1. Thermoregulation Responses of Broiler Chickens to Humidity
at Different Ambient Temperatures. II. Four Weeks of Age
H. Lin,*†,1 H. F. Zhang,† R. Du,† X. H. Gu,† Z. Y. Zhang,† J. Buyse,‡ and E. Decuypere‡
*Department of Animal Science, Shandong Agricultural University, Taian, Shandong 271018, PR China;
†Institute
of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100094, PR China; and ‡Lab of Physiology
and Immunology of Domestic Animal, Department of Animal Science, Kasteelpark Arenberg 30, 3001 Heverlee,
Belgium
ABSTRACT Two experiments were conducted to investigate
the effect of RH (35, 60, and 85%) on thermoregulation
of broiler chickens at high (35°C) and mild (30°C)
temperatures at the age of 4 wk. The effects of humidity
on rectal temperature (RT) and plumage temperature at
back (PBAT) and skin temperature at breast (SBRT) were
determined at 1, 4, 8, 16, and 24 h after exposure. The
RT, PBAT, and SBRT were all significantly increased by
high temperature (35°C). Humidity had a significant influence
on RT at 35°C but not at 30°C. The peripheral
temperatures (PBAT and SBRT) were significantly affected
by humidity but responded differently at high
(35°C) compared with mild temperature (30°C). In conclu-
(Key words: thermoregulation, broiler chicken, humidity, ambient temperature)
2005 Poultry Science 84:1173–1178
INTRODUCTION
The effect of humidity on the zootechnical performance
of broiler chickens seems to be dependent on
ambient temperature. Yahav et al. (1995) reported that
maximal growth rate and feed intake of broiler chickens
at 35°C were observed at 60 to 65% RH between the
ages of 4 and 8 wk. Humidity also has an effect on
growth performance of broiler chickens at slightly elevated
ambient temperature (28 and 30°C) (Yahav, 2000).
For broiler chickens, absolute growth rate increases with
age and reaches maximum between 4 and 5 wk of age
and decreases thereafter (Scheuermann et al., 2003). The
intensive genetic selection for fast growth rate means
that modern species of broiler chickens are very susceptible
to heat stress (Deeb and Cahaner, 2002). Hence,
it is of interest to know the effect of humidity on the
thermoregulation of broiler chickens during rapid absolute
growth.
In our previous study using broiler chickens of 1 wk
of age, humidity had an effect on the thermoregulation
o 2005 Poultry Science Association, Inc.
Received for publication December 2, 2004.
Accepted for publication May 5, 2005.
1To whom correspondence should be addressed: hailin@sdau.edu.cn.
1173
sion, high humidity above 60% impaired the heat transmission
from body core to the periphery at 35°C but
facilitated it at 30°C in4-wk-old broiler chickens. The effect
of humidity on nonevaporative heat loss was depended
on air temperature, as nonevaporative heat loss
was suppressed by high humidity (>60% RH) at high
temperature but enhanced at the mild temperature. The
effect of humidity on the relationship between peripheral
and core temperature depends on ambient temperature
as well as on the age of the broiler chicken. The disturbance
of thermal balance could not be determined only
by changes in RT or peripheral temperature at a single
time point but could be determined by mean body temperature
within a certain time frame.
at high, low, and even moderate temperatures (Lin et al.,
2005). The temperature requirement of broiler chickens
decreases (Lin et al., 2004b) and the susceptibility to heat
increases with age and body weight (Sandercock et al.,
2001; Yalcˆin et al., 2001). Moreover, the relative growth
rate of broiler chickens decreases with age (Scheuermann
et al., 2003). So we hypothesized that the effect
of humidity on thermoregulation at high temperature
would change with age of broiler chickens and that older
chickens would respond differently from young chickens,

2. as they have different growth characteristics and
heat susceptibility. On the other hand, in our pervious
study, it was shown that change in humi dity could trigger
the redistribution of heat within body of 1- wk-old
broiler chickens (Lin et al., 2005). Whether these pheno m e na
could be induce d in 4-wk-old broiler chickens
need s to be investigated further.
The objectives of the present study were to evaluate
the effect of humi dity on the thermoregulatory response
of 4-wk-old broiler chickens at high temp erature and to
investigate whether the thermoregulation response of
Abbreviation Key: NEHL = nonevaporative heat loss; PBAT = surface
temperature of plumage at back; SBRT = skin temperature at breast;
RT = rectal temperature; VP = vapor pressure.
1174 LIN ET AL.
broiler chickens to humidity was changed with age, as
presented elsewhere (Lin et al., 2005). In the present
study, 2 experiments were conducted to evaluate the
effects of humidity on the thermoregulation of 4-wk-old
broiler chickens at high (35°C) or mild (30°C) temperature.
The plumage temperature at back (PBAT) and the
skin temperature at breast (SBRT) were measured to
determine the surface temperature, whereas the rectal
temperature was used to estimate the core temperature.
MATERIALS AND METHODS
Bird and Diets
Arbor Acres broiler chicks were obtained from a commercial
hatchery at 1 d of age and were raised in battery
brooders located in an environmentally controlled room.
The temperature wasmaintained at 35°C during the first
3 d and then decreased gradually to 20°C (40% RH) by
28 d of age and maintained as such thereafter. The heat
exposure experiment was conducted in 4 environmental
chambers equipped with computerized temperature
(±0.5°C) and humidity controllers (RH ±5%) as described
by Lin et al. (1996a,b). The 4 environmental chambers
were identical in terms of size, constructing materials,
climatization equipment, cages, feeders, and drinkers.
During rearing or the heat exposure period, broiler
chickens had free access to water and feed. The lighting
schedule provided 24 h of light per day. The chicks were
fed a standard commercial starter diet (3,100 kcal of
ME/kg and 22.3% CP) from d 0 to 21 and a finisher diet
(3,100 kcal of ME/kg and 19.4% CP) from d 22 onward.
All diets were fed as mash and formulated according to
the recommendations of National Research Council
(1994).
Treatments
Trial 1. Forty broiler chickens of both sexes were selected
at 28 d of age. All chickens were assigned randomly
to 4 groups of 10 chickens by sex and body weight
to have equal numbers of males and females with similar
mean body weight (1,050 ± 39 g) in each group. After
24 h of acclimation in the climatic chambers (21°C, 60%
RH), the broilers were randomly exposed to 1 of the 4
thermal environments for 24 h, which were 21°C and
60% RH vapor pressure [(VP), 1,484 Pa], 35°C and 35%
RH (VP, 1,952 Pa), 35°C and 60% RH (VP, 3,346 Pa),
and 35°C and 85% RH (VP, 4,740 Pa). The designated
temperature and humidity values were reached within
30 min.
Trial 2.At 28 d of age, thirty broilers of both sexes were
divided into 3 groups of 10 broiler chickens according to
sex and body weight to have equal numbers of males
and females with similar mean body weights in each
group (1,057 ± 40 g). The experimental chickens were
2Qinghua University, Beijing, PR China.
exposed to 1 of the 3 environmental treatments for 24
h, which were 30°C and 35% RH (VP, 1,474 Pa), 30°C
and 60% RH (VP, 2,527 Pa), and 30°C and 85% RH (VP,
3,580 Pa), respectively. The designated temperature and
humidity values were obtained within 30 min.
Measurements

3. In both trials, the experim ental chicks were expose d
to different thermal treatments at 0800 h, and the rectal
temp erature (RT), PBAT, and SBRT of each chicken were
recorded at 1 h (0900 h), 4 h (1200 h), 8 h (1600 h), 16 h
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Thermoregulatory Responses of Chicks
(Gallus domesticus) to Low Ambient
Temperatures at an Early Age1
1. D. Shinder*,2,
2. M. Rusal*,
3. J. Tanny†,
4. S. Druyan‡ and
5. S. Yahav*
+ Author Affiliations
*
1. Institute of Animal Science, the Volcani Center, Bet Dagan 50250, Israel; †Institute of
Soil, Water and Environmental Sciences, Agricultural Research Organization, the
Volcani Center, Bet Dagan 50250, Israel; and ‡The Hebrew University of Jerusalem,
Faculty of Agricultural, Food and Environmental Quality Sciences, Rehovot 76100,
Israel
1. ↵2Corresponding author: dshinder@agri.huji.ac.il
Next Section
Abstract
The potential to induce improved thermotolerance in broiler chickens is of great importance.
Thermal conditioning is one of the management tools used to improve thermotolerance, enabling
broilers to cope with extreme environmental conditions. This study investigated the effects of
exposing chicks to low ambient temperature (Ta) on-chick body (Tb), surface (Ts) temperatures
and total sensible heat loss (SHL) by convection and radiation from the body and from 2 main
radiative organs, the face and the legs. At 3, 4, or at both 3 and 4 d of age, chicks were exposed
to 5°C for 1.5 h a day (to avoid mortality) or to 10 or 15°C for 3 h a day. In general, in all
treatments, the results during exposure to cold differed significantly from the control. A second
cold exposure (on d 4 after a first exposure on d 3) clearly enhanced the chicks’ ability to
maintain on-chick body surface temperatures during exposure to 15°C and to recover much
faster from cold exposure. A dramatic decline in average surface temperature was observed
during the first 15 min of chicks’ exposure to the various low ambient temperatures in all ages,
reaching the lowest values in the 5°C treated chicks. The face responded immediately to cold

5. exposure by significantly increasing its SHL to a level that then remained relatively steady
(15°C) or declined moderately with time (10 and 5°C). In the legs, however, a significant and
continuous decline in SHL was exhibited in all ages. The dynamics of SHL from the legs
differed from that from the face, suggesting that the legs are a major organ for vasomotor
responses, whereas the face is a more conservative vasoregulatory organ. It is concluded that
repetitive exposure to cold may enhance thermotolerance, and that this is partially related to the
vasomotor responses. This is the first report quantifying the differentiation between the legs as a
responsive vasomotor organ and the face as a conservative vasomotor one.
• body temperature
• chick
• cold exposure
• sensible heat loss
• thermotolerance
Previous SectionNext Section
INTRODUCTION
The potential to induce improved thermotolerance in broiler chickens is of great importance,
particularly in view of the effectiveness in the development of genetic selection for improved
meat production in broilers (Havenstein et al., 2003). That has made it more difficult for broilers
to cope with extreme environmental conditions (Yahav, 2000). Thermal conditioning is one of
the management tools that partially enable broilers to cope with extreme environmental
conditions. This technique takes advantage of the immaturity of the temperature-regulation
mechanism in chicks during their first week of life (Dunnington and Siegel, 1984; Modrey and
Nichelmann, 1992), a mechanism that involves sympathetic neural activity, integration of
thermal information in the hypothalamus (Rothwell, 1992), and buildup of the body-brain
temperature difference (Arad and Itsaki-Gluklish, 1991). Thus, induction of thermotolerance can
potentially be incorporated into developing thermoregulation mechanisms. For example, heat
conditioning in the first week of life has been shown to considerably improve the chick’s ability
to subsequently cope with exposure to acute heat stress by causing a significant decline in heat
production (Yahav and Hurwitz, 1996), coupled with increased sensible heat loss (SHL) via
radiation and convection (Yahav et al., 2005).
Cold conditioning applied to bantam chicks has also been shown to improve thermoregulatory
capacity in faster growth chicks (Aulie, 1977). Shinder et al. (2002) demonstrated that repeated
short periods of cold conditioning during the first week of life improves the ability of chicks to
cope with low ambient temperature (Ta). However, in the first week of life, when the body
surface-to-volume ratio is relatively high, how broiler chicks respond thermally to cold
conditioning is unknown, especially considering the effects of SHL.
The main driving force for SHL is the temperature difference between body surface temperature
(Ts) and Ta. One of the main impediments to quantifying SHL has been the inability to accurately
measure the animal’s Ts distribution and to differentiate between the contributions of different
surface regions to heat loss. However, recently, infrared thermometry has been used successfully

6. to measure Ts in mammals (Mohler and Heath, 1988; Klir et al., 1990; Klir and Heath, 1992;
Phillips and Heath, 1992) and in birds (Phillips and Sanborn, 1994; Yahav et al., 1998, 2004,
2005).
The present study was designed to elucidate the effects of exposing chicks at an early stage of
life to low Ta on their body temperature (Tb) and on total SHL via convection and radiation, to
quantify SHL from the body and from 2 main radiative organs, the face and the legs.
Previous Section
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