken Ff-Kreuzungen
Fig. 4. Plasma
3,3',5-triiodothyronine
concentrations
(T 3 ,
ng/ml) of 15-month-old, normal-sized (black bar) or dwarf
(hatched bar) Leghorn (L) and medium body weight, brown
egg-type (BE) laying hens and their reciprocal crosses
Trijodothyronin ( T 3 , ngfml) im Plasma von normalwüchsigen,
( schwarz) oder verzwergten ( weiß) weißen L eghorn und BraunlegerHennen und ihren reziproken Ff -Kreuzungen
The sex-linked dwarf gene had a significant effect
(P < 0.01) on the plasma concentrations of borh thyroid
hormones. Indeed, plasma T 4 concentrations (Figure 3) were
significantly higher in dwarf than in normal-sized hens
whereas the opposite was true for plasma T 3 levels (Figure
4). No significant effects of line or interactions for thyroid
hormones were observed.
Some heterois was obtained in dwarfs only for GH and
for IGF-I (Table 1). Superiority over purebreds was quite
high for GH in both reciprocal dwarf crosses, yielding
significant (P < 0.01) positive heterosis. Moreover, heterosis for GH was different (P < 0.05) in dwarfs andin normal
hens, mainly as a result of the BE x L cross difference. The
BE x L dwarfs showed also some significant heterosis
(P < 0.10) for IGF-when compared to purebred dwarfs.
AME within genotypes is reflected in the !arge Standard
errors. The extremely low feed intake is ascribed to adaptive
problems to the respiration chambers. This abnormal ingestive behavior was apparently more pronounced in L x BE
dw and L x L dw hens. In contrast, the mean feed intake
ofBE x Be dw hens ( ~ 87 g feed /chicken/d) can be considered as normal. Apparent metabolisability (AME/GE) was not
influenced by size or genotype and the lowest and highest
values were calculated for LX L dw and BE X BE dw,
respectively. Total heat production varied markedly between
genotypes and was highest in BE x BE dw chickens which
also consumed most feed. The THP variability within
genotypes was much less compared to that for AME. A
significant (P < 0.01) positive correlation of 0.87 between
AME and THP was calculated. There were no significant
effects of size or line on the intercepts and slopes obtained
after the linear regressions between NEP and AME. The
net efficiency for production was lowest for L x BE and
highest for BE x BE hens, irrespective of the size. Maintenance requirements estimated by interpolation of the
regression of NEP on AME to a zero net energy level could
not be compared statistically. However, maintenance re-
Energy metabolism
Data from the energy metabolism studies are summarized
in Table 2. The daily amount of feed consumed differed
markedly between genotypes, and ranged from 5 to 90 g
per chicken. The tremendous difference in feed intake or
Table 1. Crossbred superiority 1 (percentage) and its comparison (value of F and significance of contrast) for normal and dwarf hens
evaluated for combined and reciprocal crosses 2
H eterosisvergleich ( %) zwischen verz wergten und den normalen Hennen und ihren reziproken Kreuzungen
Trait
Crossbred superiority
Comparison of crossbred superiority
Normal
Dwarf
LxBE
BExL
Both
LxBE
BExL
Both
Overall
BExL
LxBE
- 7.2
-0.6
5.3
11.2
- 6.1
- 4.7
-12.5
-17.1
-6.6
-2.7
-3.6
-2.9
28.6 +
0
6.4
-18.7
46.5*
6.8+
4.6
-10.5
37.6**
3.4
5.5
-14.6
4.85*
0.01
0.68
0.11
4.51 *
0.09
1.50
0.20
2.10
0.02
0.02
0.99
-
-
1
fro m Log transformcd daca
L = Whire Legho rn li ne ; BE
• p < 0.10
• p < 0.05
• • p < 0.01
2
=
Brown egg line
Archi v für Geflügelkunde 2/1997
ZEMAN et al., Effects of the sex-linked dwarf gene on plasma somatotrophic and thyroid hormone levels
69
Table 2. Apparent metabolisable energy intake (AME), metabolisability, total heat production (THP), estimated maintenance requirements,
and characteristics of linear regression of energy for production (NEP) on AME of Leghorn (L) and medium body weight, brown egg
(BE) laying hens of normal (Dw) or dwarf (dw) size and their reciprocal crosses
Energetischer Metabolismus von normalwiichsigen oder verzwergten weißen L eghorn und Braunleger-Hennen und ihren reziproken F1 -Kreuz11ngen
Geno type
AME
Metaboli(kJ/kg 0· 75/3d) ability
THP
(kJ /kg 0·75 /3d)
characteristics of linear regress ion
ofNEP on AME
intercept a
L x LDw
LxL dw
LxBE Dw
LxBE dw
BExL D w
BEx L dw
BE x BE Dw
BEx BE dw
1447
892
1211
686
1755
1315
1030
2111
± 401
± 403
± 431
± 234
± 377
± 468
± 484
± 109
0.71
0.61
0.69
0.68
0.73
0.71
0.66
0.74
± 0.06
± 0.07
± 0.02
± 0.03
± 0.03
± 0.04
± 0.06
± 0.01
1442
1229
1471
1275
1437
1439
1415
1640
± 138
± 101
± 188
± 123
± 130
± 175
± 108
± 44
quirements apparently reached the highest values in L x BE
chickens which were also characterised by the lowest net
efficiency for production.
Dlscusslon
There are only very limited data on hormonal parameters
in dwarfhens during the laying period . Plasma T 4 concentrations have been found to be increased in Leghorn hens
during the laying period, while the circulating levels of T 3
were slightly decreased (TrxrER-Borc HARD et al., 1990).
The hormonal patterns found in SLD hens in our
experiment resemble those in juvenile dwarf chickens.
Indeed, plasma T 3 concentrations were lower and plasma
T 4 concentrations were higher in SLD than in normal-sized
hens; as also found in growing chickens (DECUYPERE et al.,
1991 ). The significant difference in plasma T 3 concentrations
between dwarf and non-dwarf L x L hens confirms the
pronounced h ypothyroid state in the Leghorn strain is
observed previously (TrxIER-BOrCHARD et al., 1989).
Higher plasma GH concentrations have been consistently
found in SLD chickens during their growing phase in all
genotypes studied till now (DECUYPERE et al., 1991 ). Also
in our experiment increased GH levels were measured in
Leghorn SLD hens and both crosses bearing the SLD gene.
However, in dwarf hens of the medium body weight brown
egg strain, plasma GH concentrations were low, thereby
contributing to the significant heterosis of GH, and they
were similar to those of normal-size genotypes. This may
be considered as another example of nonadditive effect
of the genetic background on a trait influenced by the SLD
gene. Yet no such interaction was found for thyroid
hormones, and heterosis was limited to one reciprocal cross
for IGF-I in dwarf females. Effects of genetic background
on the SLD gene manifestation was found by several
authors for different physiological variables (DECUYPERE
et al., 1991 for a review). On the other hand, recent molecular
biology studies indicated that the SLD phenotype is not
genotypically uniform and may result from different aberrations of the GH receptor gene (BuRNSIDE et al., 1992;
D uRIEZ et al., 1993). Different gene alterations may lead to
minor differences in phenotypical manifestation of the SLD
gene. However, plasma GH concentrations were high in
both reciprocal crosses, e.g. when the SLD gene came from
both the Leghorn and BE strains . lt indicates that an
interaction of SLD gene with a genetic background rather
Archiv für Geflügelkunde 2/ 1997
-358
-324
-310
-318
-348
-333
-414
-407
± 66
± 38
± 45
± 35
± 89
± 79
± 40
± 16
slope b
0.747
0.758
0.563
0.535
0.757
0.671
0.830
0.840
± 0.117
± 0.082
± 0.080
± 0.124
± 0.141
± 0.130
± 0.085
± 0.230
Maintenance
(kJ /kg0.75/d)
Ri
0.90
0.97
0.94
0.82
0.90
0.90
0.97
0.82
480
427
550
594
460
497
499
484
than different structures of the SLD gene induces different
plasma GH concentrations between L and BE strains.
The SLD gene descreases the number oflarge follicles and
increases the oviposition interval length. As a consequence,
egg number is decreased and the effect of the dwarf gene
is more pronounced in the Leghorn strain stocks than in the
medium-sized type or broiler strains (MERAT, 1990). This
conclusion was confirmed in a recent study (MERAT et al. ,
1994) using the same crosses as we used in our present
experiment. Alterations in reproductive functioning in
dwarfs may result not only from mino r chan ges of reproductive hormones (TrxIER-BorcHARD et al., 1990) but also
from a different secretory pattern of thyroid hormones and
growth factors together with a decreased sensitivity of target
organs to hormonal signals. IGF-I concentrations were
lower in dwarf than in normal hens. This pattern corroborates with data found in growing chickens (H osHINO et al.,
1982, HuYBRECHTS et al., 1985). Therefore, the impact of
the SLD gene on reproductive abilities may concern the
ovarian sensitivity to pituitary hormones in interaction with
other hormonal factors such as IGF-I that differ in dwarf
genotypes .
The primary goal of the energy balance trials was to
identify causal mechamisms underlying the genotypic differences in reproductive performance as reported by MERAT
et al. (1994). However, due to the apparent problems of
adaptation to the respiration chambers at least in terms of
eating behavior, causal links between the obtained energy
balance data and egg production characteristics are difficult
to establish. BE x BE dw hens seemed to suffer less from
the new environment as feed intake was normal. On the
other hand, the wide range in feed intake within genotypes
allowed regression of NEP on AME. Based on these
calculations, it can be inferred that BE x BE genotypes,
irrespective of size, demonstrate the highest net energetic
efficiency of production whereas the opposite was true for
L x BE genotypes. The latter genotypes also had the highest
maintenance requirements which may explain their low
efficiency of production. The absence of any differences in
energy balance data according to size or line does not concur
with the genotypic differences in reproduction but firm
conclusions cannot be drawn due to their poor adaptive
abilities to the respiration chambers. For most genotypes,
AME exceeded THP. Nevertheless, egg production of these
hens was satisfactorily. This implies that bodily energy, fat
and protein reserves must have been mobilised, as o bserved
70
ZEMAN
et al., Effects of the sex-linked dwarf gene on plasma somatotrophic and thyroid hormone levels
in fasted adult hens (BuYSE et al., 1995). This was indeed
reflected in the decrease in body weight during the balance
trials in the hens with poor feed consumption.
Stichworte
Summary
References
The effects of the dwarfing gene on somatotrophic (GH,
IGF-I) and thyreotrophic (T4 , T 3 ) hormones and on energy
metabolism in laying hens were studied. Leghorn laying
hens (L) and brown-egg laying hens (BE) were used to
investigate a possible influence of a genetic background on
the expression of the dwarf gene. Birds came from the
mating of heterozygous sires (Dwdw) with dwarf females
(dw-) from pure lines (L x L and BE x BE) and their
reciprocal crosses. In this way hens were of anormal growth
or carrying the dwarf gene and were full sisters or half
sibs.
Estimation of complete energy balance suggests that the
dwarfing gene has no significant advantage in improving
the net energetic efficiency of production in comparison to
normal hens. Also, maintenace requirements did not differ
significantly among genotypes.
Plasma concentrations of the assayed hormones followed the pattern generally found in juvenile dwarf chickens.
GH leve ls were low in normal-sized hens of all genotypes .
The presence of the dwarf gene increased GH levels in
leghorn hens and both reciprocal crosses. However, in dwarf
brown-egg laying hens, GH levels were low and not different
from normal hens. Heterosis was obtained in dwarfs only
for GH and to a lesser extent for IGF-I. Superiority over
purebreds was quite high for GH in both reciprocal dwarf
crosses, yielding significant positive heterosis. Hens of all
genotypes bearing the dwarf gene had significantly reduced
plasma IGF-I and T 3 concentrations compared to their
normal-sized counterparts whereas the opposite was true for
plasma T 4 levels. Results suggest that the dwarf gene can
be differentially expressed in relation to the genetic background.
Zusammenfassung
Der Einfluß des „dwarf' Gens auf einige Plasma-Hormonspiegel und auf den energetischen Metabolismus wurde an
Leghorn (L) und Braunleger-Henn en (BE) studiert. Die
Hennen stammten aus Kreuzung von heterozygo ten männlichen Tieren (Dwdw) und verzwergten weiblichen (dw-)
in Form von reinen Linien (L x L und BE x BE) und deren
reziproken F1 Kreuzungen. Die Hennen waren also verzwergt oder normalwüchsig und Schwester oder Halbgeschwister.
Die dwarf Allelle brachten keine signifikanten Vorteile
bezüg lich der energetischen Produktivität. Es konnten auch
keine signifikanten Unterschiede zwischen den Genotypen
im Hinblick auf den Erhaltungsmetab olismus beobachtet
werden. Die GH-Konzentratio nen waren bei allen erwachsenen Normal-Hennen niedrig. Das dwarf-Gen hat das
GH-Niveau bei Leghorn-Hennen und auch bei den beiden
reziproken Kreuzungen signifikant erhöht. Bei verzwergten
BE x BE Legehennen waren die GH-Konzentratio nen niedrig und haben sich von den normalen Hennen nicht
unterschieden. Heterosis trat auf für GH bei verzwergten
Hennen. Die Plasma-IGF-I und T 3 -Spiegel waren niedriger
bei Dwarf als bei ormal-Hennen aber der T 4 -Spiegel war
erhöht. Die Ergebnisse zeigen, daß die Expression des
dwarf-Gens verändert wird im Hinblick auf den genetischen
Hintergrund der Tiere.
Legehenne, Züchtung, Kreuzung, Genwirkung, dw-Gen,
Wachstum, Plasma, Hormone, Energie, Stoffwechsel
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KÜHN and F. V ANDESANDE, 1988: One-step purification
of chicken growth hormone from a crude pituitary extract
by use of a monoclonal immunoabsorben t. J. Endocrinol.
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BuRNSIDE, J., S. S. Lrou and L. A. COGBURN, 1991 : Molecular cloning of the chicken growth hormone receptor
complementary deoxyribonucleic acid; mutation of the
gene in sex-linked dwarf chickens. Endocrinol. 128,
3183 - 3192.
BuRNSIDE, ]., S. S. Lrou and L. A. CoGBURN, 1992: Abnormal growth hormone receptor gene expression in the
sex-linked dwarf chicken. Gen. Comp. Endocrinol. 88,
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BuYSE, J., E. DECUYPERE and E. R . K ÜHN, 1995: Effect
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TrxIER-BorCHARD and P. MERAT, 1991: Physiological
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M . GoossENS and S. AMSELEM, 1993: A naturally occuring
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common to all members of the cytokinine receptor
·
superfamily. Mol. Endocrinol. 7, 806 - 814.
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HuYBRECHTS, L. M., D. B. KrNG, T. J. LAUTERIO, J. MARSH
and C. G. ScANES, 1985: Plasma concentration of somatomedin-C in hypophysectomiz ed, dwarf and intact growing
domestic fowl as determined by heterologous radioimmunoassay. J. Endocrinol. 104, 233- 239.
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Ansc hri ft de r Ve rfasser: Dr. J. Bu yse, Lab. of Ph ys io logy and Immun o logy o f
Domestic Anima ls, Dcpartment o f Anima] Productio n. K . U. Lcuven, Kardin aal
Mercierl aan 92, 3001 Hcvcrlee, Belgium
0003-9098. © Verlag Eugen Ulmer Gm bH & Co„ Stuttgart
N and P utilization in broilers fed ad libitum diets reduced in protein
and gradually differing in protein: energy ratios
N- und P-Verwertung von Broilern bei ad libitum-Fütterung von proteinreduzierten und im Protein: EnergieVerhältnis stufenweise variierten Rationen
Margit Wittman 1 , A. D. Töws 1 and M. Kreuzer 2
Man uskript eingegangen am 9. August 1996
lntroduction
Besides the reduction of costs (ScHOLTYSSEK 1987), ecological aspects become increasingly important in broiler feeding
(HARENZ et al. 1992). The voluntary feed intake of broilers
is mainly determined by dietary energy concemration,
particularly at a low level of energy concentration, and only
to a lesser degree by protein concentration (LEESON and
SuMMERS 1989; KrRCHGESS ER and KREUZER 1990). As
a consequence, the energy concentration required should
indirectly prevent excessive and deficient consumption of
other nutrients. Dietary protein (nitrogen, N), in contrast,
may be reduced as far as is possible witho ut adverse effects
on performance. If a simultaneous reduction of energy and
protein contents is carried out the effect on
excretion
might be considerably lower than expected because of this
indirect effect of energy concentration on feed consumption
(KIRCHGESSNER and KREUZER 1990). The same is valid for
phosphorus (P) even at similar dietary P contents since a
1
2
Forschungszentrum der Universität Göttingen in Vechta
Institut für Nutztierwissenschaften der ETH Zürich
A rch iv für G eOügel kund c 2/1997
higher feed imake might reduce utilization and increase
excretion of P. A somewhat higher P excretion was even
observed at quite low protein contents associated with a
slightly higher feed intake (GuEYE 1994). The objective of
the present experiment was to obtain the effect of dietary
protein reduction as accompanied by a gradual alteration of
the protein: energy ratio using medium and high energy
levels. The still poor data base on the real levels of retention
and excretion of N and P in modern broiler strains should
be enlarged by applying two methods, the balance technique
and the comparative carcass analysis.
Material and methods
Animals and j attening period
28 day-old male Euribrid broiler chicks were individually
housed in separated wire-cages (35 cm x 30 cm x 41 cm).
Room temperature was reduced by 2 °C per week and
relative humidity was maintained by a climatic device as
generally recommended. The lighting regime provided 16 h
light and 8 h darkness from the 8th day onwards. Each
broiler had a water nipple inside its cage. For feeding,