Effects of heat conditioning at d 16 to 18 of incubation or during early

Arch.Geflügelk., 72 (2). S. 75–83, 2008, ISSN 0003-9098. © Verlag Eugen Ulmer, Stuttgart
Effects of heat conditioning at d 16 to 18 of incubation or during early
broiler rearing on embryo physiology, post-hatch growth performance and heat tolerance
Einfluss einer Temperaturbelastung zwischen dem 16. und 18. Bruttag oder in den ersten
Tagen während der Aufzucht auf die Physiologie, das Wachstum nach dem Schlupf und die
Hitzetoleranz des Embryos
K. Tona1, O. Onagbesan2*, V. Bruggeman2, A. Collin3, C. Berri3, M. J. Duclos3, S. Tesseraud3, J. Buyse2,
E. Decuypere2 and S. Yahav4
Manuskript eingegangen am 5. Mai 2007, angenommen am 23. Juni 2007
Introduction
It is well known that cells preincubated at sublethal high
temperatures can survive longer when exposed to lethal
temperatures. In addition heat shock response, regulated
to some extent by heat shock proteins, is necessary for
the acquisition of induced thermotolerance in chickens
(YAHAV et al., 1997). According to YAHAV and MCMURTRY,
(2001), the main idea behind the thermal conditioning
process is to incorporate thermoregulatory threshold response changes that enable chickens to cope, within certain limits, with acute exposure to unexpected heat spells.
Since the technique of temperature conditioning takes advantage of the immaturity of the temperature regulation
mechanism in the young chick (DUNNINGTON and SIEGEL,
1984), it is hypothesised that a potentially better thermotolerance could be induced in the developing mechanism
of thermoregulation by early conditioning during incubation or through a combination of this pre-hatch conditioning with early post-hatch conditioning. YAHAV and HURWITZ, (1996) reported that thermal conditioning at an early
age post-hatch has a negative effect on early performance
followed by an accelerated growth leading to regular or
higher body weight at slaughter age. The combination of
short-term exposure to heat during the first week and feed
restriction during the second week resulted in slow growth
rate followed by a catch up growth at the end of the second
week (YAHAV and PLAVNIK, 1999). ARJONA et al., (1990) reported that broiler cockerels conditioned to neonatal heat
(35–37.8°C for 24 hr) at 5 days of age had significantly
lower mortality when exposed afterwards to elevated temperatures (35–37.8°C) at 43 days of age.
Reports of different studies have shown that epigenetic
thermal conditioning can be applied at different periods
during the 11th to the 18th d of incubation (IQBAL et al.,
1Department of Animal Production, School of Agriculture, University of Lome,
Togo
2Lab for Physiology and Immunology of Domestic Animals, Katholieke Univer-
siteit Leuven, Heverlee, Belgium
3SRA, INRA, Nouzilly, France
4Institute of Animal Science, ARO The Vulcani Center, Bet Dagan, Israel
Arch.Geflügelk. 2/2008
1990, MORAES et al., 2003, 2004, YAHAV et al., 2004a,
2004b) and that a temperature of 38.5 – 39.5°C may elicit
optimum beneficial effects at the 16th to the 18th d of incubation (YAHAV et al., 2004a, 2004b). Reports also suggest
that post-hatch heat conditioning using a temperature of
36°C or 37.5°C had maximal effect on heat tolerance and
body weight gain to slaughter age when applied at 3 d of
age (YAHAV and MCMURTRY, 2001). A recent study also suggests an accelerated growth at 4 d of age in chicks heat conditioned both between the 16th and the 18th d of incubation
and at 3 d post-hatch compared to control chicks (COLLIN et
al., 2005). Up to date, the long-term efficiency of pre-hatch
and post-hatch heat conditioning has only been tested in
separate experiments. Thus the relative effectiveness of
each of these treatments remains unknown. Furthermore,
it is worth testing to ascertain whether a combination of
pre- and post-hatch thermal conditioning may yield further improvement in the benefits of heat conditioning.
Therefore, this study aimed to investigate the effects of heat
conditioning from 16th to 18th d of incubation and at 3 d
post-hatch, separately and in combination, on post-hatch
broiler body temperatures and production performance
parameters including heat challenge tolerance at slaughter
age as well as on some embryo and chick physiological parameters that could explain the observed effects. These parameters include blood parameters, gas pressures in egg
air chamber and embryonic heat production.
Material and Methods
Experimental Design
A total of 900 eggs produced by Cobb broiler breeders of
45 weeks of age were used for this study. The eggs were
weighed and incubated at 37.6°C, 50% relative humidity
(RH) and turned once an hour at an angle of 90°. On the
14th day of incubation, eggs were candled and all clear
eggs were removed from the incubator. At the beginning of
the 16th d of incubation, the incubated eggs were randomly
divided into two groups each of equal number of eggs; the
control (C) and the thermally conditioned (T) groups.
From the 16th to the end of the 18th d, the eggs of the T
group (3 replications of 108 eggs) were subjected to temperature conditioning (39.5°, 65% RH) while those of the
76
Tona et al.: Pre- and post-hatch conditioning for heat tolerance
C group (3 replications of 108 eggs) were kept at standard
incubation conditions (37.6°C, 50% RH). The thermal conditioning was carried out from 12.00 to 15.00 h at d 16, 17
and 18 of incubation. The regular incubation (37°C and
50% RH) was carried out in one incubator (Pasreform, Zedam, The Nederland) whereas the thermal conditioning
(39.5°C and RH 65%) was carried out in another (Karl
Weiss Giessen, Germany). At the beginning of the 19th d of
incubation, the eggs were transferred from turning trays to
hatching baskets.
At the internal pipping stage (IP), sample of eggs with
evidence of living embryos were used for gas partial pressure measurement in the air chamber. Also, from the end
of d 18 until the end of incubation, sample of eggs were
used to determine embryo heat production (HP).
Between d 19.75 and d 21.25, the number of hatched
chicks was recorded every hour. After hatching and feather
dryness (approximately 2 h post hatch) each chick was taken out from the incubator for immediate measurements,
recorded in the following order: body (rectal) temperature
(Tb) and body weight (BW). After the measurements and
for each incubation condition, chicks were divided into
two groups. The time interval of hatch was used to calculate incubation duration for individual egg as the total
number of hours from setting to hatch.
Figure 1 shows the scheme of the treatments applied to
different groups at different ages. Chicks were raised under
regular heat conditions (32° ± 1°C). At the age of 3 d, half
of the chicks of the T group (T) were subjected to thermal
conditioning and designated as TT. The other half of the T
chicks were used as control for the TT treatment and designated as TC. Similarly, half of the chicks of the C group were
subjected to thermal conditioning at 3 d post-hatch and
designated as CT, while the other half served as control and
designated as CC. Thermal conditioning at this stage was
done at 41.0°C for 6 hours, while the control groups (CC
and TC) continued to be exposed to the regular conditions
(32 ± 1°C). During the last hour of the post-hatch thermal
T reatments’ stage
Gas pressure measurements
At internal pipping (IP), samples of 6 eggs per replication
were used to measure CO2 and O2 partial pressure in the
air chamber. These measurements were done directly in
the air cell of the eggs by means of a blood gas analyzer
(Type 1610; Instrumentation Laboratories, Lexington, Illinois 1306) for the measurement of pCO2 and pO2 (DEWIL
et al., 1996; BUYS et al., 1998; TONA et al., 2003).
Measurement of blood parameters
Blood samples were collected from 6 embryos per replication at the IP stage, 15 chicks/treatment at 1, 3, and 42
d-old post-hatch. In the 42 d old broilers, blood samples
were obtained before and at 1- 2hr before the end of heat
challenge. Blood samples were used to determine plasma
T3 and corticosterone levels.
The T3 concentrations were measured in plasma samples
by radioimmunoassay (RIA) as described previously (HUY-
T reatments
E mbryonic stage:
d 16 to d 18
3 d post-hatch
conditioning, Tb and BW of 20 chicks per treatment were
recorded and blood samples from the jugular veins were
collected from 15 chicks. The 4 groups of broilers were
reared until 42 d of age. All chicks were raised within the
same environmentally controlled poultry house. Chicks
were reared under a photoperiod of 23 h light and 1 h darkness. The birds were fed ad libitum on a standard commercial pelleted diet of 2,800 kcal metabolizable energy and
18% of crude protein and 3100 kcal metabolizable energy
and 20% of crude protein respectively for starters (1–14 d)
and growers (15–42 d). Thermal challenge was conducted
in the same room and at the same time for all four groups.
During this study, 50 broilers randomly selected per treatment were weighed at 7, 14, 28 and 42 d. At the end of 42
d, 50 chickens per treatment were subjected to thermal
challenge of 35°C for 6 h to evaluate heat tolerance. During
the challenge, mortality was recorded.
C
C (CC)
T
C (CT )
C (T C)
T (T T )
42 d post-hatch
Heat Challenge
C = control with no thermal treatment applied; T = T hermal treatment applied. Nomenclature in
brackets represents the combination of treatments at a particular stage of development.
Figure 1. Scheme of thermal treatments applied at
embryonic stage, 3 d and
42 d post-hatch
Schema der Temperaturbelastungen, die im Embryonalstadium, 3 Tage sowie 42
Tage nach dem Schlupf
durchgeführt wurden
Arch.Geflügelk. 2/2008
Tona et al.: Pre- and post-hatch conditioning for heat tolerance
et al., 1989; DARRAS et al., 1992). Antisera and T3
standard was purchased from Byk-Belga (Germany). Intra-assay coefficient of variation was 4.5%. All samples were run in
the same assay in order to avoid the inter-assay variability.
Corticosterone concentrations in plasma samples were
measured using a commercially available double antibody
RIA-kit from IDS Ltd (Boldon, England) (DECUYPERE et al.,
1983; MEEUWIS et al., 1989). All samples were run in the
same assay in order to avoid inter-assay variability.
BRECHTS
Heat production
From the beginning of d 19 of incubation until the end of
incubation (508 h), 2 replications of 40 eggs from each
treatment were transferred into the respiratory cells in order to measure O2 consumption and CO2 production for
the calculation of heat production (HP). Eggs were
weighed before and after being placed in the respiratory
cells. Average egg weights were not different between the
C and T groups. The respiration cells were placed in duplicate in 2 separate climatic chambers set at 37°C and 50%
relative humidity. O2 consumption and CO2 production
based on paramagnetic and infrared measures, respectively, were continuously measured as previously described by
BUYSE et al., (1998). Airflow at standardized conditions for
pressure, temperature and relative humidity were measured. Heat production was calculated according to the formula of ROMIJN and LOKHORST, (1961) as previous described
by BUYSE et al., (1998) where HP (KJ/h) = 16.18 * O2 consumed (l/h) + 5.02 * CO2 produced (l/h).
Statistical analysis
The data were processed with the statistical software package SAS version 8.2 (SAS Institute Inc., Cary, NC
27513-2414). Generalized linear regression was used to analyse plasma T3 and corticosterone concentrations, incubation
durations, body temperature and body weights in relation to
incubator conditions x heat treatment during post-hatch
growth treatments. When the means of the general model
were statistically different, then these means were further
compared using Tukey’s test. Logistic regression model was
used to analyse mortality according to the treatments. P value
of 0.05 was retained as the degree of significance.
77
Results
Blood parameters
Table 1 shows corticosterone and T3 levels at IP and at
hatch (Table 1A), at 3 d post-hatch (Table 1B) according to
thermal conditioning treatments during incubation or heat
conditioning at 3 d post-hatch. At IP, T3 levels in the embryos of eggs from control (C) group were higher than
those of embryos from the heat conditioned eggs (T)
group (P < 0.05). At hatch, T3 levels were similar between
groups.
From IP to hatch corticosterone levels increased in both
groups (Table 1A; P < 0.01). At IP and at hatch, corticosterone levels of embryos or chicks from T group of eggs were
lower to those from C group of eggs (P < 0.01).
At 3 d post-hatch, T3 levels were similar among all
groups (CC, CT, TC and TT) regardless of the previous
treatments during incubation and post-hatch heat treatment. However, in the chicks from the eggs that were not
heat conditioned during incubation (C), corticosterone
concentrations were higher in chicks that were heat conditioned for the first time (CT) compared to the CC group
that were not heat treated, (P < 0.05). In the chicks from
eggs that received heat conditioning during incubation
(T), additional heat conditioning at 3 d (TT) had no significant effect on corticosterone levels compared to those that
were not conditioned for a second time (TC). Overall, the
second conditioning increased corticosterone levels at 3 d
while the prenatal conditioning decreased corticosterone
levels at IP and at hatch.
Table 2 shows the T3 and corticosterone concentrations of broilers before and after heat challenge at 42 d
of age. At this stage, T3 levels were similar between
groups before heat challenge. Heat challenge caused a
decrease in T3 levels in the TC group such that levels became lower than in the CT and TT but remained comparable to those of the CC. Before heat challenge, corticosterone levels were lower in the postnatally conditioned
groups (CT and TT) than in the unconditioned groups
(P < 0.05). Heat challenge increased corticosterone levels in the CT and TT (P < 0.05) but not in the CC and TC
such that corticosterone levels were similar between all
groups after challenge.
Table 1. Corticosterone and T3 levels according to incubation treatments (IT). A) Hormone levels of embryos at internal pipping
(IP) in the control (C) and thermally conditioned (T) eggs. B) Hormone levels at 3 d post hatch in the control (C) and thermally
conditioned (T) or heat challenged chicks.
Kortikosteron- und T3-Spiegel in Abhängigkeit von den Brutbedingungen (IT). A) Hormonspiegel der Embryonen beim Anpicken (IP) in
der Kontrollgruppe (C) und bei Temperaturbelastung (T). B) Hormonspiegel der Küken drei Tage nach dem Schlupf in der Kontrollgruppe
(C) und bei Temperaturbelastung (T)
A. At internal piping stage (IP)(n=18 per treatment) and at hatch
(n=15 per treatment)
B. At 3 d post-hatch according to heat challenge treatments at
3 d (n=15 per treatment)
Stages
IT
T3 (ng/mL)
Corticosterone
(ng/mL)
IT
3 d post-hatch
T3 (ng/mL)
IP
C
T
C
T
4.79 ± 0.46a
3.51 ± 0.49b
3.38 ± 0.39
3.73 ± 0.47
10.48± 1.52 a
7.99 ± 0.47 b
13.00± 0.82 a
10.42 ± 1.20 b
C
C (CC)
T (CT)
C (TC)
T (TT)
2.81 ± 0.36
3.23 ± 0.41
3.14 ± 0.22
2.58 ± 0.30
Hatch
T
Corticosterone
(ng/mL)
13.51± 0.92 b
16.10± 1.37 a
14.42± 1.79 ab
16.10 ± 1.55 a
a, b At each stage and within column, data sharing no common letter
a, b Within column, data sharing no common letter are different
are different (P < 0.05)
(P < 0.05).
Arch.Geflügelk. 2/2008
78
Tona et al.: Pre- and post-hatch conditioning for heat tolerance
Table 2. Corticosterone and T3 levels according to incubation treatment (IT), heat conditioning at d 3 post-hatch and heat challenge (HC) at 42 d post-hatch (n=15 per group).
Kortikosteron- und T3-Spiegel in Abhängigkeit von den Brutbedingungen (IT), der Temperaturbelastung drei Tage nach dem Schlupf
(HC) und der Hitzebelastung am 42. Tag nach dem Schlupf (n=15 je Gruppe)
Groups: treatments
during incubation and
at 3 d post-hatch
T3 (ng/mL)
Before HC
0.79 ± 0.12
0.90 ± 0.17
0.78 ± 0.10
0.64 ± 0.10
CC
CT
TC
TT
Corticosterone (ng/mL)
Before HC
After HC
After HC
10.35 ± 1.40 a
7.47 ± 1.06 b
10.20 ± 1.63 a
6.81 ± 0.80 b
0.75 ± 0.10 ab
0.93 ± 0.07 a
0.66 ± 0.06 b
1.01 ± 0.28 a
9.44 ± 1.35 a
9.37 ± 0.85 a*
9.93 ± 1.23 a
10.44 ± 0.89 a*
a, b Within column, data sharing no common letter are different and * indicates the difference between data before heat and after heat (P < 0.05).
Gas pressures and heat production
The partial pressures of CO2 or O2 at IP were similar between groups (data not shown). Respiratory quotients
(RQ) during the last 3 d of incubation (456 – 510 h of incubation) were similar between groups. Since the average
egg weights were not different between the C and T
groups, HP was expressed as HP/h/egg. Figure 2 shows
that the heat production (HP) of the eggs for C group was
higher than that of the eggs from T group (P<0.05). Also,
the difference in heat production between the groups increased with increasing incubation duration. The average
heat production of the C and T groups were 1.58 ± 0.05
and 1.13 ± 0.03 kJ/h/egg for C and T groups, respectively,
at the end of the 510th h of incubation (p < 0.05).
Incubation duration and chick body temperature
Table 3 indicates that chick body temperatures (Tb) at
hatch were lower than those at 3 d post-hatch (P < 0.05).
Heat production (K J/h)
2,5
At hatch, average Tb of the C group was higher compared
to that of the T group (P < 0.002). At 3 d post-hatch, the
Tb of the TC and TT chicks were higher than the Tb of the
CC with that of the CT group being intermediate (P =
0.022).
Table 4 shows the incubation duration according to the
egg treatments during incubation. Thermal conditioning
during incubation increased incubation duration by almost
2 h compared to the control group (P < 0.05). However, the
Table 3. Chick body temperatures (Tb)(°C) at hatch and during
heat challenge at 3 days post-hatch according to the treatments (n=20 per group).
Körpertemperatur der Küken (Tb)(°C) beim Schlupf und während
der Hitzebelastung drei Tage nach dem Schlupf in Abhängigkeit
von Temperaturbehandlung (n=20 je Gruppe)
Thermal conditioning during
incubation
Groups
Tb (at hatch)
C
37.26 ± 0.09a
T
36.81 ± 0.12b
P values
0.002
2
1,5
Cont
T
1
CC
CT
TC
TT
40.99 ± 0.06b
41.07 ± 0.04 ab
41.19 ± 0.07a
41.10 ± 0.07 a
0.022
a, b Within column, data sharing no common letter are different
(P < 0.05).
0,5
0
450
Thermal conditioning at 3 d
post-hatch
Groups
Tb (at 3 d post-hatch)
460
470
480
490
500
510
I ncubation duration (h)
Figure 2. Heat production according to the incubation duration and heat conditioning groups (n=80 eggs per treatment;
two replications of 40 eggs per treatment). Each data point
represents the mean heat production/hr/egg calculated from
the O2 consumption and CO2 production during 456th – 510th
hr of the incubation period. Mean egg weights were not significantly different between the C and T eggs.
Wärmeproduktion in Abhängigkeit von der Brutdauer und der
Temperaturbelastung (n=80 Eier je Behandlung; 2 Wiederholungen von 40 Eiern je Behandlung). Jeder Datenpunkt stellt die
durchschnittliche Wärmeproduktion/h/Ei dar, berechnet aus
dem Sauerstoffverbrauch und der CO2-Produktion während der
456. und 510. Stunde der Brut. Die durchschnittlichen Eigewichte
unterschieden sich nicht zwischen den Behandlungen C und T.
Table 4. Spread of hatch and incubation duration according to
egg treatments during incubation
Verteilung der Schlupfzeitpunkte und Brutdauern für die Temperaturbehandlungen während der Brut
Spread of hatch
25% of hatch
50% of hatch
75% of hatch
100% of hatch
Average incubation duration (h)
Thermal conditioned
eggs (T)
Control eggs (C)
482.89 ± 0.44 b
485.42 ± 0.36 b
487.63 ± 0.37 b
489.69 ± 0.39 b
484.32 ± 0.41 a
487.48 ± 0.43 a
489.63 ± 0.41 a
491.58 ± 0.42 a
a, b Within row, data sharing no common letter are different
(P < 0.05).
Arch.Geflügelk. 2/2008
Tona et al.: Pre- and post-hatch conditioning for heat tolerance
79
Table 5. Body weights (g) from 3 to 42 days post-hatch according to the treatments (n=50 broilers per treatment/age).
Körpergewichte (g) zwischen dem 3. und 42. Tag nach dem Schlupf in Abhängigkeit von den Behandlungen (n=50 Broiler je Behandlung
und Alter)
Broiler ages (d)
Groups
CC
3
7
14
28
42
77.94 a
147.66 a
403.89 a
1513.61 a
2793.43 ab
± 2.03
± 1.24
± 4.20
± 34.65
± 72.68
CT
75.67 a
144.24 a
398.75 a
1495.65 a
2669.47b
TC
± 2.14
± 3.42
± 7.72
± 10.49
± 50.76
76.93a
144.24 a
395.56 a
1460.14 b
2964.17 a
± 2.48
± 2.81
± 5.68
± 12.40
± 84.89
TT
75.3a
148.08 a
414.93 a
1557.78 a
2704.66b
± 2.77
± 2.53
± 6.42
± 11.45
± 33.98
a, b, c Within rows, values sharing no common letters are different (P < 0.05).
spread of hatch (dispersion around the average) was similar between treatments. At the end of the incubation period, the hatchability of fertile eggs was not different between the C and T groups (91.26% vs 90.82% respectively).
Egg weights at setting, 1-day-old chick and broiler weights,
body temperature and mortality after heat challenge at 42 d
Egg weights at setting (C = 69.56 ± 0.22 vs T = 70.06 ±
0.16) and 1-d-old chick weights (C = 52.80 ± 0.14 vs T =
51.96 ± 0.82) were not significantly different between
treatments (C vs T). Table 5 shows broiler BW from d 3 to
d 42 according to the treatments. During the first 14 d of
rearing, BW was similar between groups. At 28 d of age,
the BW was lower in the TC than in the three other groups
(P < 0.05). At 42 d of age, the highest BW was obtained in
the TC group which was almost 300 g higher than that of
the CT and TT groups. In terms of weight gain (data not
shown), the broilers from TC group grew better from d 28
to d 42 compared to those of other groups (P < 0.05).
Table 6 shows broiler mortality after 6 h of heat challenge at 42 d-old. Prenatal heat treatment (TC group) dramatically increased mortality during heat challenge while
early postnatal heat exposure decreased mortality during
heat challenge at 42 d post-hatch in both control chickens
(CT) and the chickens that were heat-treated during incubation and at 3 d post-hatch (TT).
Discussion
The present study provides significant information about
the differential effects of thermal conditioning either during incubation and/or at 3 d post-hatch on performance
and related thermotolerance parameters during the final
part of embryogenesis and growth phase of the broilers.
Heat conditioning during incubation obviously lowered
T3 and corticosterone levels at IP. This may explain the
longer incubation duration of thermally conditioned embryos. Although based on the fact that embryos were reacting as poikilotherm organisms, according to the law of
Van’t Hoff, the reverse should have been expected. It was
expected that conditioning would have increased metabolism and therefore a shorter incubation period. IGBAL et al.,
(1990) and LOH et al., (2004) reported a shorter incubation duration when eggs were exposed to pre-hatch heat
treatment. In the current experiment, the heat production
of the T group was lower as a consequence of the lower T3
levels. Even though the T3 levels of the T group had been
restored to normal levels at hatch, corticosterone levels
were still low with a consequence on body temperatures
Arch.Geflügelk. 2/2008
being lower in the T chicks. These changes did not affect
body weights at hatch significantly. The changes in triiodothyronine and corticosterone levels after heat conditioning in ovo in this study are consistent with a previous finding of MORAES et al., (2004). YAHAV et al., (2004a) reported
lower T3 and body temperatures at hatch in chicks that
were heat conditioned during incubation. Although these
authors did not measure corticosterone levels or heat production in the embryos, the lower T3 and body temperatures may suggest lower heat production. The similarity in
corticosterone levels between the control groups (CC and
TC) before and after heat challenge at 42 d post-hatch suggests that the effects of prenatal heat treatment did not last
until 42 d of age. It may suggest that d 16 to 18 of embryogenesis does not create lasting thermotolerance alteration
as previously reported by COLLIN et al., (2005). In contrast,
the increase in corticosterone levels after heat challenge at
42 d post-hatch in chicks thermally conditioned at 3 d
post-hatch (CT and TT) may be due to a consistent effect
of high temperature on neurohormonal activity leading to
low levels of corticosterone but enabling them to react with
an increased corticosterone upon stress in order to cope
with the stressor. This may be an indication of low basal
stress and metabolic levels of the broilers from these
groups before the heat challenge at 42 d.
Thermotolerance partly involves the modulation of heat
production through changes in circulating T3 and T4 (Yahav and MCMURTRY, 2001; MINNE and DECUYPERE, 1984;
DECUYPERE et al., 1979). The difference in incubation duration between the heat conditioned embryos (T) and the control group (C) suggests that heat treatment between d 16
and d 18 of incubation had a bearing on embryonic develop-
Table 6. Mortality during heat challenge at 42 d post-hatch according to incubation treatment (IT) or heat conditioning at 3
d post-hatch (n=50 broilers per treatment).
Mortalität während der Hitzebelastung am 42. Tag nach dem
Schlupf in Abhängigkeit von den Brutbedingungen (IT) oder der
Hitzebelastung am 3. Tag nach dem Schlupf (n=50 Broiler je Behandlung)
IT
3 d post-hatch
C
CC
CT
TC
TT
T
Mortality (%)
20.00 b
4.00 c
68.18 a
29.17 b
80
Tona et al.: Pre- and post-hatch conditioning for heat tolerance
ment and hatching process. This may be a consequence of
the downregulation of T3 and corticosterone, both of which
have been implicated in embryo metabolism and hatching
process (TONA et al., 2003; DECUYPERE et al., 1979; MUAMBI
et al., 1981; OCKLEFORD et al., 1983; HYLKA et al., 1986).
The major interest of this study was to determine whether thermal conditioning during embryogenesis and at early
post-hatch period, would further enhance thermotolerance during their life span. YAHAV, (2000) and YAHAV and
MCMURTRY, (2001) reported that thermal conditioning at 3
d of age post-hatch resulted in optimum thermoregulatory
threshold response. In this study, heat conditioning at 3 d
caused significant increase in corticosterone levels in
chicks that received heat treatments for the first time at 3
d but not to the same extent as those previously conditioned during embryogenesis. It is clear from the present
results that conditioning at d 3 had no effect on T3 levels in
chicks treated for the first time compared to chicks
pre-conditioned during embryonic development (see
Table 1). Except that body temperatures were higher in the
chicks previously conditioned at the embryo stage, heat
treatment at 3 d had no effect on body temperatures. These
data suggest that different mechanisms may be involved in
the acquisition of thermotolerance at different stages of
conditioning. Combining heat conditioning at incubation
and at 3 d changed corticosterone levels and body temperatures but not beyond those obtained with the separate
treatments and had no effect on T3 levels. It has to be noted
that the changes in corticosterone levels during pre- and
post-hatch thermal conditioning were in opposite directions of the control treatment. The consequences of these
directional changes may not be ignored. Whereas an increase resulting from posthatch conditioning improved
heat tolerance at d 42, a decrease resulting from prehatch
conditioning caused a strong negative effect. YAHAV et al.,
(2004) reported a downregulation of corticosterone during pre-hatch (d16 – d18) thermal conditioning. MORAES et
al., (2004) reported an increase when conditioning was
carried out from d13 – d18. Consistently, however, T3 or T4
has been shown to reduce during thermal conditioning irrespective of the timing during incubation (YAHAV et al.
2004a,b; MORAES et al., 2004).
The comparative levels of mortality between the groups
after heat challenge at 42 d suggest that thermal conditioning at 3 d may be the best method for acquiring thermotolerance in broilers. This is in agreement with the previous
finding of YAHAV and MCMURTRY, (2001). With the highest
mortality during the challenge, broilers from heat-conditioned embryos did not acquire any tolerance to heat. This
finding contrast with those reported previously by MORAES
et al., (2003, 2004) although the timing of conditioning
was different from that of the current study. Our results
suggest that d16-d18 may not be the appropriate period for
inducing thermal conditioning that would last until 42 d
post-hatch. This is consistent with the result of a similar experiment that showed higher mortality during thermal
challenge in chickens similarly heat-conditioned during incubation (COLLIN et al., 2006). Previous studies have
shown that the perturbation of embryo physiological processes especially around d 16 of incubation leads to severe
changes in embryo developmental processes that would
impact on chick quality, survivability, hatchability, and
post-hatch growth (TONA et al., 2001, 2003, 2005, 2006;
HEIBLUM et al., 2001). However, we did not record any teratogenic effects using these days. Thermal conditioning of
the chicks at 3 d post-hatch after a previous exposure during incubation actually seemed to have rescued the thermoregulatory controls to reduce the effect of heat challenge on mortality. The chickens that were able to react to
stressors with an increase in corticosterone had a lower
mortality after heat challenge while higher mortality was
obtained in those that could not react with increased corticosterone. Incidentally, those chickens that were conditioned post hatch were those that could manipulate their
corticosterone levels for thermotolerance (i.e. the CT). It
can only be assumed that the lower mortality in the TT
group compared with the TC was due to the post hatch
conditioning that reversed the effect of the early conditioning. The mechanism for thermotolerance in the CT and TT
did not seem to involve the thyroid axis. Why the embryonic exposure (TC) resulted in an increased mortality after
heat challenge at 42 d may not be fully related with corticosterone although there were negative changes during
the conditioning process at incubation but perhaps partly
with the catch up growth that was observed between 28
and 42 d. The TC group had a very fast growth during this
last two weeks. The additional heat load from the heat
challenge at 42 d may therefore have caused this spiking
mortality that was observed in this group that showed the
fastest growth (1500 g) between 28 and 42 d. The reasons
why the TC birds were unable to manipulate both T3 and
corticosterone levels to tolerate the heat challenge are unclear even though some changes (higher body temperature, lower T3) that have been previously associated with
the acquisition of long-term thermotolerance were observed during heat conditioning at incubation.
It is not clear from this study whether the effect of thermal conditioning during incubation on the growth of broiler chickens was due to differential muscle cell proliferation
or gastrointestinal development. UNI et al., (2001) reported that an early thermal manipulation enhanced the development of the gastrointestinal tract and led to heavier
broilers. HALEVY et al., (2001) pointed out that muscle
weight is linked to enhanced proliferation and accelerated
differentiation of satellite cells. Because thermal conditioning during incubation induced changes in T3 and especially HP levels but increased BW at slaughter age, it is suggested that thermal manipulation during embryonic life
may result in changes of kinetics of satellite cell proliferation. In contrast to the previous reports of YAHAV and MCMURTRY, (2001), we did not observe an enhanced body
weight in the CT broilers, but rather in the TC broilers.
It can be concluded that temperature treatment during
incubation or during post-hatch life induces completely
different effects. Thermal conditioning from d 16 to d 18 of
incubation, although prolonged incubation duration, improved BW at slaughter age but did not induce thermotolerance at 42 d. The combination of thermal conditioning
during incubation with that at 3 d post-hatch does not induce thermotolerance ability. However, single heat challenge at 3 d post-hatch contributed to thermotolerance
ability at 42 d. From the results of this study, it can be hypothesized that the period at which thermal conditioning
was applied during incubation was not during the sensitive
phase for thermotolerance improvement. Therefore, further investigations are required to define more precisely
the appropriate incubation stage when thermal conditioning can be beneficial for thermotolerance at slaughter age
and whether one can even use the concept of thermal conditioning during incubation (before the emergence of a
homeothermic response) at all.
Acknowledgements
K. Tona was granted a-postdoctoral fellow from KULeuven
during this study. V. Bruggeman has a postdoctoral FWO-grant
from the Fund for Scientific research Flanders, Belgium.
Arch.Geflügelk. 2/2008
Tona et al.: Pre- and post-hatch conditioning for heat tolerance
81
Key words
unterworfen. Die andere Hälfte der Eier diente als Kontrolle (C) und wurde unter Standardbedingungen weiter bebrütet. Zwischen dem Ende das 18. Bruttags und der gesamten Brut wurden die Wärmeproduktion des Embryos
(HP), der Gaspartialdruck in der Luftkammer zum Zeitpunkt des Anpickens (IP) und verschiedene Blutparameter
(T3 und Kortikosteron) bestimmt. Ferner wurden der individuelle Schlupfzeitpunkt, die Körpertemperatur (Tb) und
das Gewicht (BW) der Küken sowie die Anzahl geschlüpfter Küken erfasst. Die geschlüpften Küken wurden unter
Standardbedingungen aufgezogen. Im Alter von 3 Tagen
wurden die Küken der beiden unterschiedlichen Brutbehandlungen in zwei Gruppen aufgeteilt: Die eine Hälfte jeder Vorbehandlungsgruppe wurde einer Hitzebelastung
(41°C über 6 Stunden) unterworfen. Die andere Hälfte
diente als Kontrolle. Die 4 Broilergruppen wurden bis zum
42. Tag weiter aufgezogen. In der Aufzuchtphase nach
dem Schlupf wurden erneut die Körpertemperatur, die
Blutparameter und das Körpergewicht erfasst. Am 42. Lebenstag wurden alle Broiler einer Hitzebelastung (35°C für
6 Stunden) unterzogen. Nach der Hitzebelastung wurden
die Mortalität erfasst und Blutproben gezogen.
Die Ergebnisse zeigen, dass die Temperaturbelastung
während der Brut zwar keinen Einfluss auf die Schlupffähigkeit der Eier hatte, aber die Brutdauer verlängert wurde, der T3-Spiegel zum Zeitpunkt des Anpickens, der Kortikosteron-Spiegel sowohl zum Zeitpunkt des Anpickens
als auch zum Schlupfzeitpunkt sowie HP und Tb abnahmen. Am dritten Tag nach dem Schlupf war der Kortikosteron-Spiegel in Abhängigkeit von den Bedingungen vor
dem Schlupf höher, während die Bedingungen nach dem
Schlupf zu einer Abnahme der Kortikosteron-Spiegel führten. Die Hitzebelastung am 42. Tag nach dem Schlupf verminderte die T3-Spiegel bei der Behandlung TC und erhöhte den Kortikosteron-Spiegel in der nach dem Schlupf konditionierten Gruppe. Unterschiede zwischen den Körpergewichten konnten ab dem 28. Tag nach der Brut in der folgenden Reihenfolge beobachtet werden: TT > CC = CT >
TC. Am 42. Lebenstag wiesen die Broiler der Behandlung
TC die höchsten Körpergewichte auf. Die Hitzebelastung
am 3. Lebenstag verbesserte die Reaktion auf die Hitzebelastung am 42. Tag in positiver Weise und verbesserte so
die Hitzetoleranz, während sich die Behandlungen während der Brut deutlich negativ auswirkten. Es kann der
Schluss gezogen werden, dass eine Temperaturbelastung
während der Brut völlig andere Auswirkungen hat als eine
Temperaturbelastung nach dem Schlupf.
Broiler, thermotolerance, heat conditioning, heat stress,
physiological parameters, growth
Stichworte
Zusammenfassung
Broiler, Thermotoleranz, Temperaturbelastung, Hitzestress,
Physiologie, Wachstum
Summary
This study was designed to test the effect of pre- and
post-hatch temperature conditioning or a combination of
both, on the acquisition of heat tolerance during the adult
life of broiler chickens. Nine hundred hatching eggs produced by Cobb broiler breeders were incubated at standard
incubation conditions until d 16. Half of the eggs were subjected to temperature conditioning for 3 h/day (39.5°C,
65% relative humidity (RH)) at d 16, 17 and 18 of incubation (T group) while the other half Control group (C
group) were kept at standard incubation conditions. From
the end of d 18 until end of incubation, embryo heat production (HP), gas partial pressure in the air chamber at IP,
and blood parameters (T3 and corticosterone) were measured. Also, hatching time for individual chick, body temperature (Tb) and body weight (BW) and the number of
hatched chicks were recorded. Hatched chicks were raised
under regular conditions. At the age of 3 d, the chicks of
each incubation condition group were divided into 2
groups: half of the chicks of each group (C and T) were
subjected to thermal conditioning (41.0°C for 6 hours).
The other half of the chicks was used as control. The 4
groups of broilers were reared until 42 d of age. During
post-hatch period, Tb, blood parameters and BW were
again measured. At 42 d all broilers were heat challenged
at 35°C for 6 h. After heat challenge, mortality was recorded and blood samples were collected. The results indicate
that thermal conditioning during incubation had no effect
on hatchability of eggs but prolonged incubation duration,
decreased T3 (at IP), corticosterone (at IP and hatch), HP
and Tb. Overall, at 3 d post-hatch, prenatal condition increased while post-natal conditioning decreased corticosterone levels. Heat challenge at 42 d post-hatch decreased
T3 levels in the TC group and increased corticosterone levels in postnatally conditioned group. Differences between
BW become obvious from 28 d post-hatch and were in the
following order: TT > CC = CT > TC. At 42, the highest BW
was obtained in the broilers of TC group. Heat conditioning at 3 d of age improved heat tolerance in response to
heat challenge at 42 d. post-hatch whereas prenatal treatment had a strong negative effect. It is concluded that heat
treatment during incubation or during post-hatch life induces completely different effects.
Einfluss einer Temperaturbelastung zwischen dem
16. und 18. Bruttag oder in den ersten Tagen während der Aufzucht auf die Physiologie, das Wachstum nach dem Schlupf und die Hitzetoleranz des
Embryos
Das Ziel der Studie war, den Einfluss der Temperaturbedingungen vor und nach dem Schlupf (sowie einer Kombination von beidem) auf die Entwicklung von Hitzetoleranz
im Erwachsenenstadium bei Masthühnern zu untersuchen. Insgesamt 900 Bruteier einer Cobb Elterntierherde
wurden unter normalen Brutbedingungen bis zum 16.
Bruttag ausgebrütet. Die Hälfte der Eier wurde am 16., 17.
und 18. Bruttag (Behandlung T) einer Temperaturbelastung über 3 Stunden je Tag (39,5°C, 65% relative Feuchte)
Arch.Geflügelk. 2/2008
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Buchbesprechung
Verrückte Hühner
Stephen Green-Armytage, aus dem amerikanischen übersetzt von Thomas Hellmann, Verrückte Hühner; Verlag
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Arch.Geflügelk. 2/2008
83
mance and thermoregulation after hatch. J. Therm. Biol.
29, 245-250.
Correspondence: Okanlawon Onagbesan, Lab for Physiology and Immunology
of Domestic Animals, Katholieke Universiteit Leuven, Kasteelpark Arenberg
30, B-3001 Heverlee, Belgium; e-mail:
[email protected]
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