Awt. 3. Exp. Agric. Anim. Hub. 7987, 21: 189-1 95
189
Responses of laying hens to gradual and abrupt
increases in ambient temperature and humidity
Madalene Daniel and D. Balnave
Summary-White Leghorn x Australorp laying hens were gradually or abruptly exposed to natural
summer climate regimens in which high relative humidities and temperatures in excess of 35°C were
simulated. Food intake, feeding patterns, egg production, egg weight, egg quality and time of oviposition
were recorded.
Mortality was high when hens were subjected to abrupt increases in ambient temperature but no
deaths from heat stress were observed when hens were able to acclimatize to high temperatures.
Food intakes were reduced significantly at high temperatures but less marked reductions were
observed in egg production. Therefore, food was used more efficiently in heat-stressed hens. Food
conversion ratios of heat-stressed and control hens were, respectively, 2.99 and 3.07 (Experiment 1),
2.82 and 3.04 (Experiment 2), and 2.09 and 2.45 (Experiment 3) g food/g egg.
Heat-stressed hens consumed less food during the hot afternoon period. Extending the daily
photoperiod from 16 to 20 h had no beneficial effect on total food intake or egg production. Egg quality,
including egg shell thickness, did not deteriorate at high temperatures and this appeared to be related to
a high atmospheric concentration of carbon dioxide produced by excessive panting.
A m b i e n t temperatures above ~ Y C
are normally considered to have a detrimental effect on the performance of
laying hens (Payne 1968; Smith and Oliver 1972). In particular, reductions in food intake, egg production, egg
weight and egg quality occur (payne 1968; El Jack and
Blum 1978). However, although Ernrnans (1974) concluded that the benefits of fluctuating temperatures were
uncertain, some reports have indicated that the detrimental effects of high ambient temperatures may be offset by
using fluctuating temperature regimens which allow the
hens a period of time each day at less extreme temperatures. Thus egg production and egg weight may be
maintained at satisfactory levels even when hens are
exposed to extremely high temperatures during part of the
day ( ~ u t c h i n s o nand Sykes 1953; Ben-Adam 1962). Also,
the reduction in egg-shell thickness in hens kept at high
temperatures appears to be more severe under constant as
opposed to fluctuating temperature regimens (petersen et
al. 1961; Andrade et aL 1977). However, some workers
have concluded that constant high temperatures are less
detrimental to shell strength (~1-Boushy1966; Miller and
Sunde 1975).
The Authors-Miss M. Daniel and Associate Professor D.
Balnave, Department of Animal Hwbandry, University of
Sydney, Werombi Road Camden, New South W a h , 2570.
Although many investigations into the effects of elevated temperatures have been made during recent years,
most of this work has been carried out overseas, and few
trials have been conducted in Australia with commercial
White Leghorn x Australorp layers. The identification of
genetic X environmental temperature interactions ( ~ u t t
1938; Berman and Snapir 1965; Emmans 1974) indicates
the importance of obtaining specific data relating to
Australian conditions and stock.
Two distinct types of high temperature stress occur in
Australia. First, there is the situation where ambient temperatures gradually rise and remain high for an extended
period: under these conditions birds can acclimatize to the
environmental changes (Balnave 1974). However, sudden
heatwaves may rapidly elevate ambient temperatures for
short periods: under these conditions birds do not have a
chance to acclimatize. In addition, the effects of high temperatures are exacerbated by high relative humidity
( ~ e a t e et
s aL 1941; Payne 1968) which is a common problem in many egg-producing regions of Australia.
Therefore, both relative humidity and degree of
acclimatization should be considered in any attempt to
estimate the responses of laying hens to elevated temperatures.
The present experiments were carried out to compare
the effects of gradual or abrupt increases in temperature,
1 90
Australian Journal of Experimental Agriculture and Animal Husbandry:
Volume 27 April 1987
combined with high relative humidity, on the production
responses of commercial Australian crossbred layers. No
such studies have previously been conducted as far as the
present authors are aware. Conditions and times of
exposure were chosen to simulate typical 'summer conditions at Camden. Feeding patterns and time of oviposition
were also studied, together with .the extension of the daily
photoperiod, in an effort to identify factors which might
help overcome the detrimental effects of heat stress.
weeks at the start of the trial. These hens had never been
exposed, except during brooding, to high ambient temperatures. They were randomly distributed with 18 hens in
the control group kept at 20°C and 21 hens in the experimental group. Following the completion of the 9-week
experimental period used in Experiment 1, the minimum
28"C, high R H (night)/maximum 36"C, high R H (day)
regimen was maintained for a further 3 weeks during
which time the daily photoperiod was extended from
5 a.m.-9 p.m. to 5 a.m.-1 a.m.
Materials and methods
Experiment 7
White Leghorn x Australorp crossbred laying hens aged
70 weeks (July,-7978) were randomly selected from a
larger population and placed in individual cages in one of
two environmentally controlled rooms with a 16 h photoperiod from 5 a.m.-9 p.m. The control group of 24 hens
was maintained at a constant 18°C with a normal relative
humidity (RH) pattern (high at night, low during the day).
The experimental group of 18 hens was gradually
acclimatized over a period of 6 weeks through a daily pattern of minimum 18"C, high R H (night)/maximum 3 6 T ,
low R H (day) to minimum 28"C, high R H (night)/maximum 36"C, high R H (day). The maximum R H ranged
from 80% at 18°C to 7000 at 28°C to 60'% at 36°C. The
environmental conditions were varied in such a way as to
simulate ambient daily temperature and R H patterns
recorded at Camden airport. The birds were kept under
these conditions for a further 3 weeks.
Diet
Hens in all studies had free access to water. In all experiments they were fed daily at 11 a.m. a proprietary layers'
mash, the composition of which is given in table 1.
TABLE 1
Mean determined chemical composition @er kg) of the proprietary
layer diet.
ME fMJ)
Srude protein (g)
5ther extract
@!
:?A f 2.3 (7)
rota1 phosphorus (g)
7.4 1- 0.3 (7)
$odium @)
121 1-0.1 (7)
bfanganese (mg)
!inc (mg)
87 1-6.0 (7)
110 1-9.6 ( 7 )
imino acids @)
Hydroxyproline
Threonine
Experiment 3
Experiment 1 was repeated (October, 1979) using White
Lerrhorn x austral or^ crossbred laving hens aeed 32
32 f 0 . 9 (7)
Salcium (.g)
Aspartic acid
Experiment 2
Hens from the same population as used in Experiment 1
(aged 80 weeks) were distributed as before with the control
group of 20 hens maintained at 20°C with a normal R H
pattern. The experimental group of 22 hens was
acclimatized to a pattern of minimum 20°C (night)/maximum 30°C (day) with a normal R H pattern. They were
then exposed on three separate occasions at 10-day intervals for periods of 3 days to temperatures of minimum
28°C (night)/maximum 40°C (day) with continuous high
R H . The maximum R H patterns ranged from 80% at
28-30°C to 55% at 40°C. A similar photoperiod to Experiment 1 was used.
11.42 1-O.Oi(7).
158 f 4 . I (7)
Serine
5.6 +0.56(5)
10.6 *0.29(5)
. i 0 f0.14(5j
6.8 f0.1:1(5)
Glutamic acid
32.5 f 1.30(5)
Proline
I 1.8 t0.29(5)
Glycine
11.0 t 0 . 5 1 ( $
Alanine
10.0 t0.32(5)
Valine
7.6 1-0,15(5)
Cystine
1.8 1-0.06(5)
Methionine
2.6 +0.10(5)
Isoleucine
5.6 +0.10(5)
Leucine
11.1 *0.10(5)
Tyrosine
3.8 *0.13(5)
Phenylalanine
.5.9 1-0.06(5)
Lysine
5 3 1-0.34(5)
Hystidine
2.9 1-0.05(5)
Arginine
8.3 1-0.21 (1)
Number nf dietary mixes analyzed.
Daniel and Balnave:
Responses of laying hens to heat stress
Measurements
Feed intake and egg production were recorded at
11 a.m., 4.30 p.m. and 8.30 p.m. All eggs were kept at
18-20°C and egg weight, yolk weight, egg specific gravity
and Haugh Unit Index were measured within one day of
oviposition on all eggs laid on one day of each week. In
Experiment 2 these egg quality measurements were also
191
made on each of the three consecutive days during each
period of heat stress.
Samples of air were taken for the determination of carbon dioxide content during the acdimatization period and
during the times of the simulated 'heatwaves' in Experiment 2 and during the maximum heat stress period in
Experiment 3.
TABLE 2
Mean food intake and production attributes of birdr from Experiments 7 and 2.
Attribute
Experiment 1
Exptl. group
Control group
Exptl. group
Control group
Acclima-
Heat
Acclima-
Heat
Acclima-
Heat
Acclima-
Heat
tization
stress
tization
stress
tization
stress
tization
stress
Food intake [T/birdday-~')
126.9at
11 1.8b
Egg production (lbzrd day- ')
0.70a
Egg weight @I
Yolk wt./egg
M t,
('Y)
Haugh units
0.63b
134.5a
138.3a
O.67a
0.70a
117.7a
0.65a
1043b
O..59a
131.3a
O.67a
124.8b
0.6lb
61.9a
59.4b
63.la
64.9a
63.7a
f2.8a
66.Ya
67.4a
31.5a
:1 1.2a
3 1.Oa
31.5a
30.3a
30.7a
31.7a
31.5a
I .07,ja
Specific gravity
t
Experiment 2
85.6a
1 .076a
82.5a
1.077a
1.077a
88.la
82.913
1.079a
80.2a
1.076b
80.4a
1.076a
73.9a
1.076a
74.la
Within treatments, within experiments, means not followed by a common letter differ significantly ( P < 0.051.
TABLE 3
Mean food intake and production attributes of birds from Experiment 3.
Attribute
Food intake @birddaj'-~')
Egg production (/bird day- ')
Experimental group
Acclimatization
Heat
stress
Weeks
1-6
92.laS
0.77a
Control group
Heat
stress
(20 h)
Weeks
.4cclimatization
Heat
stress
Weeks
Heat
stress
(16 h)'
Weeks
Weeks
7- 12
7-9
10-12
1-6
88.5~
87.0~
116.0a
87.7b
0.74a
0.78~
0.71y
0.80a
Weeks
Heat
stress
(16 h)
Weeks
Heat
stress
(20 h)
Weeks
7-12
7-9
10-12
118.la
121.6~
114.5~
0.85b
0.86~
0.83~
Egg weight (g!
,533a
,333a
54.3~
52.5~
56.3a
.57.la
57.7~
,56.4x
Yolk wt./egg wt. ('$')
27.6a
28.3b
28.4~
28.3~
27.2a
28.4b
27.9,
28.8~
Specific gravity
Haugh units
1.08Ya
90.6a
I .089a
87.5b
1.089~
89.2~
1.088~
85.9~
1.089a
93.la
I .087b
90.2b
1.088~
91 .9x
1.087~
88.6y
:Length of photoperiod in parentheses.
t. Within treatments, m a n s not followed by a common letter differ significantly (P< 0.03). [a, b for comparison of weeks 1-6
x , y for comparison of weeks 7-9 with weeks 10-12.)
with weeks 7-12;
Australian Journal of Experimental Agriculture and Animal Husbandy:
192
Volume 21 April 7981
Carbon dioxide determination
Results
Atmospheric carbon dioxide concentrations were determined by precipitation as barium carbonate as described
by Vogel (1961) with the modification that all titrations
were carried out under nitrogen.
The results of these studies are shown in tables 2-5.
Statistical analyses
All data were statistically analyzed by analysis of variance.
Orthogonal comparisons, within rooms, were made between the acclimatization and heat stress periods in
Experiments 1 and 2. In Experiment 3, similar comparisons were made between the acclimatization and the
total 6-week heat stress period, and also between the 3week 16 h and 20 h photoperiods during heat stress. All
statistical analyses were carried out according to Chapters
7 and 11 in Steel and Torrie (1960).
Mortality
No mortality from heat stress occurred in Experiments 1
or 3. In Experiment 2 five hens collapsed from heat during
the first day of the initial heat stress period and were
removed. Two of these hens subsequently died but the
other three were returned to the experiment after the
initial heat stress period was completed. On the first day of
the second period of heat stress 4 hens were removed, only
one of which had collapsed previously. One of these died
and the other three were returned that evening when the
temperature fell. During the third heat stress period only
one hen had to be removed, and this hen had collapsed
previously during the initial period of heat stress. Six of the
TABLE 4
Feeding pattam of birds under various climatic conditions.
Attribute and Period
Mt
Experimental group
A
E
M
--
Experiment 1
Intake (glbird day-')
Acclimatization
Heat stress
Intake (percentageof totad
Acclimatization
Heat stress
Experiment 2
Intake @bird day-')
Acclimatization
Heat stress
Intake (percentageof totad
Acclimatization
Heat stress
Experiment 3
Intake (glbird day-')
Acclimatization
Heat stress (16 h)
Heat stress (20 h)
Intake (percentageof totad
Acclimatization
Heat stress (16 h)
Heat stress (20 h)
t M = morning (measured at 11 a.m.); A = afternoon (measured at 4.30 p.m.); E
=
evening (measured at 8.30
Control group
A
E
Daniel and Balnave: Responses of laying has to heat stress
eight hens that collapsed at various times were the six
heaviest in the group with a mean bodyweight of 2.49 kg
compared with the group average of 2.19 kg.
Food intake
Food intake was significantly reduced in all experiments
during periods of maximum heat stress. These reductions
amounted to 19, 16 and 27%, respectively, in Experiments
1, 2 and 3. Examination of feeding patterns (table 4)
showed that control hens tended to eat more food during
the afternoon and evening, whereas the food intake of hens
exposed to high temperatures was only 50% that of controls during the afternoon period of maximum heat stress.
In Experiment 3 the control hens ate considerably more
food (15th) between 8.30 p.m. and 11 a.m. when the photoperiod was extended to 20 h although the total daily food
intake was decreased. The extended photoperiod produced similar quantitative increases in food intake in the
heat stressed group during the 8.30 p.m.-11 a.m. period,
so that these hens consumed 50% of their daily intake during these hours without any reduction in total daily food
intake.
Egg production and egg weight
In all three experiments the egg production of the experimental hens was maintained at similar levels to controls
during the acclimatization period. However, the major
reduction in egg weight in all three experiments occurred
during this period of temperature acclimatization.
193
The responses in egg production and egg weight to heat
stress were variable between experiments. In Experiment
1 significant reductions in both measurements were
observed during the maximum heat stress period. No
sigmficant effects were observed in Experiment 2 during
the short periods of heat stress. In Experiment 3 no overall
significant reductions were observed during the total 6week heat stress period, but significant reductions in both
measurements occurred during the final 3 weeks when the
daily photoperiod was extended to 20 h.
Time of oviposition
The time of oviposition of control hens in Experiments 1
and 2 was fairly evenly distributed between morning and
afternoon, while heat-stressed hens tended to lay more
eggs in the afternoon (table 5). This pattern was not so evident in Experiment 3 where both groups laid substantially
more eggs in the afternoon and evening when the daily
photoperiod was extended to 20 h:
Egg quality
The shell strength of eggs, as determined bf specific gravity measurements, was reduced significantly during heat
stress only in Experiment 2, although even in this experiment the final shell strength was similar in eggs from both
control and heat-stressed hens. There was no evidence in
any experiment of a detrimental effect of heat stress on the
Haugh Unit Index of eggs. Significant reductions of simi-
TABLE 5
Time of ovt$osition of birds under various climatic conditions, memured by the percentage of total eggs laid at different times of the day.
Period
Mt
Experimental group
A
E
Experiment 1
Acclimatization
Heat stress
Experiment 2
Acclimatization
Heat stress
Experiment 3
Acclimatization
Heat stress (16 h)
Heat stress (20 h)
f
M = morning (5 a.m.-11 a.m.); A = afternoon (11 a.m.-4.30 p.m.); E
=
evening (4.30 p.m.-9 p.m.).
M
Control group
A
E
194
Australian Journal of Experimental Agriculture and Animal Husbandry:
lar magnitude in the Haugh Unit Index of eggs
from both
..
groups of hens were observed in Experiment 3 when the
daily photoperiod was extended to 20 h.
Volume 27 April 1987
more pronounced in heavier hens, thus indicating an
advantage of controlling excess food intake and body fat
deposition in laying hens likely to be exposed to high
ambient temperatures during the laying cycle.
Significant reductions in food intake were observed at
Atmospheric COP
high temperatures in all three experiments. When based
Measurements of atmospheric C O P concentration indi- on the maximum daytime temperatures applied in the
cated that during the acclimatization period in Experi- experiments, the compound percentage reductions in food
ment 2 the mean atmospheric C O P concentration in the intake during either the acclimatization or maximum heat
high temperature room was 0.0740,while under maximum stress periods ranged from 0.3 to 2.OU0per "C. Overseas
heat stress conditions in this experiment and in Experi- estimates of changes in food intake at constant temment 3, the mean atmospheric C O P concentration was peratures have indicated a compound percentage reduc0.08%. Mean C O P concentratons in the control room at tion of approximately l.6"0 per "C between -5°C and
18°C and outdoors at 20-28°C were 0.05 and 0.03"11, +30°C (Payne 1968; ARC 1975) with much larger reducrespectively.
tions at higher temperatures (Smith 1972, 1973; ARC
1975). Therefore, even under maximum heat stress, with
high day and night temperatures and high relative
humidities, the reduction in food intake was much lower
Discussion
than expected from overseas estimates.
In the present studies many of the known detrimental
The reduction in appetite at high environmental temeffects of heat stress on laying performance were not peratures results in a reduced intake of dietary nutrients.
observed. This was unexpected since the high tem- Previous studies have shown that laying hens make more
peratures were combined with high relative humidity and efficient use of dietary nutrients when these are given as an
reports of studies using constant temperature conditions evening rather than as a morning feed (Simon 1973;
have indicated that the maximum temperature associated Balnave 1977).Therefore, the daily photoperiod in Experiwith satisfactory laying performance is approximately ment 3 was extended to 20 h by use of additional light dur30°C at high relative humidity (payne 1968; Smith and ing the cooler evening period, but no beneficial responses
Oliver 1972). It is likely that part of the reason for the were observed with the heat-stressed hens as a result of this
satisfactory egg production observed in the present work procedure. In general, this procedure proved detrimental
was the use of natural fluctuating temperature regimens, in to both groups of hens.
that Hutchinson and Sykes (1953) and Ben-Adam (1962)
Although food intakes under maximum heat stress were
were also able to maintain satisfactory egg production in reduced by 19, 16 and 27"0,respectively, in Experiments 1,
hens acclimatized to temperatures above 3,YC when 2 and 3 the corresponding rates of egg production were
fluctuating temperature regimens were used. However, only reduced by 10, 3 and goo, respectively. The reduction
this procedure failed to maintain egg weight in the present in mean egg weight corresponded to percentage decreases
work. In fact, most of the 4-5 g reduction in egg weight of 8 , 7 and 6"0,respectively. Therefore, in the present work,
observed in hens exposed to the high temperatures occur- food was used more efficiently for egg production in hens
red during the initial acclimatization period, before any under heat stress. The food conversion ratios (g foodlg
major reduction in food intake. This indicates that tem- egg) of the heat-stressed and control hens were 2.99 and
perature as such had a detrimental effect on egg weight, 3.07 ( ~ x ~ e r i m e 1)
n t and 2.82 and 3.04 ( ~ x ~ e r i m e 2)
nt
and suggests that under high summer temperature condi- respectively, but with the younger hens in Experiment 3
tions losses in egg weight are unlikely to be overcome by the improvement was more marked: the experimental
nutritional means.
hens under heat stress having a food conversion of 2.09
The importance of acclimatization was demonstrated in compared with 2.45 for the control hens.
Experiment 2, where high mortalities were observed in
The maintenance of optimum egg quality in hens under
hens suddenly exposed to heatwave conditions. However, heat stress in the present studies contrasts with previous rein this experiment the hens appeared to acclimatize by the ports (Miller and Sunde 1975; El Jack and Blum 1978).
third simulated heatwave. In addition, no mortalities were However, earlier studies by Helbacka et al. (1963) and
observed in either of the other experiments where hens Frank and Burger (1965) suggest that the higher
were gradually acclimatized to high temperatures. The atmospheric carbon dioxide concentrations in the high
mortalities occurring under the heatwave conditions were temperature room probably explain the lack of deteriora-
Daniel and Balnave:
Responses of laying hens to heat stress
tion in egg quality normally associated with high ambient
temperature.
The present studies indicate that the White Leghorn x
Australorp laying hen is well suited to the hot Australian
summer environment. However, the detrimental effects of
summer heat stress may be lessened by acclimatizing birds
to high environmental temperatures. Such a procedure is
especially important where heatwave conditions are likely
to be experienced in early spring before the onset of stable
summer conditions.
Acknowledgments
The authors thank Mr P. Aitken and Mr P. de Bono for
help with the care and maintenance of birds and Ms A.
Kirby for advice with statistical procedures. This work was
supported by the Poultry Research Advisory Committee
of the Council of Egg Marketing Authorities of Australia.
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Manuscript received May 2 7, 1980; accepted October 2 1, 7980