Reprinted from Poultry Science, Volume 59, No. 8, August 1980. Pages 1864-1872.

Effect of Dietary Protein and Fat Levels on Fattening ofCorticosterone-injected Broiler Chicks

I. BARTOV,' L. S. JENSEN, and J. R. VELTMANN, JR.

Department of Poultry Science, University of Georgia, Athens, Georgia 30602

(Received for publication October 16, 1979)

ABSTRACT The effect of dietary composition on fattening of corticosterone-injected broilerswas studied with Hubbard male chicks. Corticosterone was injected daily from 26 days of ageduring 9 days at a concentration of 600 ng/bird/day.

Dietary energy to protein (E:P) ratio or fat level did not significantly affect body weight gain,abdominal fat pad size, skin dry matter, or liver parameters in corticosterone-injected chicks.However, corticosterone-injected birds fed the diet containing the narrower E:P ratio had smallerlivers which also contained less fat than chicks fed the diet with a wide E:P ratio. This effect,although consistant in three experiments, was significant (P<.01) only in one.

It is concluded that dietary fat level and E:P ratio do not affect carcass fat content of corticosterone-injected chicks, but diets containing wide E:P ratios may increase fattening of the liverconsiderably.(Key words: chick, corticosterone, dietary protein, dietary fat, fattening, liver fat)

1980 Poultry Science 59:1864-1872

INTRODUCTION

Injection of chicks with corticosterone hasbeen reported to depress body weight in spiteof increased feed consumption and to increasecarcass and liver fat (Baum and Meyer, I960;Nagra and Meyer, 1963; and Bartov et ai,1980).

Environmental factors have a considerable

effect on plasma corticosterone levels in birds.Resko et ai. (1964) observed increased plasmacorticosterone levels in chickens in winter.

Dusseau and Meier (1971) also reported thatplasma adrenal steroid levels in the White-throated sparrow were highest in the winter.Brown and Nestor (1973) and El-Halawani etat (1973) demonstrated that both heat andcold stress resulted in a significant elevation inplasma corticosterone in turkeys. Edens andSiegel (1975) and Edens (1978) observed asignificant elevation in plasma corticosterone inchickens due to acute heat stress. Siegel (1971)reported that chickens exposed to social stresshad increased adrenal weights. These studiesindicate that an increase in plasma corticosterone level may be expected when an environmental stressor is imposed on the birds.

1Present address: Division of Poultry Science,Agricultural Research Organization, The VolcaniCenter, Bet Dagan, Israel.

2Sigma Chemical Company. St. Louis, MO.

Broiler chicks have a marked tendency toaccumulate carcass fat and high environmentaltemperature enhances this tendency (Edwards,1975). This effect might be partly due toincreased corticosterone production followingthe stress of the elevated temperature.

Dietary energy-to-protein (E:P) ratio is oneof the most important nutritional factorsaffecting fattening, although dietary fat per sedoes not have a considerable effect (Bartov,

1979). In overfed chicks, oil causes less increasein liver size and liver fat content than glucose(Shapiraer ai, 1978a).

The purpose of the present study was todetermine if fattening of corticosterone-injectedchicks was affected by dietary E:P ratio and fatlevel.

GENERAL EXPERIMENTAL METHODS

Chicks, Diets, and Hormones. Hubbard malebroiler chicks were housed in electrically heatedbattery brooders up to 24 days of age and thenwere transferred to growing cages in a roomwith a constant temperature (26 ± 1 C). In bothplaces the chicks were kept on continuouslighting (white fluorescent) and the lightintensity in each pen in the growing cagesranged from 100 to 460 Ix. At the time oftransfer 70% of the chicks with body weightnearest the mean were wing-banded and dividedinto experimental groups, each consisting of 8birds. Both mean weight and weight distribution

1864

CORTICOSTERONE, DIETARY COMPOSITION. AND FATTENING 1865

among the experimental groups were equalized.This procedure was followed to reduce variability and to allow for the injection of the samequantity of hormone in each bird. The dietsused are described in Table 1. They containedthe same energy levels but differed in E:P ratioand in the percentage of energy derived fromfat or carbohydrates. Feed and water weresupplied ad libitum. The diets were fed fromday of age through the experimental periodexcept in Experiment 3 where some treatmentswere fed diets of different composition at thestart of the injection period.

Corticosterone2 (600 fig/bird) was injectedinto the thigh muscle in .4 ml of physiologicalsaline (.9%). Control chicks were injectedwith saline alone and a group of uninjectedbirds was also included in the first experiment.The injections were given daily at 1600 hrfrom the 26th to 34th day of age.

The chicks were individually weighed at 26days of age and at 31 and 36 days. The amountof feed consumed during these periods was alsorecorded.

Forty hours after the last injection, chickswere killed by cervical dislocation. The abdom

inal fat surrounding the bursa, gizzard, andintestines was carefully removed for weighing.A piece of the back skin was taken (Moran etai, 1968) for dry matter determination, aparameter which is correlated with skin andbody fat content (Bartov et ai, 1974) and thelivers were removed, blotted, weighed, andkept at —18 C until analyzed.

Chemical Methods. Liver fat content was

determined gravimetrically after extractionwith chloroform:methanol (2:1) as described

by Folch et al. (1957). Dry matter content inback skin was determined after drying in aforced air oven (105 C) for 12 hr.

Statistics. Results were subjected to analysisof variance (Snedecor, 1956). Analysis ofvariance of liver parameters of corticosterone-treated and untreated birds was carried out

separately because of the large differences instandard deviations in these chicks. Differences

between treatment means were analyzed byDuncan's multiple range test (1955).

PROCEDURE AND RESULTS

Experiment 1. The purpose of this experiment was to determine if the effects of cortico-

TABLE 1. Composition of the experimental diets (%)

Diet

A B C D

Yellow corn 45.527 60.145 46.016 37.823

Soybean meal (48.5% protein) 43.300 31.000 33.510 44.600

Poultry fat 7.200 4.850 10.000 10.000

DL-methionine .193 .137 .148 .197

L-lysine . . . .088 .036

Sand . . . 4.340 2.400

Solka floe 2.170 1.200

Constant ingredients' 3.780 3.780 3.780 3.780

Calculated analysis

Crude protein (%) 24.96 20.26 20.25 24.92

ME (kcal/kg) 3245 3245 3245 3245

Energy-to-protein ratio 130 160 160 130

Fat (%) 9.31 7.40 12.10 11.81

Calorie from fat (%) 25.0 19.4 30.9 30.2

1Dicalcium phosphate, 2.05%; limestone, .88%; salt, .4%; vitamin mixture, .25%; coban 45, .1%; trace mineral mixture .05%; Se concentrate, .5%.

Vitamin mix suppled per kilogram feed: vitamin A, 4400 IU; vitamin D3, 800 ICU; a-tocopheryl acetate, 11mg; menadione sodium bisulfite, 3.5 mg; riboflavin, 4.4 mg; Ca pantothenate, 9.6 rag; nicotinic acid, 44 mg:choline chloride, 220 mg; pyridoxine. 2.2 mg: thiamine mononitrate. 2.2 mg; folic acid, .55 mg; biotin, .11 mg;vitamin B,,, 6.6 Mg: and ethoxyquin, 125 mg.

Coban 45 supplied 100 mg monensin sodium/kg diet.Trace mineral mix supplied mg/kg feed: Mn, 60; Zn, 50; Fe, 30: Cu, 5; 1, 1.05.Se concentrate supplied .1 mg Se/kg diet.

1866 BARTOV ET AL.

sterone and fattening could be modified bydietary E:P ratio. Diets A and B (Table 1),differing in E:P ratio and fat content, were fedfrom day of age to the termination of theexperiment.

Corticosterone injection increased feed consumption and significantly (P<.01) depressedbody weight gain and increased abdominalfat pad size, skin dry matter, relative liverweight, and liver fat content (Table 2). DietaryE:P ratio did not affect any of the parametersof performance and of fattening in uninjectedor saline-injected chicks. The diet with thewider E:P ratio significantly (P<.01) increasedrelative liver size and liver fat content comparedwith the effect of the diet containing thenarrower E:P ratio.

Experiment 2. The purpose of this experiment was to clarify whether the differences inliver fat content observed in the previousexperiment in corticosterone-injected chicksfed the diet with the narrower E:P ratio andthose fed the diet with the wide E:P ratiowere the result of the difference in dietary fatlevel. Diets B and C (Table 1), havingthe sameE:P ratio but differing in their fat content, wereused.

The response of the chicks to corticosteroneinjection was the same as in the previous

experiment, i.e., increased feed consumption,decreased body weight gain, and increasedfattening (Table 3). Dietary fat level did notaffect fattening in saline-injected birds. However, corticosterone-injected birds fed the highfat diet had numerically larger abdominal fatpads and significantly (P<.01) more dry matterin their skins than chicks fed the low fat diet.

Dietary fat level did not affect relative liver sizeand liver fat content either in saline or in

corticosterone-injected chicks.Corticosterone injection significandy de

creased spleen weight (Table 4). This effect wasalso evident when spleen weights were adjustedto body weights. Weights of spleens from chicksfed the high fat diet (diet C) were significandy(P<.01) higher than the weights observed inchicks fed the relatively low fat diet (diet B).There was no interaction between the effect of

dietary fat level and corticosterone injection onspleen weights.

Experiment 3. The purpose of this experiment was to confirm the effect of the wide

dietary E:P ratio on enhancing the effect ofcorticosterone on increasing liver fat which wasobserved in the first experiment and to find outwhether the effect of the diets was dependenton the periods in which they were being fed.Diets B and D (Table 1), differing in their E:P

TABLE 2. Effectof energy-to-protein (E:P) ratio andcorticosterone1 injection onperformanceand fattening of broiler chicks (Experiment 1)

Treatment

Bodyweight Feed con Abdom Skin

D iet2

Desig E:P gain3'" sumption5 inal dry Liver Livernation ratio Injection 26-36 days 26-36 days fat pad4 matter4 wt/kg BW4 lipids4

(g) (g/chick) (% BW) (%) (g) (% wet wt)

A 130 None 519a 924 2.4b 67.8b 25.1 ± 1.5a 3.3 ± .laB 160 None 518a 932 2.6b 67.5b 24.7 t 1.1* 3.7 + .2aA 130 Saline 537a 897 2.4b 67.7b 25.6 ± .8a 3.4 ± ,2aB 160 Saline 494a 906 2.4b 68.5b 25.0 ± lja 3.5 ± ,iaA 130 Corticosterone 378b 1115 4.8a 77.5a 36.2 * 2.0b 10.7 ± 1.5bB 160 Corticosterone 344b 1103 5.2a 80.5a 47.5 ± 2.3C 20.7 ± 1.2C

SE 19.6 .24 1.15

' Values within a column not having one letter in common differsignificantly (P<.01).1Corticosterone, 600 jug/bird/day, was injected daily at 1600 hr from 26 to 34 days ofage.2See Table 1.

3Initial body weights at 26 days ofage ofchicks fed diet Aand Bwere 795 and 719 g, respectively."Mean or mean 1 standard error of 8 birds.

One replicate for each treatment.

CORTICOSTERONE, DIETARY COMPOSITION, AND FATTENING 1867

TABLE 3. Effect ofdietary fat level and corticosterone* injection on performanceandfattening of broiler chicks (Experiment 2)

Treatment

Diet'

Desig- Fatnation level Injection

Bodyweight Feed con- Abdom-gain3'4 sumption5 inal26-36 days 26-36 days fat pad4

Skin

drymatter4

Liver

wt/kg BW4Liver

lipids

(%) (g) (g/chi

B

CB

C

7.4

12.1

7.4

12.1

Saline

Saline

Corticosterone

Corticosterone

512a

502*

286b30lb

897

931

1000

1131

SE 28.5

(% BW)

2.2b2.0b4.4a

5.1a

.25

(%)

71.4C

72.4C

81.lb85.6a

1.06

(g)

22.1 ± .8a

24.8 ± .9a

42.4 ± 4.4b45.1 ± 3.3b

(% wet wt)

4.0 ± .2a

3.5 ± .la

19.3 t 4.lb20.7 ± 1.9b

cValues withina columnnot having one letter in commondiffer significantly (P<.01).

1Corticosterone, 600 Mg/bird/day, was injected daily at 1600 hr from 26 to 34 daysof age.

2See Table 1.

3Initial body weights at 26days of age of chicks fed dietBand C were 752 and820g, respectively.

4Mean or mean ± standard error of 8 birds.

5One replicate for each treatment.

a,b,c.

ratios, were used in this study. At 26 days ofage, before starting injections, halfof the chickswhich had been fed diet B from day of age wereswitched to diet D and half of those which hadbeen fed diet D from day of age were switchedto diet B. The detailed outline of this experiment and its results are given in Table 5.

Dietary E:P ratios did not significantly affectweight gain, abdominal fat pad size, relativeliver weight, or the fat content of the liversin saline-injected chicks. However, chicks fedthe diet containing the wide E:P ratio from 1 to36 days had a significantly (P<.05) higherpercentage of dry matter in their skins thanthose fed the narrow E:P ratio during the sametime.

Corticosterone injection increased feed consumption, decreased weight gain, and increasedfattening with all the treatments, but growthdepression was lower in chicks fed the narrowerE:P diet during the whole study. Abdominal fatpad size and percentage of skin dry matter wereessentially the same in all the corticosterone-injected chicks. Chicks fed the diet with thenarrower E:P ratio either during the wholeexperimental period or only during the prein-jection period had smaller livers with a relativelylower fat content compared with the chicks fedthe wide E:P diet. These differences, however,were not always significant because of the great

individual variability among the cortico-sterone-treated chicks.

Corticosterone injections significantly(P<.01) decreased mean absolute spleen weight

in all experiments and mean spleen weightsper unit of body weight in Experiment 3 (Table4).

Experiment 4. The purpose of this study wasto confirm the results obtained in the previousexperiments showing that liver fat content incorticosterone-injected chicks was affected bydietary E:P ratio but not by dietary fat levels.Diets A, B, C, and D (Table 1) were used in thisexperiment.

Dietary E:P ratio did not significantly affectweight gain and liver parameters in saline-injected birds (Table 6). However, on a factorialbasis the wide E:P ratio resulted in significantly(P<.05) increased abdominal fat pad size andskin dry matter.

As in the previous experiments, corticosterone injection increased feed consumption,decreased body weight gain, and increasedfattening (Table 6). There were no significantdifferences in body weight gain or in parametersassociated with fattening including those of theliver among chicks fed the various diets, but inchicks fed diet A (narrow E:P ratio), all theparameters of fattening were consistentlylower. Corticosterone injection decreased spleen

1868

Experimentno.

BARTOV FT AL.

TABLE 4. Effect of corticosterone1 injection and diets on spleen weight of36-day-old chicks (Experiments 2, 3, 4)

Spleen weight Relative spl een weight

Injection

Cortico Cortico

Diet2 Saline sterone Saline sterone

(g) (g/kg

B3 1.88b 1.22C l.49ab 1.20b

C 2.72a 1.72b 2.07a 1.61ab

Ave 2.30a 1.47b 1.78* 1.4ia

B(B)4 2.47a 1.54bc 2,19ab 1.61bcD(B) 2.87a 1.33c 2.31a 1.40C

D(D) 2.45a 2.14ab 1.89abc 1.85abc

B(D) 2.25ab 1.67bc 179abc 1.57<-"

Ave 2.50a 1.66b 2.04a 1.60b

A 2.15

1.91

1.72

1.47

1.69 1.61

B5 1.64 1.36

C 2.11 1.57 1.69 1.42

D 2.44 1.90 1.81 1.78

Ave 2.15* 1.66b 1.7ia 1.54a

' ' Values for each parameter in each experiment not having a common letter differ significantly (P<.01).

'Corticosterone, 600 jig/bird, was injected daily at 1600 hr from 26 to 34 days of age.

2See Table 1.

'Weights and relative weights of spleens from chicks fed diet B were significantly (P<.01) lower than thevalues observed in chicks fed diet C.

4In parenthesis the diets fed up to 26 days of age.

5Weight of spleens of chicks fed this diet were significantly (P<.05) lower than the values observed in birdsfed diet D.

weight and its relative weight (Table 4), but thiseffect was significant (P<.01) only on a factorialbasis. Spleen weights of chicks fed diet B weresignificantly (P<.05) lower than those of chicksfed diet D.

DISCUSSION

Corticosterone injection consistendy causedhyperphagia, depressed growth, and increasedfattening in broiler chicks (Tables, 2, 3, 5, and6) which is in agreement with earlier reports(Baum and Meyer, 1960; Nagra and Meyer,1963; and Bartov et ai, 1980). The effect of

this hormone on increasing fattening, which ismediated at least partly through hyperphagia, issimilar to the effect of overfeeding (Shapira etat, 1978a,b). In both cases there is an increasein carcass fat, liver size, and liver fat content.

However, overfed chicks are heavier, whereas

corticosterone-injected birds are lighter thantheir corresponding controls. The last pheno

menon may be due to the inhibitory effect ofcorticosterone on growth hormone (Grant,1967) and/or altered metabolism such as

increased gluconeogenesis from protein (Nagraand Meyer, 1963).

Dietary E:P ratio, which is one of the mainnutritional factors affecting fattening in chicks(Bartov, 1979), only slightly (and not alwayssignificantly) affected abdominal fat pad sizeand skin dry matter in the saline-injected birds(Tables 2, 5, and 6). In a separate study weobserved that a diet containing a relativelynarrow E:P ratio (127) fed from 3 to 7 weeks

of age to chicks of the same breed used in thepresent study only slightly decreased and didnot prevent excess carcass fat accumulation. Itappears, therefore, that Hubbard chicks mayhave a genetic tendency to accumulate fat intheir carcass, and relatively narrow dietary E:Pratios can only slightlv counteract this tendency.

CORTICOSTERONE, DIETARY COMPOSITION, AND FATTENING 1869

TABLE 5. Effect of energy-to-protein (E:P) ratio in diets fed to chicks before and duringcorticosterone' injection on performance andfattening of broilerchicks

(Experiment 3)

Treatment

Bodyweight Feed con Abdom SkinDietary E:P ratio

1-25 26-36 gain2'3 sumption4 inal dry Liver Liver

days days Injection 26-36 days 26-36 days fat pad3 matter3 wt/kg BW3'5 lipids3'5

(g) (g/chick) (% BW) (%) (g) (% wet wt)

1306 130 Saline 520a 934 2.4b 67.7C 26.3 ± 1.1 3.8 ± .1

130 1607 Saline 484ab 943 2.6b 70.5bc 24.6 ± 1.3 4.5 ± .3

160 160 Saline 436ab 845 2.4b 72.9b 24.8+ 1.0 3.8 ± .1

160 130 Saline 514ab 868 2.2b 71.3bc 28.1 ± 1.6 4.0 i .2

130 130 Corticosterone 388bc 1023 4.4a 81.9a 38.6 ± 2.5b 7.7 ± 1.6

130 160 Corticosterone 299cd 1055 4.3a 80.9a 40.1 t 2.2b 11.9 ± 2.3

160 160 Corticosterone 252d 962 4.2a 83.3a 47.7 ± 2.9ab 14.8 ± 3.0

160 130 Corticosterone 263d 940 4.5a 82.9a 54.2 ± 4.7a 13.1 ± 3.0

SE 28.9 .27 1.17

1 'L' Values within a column not having one letter in common differ significantly (P<.01).

1Corticosterone, 600 Mg/bird/day, was injected daily at 1600 hr from 26 to 34 days of age.

2Initial body weight at 26 days of age of chicks fed up to thisage the dietswith the narrow6 and the wide1E:P ratio were 769 and 709 g, respectively.

3Mean or mean ± standard error of 8 birds.

"One replicate for each treatment.

5Mean difference between corticosterone and saline injected chicks was significantly different (P<.01).

6Diet D (Table 1).

'Diet B (Table 1).

Dietary E;P ratio did not affect abdominalfat pad size and skin dry matter in corticosterone-injected chicks (Tables 2, 5, and 6).The effect of dietary E.P ratio on fattening ismediated mainly through its effect on voluntaryfeed intake. Feed consumption is usually highwhen diets slightly deficient in protein (i.e.,with wide E:P ratio) are being used (Bartov,1979). Corticosterone, at the level used in thisstudy, markedly increased hyperphagia andfattening with all the diets. Therefore, theeffect of E:P ratio was probably completelymasked by the effects of the hormone. However, the possibility that a narrow E:P ratio maydecrease fattening induced by naturally elevatedcorticosterone levels cannot be ruled out.

The narrow dietary E:P ratio, however,appears to decrease liver size and liver fatcontent in corticosterone-injected chicks. Thiseffect was evident in three out of four com

parisons but significant (P<.01) only in one ofthem (Experiment 1, Table 2). The differencesbetween liver parameters of cortico

sterone-injected chicks fed either the narrow orthe wide E:P ratio diets in Experiment 3 (Table5) were pronounced but not significant becauseof the great individual variation within thetreatments. Increased fat transportation fromthe liver to other tissues in corticosterone-

injected chicks fed the diet with the narrow E:Pratio does not seem to explain the lowerliver fat content in these chicks, since no

differences were observed in abdominal fat padsize and skin dry matter between chicks fedthe diets varying in E:P ratio.

High protein diets were reported to decreaseliver lipogenesis, although they did not decreaseliver fat content (Yeh and Leveille, 1969). The

effect of the diets containing the narrow E:Pratio on decreasing liver fat content in corticosterone-injected chicks might be partly due todecreased lipogenesis.

Of particular interest and deserving furtherinvestigation, are results obtained in Experiment3 (Table 5) which show that the diet fed in

early stages of life may affect liver fattening

TABL

E6.

Effe

ctof

dieta

ryen

ergy

-to-p

rotei

n(E

:P)r

atio

andf

atco

nten

ton

perfo

rman

cean

dfa

tteni

ngof

cort

icos

tero

ne'

inje

cted

broi

ler

chic

ks(E

xper

imen

t4)

Des

ign

ati

on

A D B C A D B C SE

Die

t2

E:P

rati

o

130

130

!60

160

130

130

160

160

Treatm

en

t

Fat

lev

el

(%)

Inje

ctio

n

9.3

Sali

ne

11

.8S

ali

ne

7.4

Sali

ne

12

.1S

ali

ne

9.3

Co

rtic

oste

ron

e1

1.8

Co

rtic

oste

ron

e

7.4

Co

rtic

oste

ron

e1

2.1

Co

rtic

oste

ron

e

Bo

dy

wei

gh

tga

in3'

42

6-3

6d

ays

(g)

501a

537a

458a

469a

308b

256b

329b

324b

28.8

Feed

cons

umpt

ion5

26

-36

day

s

(g/chick)

952

977

911

910

1020

1049

1059

1014

Ab

do

min

al

fat

pad4

(%B

W)

1.8

d2

.0d

2.5

cd2

.6b

cd3

.4ab

3.6

ab3

.7a

3.6

ab

.25

Sk

in

dry

matt

er4

(%)

66

.6C

68.4

b<-'

72

.3b

70

.9b

c7

9.9

a

81

.3a

81

.la

80

.3a

1.3

2

a,b

,c,d

,,,

...

..

Val

ues

with

ina

colu

mn

noth

avin

gon

ele

tter

inco

mm

ondi

ffer

sign

ifica

ntly

(P<

.01)

.1C

ortic

oster

one,

600

ug/bi

rd/da

y,wa

sinje

cted

daily

at16

00hr

from

26to

34da

ysof

age.

2See

Tab

le1.

3Initia

lbod

ywe

ighta

t26d

ayso

fage

ofch

icksf

eddie

tsA,

D,B,

andC

were

783,

806,

745,

and

798g

,resp

ectiv

ely.

4Mea

nor

mea

n±

stan

dard

erro

rof

8bi

rds.

On

ere

plic

ate

for

each

trea

tmen

t.

'Mea

ndi

ffere

nce

betw

een

corti

coste

rone

and

salin

ein

jected

chick

swas

signi

fican

t(P<

.01)

.

Liv

er

wt/

kgB

W4'

6

(g)

26

.2±

1.3

24

.6+

.3

23

.5±

.8

23

.6±

.9

40

.1+

3.3

42

.2+

1.8

44

.5+

2.5

40

.6±

2.9

Liv

er

lipid

s4'6

(%w

et

wt)

3.4

+.1

3.4

±.1

3.9

±.2

3.7

+.1

7.7

+1

.4

11

.01

2.5

11

.1±

2.1

9.9

+1

.8

00

o as > x H 0 < H > r

CORTICOSTERONE, DIETARY COMPOSITION, AND FATTENING 1871

more than the diet used during the period ofcorticosterone injection.

Fat level in diets having the same E:P ratioaffected abdominal fat pad size, skin drymatter, liver weight, and fat content eitherin saline or in corticosterone-injected birds inonly one of the comparisons (Tables 3 and 6).The lack of effect of dietary fat levels on theparameters of fatness in the saline-injected birdswas expected, since there is an agreement frommost studies that these parameters are mainlydependent on dietary E:P ratio (Bartov, 1979).However, the lack of effect of dietary fat levelon liver parameters in corticosterone-injectedchicks observed consistently (Tables 3 and 6)was rather unexpected. Yeh and Leveille (1969)and Leveille et al. (1975) reported that addedfat reduced hepatic lipogenesis in chicks whichwas at least partly due to the decrease indietary carbohydrates. Moreover, Shapira et al.(1978a) demonstrated that administering iso-energetic levels of glucose or oil in overfedchicks resulted in a similar increase in lipidcontent of carcass and adipose tissue, but liverweight and fat content were increased muchmore by the glucose supplement than by theoil. In the present study, chicks fed diets B andC in Experiments 2 and 4 consumed similarenergy levels. However, dietary oil supplied19.4% of the energy of diet B and 30.9% of theenergy of diet C. Nevertheless, liver parameterswere similar in corticosterone-injected birds fedthese diets (Table 3 and 6). The results, therefore, suggest that the ratio of carbohydrate tofat in the diets used in the present study didnot play an important role in fattening of liversof corticosterone-injected chicks.

Corticosterone injection consistendy (P<.01) increased liver weight and liver fatcontent (Tables 2, 3, 5, and 6) in agreementwith Baum and Meyer (1960) and Bartov et al.(1980). However, Nagra et al. (1963) andSimpkins and Smith (1976) did not observesuch an effect. The results obtained in the

present study showing that the effect of corticosterone on fattening of the liver is partlydependent on dietary composition, mainlyprotein level, may explain this disagreement. Itis also possible that the extent of corticosteroneeffect on liver fattening is dependent on thebreed of the chicks. Shapira et al. (1978b)reported on such differences between overfedlight and heavy breed chicks.

Corticosterone injection consistendy, and attimes significantly (P<.01), decreased absolute

and relative spleen weight (Table 4). Theseresults supported data reported by Siegel andBeane (1961) who obtained a similar effect byACTH injection. Spleen weights were alsoaffected by the diets (Table 4). Chicks fed dietB had smaller spleens in two out of the threeexperiments. Diet B contained the lowest fatlevel. Therefore, the possiblity that spleenweight is related to dietary fat level should beconsidered.

REFERENCES

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