Adaptive behaviour in chickens in relation to thermoregulation

Arch.Geflügelk., 70 (5). S. 199–207, 2006, ISSN 0003-9098. © Verlag Eugen Ulmer, Stuttgart
Adaptive behaviour in chickens in relation to thermoregulation
Adaptives Verhalten bei Hühnern im Zusammenhang mit der Thermoregualation
Martina Gerken, R. Afnan and J. Dörl
Paper presented at the Symposium ‘Recent Advances in the Assessment of Behavioural Demands in Poultry and Rabbits’, October 27, 2006 in Stuttgart-Hohenheim, Germany, in honour of the 60th birthday of Prof. Dr. Werner Bessei
Introduction
Behaviour offers the animal an important means of adapting to the physical and social environment. Based on genetically predisposed patterns, this complex instrument allows rapid reactions towards environmental and internal
stimuli with high response plasticity. Among adaptive behavioural and physiological reactions of fowl, thermoregulation is well investigated for its importance in poultry production (reviewed by LIN et al., 2006).
In the context of thermoregulation, plumage plays an
important role due to its isolating capacities. Feathers are
complicated integumentary structures (NICKEL et al., 1992;
BUSCHING, 2005). There are two basic types of feathers:
contour feathers (pennae conturae) that form continuous,
coherent vanes and soft underlying down feathers
(plumae). Feathers are not evenly distributed on the body
(NICKEL et al., 1992). As in most bird species, chicken feathers are grouped in areas (pterylae) separated by nearly
bare spaces without contour feathers (apteria), but which
are frequently covered with downs. In naked neck (Na)
genotypes the number of pterylae is reduced thus resulting
in an increased area of apteria. A net of fine muscles (Mm.
pennales) allows to lift or turn the feathers within limits
(NICKEL et al., 1992).
In birds, heat is dissipated through different mechanisms (YAHAV et al., 2005). In this context, featherless areas
appear to act as “thermal windows” (FOWLER, 1994) where
heat dissipation is most efficient. There are several major
genes that change the insulation efficiency of the feather
coverage among which the naked neck (Na) gene and the
frizzle (F) gene are most studied (reviewed by HORST,
1998; SHARIFI, 2004; LIN et al., 2006). Several studies
showed that a reduced feather cover can be of advantage
in thermoregulation at high temperatures in broilers
(YALÇIN et al., 1997; YAHAV et al., 1998), laying hens (HORST
and MATHUR, 1994; VON HAAREN-KISO et al., 1994) and
broiler breeders (SHARIFI, 2004). The intact plumage is frequently perceived as quite homogeneous body cover. However, the chicken disposes of several possibilities for short
term modification of its plumage. Plumage related adaptive behaviour in the context of thermoregulation include:
lifting of the wings (thus more air is moved between body
and wing), ruffling of feathers, preening (usually accompanied by ruffling of feathers), and dustbathing.
Institute of Animal Breeding and Genetics, University of Goettingen, Germany
Arch.Geflügelk. 5/2006
Several models have been developed to describe heat
transfer in animals (GATES, 1980). YAHAV et al. (2005) calculated convective and radiative heat transfer from the
fowl by describing each part of the surface represented by
a corresponding geometrical shape. Objects that are close
to physiological temperatures emit most of the radiation in
the middle infrared (SCHMIDT-NIELSEN, 1997). Infrared
technology offers a possibility for non-invasive measurement of surface body temperature and thus allows conclusions on heat loss by radiation. Thermal imaging has been
used in veterinary clinics in mammals (STEPHAN and GÖRLACH, 1971) and physiological studies in mammals (DE LAMO, 1990; GERKEN, 1996; GERKEN and BAROW, 1998;
SCHWALM et al., 2006) and birds (YAHAV et al., 1998, 2004;
KHALIL, 2004).
The present studies were designed to investigate into the
role of behaviour in behavioural thermoregulative adaptation to heat. In the first study details of the chicken plumage were studied by infrared thermography to investigate
possible thermal windows and their relation to behaviour
(experiment 1). In experiment 2 plumage of the birds was
manipulated and the behaviour under short term heat
stress was studied.
Experiment 1: Role of “thermal windows” in relation to
adaptive behaviour
A commercial infrared thermography system (Thermovision© 900, AGEMA, 1992) was used to measure the infrared radiation on the boundary layer of the bird. The
non-invasive technique allows the very detailed evaluation
of surface temperatures with high resolution of 0.1°C, accuracy of ±0.5°C and temperature measurement range
from –30° to 1.500°C. A scanner operating in the 8-12 µm
band of the infrared spectrum was used as infrared
detector. The signals are used by a processor to generate
single infrared frames built up like a TV picture with an
image resolution of 230 elements per line, 136 lines, and
272 pixels per line. The measurement formula is (AGEMA,
1992):
Im
Where
I(T)
Im
τ
ε
Tatm
Tamb
= I(Tobj) * τ * ε + τ * (1 - ε) * I(Tamb) + (1 -τ) * I(Tatm)
=
=
=
=
=
=
Thermal value
Thermal value for the measured total radiation
Efficient atmospheric transmission
Emissivity of the object
Atmospheric temperature
Temperature of surroundings
For each measurement situation the following object parameters have to be given by the operator: emissivity of the
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Gerken et al.: Adaptive Behaviour in chickens
Figure 1. Thermal image of a sitting broiler, lateral view. The
image demonstrates the variation in surface temperature
across the body. Warm (lighter shades according to the right
temperature scale) parts are the head, the cloacal area and in
particular the foot (light part under the wing).
Infrarotthermographie-Bild eines sitzenden Broilers, laterale Ansicht. Das Bild veranschaulicht die Variation in der Oberflächentemperatur des Körpers. Warme (helle Schattierung gemäß der
rechten Temperaturskala) Partien sind der Kopf, der Kloakenbereich und insbesondere der Fuß (heller Teil unterhalb des Flügels).
Figure 2a.Thermal image of the head of a broiler, lateral front
view. The beak has a lower temperature than the surrounding
feathers. Average surface temperatures were (means±SD) calculated for the wattle (32.20±1.88°C; area 1), the comb
(29.95±1.04°C; line 3) and the areas next to the base of the
comb (33.54±1.47°C; line 2 and 34.65±1.24°C line 4).
Infrarotthermographie-Bild des Kopfes eines Broilers, Halbprofil.
Der Schnabel weist eine niedrigere Temperatur als die umgebenden Federn auf. Die durchschnittlichen Oberflächentemperaturen
(Mittelwerte±SD) waren 32.20±1.88°C (Kehllappen, Fläche 1),
29.95±1.04°C (Kamm, Linie 3) und für die Kammbasis
33.54±1.47°C (Linie 2) bzw. 34.65±1.24°C (Linie 4).
Figure 2b.Thermal image of the head of a broiler, lateral view.
Average surface temperatures were (means±SD) calculated for
the eye (33.57±0.45°C; right area) and the nostril
(24.14±0.52°C, left area).
Infrarotthermographie-Bild des Kopfes eines Broilers, seitliche
Ansicht. Die durchschnittlichen Oberflächentemperaturen (Mittelwerte±SD) betrugen 33.57±0.45°C für das Auge (rechte Fläche) und für die Nasenöffnung 24.14±0.52°C (linke Fläche).
Figure 3. Thermal image of a sitting broiler, right wing. The
wings are quite heterogeneous with regard to the size and distribution of feathers. The surface of the long flight feathers is
close to the environmental temperature (means±SD; 18.93±
0.38°C, left area), similar to that of the upper smaller contour
feathers (19.55±0.53°C, middle), whereas the small areas of the
scarcely feathered Apteria humerale and cubitale emit higher
temperatures (34.47±1.1°C; right area).
Infrarotthermographie-Bild eines sitzenden Broilers, rechter Flügel. Die Flügel sind recht heterogen bezüglich der Verteilung und
Größe der Federn. Die Oberfläche der langen Schwungfedern ist
nahe der Umgebungstemperatur (Mittelwerte±SD; 18.93±
0.38°C, linke Fläche) vergleichbar mit der der kleineren Deckfedern (19.55±0.53°C, Mitte), während die kleinen Bereiche der
kaum befiederten Federraine (Apteria humerale und cubitale) höhere Temperaturen abgeben (34.47±1.1°C, rechte Fläche).
Figure 4. Thermal image of a broiler, caudal view. In a sitting
bird the left wing is lifted by hand (note dark shade on the left)
to demonstrate the Apterium trunci laterale (means±SD
37.44±1.66°C; right area) otherwise covered by the wing. Left
area: contour feathers of the wing (25.84±1.29°C).
Infrarotthermographie-Bild eines Broilers, Ansicht von kaudal.
Bei einem sitzenden Broiler wird der linke Flügel mit der Hand angehoben (siehe dunkler Schatten links), um die Federraine (Apterium trunci laterale) zu demonstrieren, die sonst durch die Flügel
bedeckt werden (Mittelwerte±SD 37.44±1.66°C; rechts). Links:
Konturfeder des Flügels (25.84±1.29°C).
object, object distance, relative humidity, atmospheric
temperature and reflected ambient temperature. The average emissivities (ε ) of chicken feathers, skin and wood
shavings were determined to be 0.976, 0.950, and 0.925,
respectively. The information from selected frames was analysed by the integrated software ERICA which allows to
calculate means and standard deviations across the measurement points of specific areas or geometric figures. The
black and white scale on the right side (Figure 1 to 7) indicates the surface temperatures ranging from low (dark
shades) to high temperatures (light shades).
Infrared thermography measurements were made on
the same day during 2 h on a fully feathered female standard broiler (Ross) of 35 days of age at the Institute of Animal Breeding and Genetics, University of Goettingen.
Arch.Geflügelk. 5/2006
Gerken et al.: Adaptive Behaviour in chickens
Figure 5. Thermal image of a sitting broiler, caudal view. Surface temperatures (means±SD) were quite different for the cloacal area (36.10±1.32°C; area at the bottom left), the middle of
the back (26.81±2.16°C; area at the top) or the tail feathers
(17.94±0.99°C; area at the bottom right).
Infrarotthermographie-Bild eines Broilers, Ansicht von kaudal.
Die Oberflächentemperaturen (Mittelwerte±SD) sind recht unterschiedlich für den Kloakenbereich (36.10±1.32°C; Fläche unten
links), die Rückenmitte (26.81±2.16°C; Fläche oben) oder die
Schwanzfedern (17.94±0.99°C; Fläche unten rechts).
Figure 6. Thermal image of a sitting broiler, from above. During
preening the contour feathers of the back are ruffled. Single
feather temperatures (means±SD) were: 21.42±0.81°C (left top)
and 20.43±1.07°C (left bottom). The tail feathers are extended
and moved downwards thus allowing the bird to reach the
uropygial gland (31.15±0.93°C; area on the right).
Infrarotthermographie-Bild eines sitzenden Broilers, Ansicht von
oben. Während des Putzens sind die Deckfedern des Rückens gesträubt. Die Oberflächentemperaturen (Mittelwerte±SD) einzelner Federn betrugen: 21.42±0.81°C (oben links) und
20.43±1.07°C (unten links). Die Schwanzfedern sind ausgebreitet
und nach unten gebogen, so dass das Huhn die Bürzeldrüse erreichen kann (31.15±0.93°C; Fläche rechts).
Room temperature ranged between 18.5 and 20.5°C, relative humidity between 51.5 and 54.0%. Rectal temperature of the bird ranged between 41.5 and 42.10°C. The bird
was placed on a tray with wood shavings and allowed to
move freely. The distance between scanner and animal was
between 42 cm and 1.34 m.
Results and discussion
The thermal imaging allows to analyse the plumage structure in very detail (Figure 1). The head has highly differentiated structures (Figure 2a, b): the warmest parts are the
unfeathered areas of the skin such as comb, eyes, wattles
and the area around the eyes, where only very short bristles are found. The nostrils are cooler due to evaporative
heat loss through respiration. Due to the close vicinity of
nostrils and brain, panting might also have some direct
cooling function for the brain. The protection of the brain
Arch.Geflügelk. 5/2006
201
Figure 7. Thermal image of a standing broiler, lateral view. The
sitting bird was lifted and kept standing (note hand on the
right side). The surface temperature (means±SD) of the left leg
was about 3-4°C below rectal body temperature (38.53±0.19°C;
line). The litter (wood shavings) under the bird was warm
(31.04±1.35°C; left circle).
Infrarotthermographie-Bild eines stehenden Broilers, seitliche
Ansicht. Das sitzende Huhn wurde angehoben und festgehalten
(beachte Hand auf der rechten Seite). Die Oberflächentemperatur
(Mittelwerte±SD) des linken Beins war ca. 3 bis 4°C niedriger als
die Rektaltemperatur (38.53±0.19°C; Linie). Die Einstreu (Hobelspäne) unter dem Tier war warm (31.04±1.35°C; linker Kreis).
during heat stress is most important because the high protein mass is particularly sensitive to degeneration caused
by high temperatures. In a number of ungulates, a vascular
network (rete mirabile) located at the base of the skull was
found that functions as a biological heat exchanger (TAYLOR, 1972). Similar mechanisms are not described for
chickens, but the comb might have an analogue function
for heat dissipation and keeping the brain at a cooler temperature (Figure 2a).
Thermal windows
In model computations (YAHAV et al., 2005) for determining sensible heat loss in poultry, the area of the feathered
body is usually treated as homogenous surface. The
present detailed pictures reveal large differences in feather
cover (Figure 3) and allow to identify thermal windows
that can be used for heat dissipation. In addition to the unfeathered parts such as head and legs (Figure 1, 2a, b),
there exist thermal windows within the plumage cover that
can be exposed or closed with flexibility by the bird
through adaptive behaviour. The highest temperature was
found at the Apteria otherwise covered by the wing
(Figure 4) and the ventral apteria that are equipped with
down feathers (e.g., cloacal area) (Figure 5).
Several behavioural patterns allow the chicken to modify these thermal windows with high flexibility.
Preening. During preening, the back feathers are ruffled
(Figure 6). Thermal imaging allows to distinguish the
erected contour feathers from the underlying downs and
skin. Thus, through ruffling warm air trapped between the
feathers can be emitted and body heat can be dissipated
from the skin. Of particular interest is to observe the opening of the plumage around the uropygial gland shortly
before the bird takes some material from it to distribute it
into the plumage.
Exposure of apteria. In a hot environment, chickens frequently separate their wings from the body. Under the
wings the plumage is very scattered due to several ventral
apteria of the wing and the apteria laterale of the body
(Figure 4). On the ventral side of the wings, numerous
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Gerken et al.: Adaptive Behaviour in chickens
blood vessels run very close to the surface of the skin (NICKEL et al., 1992). Thus, the lifting of the wings helps to expose the thermal windows under the wings and the body
sides by forming two channels through which airflow can
enhance cooling (YAHAV et al., 2005).
Accordingly, the extended contact with the litter during sitting might also serve as mechanism for heat dissipation in
broilers and should be considered in model computations
for heat loss in broilers.
Dustbathing. Several possible functions have been attributed to dustbathing, including feather maintenance (HEALY
and THOMAS, 1973), regulation of lipid content of the plumage (VAN LIERE et al., 1991) and removal of ectoparasites
(SIMMONS, 1964). Dustbathing is organised in fixed action
patterns, one bout consisting of several components (VESTERGAARD, 1982; GERKEN and PETERSEN, 1987, 1992a,b). Dust
toss or bilateral vertical wing shaking is the most prominent dustbathing component. During dust tossing the birds
squats and looses the substrate beneath it by foot scratching. The extended primary wing feathers are vigorously
moved to raise the dust bathing material through the ruffled plumage into the air above the bird. Most of the material thrown up passes between the wings which are separated from the body. It is suggested that body heat from the
vessels and apteria under the wings and along the body
sides is transferred to the dustbathing material via conduction. Accordingly, dustbathing could also enhance thermoregulation. Several observations support this hypothesis: Ruffling during dustbathing opens the plumage
(Figure 6) and heat is dissipated. Dustbathing follows a diurnal distribution with a peak in the middle of the light day
usually coinciding with higher temperatures (VESTERGAARD,
1982). Laying hens on free range preferably scratch holes
in earth under shaded areas. This might have a function as
protection from predators but could also be explained by
the humid and cooler earth thus enhancing heat dissipation.
Experiment 2: Response to changes in feather cover
Conduction via sitting. Figure 7 reveals how conduction is
involved in heat dissipation. During sitting, body heat can
be transferred through the feather coverage to the litter
material. This is in contrast to Yunis and Cahaner, (1999)
who assumed that because of the good insulation provided
by normal plumage, chickens dissipate heat by conductivity mainly through the unfeathered body surfaces and by
respiratory evaporation. In Figure 7 the sitting bird was
lifted and moved away. The same circled litter area under
the bird was repeatedly measured to follow the development of the litter temperature and resulted in the following
values (means±SD): 30.72±1.67°C (1.55 min after lifting),
22.60±0.90°C (after 2.34 min), 19.99±0.50°C (after
4.12 min), and 19.59±0.41°C (after 5.45 min), respectively, which was close to the ambient temperature.
In broilers, the emphasis on breeding for high amount of
breast muscle has caused the broiler’s centre of gravity to
move forward and breasts became broader (European
Commission 2000). Due to changed body proportions, feet
are placed more to the side of the body during sitting
(Figure 1) and the breast comes into closer contact with
the litter surface.
The extended sitting periods observed in conventional
fast growing broilers where broilers may spend more than
75% of the time sitting over the whole growing period
(JAENECKE, 1997; European Commission 2000) could also
be interpreted in the light of thermoregulation. On the ventral side, there are quite extended apteria partly covered by
down while the contour feathers of the vent are rather
small. In addition, vent plumage in boilers is frequently deteriorated depending on litter quality. It is documented,
that the intensive metabolic processes involved in rapid
growth cause problems regarding heat dissipation in fast
growing broilers (reviewed by GERKEN and BESSEI, 2006).
This experiment was part of a larger study on broiler
breeders involving 120 females (JA57) and 12 males (I66)
from commercial broiler parent stocks (Hubbard ISA,
France). Characteristics of the female broiler line strain
were: medium heavy bodyweight, red feathers, yellow
shanks, beak and skin.
The birds were reared in France until the age of 19 weeks
and then transferred to the Institute of Animal Breeding
and Genetics, University of Goettingen. Birds were kept in
4 pens (9.60 m2/pen), with two pens having access to an
outdoor run (12 m2/pen). Each pen housed 30 females and
3 males with a stocking density of 3.44 birds/ m2. From 24
weeks of age birds received 16 h of light and 8 h of darkness. The lighting schedule included 15 minutes dawn before light onset or offset. Birds were fed a diet with 18.9%
CP and 12.97 MJ of ME/ kg. The restricted feeding was applied according to sex and productive performance following the breeder’s recommendation. Water was provided ad
libitum.
The two pens with outdoor runs were maintained at
constant ambient temperatures of 20oC inside the house
(control), whereas 2 other pens without run were continuously maintained at 28oC. Temperatures inside the house
varied between 20-22oC or 27-29oC, respectively.
At 39 weeks of age, 24 females from each housing temperature (total N = 48) were randomly chosen and individually exposed for 10 minutes to short term heat (28 or
32oC). Each hen was tested under both challenge temperatures, with the temperature per test (28 or 32oC) being at
random for the individual bird. Birds were placed into a
heat challenge compartment measuring 80 x 50 x 40 cm
(height x width x depth). On the top of the wooden box, 4
lamps of each 250 Watt were installed. At the front side, a
nylon net and a thin transparent plastic foil were fixed to
maintain the temperature and to prevent the bird from escaping. Air could enter via small holes at the bottom of the
box.
Rectal temperatures were measured before (T0) and immediately after the heat exposure (T1) by a digital thermometer to the nearest 0.1°C. During the heat challenge
test the experimenter stood in front of the apparatus at a
distance of 2 m and directly measured the latency until
panting using a stopwatch. For birds that did not start
panting within 10 minutes, latency until panting was set to
10 minutes. In addition, the frequencies of birds panting
were calculated.
After the short term heat challenge test in wk 39, the
neck plumage was modified in half of the birds (12 hens in
each housing treatment, total N=24). The necks of the experimental birds were shorn by a shearing machine for
small pets between the first and last cervical vertebra. The
length of the remaining feathershafts was between 3 and
5 mm. Birds were then kept as before. After one week (wk
40), all birds were re-tested using the same heat challenge
procedure.
The data were analysed in separate runs for each week
by ANOVA with housing, challenge temperature, and neck
plumage condition as fixed and the animal as random effects; the respective interactions were also included. The
effects of housing, neck plumage condition, and their interactions were tested against the between-bird error term.
Arch.Geflügelk. 5/2006
Gerken et al.: Adaptive Behaviour in chickens
203
Table 1. Results of analyses of variance for latency until panting and rectal temperatures before and after neck plumage modification
Ergebnisse der Varianzanalysen für die Latenzzeit bis zum Hecheln und die Rektaltemperaturen vor und nach der Modifikation des
Halsgefieders
Week 39 (before shearing)
Week 40 (after shearing)
Trait
Source
Latency
until panting
T0
T1
Latency
until panting
T0
T1
0.000
0.000
NS
NS
NS
NS
NS
NS
0.000
0.000
NS
0.001
0.036
NS
NS
NS
0.000
0.000
NS
0.018
NS
NS
NS
0.040
P
Housing temperature (HT)
Challenge temperature (CT)
Neck plumage condition (NP)
Animal (HT NP)
HT * CT
HT * NP
CT * NP
HT * CT * NP
0.016
0.047
NS
NS
NS
NS
NS
NS
0.000
NS
NS
NS
NS
NS
NS
NS
0.000
NS
NS
NS
NS
NS
NS
NS
NS= Not significant; T0= rectal temperature before heat challenge; T1= rectal temperature after 10 minutes of heat challenge;
NP= Neck plumage condition after week 39: sheared (N=24) or intact (N=24)
Table 2. Effect of housing (HT) and challenge temperatures (CT) on latency until panting and rectal temperatures before and after
neck plumage modification (LS-Means±SD)
Einfluss von Stall- und Hitzestress-Temperaturen auf die Latenzzeit bis zum Hecheln und die Rektaltemperaturen vor und nach der Modifikation des Halsgefieders (LS-Mittelwerte± SD)
Treatment
Latency until panting
(minute)
Trait
T0
(°C)
T1
(°C)
Week 39 (before shearing)
Housing temperature
20°C
28°C
7.72 ± 2.50 a
6.22 ± 2.92 b
41.55 ± 0.18 b
41.85 ± 0.25 a
41.87 ± 0.17 b
42.05 ± 0.23 a
Challenge temperature
28°C
32°C
7.46 ± 2.82 a
6.48 ± 2.73 b
41.74 ± 0.27
41.66 ± 0.26
41.98 ± 0.22
41.94 ± 0.23
Housing temperature
20°C
28°C
9.22 ± 1.85 a
7.40 ± 2.71 b
41.38 ± 0.17 b
41.64 ± 0.30 a
41.64 ± 0.18 b
41.85 ± 0.33 a
Challenge temperature
28°C
32°C
9.17 ± 1.97 a
7.44 ± 2.66 b
41.45 ± 0.22 b
41.57 ± 0.31 a
41.67 ± 0.22 b
41.82 ± 0.32 a
Neck plumage condition
Sheared
Intact
8.70 ± 2.12
7.92 ± 2.77
41.53 ± 0.31
41.48 ± 0.24
41.77 ± 0.34
41.72 ± 0.22
Week 40 (after shearing)
a, b Means with different superscripts within the same treatment and column differ significantly (<0.05)
T0= rectal temperature before heat challenge; T1= rectal temperature after 10 minutes of heat challenge
All other effects were tested against the between-measurement error term using general least square models (SAS INSTITUTE, 1999). For the analysis of the paired proportions of
birds panting a modified binomial test was applied according to SIEGEL (1987).
Arch.Geflügelk. 5/2006
Results and discussion
Long-term keeping of birds at 28°C resulted in an increased rectal temperature and a reduced latency until
panting in the heat challenge test (Table 1). When exposed
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Gerken et al.: Adaptive Behaviour in chickens
Table 3. Effect of housing (HT) and challenge temperatures (CT) on latency until panting and rectal temperatures in sheared and
intact birds at wk 40 (LS-Means±SD)
Einfluss von Stall- und Hitzestress-Temperaturen auf die Latenzzeit bis zum Hecheln und die Rektaltemperaturen bei geschorenen und
intakten Hennen in Woche 40 (LS-Mittelwerte±SD)
Treatment
HT
(°C)
CT
(°C)
Latency until panting
(min)
Trait
T0
(°C)
Neck plumage sheared
20
20
28
28
28
32
28
32
10.00 ± 0.00
8.84 ± 1.75
9.38 ± 1.47
6.56 ± 2.56
41.40 ± 0.13
41.42 ± 0.22
41.46 ± 0.18
41.85 ± 0.40
41.62 ± 0.18 c
41.69 ± 0.23 bc
41.66 ± 0.17 bc
42.12 ± 0.44 a
Neck plumage intact
20
20
28
28
28
32
28
32
9.41 ± 2.01
8.60 ± 2.51
7.88 ± 2.76
5.76 ± 2.61
41.31 ± 0.17
41.38 ± 0.15
41.62 ± 0.28
41.62 ± 0.15
41.57 ± 0.13 c
41.68 ± 0.17 bc
41.81 ± 0.31 b
41.81 ± 0.16 b
T1
(°C)
a, b, c Means with different superscripts within the same column differ significantly (P<0.05)
T0= rectal temperature before heat challenge; T1= rectal temperature after 10 minutes of heat challenge
Table 4. Frequencies (n) of birds panting by neck plumage condition, housing and challenge temperatures in wk 39 (before shearing) and wk 40 (after shearing)
Einfluss von Halsgefiedermodifikation, Stall- und Hitzestresstemperaturen auf die Häufigkeit (n) des Hechelns in Woche 39 (vor Schur)
und 40 (nach Schur)
Neck Plumage condition
HT (°C)
Week 391
CT (°C)
N
Week 40
%
n
%
Sheared
20
20
28
28
28
32
28
32
4
10
10a
10
33.3
83.3
83.3 a
83.3
0
5
2b
10
0
41.7
16.7 b
83.3
Intact
20
20
28
28
28
32
28
32
4
9
6
10
33.3
75.0
50.0
83.3
1
4
5
11
8.3
33.3
41.7
91.7
1 Birds were subjected to shearing after the tests
a, b Individual reactions between re-tests significantly different
(P<0.05), binomial test for paired proportions
to 32°C, the same birds started panting earlier in both
weeks and had higher rectal temperatures in wk 40 (T0 ,
T1). The effect of the challenge temperature on the body
temperature (T0) prior to onset of the test was not expected (wk 40). For the tests, birds were taken from their home
pens and this short term transport might have already
caused increases in body temperature due to stress.
In wk 39, birds did not differ with regard to their later
neck plumage treatment. In addition, 36 wk body weights
of intact and shorn birds were not different (LS-means ±
SD 2180.8± 219.8 vs. 2191.4±169.1 g). The modification of
neck plumage (wk 40) had no significant (P=0.111) effect
on latency until panting or rectal temperature prior to the
challenge test (Table 1, Table 2). However, there was a
tendency for birds kept at high temperatures to have retarded latencies until panting when re-tested at 28°C in wk
40. The complex interaction found for T1 in wk 40 is attributable to the high increment in rectal temperature in
sheared birds housed at high temperatures and tested at
32°C (Table 1, Table 3).
Matched pair comparisons, however, revealed a significant (P<0.05) influence of neck plumage shearing, as less
birds kept at heat conditions panted after shearing when
exposed to 28°C (Table 4).
Latency until panting had a close relation with initial
body temperature and birds with high T0 started panting
earlier. Thus, this behavioural trait appears to be a valid
and easy to measure indicator for complex thermoregulative physiological processes otherwise difficult to evaluate. The measurement of rectal temperatures as conducted
in the present experiment was probably too short for adequate evaluation. The challenge duration had been set to
10 min according to previous experiments with broilers,
where most of the birds started panting within 10 minutes
(unpublished data). However, this time limit appears too
short in the broiler breeder females tested and a longer
Arch.Geflügelk. 5/2006
Gerken et al.: Adaptive Behaviour in chickens
testing period might allow a more detailed differentiation
between treatments.
The present results indicate only minor beneficial effects
of reduced feather coverage of the neck. In broilers (YALÇIN
et al. 1997; DEEB and CAHANER, 1999; YUNIS and CAHANER,
1999) and broiler breeders (SHARIFI, 2004), the introduction of the naked neck gene was suitable to alleviate heat
stress. The shearing of the neck was expected to have similar effects. YAHAV (2000) described that the thermoregulatory acclimation process in the domestic fowl requires
from 4 to 7 d to be completed. However, in the present
adult broiler breeders with high egg production adaptive
changes might take longer. On the daily routine inspections, birds housed at high temperatures frequently
showed panting and might have adopted this behaviour as
feedforward control strategy (BUDGELL, 1970) under both
heat challenge test situations.
Conclusions
Different from the hair coat in mammals, birds can use
their feather cover in a more flexible way. Due to the connecting net of fine muscles, rather controlled movements
of groups of feathers can be exerted. Behavioural patterns
play an important role as they allow to modify morphologically preformed thermal windows (experiment 1).
The observed reactions (experiment 2) to external modifications of the plumage underlines that behaviour allows
the fine adjustment of genetically predisposed physiological regulation mechanisms. In the present study, juvenile
broiler breeders close to maturity were exposed to continuous heat conditions from 19 wks of age. NICHELMANN and
TZSCHENTKE, (2002) demonstrated that a lifelong adaptation may be induced during the prenatal or early postnatal
ontogeny within critical developmental phases that influence gene expression. Early heat conditioning has been
shown to induce the heat tolerance of broiler chickens at
later growth stages (YAHAV and HURWITZ, 1996; YAHAV and
MCMURTRY, 2001). Chickens under early heat conditioning
had lower body temperatures when exposed to high temperature (BASILIO et al., 2003), suggesting changes in the
metabolic status. It is open to question to which extend
early thermal conditioning might also apply to broiler
breeders. Apart from the early ontogeny, the age around
maturity could be another critical developmental phase for
adaptive processes in chickens. However, the present results do not support this hypothesis for thermoregulation.
Summary
Based on genetically predisposed patterns, behaviour allows rapid reactions towards environmental and internal
stimuli with high response plasticity. Among adaptive behavioural and physiological reactions of fowl, thermoregulation is well investigated for its importance in poultry production. In the context of thermoregulation, plumage
plays an important role due to its isolating capacities. Several studies showed that a modified feather cover (e.g.,
through the major genes Na or F) can increase heat tolerance in chickens.
The present studies were designed to investigate into behavioural thermoregulative adaptation to heat. In the first
study details of the chicken plumage were studied by infrared thermography to investigate possible thermal windows
suitable for heat dissipation and their relation to behaviour. In addition to the unfeathered parts such as head and
legs, there exist thermal windows within the plumage covArch.Geflügelk. 5/2006
205
er, in particular through the nearly bare areas (apteria) under the wings and the body sides. Adaptive behavioural
patterns involving preening, feather ruffling, dustbathing,
and conductive heat loss via sitting are used by the bird to
expose or close these thermal windows with flexibility.
In experiment 2, plumage of the birds was manipulated
and the behaviour under short term heat stress was studied. Twenty-four female broiler breeders were kept in floor
pens from 19 wk of age at constant temperatures of 20°C
(control) or 28°C (heat). At 39 wks of age they were subjected to short term heat challenges at 28° and 32°C for
10 min. The latency until panting and rectal temperatures
before and after the test was measured. In half of the birds
(N=24) the neck plumage was sheared and birds were
re-tested at 40 wks. Hens housed at high temperatures had
reduced heat tolerance as shown by more rapid onset of
panting and higher body temperatures. Number of birds
panting was significantly reduced in sheared birds, underlining the adaptive role of behaviour. But in all, shearing of
the neck revealed only minor beneficial effects during
short term heat exposure. However, the comparison of
sheared hens with Naked neck genotypes is only partly valid, because the Na gene acts as major gene affecting not
only the plumage distribution but also other characteristics.
Key words
Broiler, Broiler breeder, adaptive behaviour, thermoregulation, infrared thermography
Zusammenfassung
Adaptives Verhalten bei Hühnern im Zusammenhang mit der Thermoregualation
Mit dem Verhalten verfügt das Tier über ein sehr flexibles
Instrument zur raschen Adaptation an externe und interne
Reize. Unter den Anpassungsreaktionen des Geflügels ist
die Thermoregulation aufgrund ihrer Bedeutung für die
Geflügelproduktion besonders gut untersucht. Im Rahmen
der Thermoregulation spielt das Gefieder eine besondere
Rolle aufgrund seiner isolierenden Eigenschaften. Verschiedene Studien haben gezeigt, dass eine modifizierte
Befiederung (z.B. durch die Majorgene Na oder F) die Hitzetoleranz bei Hühnern erhöht.
In den vorliegenden Versuchen sollte die Rolle des Verhaltens im Zusammenhang mit der Thermoregulation untersucht werden. In der ersten Studie wurden an einem
Broiler das Gefieder mittels Infrarotthermographie untersucht, um mögliche ”thermale Fenster” innerhalb des Gefieders zu identifizieren, die für die Wärmeabgabe geeignet sind. Zusätzlich zu den unbefiederten Körperteilen wie
Kopf und Beine, existieren thermale Fenster innerhalb des
Gefieders, insbesondere in Form von nahezu federlosen
Federrainen (Apteria) unterhalb der Flügel und an den
Körperseiten. Verhaltensmerkmale wie Putzen, Gefiedersträuben, Staubbaden und konduktive Wärmeabgabe beim
Sitzen werden von den Hühnern eingesetzt, um im Rahmen der Thermoregulation diese Fenster flexibel zu öffnen
oder zu schließen.
In Experiment 2 wurde das Gefieder von Broilereltern
verändert und ihr Verhalten bei kurzzeitigem Hitzestress
untersucht. Vierundzwanzig Broilermütter wurden ab
der 19. Lebenswoche bei konstant 20°C (Kontrolle) oder
28°C (Hitze) in Bodenhaltung gehalten. Im Alter von 39
Wochen wurden die Hennen einer kurzfristigen Hitzebelastung bei 28° und 32°C für 10 Minuten ausgesetzt. Die
206
Gerken et al.: Adaptive Behaviour in chickens
Latenzzeit bis zum Hecheln sowie die Rektaltemperaturen vor und nach dem Test wurden gemessen. Bei der
Hälfte der Tiere (N=24) wurde das Nackengefieder geschoren und die Hennen wurden im Alter von 40 Wochen
erneut getestet. Broilermütter, die bei Hitze gehalten
wurden, hechelten schneller und hatten höhere Körpertemperaturen in den Belastungstests, was auf eine reduzierte Hitzetoleranz hinweist. Die Häufigkeit der Tiere,
die hechelten, war bei den geschorenen Hennen signifikant niedriger, was die Bedeutung dieses Verhaltens für
die Adaptation unterstreicht. Insgesamt jedoch hatte das
Scheren des Nackengefieders nur einen geringen positiven Effekt während einer kurzfristigen Hitzebelastung.
Allerdings ist ein Vergleich mit Nackthals-Genotypen nur
eingeschränkt möglich, da das Na-Gen als Majorgen nicht
nur die Gefiederausprägung sondern auch andere Merkmale beeinflusst.
Stichworte
Broiler, Broilereltern, adaptives Verhalten, Thermoregulation, Infrarotthermographie
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Correspondence: Prof. Dr. Martina Gerken; Institute of Animal Breeding and
Genetics; Albrecht-Thaer-Weg 3; 37075 Göttingen, Germany; e-mail:
[email protected]