Performance of Naked Neck and Normal Broilers in Hot, Warm, and Temperate Climates

Abstract

Chickens suffer at high ambient temperatures because their feather coverage hinders internal heat dissipation. Naked neck broilers (Na/na) and their normally feathered sibs (na/na) were evaluated in three natural climates. Three experiments were conducted in Turkey, during the summer in the extremely hot region of Adana (Ad-Sm), and in the moderate region of Izmir during the spring (Iz-Sp) and summer (Iz-Sm), always following the same experimental protocol. Ambient temperatures averaged 19, 28, and 32 C in Iz-Sp, Iz-Sm, and Ad-Sm, respectively. About 300 birds per genotype were included in each experiment. Feather weight was lower by about 20% in Na/na broilers than in na/na ones, independent of climate, sex, and age (6 or 7 wk). The Na/na broilers exhibited higher breast weight in all cases, from 2.5 to 10.9% higher than their na/na counterparts. Body weight gain from 4 to 7 wk (BWG4-7) clearly reflected the differences in ambient temperature among climates. The effect of the Na/na genotype on BWG4-7 interacted with climate and sex. In the hottest climate (Ad-Sm), both male and female Na/na broilers exhibited a highly significant advantage over their na/na counterparts. In the more moderate climate (Iz-Sm), the Na/na genotype exhibited superior growth only among males, and the magnitude of this advantage was lower than in Ad-Sm. In the cool temperate climate (Iz-Sp), BWG4-7 and BW7 (BW at 7 wk) means were similar for both genotypes. In Iz-Sp, feed efficiency (FE) of the Na/na birds was lower by about 4%, but in the two summer climates (Iz-Sm and Ad-Sm), FE of the Na/na birds was about 9% higher than that of their na/na counterparts. Body temperature was lower in the Na/na broilers than in their na/na counterparts; in all cases, the difference increasing with ambient temperature. The results indicate that the reduction in feather coverage provided relative heat tolerance, and therefore, under hot climates the Na/na broiler were superior to their normally feathered counterparts. It is concluded that naked neck broilers should be preferred in hot climates.

Full text

930
Received for publication August 19, 1996.
Accepted for publication February 17, 1997.
1To whom correspondence should be addressed.
Performance of Naked Neck and Normal Broilers in Hot, Warm,
and Temperate Climates
S. YALC
¸IN,* A. TESTIK,†S. OZKAN,* P. SETTAR,* F. C
¸ELEN,†and A. CAHANER‡,1
*The Aegean University, Faculty of Agriculture, Izmir 35100, Turkey, †University of C
¸ukurova, Faculty of Agriculture,
Adana 01330, Turkey, and ‡The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot 76100, Israel
ABSTRACT Chickens suffer at high ambient tempera-
tures because their feather coverage hinders internal
heat dissipation. Naked neck broilers (Na/na) and their
normally feathered sibs (na/na) were evaluated in three
natural climates. Three experiments were conducted in
Turkey, during the summer in the extremely hot region
of Adana (Ad-Sm), and in the moderate region of Izmir
during the spring (Iz-Sp) and summer (Iz-Sm), always
following the same experimental protocol. Ambient
temperatures averaged 19, 28, and 32 C in Iz-Sp, Iz-Sm,
and Ad-Sm, respectively. About 300 birds per genotype
were included in each experiment. Feather weight was
lower by about 20% in Na/na broilers than in na/na ones,
independent of climate, sex, and age (6 or 7 wk). The Na/
na broilers exhibited higher breast weight in all cases,
from 2.5 to 10.9% higher than their na/na counterparts.
Body weight gain from 4 to 7 wk (BWG4-7) clearly
reflected the differences in ambient temperature among
climates. The effect of the Na/na genotype on BWG4-7
interacted with climate and sex. In the hottest climate
(Ad-Sm), both male and female Na/na broilers exhibited
a highly significant advantage over their na/na counter-
parts. In the more moderate climate (Iz-Sm), the Na/na
genotype exhibited superior growth only among males,
and the magnitude of this advantage was lower than in
Ad-Sm. In the cool temperate climate (Iz-Sp), BWG4-7
and BW7 (BW at 7 wk) means were similar for both
genotypes. In Iz-Sp, feed efficiency (FE) of the Na/na
birds was lower by about 4%, but in the two summer
climates (Iz-Sm and Ad-Sm), FE of the Na/na birds was
about 9% higher than that of their na/na counterparts.
Body temperature was lower in the Na/na broilers than
in their na/na counterparts; in all cases, the difference
increasing with ambient temperature. The results indi-
cate that the reduction in feather coverage provided
relative heat tolerance, and therefore, under hot climates
the Na/na broilers were superior to their normally
feathered counterparts. It is concluded that naked neck
broilers should be preferred in hot climates.
(Key words: naked neck, ambient temperature, hot climate, body temperature, growth)
1997 Poultry Science 76:930–937
INTRODUCTION
The strong negative effect of high ambient tempera-
tures on poultry production, especially broiler growth
and meat yield, has been intensively studied and
reviewed (Adams and Rogler, 1968; Chwalibog and
Eggum, 1989; Howlider and Rose, 1989; Osman et al.,
1989; Cahaner and Leenstra, 1992; Leenstra and Ca-
haner, 1992). Moreover, broiler lines with a higher
potential for growth rate have been found to be more
sensitive to constant high ambient temperatures (Ca-
haner and Leenstra, 1992; Leenstra and Cahaner, 1992;
Cahaner et al., 1995). Natural heat stress, induced by the
summer season in Izmir (Turkey), reduced 7-wk BW and
4- to 7-wk weight gain (BWG) of commercial broilers by
about 23 and 33%, respectively, compared to their
counterparts reared under the same management during
the temperate fall season (Yalc
¸in et al., 1996). It appears
that the broiler stocks bred for high growth rate and
meat yield in optimal environments, are not able to fully
express their genetic potential when reared in hot
climates, unless their selection programs include breed-
ing for heat tolerance. Whereas studies on alleviation of
heat stress have focused on costly management adjust-
ments, genetic improvement of heat tolerance may
provide a low-cost solution, particularly attractive to
developing countries with hot climates.
Chickens suffer under high ambient temperature
because their feather coverage hinders internal heat
dissipation, leading to elevated body temperature (BT)
(Yahav et al., 1996). To avoid a lethal increase in BT,
chickens minimize endogenous heat production by
reducing feed intake, resulting in decreased growth and
meat yield in broilers (Yahav et al., 1996). Reduced
feather coverage should improve and enhance heat
dissipation and consequently alleviate the effects of heat
on chickens reared in hot climates. In addition, reduced
feathering saves on feather proteins, which may be used
for meat tissues (Cahaner et al., 1987; Ajang et al., 1993).

NAKED NECK AND NORMAL BROILERS IN HOT, WARM, AND TEMPERATE CLIMATES 931
2ANAK Breeders Ltd., Natanya, Israel.
The naked neck (Na) gene reduces feather coverage in
chickens by about 20 and 40% in the heterozygous (Na/
na) and homozygous (Na/Na) states, respectively. The
effects of this gene have been reviewed comprehen-
sively, especially with regard to egg-type chickens
(Merat 1986, 1990). The potential usefulness of naked
neck broilers at high ambient temperature was studied
in the early 1980s (Hanzl and Somes, 1983), but its
importance became more apparent in the 1990s (Lou et
al., 1992; Cahaner et al., 1993, 1994; Eberhart and
Washburn 1993a,b). These studies demonstrated the
advantage of naked neck broilers over their normally
feathered counterparts, when reared at constant high
ambient temperatures (above 30 C). The increase in BT
in high ambient temperatures was higher in normally
feathered than in naked neck broilers, due to the
reduced feathering of the latter. Consequently, the
naked neck broilers exhibited higher feed intake, growth
rate, and meat yield than their normally feathered
counterparts (Deeb and Cahaner, 1994).
However, all of these studies were conducted in
artificially controlled climates, mostly with constant
temperature. Natural hot climates are characterized by a
diurnal cycle of ambient temperature, which varies
among geographical locations and seasons. Broilers,
whose appetite and growth are depressed by the higher
mid-day temperatures, may exhibit compensatory feed
intake and weight gain during the cooler night hours. In
this case, the advantage exhibited by naked neck broilers
in cyclic hot climates could be much lower than that
observed under a constant ambient temperature that
equals the cycle’s maximum or even average tempera-
ture. To simulate natural climates, variations in relative
humidity and air velocity need to be integrated with
various diurnal cycles of ambient temperature, substan-
tially increasing the number of possible combinations
and the complexity of such a simulation. A more
practical approach consists of conducting experiments
under the relevant natural climates. A preliminary
experiment with Na/na and na/na broilers was conducted
during the spring and summer in Israel (Cahaner et al.,
1992). However, ambient summer temperatures during
the research period were not high enough due to
effective cooling systems, which are rarely found in
broiler houses in most hot regions. The purpose of the
present study was to evaluate the performance of naked
neck broilers (Na/na) relative to their normally feathered
sibs (na/na), in natural temperate and hot climates, in
different seasons and locations.
MATERIALS AND METHODS
Climate in Poultry Houses
Three experiments were conducted in Turkey, two in
the moderate region of Izmir and one in the extremely hot
region of Adana. The experiments were performed in the
spring (April–May) and early summer (June–July) in
Izmir (Iz-Sp and Iz-Sm, respectively) and in June–July in
Adana(Ad-Sm).The poultry houses at both sites had only
windowswithcurtainsinthewalls,andminimaleffectsof
outside winds. Ambient temperature within the broiler
houses was not controlled, but it was continuously
monitored during the experiments, from the 2nd wk
onward. Mean temperature after brooding (3 to 7 wk of
age)was18.7, 27.8, and 31.5 C in Iz-Sp, Iz-Sm,and Ad-Sm,
respectively. Temperature fluctuations were summarized
as weekly averages of six daily measurements, taken at
4-h intervals (Figure 1).
Genetic Stock and Management
Naked neck (Na/na) chicks and their normally
feathered (na/na) sibs were sired by Na/na males from an
experimental meat-type stock obtained from P. Horst
(Humboldt University, Berlin, Germany) in 1989, which
has since then been continuously backcrossed to an Israeli
commercial sire-line (Cahaner et al., 1993). For both
seasons, Na/na males were mated to the same normally
feathered (na/na) ANAK hens.2Day-old chicks were
shipped by air to the experimental sites in Turkey. In each
experiment, an imported commercial broiler strain was
also included, to verify that the genetic growth potential
of the experimental stock was at least as good as that of
standard commercial broilers.
Chicks were sexed at the hatchery, wing-banded, and
randomly assigned to 12 electrically heated floor pens
with3 pens per genotype and sex. Pensize was 5 and 4 m2
in Iz and Ad, respectively. Aiming at densities of 10 to 12
birds per square meter, 60, 50, and 40 chicks were housed
in each pen in Iz-Sp, Iz-Sm, and Ad-Sm, respectively.
Starter (22% protein and 3,000 ME kcal/kg) and grower
(21% protein and 3,100 kcal ME/kg) corn-based standard
mashdiets were given from 0 to 3wk and 4 to 7 wk of age,
respectively. Birds were provided ad libitum access to feed
and water. Incandescent lighting supplemented natural
daylight to provide 23 h light and 1 h dark.
Measurements
Chicks were weighed individually upon arrival at the
experimental sites (BW0), and at 4 (BW4) and 7 wk (BW7)
of age. Body weight gain from 4 to 7 wk (BWG4-7) was
calculated for each chick. Total feed consumption (FC)
was measured for each pen, and corrected for mortality.
Feed efficiency (FE) was calculated as the ratio between
total BW gain to total FC of all birds in each pen.
During the afternoon of Day 41, about 12, 18, and 6
birdswererandomlyselectedfromeachgenotypeand sex
in Iz-Sp, Iz-Sm, and Ad-Sm, respectively, equally
representing all pens. The same sampling procedure was
repeated on Day 48. Rectal temperature, as a measure of
body temperature (BT), was recorded for each of these
birds when sampled (BT1), using a thermocouple ther-
mometer inserted approximately 3 cm into the colon.
These birds were then deprived of feed overnight for 10 h
and their rectal temperature was measured again in the

YALC
¸IN ET AL.
932
FIGURE 1. Broiler house ambient temperatures in three different climates in Turkey: Spring in Izmir (Iz-Sp; ÿ); Summer in Izmir (Iz-Sm; ⁄);
Summer in Adana (Ad-Sm; π). Daily fluctuations are summarized and presented as weekly averages of six daily measurements, taken daily at
4-h intervals.
morning (BT2). Whereas BT1 was measured at the highest
daily ambient temperatures, BT2 was measured when
daily ambient temperatures were lower by about 4 to 6 C
(Figure 1), after 10 h of feed withdrawal.
All the birds sampled for BT measurements were killed
bycervicaldislocation,weighed,scaldedfor2minat60 C,
plucked mechanically, and reweighed to calculate feather
weight by subtraction. The birds were manually eviscer-
ated. Neck, head, and shanks were removed, and ready-
to-cook carcasses were individually weighed. Breasts,
including meat, bone and skin, were weighed for each
bird. Feather mass, carcass yield, and breast weight were
expressed as percentages of BW after 10 h without feed
(%F, %C and %B, respectively).
Statistical Analysis
Several general linear models were fitted to the data by
JMP (SAS Institute, 1995). A three-way factorial model
with a covariate was used to analyze individual BW and
BWG data. The model included three climates, two
genotypes (Na/na and na/na), and two sexes as main
effects, and all their interactions. Although Na genotypes
did not differ in BW0, it was included as a covariate in the
analysis of BW4, to correct for variation in initial weight
due to age of dams (2 mo older in summer than spring)
and differences in conditions during transportation. For
BWG4-7andBW7,themodelincludedBW4asa covariate.
The data for BW and BWG were also analyzed separately
within each sex, using similar models but excluding the
effects of sex and interactions with sex. The same models
were used to analyze pen data on FC and FE.
Data on BT, %F, %C, and %B were analyzed according
to a four-way model that included climate, genotype, sex,
age, and their second- and third-degree interactions. Data
were also analyzed for each age separately using a similar
model, without age or interactions with age.

NAKED NECK AND NORMAL BROILERS IN HOT, WARM, AND TEMPERATE CLIMATES 933
TABLE 1. Least squares means of BW at 4 wk (BW4) and 7 wk (BW7), and BW gain from 4 to 7 wk (BWG4–7) for male (M)
and female (F) heterozygous naked neck (Na/na) and normally feathered (na/na) broilers reared in spring (Sp)
and summer (Sm) climates at two locations in Turkey (Iz = Izmir, Ad = Adana)
Na/na na/na 100 ×(Na/na-na/na):(na/na)
Sex Climate n BW4 BWG4–7 BW7 n BW4 BWG4–7 BW7 BW4 BWG4–7 BW7
(g) (%)
M Iz-Sp 163 961b1,314a2,264a163 1,011a1,329a2,279a–4.9*** –1.1 –0.7
Iz-Sm 146 878c1,133b2,082b114 860b1,070b2,019b+2.1 +5.9*** +3.1***
Ad-Sm 87 1,001a1,125b2,074b100 994a1,033c1,983b+0.7 +8.9*** +4.6***
F Iz-Sp 186 904a1,055a1,916a200 912a1,033a1,894a–0.9 +2.1* +1.2*
Iz-Sm 124 779b944b1,804b141 749b960b1,821b+3.9** –1.7 –0.9
Ad-Sm 97 908a919c1,780b86 900a799c1,660c+0.9 +15.0*** +7.2***
M + F Iz-Sp 349 932b1,185a2,088a363 961a1,181a2,085a–3.5*** +0.3 +0.1
Iz-Sm 270 828c1,038b1,941b255 804b1,014b1,918b+3.0*** +2.4* +1.2
Ad-Sm 184 954a1,022b1,925b186 947a916c1,820c+1.2 +11.6*** +5.8***
a–cClimate means within sex and genotype with no common superscript differ significantly (P< 0.05).
1BW0 as a covariate in the ANOVA of BW4, and BW4 as a covariate in the ANOVA of BWG4–7 and BW7.
*Differences between genotypes were significant at P< 0.05.
**Differences between genotypes were significant at P< 0.01.
***Differences between genotypes were significant at P< 0.001.
Source of variation Males + females Males Females
(P(F))
Genotype (G) NS <0.001 <0.001 NS <0.001 <0.001 0.094 <0.001 <0.001
Climate (C) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001
G×C <0.001 0.001 0.001 <0.001 0.001 0.001 0.013 <0.001 <0.001
Sex (S) <0.001 <0.001 <0.001
C×S 0.051 <0.001 <0.001
G×S 0.052 NS NS
G×C×S NS 0.001 0.001
BW0/BW41<0.001 0.016 <0.001 <0.001 NS <0.001 <0.001 0.024 <0.001
RESULTS
Ambient Temperatures
The seasonal and geographical differences between the
three experimental sites substantially affected ambient
space temperatures in the broiler houses. Figure 1
presents the daily fluctuations of ambient temperature,
averaged weekly from Weeks 2 to 7. Spot-heating was
provided for the chicks in each pen for the first 2 wk, and
hence during this period the chicks’ actual ambient
temperature could be either equal to or higher than the
space temperature in the broiler house. Mean BW4 of the
Iz-Sm chicks was substantially lower than their Iz-Sp and
Ad-Smcounterparts, reflecting insufficient spot heating in
the Iz-Sm experiment, independent of climate. This
undesired effect was statistically corrected for by includ-
ingBW4 as acovariatein the analysesofBWG4-7 and BW7
(Table 1).
Body Weight and Weight Gain
The normally feathered na/na broilers exhibited a 4%
higherBW7thanthe standard commercial broilers in each
of the three climates (data not shown). Table 1 presents
mean BW4, BWG4-7, and BW7 of the two genotypes by
climate(i.e.,experimentalsiteandseason)and sex, as well
as the level of significance of these main effects and their
interactions. A significant three-way interaction was
found for BWG4-7 and BW7; therefore, the effects of
climate (C) and genotype (G) were tested separately for
eachsex (S), and their interaction (G×C) was significantin
all cases (Table 1). Relative to the normally feathered (na/
na) broilers, BW4 was lower in the naked neck (Na/na)
males and females in the spring (Iz-Sp) and higher in the
twosummerclimates(Iz-Sm and Ad-Sm). The BWG4–7 of
the naked neck birds was higher than that of their
counterparts in Ad-Sm (males and females), in Iz-Sm
(males)and Iz-Sp (females). These interactions in BWG4–7
mayreflect some compensatory growth, which should not
affect BW7. For the latter trait, the naked neck males had a
3.1and4.6%advantageinIz-SmandAd-Sm, respectively.
The naked neck females were either slightly heavier or
similar to their fully feathered counterparts in both Iz
climates,butexhibiteda7.2%advantageinthe hot Ad-Sm
climate. In all cases, the relative advantage of the naked
neck broilers was about twice as large for BWG4–7 than
for BW7 (Table 1).
Feed Consumption and Feed Efficiency
Feed consumption was significantly affected by
climate—it decreased as ambient temperatures
increased—but not by genotype. The G ×C×S interaction

YALC
¸IN ET AL.
934
TABLE 2. Least squares means of feed consumption1(FC) and feed efficiency (FE = WG/FC) from hatch to 7 wk of age for
male (M) and female (F) heterozygous naked neck (Na/na) and normally feathered (na/na) broilers reared in
spring (Sp) and summer (Sm) climates at two locations in Turkey (Iz = Izmir, Ad = Adana)
a–cClimate means within sex and genotype with no common superscript differ significantly (P< 0.05).
1FC and FE were calculated for each pen (three pens per genotype per sex).
*Differences between genotypes were significant at P< 0.05.
**Differences between genotypes were significant at P< 0.01.
***Differences between genotypes were significant at P< 0.001.
Na/na na/na 100 ×(Na/na –na/na):(na/na)
Sex Climate FC FE FC FE FC FE
(g) (g:g) (g) (g:g) (%)
M Iz-Sp 5,380a0.418c5,149a0.440a+4.5 –5.0*
Iz-Sm 4,689b0.443b4,881ab 0.408b–4.0 +8.5**
Ad-Sm 4,449b0.468a4,535b0.436a–1.9 +7.3*
F Iz-Sp 4,930a0.391c4,721a0.404 +4.4 –3.2
Iz-Sm 4,235b0.425b4,460ab 0.399b–5.0 +6.5*
Ad-Sm 3,963b0.453a4,131b0.402 –4.1 +12.7**
M + F Iz-Sp 5,155a0.404c4,935a0.422a+4.4 –4.3*
Iz-Sm 4,462b0.434b4,670b0.403b–4.5 +7.7**
Ad-Sm 4,206c0.461a4,333c0.419a–2.9 +10.0***
Source of variation Males + females Males Females
(P(F))
Genotype (G) NS 0.003 NS 0.035 NS 0.047
Climate (C) <0.001 0.002 <0.001 0.009 <0.001 0.073
G×C NS <0.001 <0.052 0.004 NS 0.032
Sex (S) <0.001 <0.001
C×SNSNS
G×SNSNS
G×C×S NS 0.023
was significant for FE, and, therefore, the effects of G and
C were tested separately for each sex (Table 2). The G ×C
interaction affected FE in both sexes. In males, the naked
neck significantly reduced FE in Iz-Sp and increased it in
Iz-Sm and Ad-Sm. In females, the effect of the naked neck
on FE changed gradually with ambient temperature, from
–3.2% in Iz-Sp, to +6.5% in Iz-Sm and +12.7% in Ad-Sm
(Table2). Averaged oversexes,FE of the naked neck birds,
as compared to their fully feathered counterparts, was
4.3% lower in the cool climate (Iz-Sp), and 7.7 and 10%
higher in the hot climates (Iz-Sm and Ad-Sm, respective-
ly).
Body Temperature
Sex and interactions with sex had no significant effect
on BT and therefore means of males + females are
presented in Table 3, by G, C and age (A). The G ×C×A
interaction was highly significant (P= 0.002) for BT2, and
almost significant (P= 0.090) for BT1; hence, G ×C
interaction was tested using a separate ANOVA for each
age.
At 6 wk of age, BT under the relatively higher heat
effect (BT1) increased with ambient temperature (i.e., Iz-
Sp < Iz-Sm < Ad-Sm) in both genotypes (Table 3). The
genotype effect also increased with ambient temperature:
relative to the fully feathered birds, BT1 of the naked neck
birds was similar in Iz-Sp, and lower by 0.35 C in Iz-Sm
and by 0.43 C in Ad-Sm (Table 3). At 7 wk of age, BT1 of
the naked neck broilers was also lower than that of their
counterparts in all three climates; the difference was twice
as large in Ad-Sm (0.83 C) and not significant in Iz-Sm,
leading to a significant G ×C interaction at that age.
Body temperature under the relatively lower heat load
(BT2) was affected by G ×C interaction, especially at 7 wk
of age (Table 3). Birds reared at higher ambient tempera-
tures exhibited higher BT2, but climate effects were larger
in the fully feathered broilers than in the naked neck ones.
The increase in age, from 6 to 7 wk, increased BT1 in both
genotypes,apparently due to the increase in BW and daily
FC. In contrast, BT after feed withdrawal (BT2) increased
from 6 to 7 wk only in the normally feathered broilers, but
not in the naked neck broilers.
Relative Weight of Feathers,
Carcass, and Breast
The relative (to BW) weights of feathers, carcass, and
breast were more affected by interactions with age than
sex; therefore, means of males + females are presented by
genotype, climate, and age (Table 4). The effects of
genotype, climate, age, and their interactions were tested
by a separate three-way ANOVA for each age. The
interactions were insignificant in most cases, but the main
effect of genotype with climate or sex was highly
significant in all cases.

NAKED NECK AND NORMAL BROILERS IN HOT, WARM, AND TEMPERATE CLIMATES 935
TABLE 3. Least squares means (males + females) of on-feed (BT1) and off-feed (BT2) body temperatures of 6- and 7-wk-old
heterozygous naked neck (Na/na) and normally feathered (na/na) broilers, reared in spring (Sp) and
summer (Sm) climates at two locations in Turkey (Iz = Izmir, Ad = Adana)
a–cClimate means within age with no common superscript differ significantly (P< 0.05).
*Differences between genotypes were significant at P< 0.05.
**Differences between genotypes were significant at P< 0.01.
***Differences between genotypes were significant at P< 0.001.
Na/na broilers na/na broilers Na/na –na/na
Age Climate n BT1 BT2 n BT1 BT2 BT1 BT2
(C) (C) (C)
6 wk Iz-Sp 25 41.00c40.99 24 41.06c40.83c–0.06 +0.16
Iz-Sm 37 41.84b41.07 24 42.19b41.22b–0.35*** –0.15
Ad-Sm 12 42.57a41.20 12 43.00a41.45a–0.43*** –0.25*
x 74 41.81 41.09 60 42.09 41.17 –0.26*** –0.08
7 wk Iz-Sp 23 42.02b40.78 24 42.35b40.88b–0.33** –0.10
Iz-Sm 37 41.78c41.07 23 41.93c41.06b–0.15 +0.01
Ad-Sm 10 42.79a41.25 12 43.62a42.29a–0.83*** –1.04***
x 70 42.20 41.03 59 42.64 41.41 –0.44*** –0.38***
Source of variation 6 + 7 wk of age 6 wk of age 7 wk of age
(P(F))
Genotype <0.001 <0.001 0.003 NS <0.001 <0.001
Climate (C) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001
Sex (S) NS NS NS NS NS NS
G×C 0.026 <0.001 NS 0.068 0.011 <0.001
C×S NSNS NSNSNSNS
G×S NSNS NSNSNSNS
G×C×S NSNS NSNSNSNS
Age (A) <0.001 0.079
G×A NS 0.004
C×A <0.001 <0.001
S×ANSNS
C×S×ANSNS
G×C×A 0.090 0.002
G×S×ANSNS
The age effect was significant for %F, which increased
from6 to 7wkof age. However, at bothages%Fwaslower
in the naked neck birds than in their normally feathered
counterparts within each climate, with the relative
reduction ranging from 18.5 to 23.1% (Table 4).
Relative to their normally feathered counterparts, the
naked neck broilers exhibited higher %C and %B in the
three climates at both ages. However, the genotype effect
was more pronounced and significant for %B: averaged
overclimates, it washigherin the Na/nabroilersby6.5 and
3.7% at 6 and 7 wk of age, respectively (Table 4). Only in
Ad-Sm at 7 wk was the %B advantage of theNa/na birds
not significant. However, absolute breast weight (%B
multiplied by BW7) in Ad-Sm was significantly higher in
the Na/na vs na/na birds, by 8.5% (383 vs 353 g).
DISCUSSION
The purpose of the present study was to compare
naked neck broilers with their normally feathered
counterparts in temperate, warm, and hot natural
climates. To this end, the experiments were conducted in
Izmir during the spring (Iz-Sp) and summer (Iz-Sm),
and in Adana during the summer (Ad-Sm). Due to
seasonal and geographical differences, the three experi-
ments were characterized by temperate, warm, and hot
climates (Iz-Sp, Iz-Sm, and Ad-Sm, respectively), which
resulted in substantially different temperatures in the
broiler houses (Figure 1). In the Iz-Sp experiment,
broiler house ambient temperatures were lower than the
standard broiler recommendation (Yahav et al., 1996)
most of the time, quite typical for a cool season in
temperate regions. Ambient temperatures in Iz-Sm were
typical of a warm summer climate, whereas those in the
hot-climate Ad-Sm experiment were higher by about 5
and 2 C during the day and at night, respectively.
Averaged over Weeks 4 to 7, ambient temperature
exceeded 30 C for 16 h daily in Ad-Sm and for only 5 h
in Iz-Sm.
Each of the three experiments was therefore con-
ducted under clearly different climates. The same
experimental protocol was applied in all three cases, so
that climatic conditions would have the most substantial
effect on the differences in broiler performance between
experiments. However, this could not be positively
verified, and therefore emphasis was placed on the
genotype effect and its consistency across experiments,
i.e., interactions between Na genotypes and climates (G
×C).

YALC
¸IN ET AL.
936
TABLE 4. Least squares means (males + females) of feathers (%F), carcass (%C), and breast meat + bone + skin (%B), as
percentage of BW at slaughter, of 6- and 7-wk-old heterozygous naked neck (Na/na) and normally feathered (na/na)
broilers, reared in spring (Sp) and summer (Sm) climates at two locations in Turkey (Iz = Izmir, Ad = Adana)
a–cClimate means within age with no common superscript differ significantly (P< 0.05).
*Differences between genotypes were significant at P< 0.05.
**Differences between genotypes were significant at P< 0.01.
***Differences between genotypes were significant at P< 0.001.
Na/na broilers na/na broilers 100 ×(Na/na –na/na):(na/na)
Age Climate n %F %C %B n %F %C %B %F %C %B
(%)
6 wk Iz-Sp 25 4.14a73.8a19.4b24 5.26a72.0c17.5b–21.7*** +2.5*** +10.9***
Iz-Sm 37 4.10a74.9b18.8b24 5.03a74.4b17.7b–18.5*** +0.7 +6.2**
Ad-Sm 12 3.15b76.2b20.6a12 3.89b75.9a19.9a–19.0*** +0.4 +3.5*
x 74 3.80 74.9 19.6 60 4.74 74.1 18.4 –19.8*** +1.1** +6.5***
7 wk Iz-Sp 23 4.95a72.9b18.3b24 6.11a72.4b17.4b–19.0*** +0.7 +5.2**
Iz-Sm 37 4.35a75.4a20.5a22 5.68a73.1b19.8a–23.4*** +3.1*** +3.5*
Ad-Sm 10 3.79b76.3a19.9a12 4.93b74.4a19.4a–23.1*** +2.6* +2.5
x 70 4.36 74.9 19.6 58 5.57 73.3 18.9 –21.7*** +2.2*** +3.7*
Source of variation 6 + 7 wk of age 6 wk of age 7 wk of age
P(F)
Genotype
(G) <0.001 <0.001 <0.001 <0.001 0.009 <0.001 <0.001 <0.001 0.014
Climate (C) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001
Sex (S) <0.001 NS <0.001 <0.001 NS 0.009 <0.001 NS <0.001
G×C NS NS NS NS 0.039 NS NS NS NS
G×S 0.019 NS NS NS NS 0.061 0.002 NS NS
C×S NSNSNS NSNSNS NS NSNS
G×C×S NS NS NS NS NS 0.008 NS NS NS
Age (A) <0.001 NS NS
G×A NS NS 0.053
C×A <0.001 NS <0.001
S×ANSNSNS
G×C×A NS 0.045 NS
G×S×A 0.026 NS NS
C×S×ANSNSNS
As in all previous studies with naked neck chickens
(Merat, 1986, 1990; Cahaner et al., 1993), the Na/na
genotype reduced %F by about 20%, independent of
climate, sex or age (6 or 7 wk). The naked neck broilers
exhibited higher %B in all cases, ranging from 2.5 to
10.9% more than their normally feathered counterparts.
A similar advantage has been reported previously
(Cahaner et al., 1993) for breast meat. In the present
study, breast weight included breast skin, and carcass
included the entire skin. Because skin weight is reduced
in naked neck broilers (Cahaner et al., 1993), the actual
advantage in meat yield of the naked neck birds was
probably larger than that obtained for %B and %C in the
present study.
The effect of the naked neck genotype on BWG4–7
and BW7 clearly interacted with climate and sex. In the
hottest climate (Ad-Sm), both male and female naked
neck broilers exhibited a highly significant advantage
over their normally feathered counterparts, in both
BWG4–7 and BW7. In the more moderate, warm climate
(Iz-Sm), the Na/na genotype exhibited superior growth
only among males, and the magnitude of its advantage
was lower than in Ad-Sm. In the cool temperate climate
(Iz-Sp), BWG4–7 and BW7 means were similar for both
genotypes.
The higher FC of naked neck birds under the cool
conditions of Iz-Sp could be expected, due to their
higher rate of heat dissipation, and resulted in about 4%
lower FE than the na/na birds under these cool
conditions. However, in both summer climates, the
naked neck broilers exhibited superior FE in both sexes.
In several temperature-controlled studies in cages
(Hanzl and Somes, 1983; Merat, 1986; Cahaner et al.,
1993), heterozygous naked neck birds exhibited a
nonsignificant advantage in FE at ambient temperatures
of 31 to 38 C. The significantly higher FE of the Na/na
birds in the present study could be attributed to the
higher growth potential of the broilers used, the rearing
system, or the natural climatic high temperature.
Body temperature was measured at the highest daily
ambient temperatures (BT1), and again (BT2) when
ambient temperatures were lower by about 4 to 6 C
(Figure 1) and internal heat production was reduced due
to 10 h feed withdrawal (Teeter et al., 1987). Thus,
extreme conditions of heat load were obtained by
combinations of high levels (BT1) or low levels (BT2) of

NAKED NECK AND NORMAL BROILERS IN HOT, WARM, AND TEMPERATE CLIMATES 937
ambient temperatures and internal metabolism. Climates
affected BT1 in both genotypes, BT2 in the normally
feathered broilers only. Apparently, the reduced feather
coverage of the naked neck birds fully overcame the
lower heat load (BT2), but not the higher one (BT1).
Nevertheless, the increase in BT1 due to climate was
more pronounced in the fully feathered broilers than in
their naked neck counterparts, especially at 7 wk of age,
when BW and FC were certainly higher than at 6 wk of
age. Mean BT1 of the naked neck broilers was lower
than that of their normally feathered counterparts in all
cases, clearly indicating that the 20% reduction in
feather coverage allowed for a higher rate of heat
dissipation, which is probably the inherent mechanism
responsible for the relative heat tolerance of naked neck
broilers.
In summary, although ambient temperatures were
not controlled in the present study, the information
presented on their level and daily fluctuations may
facilitate a cautious extrapolation of the results to an
array of similar natural climates. In contrast to some
previous studies with naked neck broilers, this study’s
findings are relevant to modern industrial broiler
production, because advanced commercial stocks were
included as reference in each experiment, and they were
outperformed by both Na/na and na/na genotypes in all
cases. These data were not presented because different
reference stocks were used at each location. It can be
concluded, therefore, that naked neck broilers should be
preferred for industrial production in hot climates. The
magnitude of their relative advantage in BW, FE, and
meat yield increased as ambient temperatures inside the
broiler house rose. Although as expected, the naked
neck genotype had no advantage in Iz-Sp, this cool
temperate climate had no negative effect on the growth
of naked neck birds.
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