CLOACAL AND SURFACE TEMPERATURES OF BROILERS SUBJECT TO THERMAL STRESS

ABSTRACT:

The cloacal and surface temperatures are important physiological parameters to quantify the thermal comfort of animals, its variations may occur as a function of thermal variables. In this context, the goal of the present study was to evaluate the cloacal (t_clo) and surface (t_sur) temperatures of Cobb 500^® broilers, in the second week of life, subjected to different air dry-bulb temperature (24, 27, 30 and 33 °C) and stress durations (1, 2, 3 and 4 days). The experiment was carried out in four climate-controlled wind tunnels. Air relative humidity and air velocity were set at 60% and 0.2 m s-1, respectively. The t_clo and t_sur were measured daily through digital thermometer and thermographic camera, respectively. Analysis of variance and Scott Knott mean test at 5% probability were applied to the data. The results indicate that the stress by low air temperature (24 and 27 °C) resulted decreased of t_clo and t_sur (p<0.05, Scott-Knott test). When subjected to high air temperature stress (33 °C), there was no significant difference (p>0.05, Scott-Knott test) compared to the control treatment (30 °C). Acclimation of broilers to thermal stress occurred from the second day of stress.

KEYWORDS:
animal environment; aviculture; thermal comfort; thermographic image; physiologic parameters

INTRODUCTION

Brazil, a country with a large territorial extension presents great climatic diversity with temperature amplitudes during the year, in which promotes complications in the broilers breeding due to the variations that occur in the environment production (Nääs et al., 2010).

Thus, in the current scenario of Brazilian poultry development it is necessary that the poultry be raised in appropriate environments so they can achieve high performance maximizing their genetic potential. Under these conditions, characterized as thermal comfort, obtain low energy expenditure to control the homoeothermic thus increasing the performance (Nascimento et al., 2014).

The cloacal (t_clo) and surface (t_sur) temperature are among the main physiological indicators for thermal comfort on broilers, as they change with the variation of air dry bulb temperature (t_db), relative humidity (RH) and luminosity (Costa et al., 2012; Ferreira et al., 2012). When t_sur and t_clo variation occur, the broilers dissipate or retain heat, and part of the energy that should use to gain weight will be applied in the thermoregulatory process reducing productive responses.

Any variation in body temperature of broiler indicates that the performed changes on their surface were not enough to maintain the thermal equilibrium (Nascimento et al., 2013) indicating physiological changes.

The increase of t_clo is proportional to the age (Marchini et al., 2007), and the stress caused by high t_clo results in decrease in weight gain (Costa et al., 2012). According to Oliveira et al. (2006) the body core temperature for the second week of life varies between 41 to 42 °C consistent with the values found by Bueno et al. (2014).

According to Nääs et al. (2014), through skin analysis temperature it is possible to determine the physical healthy state of the animal. One way to evaluate the t_sur on broilers is through infrared thermography which is a procedure that does not cause interference in the ecological niche of the evaluated animal (Nascimento et al., 2011a).

Although feathers obstruct the infrared emission of the skin, the thermography allows the thermal mapping of the body (Castilho et al., 2015; Souza Junior et al., 2013) and is used in several studies to obtain the thermal responses (Barnabé et al., 2015; Mayes et al., 2014; Roberto & Souza, 2014), since the variation of the t_sur is instantaneously modified when thermal changes occur in the thermal environment of the breeding.

The aim of this study was to evaluate the average surface and cloacal temperature on broilers in the second week of life submitted to different intensities and duration of thermal stress, adjusting correlation equations between these variables.

MATERIAL AND METHODS

This research was carried out in an animal environment laboratory equipped with two air conditioning systems 18,000 BTUs each used to control and maintain room air temperature. It also contains four climate-controlled wind tunnels. Inside each wind tunnels there was a cage with dimensions of 0.40 × 0.60 m divided into three sub-distributions equal to 0.08 m² each, equipped with feeders and water fountains.

Two hundred and forty males and females broilers Cobb 500^® lineage were used from same commercial hatchery, of one day of life. For each stage were used sixty broilers with distribution of five broilers per division during the first seven days of life, that is, fifteen broilers per tunnel. Subsequently, in the second week of life, only four chicks were kept in each replicate maintaining the breeding density recommended by the manual (Cobb, 2012).

During the experimental period the broilers were fed with a balanced diet based on corn and soybean, following the nutritional recommendations by Rostagno et al. (2011). Feed and water were available ad libitum. The hygienization of the wind tunnels and cages was carried out every day to avoid formation of gases, providing an adequate environment for broilers performance. The t_clo and t_sur of the poultries were also daily evaluated.

The experiment was carried out in different stages varying the intensity of t_db applied on broilers on second week of life. In the first seven days, the birds were kept in thermal comfort at 33 °C (Cony & Zocche, 2004). From the eighth day, the t_db levels at each stage were 24, 27 and 33 °C, in order to provide thermal stress at both low and high air temperatures (Cony & Zocche, 2004; Curtis, 1983).

The thermal stress was applied in four levels of duration and performed on days 8, 9, 10 and 11 of the experimental period of each stage. During the second week, the air temperatures returned to thermo neutrality zone. Table 1 shows how the treatments were divided.

TABLE 1
The air dry-bulb temperature and days of maintenance of heat stress condition (in bold), applied to broilers from 1 to 21 days of age kept in climate-controlled wind tunnels.

			Air dry-bulb temperature (°C)
Stage	Tunnel	Days of Life
		1 to 7	8	9	10	11	12	13	14
1	A	33	33	30	30	30	30	30	30
	B		33	33	30	30	30	30	30
	C		33	33	33	30	30	30	30
	D		33	33	33	33	30	30	30
2	A	33	27	30	30	30	30	30	30
	B		27	27	30	30	30	30	30
	C		27	27	27	30	30	30	30
	D		27	27	27	27	30	30	30
3	A	33	24	30	30	30	30	30	30
	B		24	24	30	30	30	30	30
	C		24	24	24	30	30	30	30
	D		24	24	24	24	30	30	30
4	A, B, C and D	33				30

For the experiment, the air relative humidity was maintained at 60 ± 1% and air velocity at 0.2 ± 0.1 m s-1, characterized as comfort for broilers (Medeiros et al., 2005). The illuminance was adjusted by means of a luxmeter (LDR-380, accuracy of ± 3%), with intensities of 25 and 10 lux for the first and second week of life, respectively (Cobb, 2012).

Thermographic images were used to obtain surface temperatures. The images were acquired by means of a Fluke thermographic camera (model TI55FT20/54/7.5), positioned 1 meter high from the cage, in order to allow a wide view and comprehensiveness of all the animals.

The thermographic evaluation was elaborated using the Fluke Smart View 3.0.126.0 software, in which the adopted emissivity was 0.95 (Ferreira et al., 2011; Nääs et al., 2014). For each replicate of the cage a bird was randomly selected (Figure 1) and the average t_sur was obtained as a function of the surface areas of three broilers (Case et al., 2012; Nascimento et al., 2011b).

FIGURE 1
Thermographic image of broilers subjected to determined thermal conditions inside the climate-controlled wind tunnels.

With respect to the t_clo a broiler from each part of the cage was captured randomly to have its cycle measured, that is, twelve broilers per day totalizing forty-eight verifications per step. The measurement of t_clo was performed by digital thermometer (INSTRUTHERM^® São Paulo, Brazil, Model THR-080, accuracy ± 0.01 °C), and before each use the sensor was sterilized and introduced into the broilers cloaca, obtaining the value of the t_clo until the reading was stabilized (Costa et al., 2012).

For the statistical analysis of the variables was used completely randomized design (C.R.D.) with three replications, assembled according to the 4×4 factorial arrangement, that is, four t_db in the second week of broilers life (33, 30, 27 and 24 ˚C) and four stress durations (1, 2, 3 and 4 days), according to equation 1. The variables were treated by the statistical program SISVAR 5.3 (Ferreira, 2010) submitted to variance analysis and comparison means using the Scott Knott test at the 5% probability level. The data were submitted to clustering analysis (R Development Core Team, 2012), for the construction of the dendogram of broilers t_clo using Ward's method which calculates the smallest sum of squares within the groups (Biagiotti et al., 2015).

(1) $$Y_{ijk}=\mu +{\alpha }_i+{\beta }_j+\alpha {\beta }_{ij}+e_{ijk}$$

In which,

Y_ijk is the observation of the repetition k of the i-th temperature in the j-th duration with i, j = 1, 2, 3, 4 and k = 1,2,3;

μ is the constant associated with each observation;

α_i is the effect of the i-th temperature;

β_j the effect of the j-th duration;

αβ_ij interaction between dry air bulb temperature and duration, and

e_ijkerror associated with each observation, being $e_{ijk}~N(0,{\sigma }^2)$.

RESULTS AND DISCUSSION

To verify the t_db and RH which the broilers were submitted, the thermal environment inside the wind tunnels was monitored during the experimental period. The mean values and standard deviations observed during the second week of life are listed in Table 2.

TABLE 2
Values of air dry-bulb temperature (t_{db, desired}) and air relative humidity (RH_desired) desired, means observed (t_db,obs and RH_obs) and standard deviations (in parentheses) inside the climate-controlled wind tunnels.

Stage	Thermal variables	Stress duration
		1 day	2 days	3 days	4 days
1	tdb,desired (°C)		24.0
	tdb,obs (°C)	24.3 (0.3)	24.3 (0.3)	24.3 (0.3)	24.3 (0.3)
	RHobs (%)	60.4 (0.7)	60.4 (0.8)	59.9 (1.0)	60.8 (0.6)
2	tdb,desired (°C)		27.0
	tdb,obs (°C)	27.2 (0.3)	27.2 (0.2)	27.1 (0.2)	27.2 (0.3)
	RHobs (%)	60.0 (1.6)	60.3 (1.0)	60.0 (0.9)	60.4 (0.9)
3	tdb,desired (°C)		33.0
	tdb,obs (°C)	33.0 (0.3)	33.0 (0.3)	33.0 (0.3)	33.0 (0.3)
	RHobs (%)	60.0 (1.7)	60.1 (1.3)	59.9 (1.4)	60.5 (1.3)
4	tdb,desired (°C)		30.0
	tdb,obs (°C)		30.2 (0.2)
	RHobs (%)		60.3 (0.7)

• t_{db, desired} = air dry-bulb temperature desired;
• t_{db, obs} = air dry-bulb temperature observed;
• RH_obs = air relative humidity observed.

The observed air dry-bulb temperatures obtained low standard deviations, being close to the desired temperatures (Table 2). The highest standard deviations were 0.3 ° C for t_db and 1.7% for RH. These variations indicate the efficiency of climate-controlled wind tunnels in maintaining the desired thermal environment, corroborating with Schiassi et al. (2014).

The interaction between t_db and duration of thermal stress for the averages t_clo was not significant (P <0.05, test F) however, the different t_db and thermal stress durations presented significant difference (P <0.01, Test F), and the means test is listed in Table 3. The lowest t_clo (40.5 °C) occurred when the broilers were submitted to the lowest thermal stress of the t_db (24 °C) with the t_clo observed being below the lower limit for the range considered as comfort which varies from 41 to 42 °C (Oliveira et al., 2006). Thus, it is observed that the t_db of 24°C provided a significant decrease in t_clo of the broilers (P <0.05, Scott-Knott test), thus characterizing cold stress condition (Castilho et al., 2015).

TABLE 3
Mean and standard deviations (in parentheses) of the cloacal temperature (t_clo) of broilers submitted to different intensity and duration of thermal stress during the second week of life.

tdb (°C)	tclo (°C)	Stress duration (days)	tclo (°C)
24	40.5 (0.33) a	1	41.0 (0.71) a
27	41.3 (0.39) b	2	41.3 (0.63) b
30	41.8 (0.08) c	3	41.4 (0.55) b
33	41.6 (0.36) c	4	41.5 (0.47) b

• Means followed by different letters differ from one another by the Scott Knott test (P <0.05).

For t_db of 27°C it is observed that the t_clo is within the comfort range however, significant difference (P <0.05, Scott-Knott test) occurs in relation to the other temperatures of thermal stress. In the control treatment (t_db = 30 °C) that characterizes thermal comfort condition (Schiassi et al., 2015, Cony & Zocche, 2004), the value of the t_clo is within the comfort range. However, when broilers were submitted to t_db of 33 °C it was found no significant difference (P <0.05, Scott-Knott test) in relation to the control treatment. This is due to the fact that the broilers have been able to dissipate the produced heat by the metabolism to the environment (Abreu & Abreu 2011), because this value of t_db is still not enough to provide significant increase of the t_clo.

Regarding the thermal stress duration there was a significant difference (P <0.05, Scott-Knott test) between the first day in relation to the others (2^nd, 3^rd and 4^th day), which are statistically the same (P >0.05, Scott-Knott test). In this way, the broilers' ability to acclimatize confirm as reported in several studies (Alves et al., 2010; Baêta & Souza, 2010; Schiassi et al., 2015; Silva & Vieira, 2010).

When applying the cluster analysis methodology on the t_db as a function of the t_clo it is observed that the classifications of t_db associated with the distance scale in the dendogram (Figure 2) presented similar results to those obtained by the variance analysis and the mean test by Scott-Knott at the 5% probability level.

FIGURE 2
Analysis in dendrogram of air dry-bulb temperature (t_db) according to the cloacal temperature (t_clo) of broilers subjected to different intensities of stress in the second week of life.

By means of the thermographic images it was verified that the broilers average t_sur reduced and increased when submitted to low and high stress temperatures respectively, corroborating with the results obtained by several authors (Welker et al., 2008; Yahav et al., 2005).

The interaction between t_db and the thermal stress duration for the means of the t_sur was significant (P <0.05, F test) (Table 4). For one day of stress, it was observed significant difference (P <0.05, Scott-Knott test) for all used temperatures with the average variation of the t_sur being 5.0 °C.

TABLE 4
Mean and standard deviations of surface temperatures (t_sur) of broilers submitted to different durations of thermal stress during the second week of life.

tdb (°C)	Thermal stress duration (days)
	1	2	3	4
24	30.0 (0.43) a A	31.6 (0.60) a B	31.6 (0.32) a B	30.7 (1.80) a A
27	32.0 (0.37) b A	31.0 (0.37) a A	31.2 (0.46) a A	31.4 (0.28) a A
30	34.2 (0.10) c A	33.6 (0.17) b A	33.2 (0.40) b A	33.6 (0.32) b A
33	35.0 (0.40) d A	34.1 (0.23) b B	34.0 (0,25) b B	33.6 (0.40) b B

• Averages with different letters (uppercase in the row and lowercase in the column) indicate statistical differences (P <0.05) by the Scott Knott test.

For the durations of thermal stress of two, three and four days there was no significant difference (P> 0.05, Scott-Knott test) of the t_sur between t_db at 24 and 27 °C (stress due to low temperatures) and also between t_db at 30 °C (comfort) and 33°C (stress with high temperature). However, there was a statistical difference (P <0.05, Scott-Knott test) from t_sur between the two groups of t_db (24 °C / 27 °C and 30 °C / 33 °C).

Based on the results it can be verified that when the broilers were exposed to thermal stress at low air temperature (27 °C), in relation to comfort t_db (30 °C) significant difference was found (P <0.05, Scott-Knott test) for the t_sur in four thermal stress duration. According to Cassuce et al. (2013) the air temperature of 27 °C is comfortable in the second week of life for broilers, but the recommended comfort value in the literature for the second week is 30 °C (Schiassi et al., 2015; Cony & Zocche, 2004), and can be confirmed through the t_clo and t_sur observed in this study. However, it should be emphasized that this analysis represents only the variation of two physiological parameters without considering the zootechnical responses.

Equations for estimation of the t_clo and t_sur were adjusted as a function of t_db (equations 2 and 3, respectively). The adjusted equations were significant (P <0.05, F test) and showed determination coefficients (R2) of 0.75 and 0.76, respectively. The adjusted coefficients for eqs (2) and (3) were significant (P <0.01, t test), and the standard errors of b₀ constant were 0.39 and 0.87 and for b₁ of 0.13 and 0,03, respectively.

(2) $$t_{clo}=37.53+0.13\cdot t_{db}$$

(3) $$t_{sur}=22.30+0.36\cdot t_{db}$$

According to eqs (2) and (3) for each degree of variation in the t_db occurs the modification of 0.13 °C and 0.36 °C for the t_clo and t_sur, respectively. According to Carvalho et al. (2004), the surface temperature of broilers is subject to faster alteration, since the dissipation of the blood flow occurs through the convection. This behavior can be verified through eqs (2) and (3) in which for each degree of variation, t_sur varies 2.77 times more than t_clo.

Thus, when subjected to stress at low intensities (24°C) there is reduction of 0.78 and 2.16 °C for t_clo and t_sur respectively, and when stress occurs with high intensity (33 °C) the increase is 0.39 and 1.08 °C for t_clo and t_sur, respectively, when compared to comfort temperatures (30 °C).

Considering the importance of statistical analysis for correlation equations formulation between t_clo as a function of t_sur (Nascimento, 2010), [eq. (4)] was adjusted in which R² was 0.75.

(4) $$t_{clo}=37.93+0.32\cdot t_{sur}$$

Through the [eq. (4)] it is possible to determine the t_clo in a non-invasive way, through the use of infrared sensors for the measurement of the t_sur. Thus, it is possible to estimate t_clo with minimum stress for broilers, and in the usual methodology for the determination of t_clo it is necessary the direct contact of the thermometer with the cloaca of the broilers occurring in this way a stress factor. Equation 4 can be used in an algorithm to be shipped in microcontrollers to help the decision making regarding the activation of ventilation and evaporative cooling systems.

CONCLUSIONS

Based on the values of surface temperature (t_sur) and cloacal temperature (t_clo) it was found that the thermal comfort temperature for broilers in the second week of life is 30 °C. The acclimatization of broilers to thermal stress occurred from the second day of stress. The highest variation of the t_clo occurred when the broilers were submitted to low stress temperatures, and the t_sur varied according to the applied stress intensities. The correlation equations developed can be used to support the decision making.

ACKNOWLEDGMENTS

The authors express their thanks to CAPES, to CNPq and FAPEMIG for the financial support to this research.

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Publication Dates

• Publication in this collection
  Sep-Oct 2017

History

• Received
  31 Mar 2016
• Accepted
  03 May 2017