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The climate type influences the body surface temperature of naked neck hens

João Batista Freire de Souza Jr, Vanessa Raquel de Morais Oliveira, João Paulo Araújo Fernandes de Queiroz, Ligiane Nadja da Silva, Alex Martins Varela de Arruda and Leonardo Lelis de Macedo Costa

Department of Animal Sciences, Federal Rural University of Semi-Arid, Mossoró, RN state, Brazil


The thermal equilibrium of an animal species is influenced differently in geographical regions with different climatic types. This occurs because environmental conditions vary in different regions. The present study deals with the evaluation of the surface temperature (TS) by infrared thermography in laying hens managed in different climates. Two experiments were conducted in the Northeastern Brazil using naked neck hens. The climates types evaluated were semi-arid climate type (Bsh) and a region of tropical climate (Aw). In both locations the environmental variables were measured at the center of the shed: air temperature, wind speed, relative humidity, as well as rainfall.

Thermal environment showed significative difference between the two locations (p <0.01) for all variables, where Aw had the highest averages for all the variables observed except for relative humidity. There was significant difference between the locations to all body regions (P <0.01). The highest averages were found in Aw. The highest average difference was found in the legs (4.6 °C). Comparing the means of the body regions in the same location, there were significant differences among all regions in the two locations. In both locations, the neck had the highest average. In the two locations the feathered area had the lowest average. All body regions were different from each other in both locations. The climate type Aw was presented as hotter than Bsh. This caused higher TS for the hens in this location. These high TS in regions devoid of feathers were an indicative of activation of sensible heat loss in these body parts, because this occurs in heat stress.

Keywords: heat stress, hot environments, infrared thermography, rearing systems


Brazil is a continental country and has several different climates. This same reality is found within a same state. This difference climatic influences differently thermal equilibrium of a same animal species. Geographical regions of low latitude, ie near the Equator, are characterized by intense solar radiation throughout the year (Silva et al 2013; Oliveira et al 2014), generating high temperatures that cause damage to livestock, especially poultry (Souza et al 2015).

Another important feature that can change the thermal status of laying hens is rearing system. When these animals are kept in cages, they are fully protected from direct solar radiation, but have restrictions on welfare (Silva et al 2006). In the semi-intensive system, the hens are raised on the floor and are free to express their natural behavior as it has access to a larger area (Weeks and Nicol 2006). Despite having access to a larger area, these hens can be exposed to direct solar radiation which provides to animals a high thermal load.

As a way of measuring the heat stress status without the handling of animals, infrared thermography has been used with poultry in recent studies (Case et al 2012; Zhao et al 2013; Hester et al 2015; Mayes et al 2015). In this context, the present study deals with the evaluation of the surface temperature by infrared thermography in laying hens managed in different climates.

Materials and methods

Location and animal raising system

Two experiments were conducted in the Northeastern Brazil using laying hens of the lineage Label Rouge (Naked Neck), which were fed with mash rations (isonutritive) prepared according to recommendations of Rostagno (2005) for semi-heavy laying hens (Table 1).

Table 1. Ingredients and nutritional composition of feed for Label Rouge hens.

Ingredients (kg)

Basal Ration



Soybean meal








Vitamin supplement#


Mineral supplement##


Nutrients (%)

Dry matter




Available phosphorus


Ethereal extract


Neutral detergent fiber


Acid detergent fiber


Crude protein


Apparent metabolizable (Kcal/Kg)


# assurance levels per kg of product: 10,000,000 IU vitamin A, 2,000,000 IU vitamin D, vitamin E 30,000 IU, Vitamin K 3.0 g, thiamine 2.0 g, riboflavin 2.0 g, pyridoxine 6.0 g, cobalamin 1.5 g, pantothenic acid 12 g, folic acid 1.0 g, biotin 1.0 g, niacin 50 g;
## assurance levels per kg of product: copper 20 g, iron 100 g, selenium 0.25 g, iodine 2.0 g, manganese 160 g, zinc 100 g, qs vehicle.

The first experiment was conducted in Mossoró, RN state, Brazil (latitude 05°11'S, longitude 37°22'W and altitude of 16 m above sea level). According to the climatic classification of Köppen-Geiger, the region is semi-arid climate type (Bsh). This study was conducted in the poultry sector of the Federal Rural University of Semi-Arid. Sixty laying hens that were between the ages of 32 and 35 weeks were individually housed in galvanized wire cages (L: 0.50 m × W: 0.45 m × H: 0.40 m) with feeders and nipple drinkers. The cages were arranged in a line in a shed (L: 4.0 m × C: 18.0 m × A: 2.5 m).

The second experiment was conducted in Natal, RN state, Brazil (latitude 05°47'S, longitude 35°12'W and altitude of 30 m above sea level). According to the climatic classification of Köppen-Geiger, the region has tropical climate with a dry season (Aw). This study was conducted in the Agricultural Research Corporation of the RN state. 128 laying hens were used during the period 32-40 weeks old, housed in experimental sheds divided into 16 enclosures, with 8 hens per enclosure (L: 2.4 m × W: 2.4 m × H: 3.0 m). In each of the enclosures was provided bell drinkers and tubular feeders. The concrete floor was covered with wood shavings. The roof is clay tile, masonry side low walls, screen fence and with free access to an external solarium (L: 2.4 m × W: 8.0 m).

Environmental data

In both experiments the measurements were conducted for four weeks, starting at 7 am, and all of the hens were measured daily and continuously. The air temperature (TA, °C) and relative humidity (RH, %) were measured using a digital thermohygrometer (Instrutherm, HT-300, São Paulo, Brazil). The wind speed (U, m s-1) was measured with a hot wire anemometer (Lutron, YK-2005AH, Kolkata, India).

The mean radiant temperature (MRT, K) was estimated from the following data: air temperature, wind speed and black globe temperature (0.15 m diameter copper black globe), which was measured with a thermocouple sensor (Type K) connected to a digital thermometer (Minipa, MT-600, São Paulo, Brazil). These facilities were installed at the center of the shed where the hens were evaluated. The MRT was used to calculate the radiant heat load (RHL=σMRT 4, W.m-2) and was estimated using the equation proposed by Da Silva et al (2010).

Infrared thermography

A total of 1,372 data were obtained where 788 observations in Mossoró (Bsh) and 584 observations in Natal (Aw) for surface temperature and environmental variables. The images (Figure 1) were taken at a distance of 1.5 meters with a portable infrared camera (b60 ThermaCAM®, Flir Systems), which was calibrated for ambient temperature and emissivity of the biological surface tissue (emissivity=0.98). The resolution of the infrared camera was 0.01 °C with an accuracy of 2 %. After obtaining the images, specific areas of the body surface (feathered area, legs, face and neck) were selected with the appropriate computer software (Flir QuickReport 1.2).

Figure 1. Thermal images obtained during the present study
Data analysis

An analysis of variance (ANOVA) was performed by the method of least squares for unbalanced data using SAS (SAS 1999). The comparison of the means was performed by Tukey-Kramer (p <0.01). The statistical model used is described below:

Yijk = μ + Li  + Rj  + Iij  + eijk

 where Yijk is the observation of the kth body surface temperature on the ith Location in the jth body region; Li is the fixed effect of the ith Location (i=1, 2); Rj is the fixed effect of the jth body region ( j=face, legs, neck or feathered area); Iij is the effect of the interaction between the ith Location with the jth body region; eijk is the residual effect which includes all sources variations not considered in the model and μ the overall mean.


Regarding the thermal environment, the F ANOVA test showed significative difference between the two locations (p <0.01) for all variables, where Natal had the highest averages for all the variables observed except for RH (Table 2).

Table 2. The means and standard errors, including maximum and minimum values, of the meteorological variables observed in the two locations during the study.

Location and Variables





    TA (°C)




    RH (%)




    U (m s-1)




    RHL (W.m-2)




    Accumulated rainfall (mm)



    TA (°C)




    RH (%)




    U (m s-1)




    RHL (W.m-2)




    Accumulated rainfall (mm)


ab The different letters in the same variable indicate a significant difference (F ANOVA test, P<0.01)

The average difference between two locations as TA was 2.0 °C and RH was almost 20%. In both locations, U was zero in many observations and the means in the two locations were smaller than 1.0 m s-1. Despite the significant difference of the RHL in the locations, the difference was only 15 W.m -2. But it is worth noting that there was a high variation of RHL in Natal and a low variation in Mossoró. The difference between the minimum and maximum values in Mossoró was only 56.6 W.m-2 and Natal was 332.3 W.m-2. The accumulated rainfall in the experiment period in Mossoró was about six times higher compared to Natal. This meteorological event caused a higher RH during the study in Mossoró.

The ANOVA showed significant effects of the location, body region and the interaction between these two effects on the surface temperature. The least squares means of the TS for the interaction between the different body regions and the locations studied are shown in Figure  2.

There was significant difference between the locations to all body regions (P <0.01). The highest averages were found in Natal where TS increased significantly with the increase in TA in this location. Between body regions studied, the highest average difference was found in the legs (4.6 °C). Comparing the means of the body regions in the same location, there were significant differences among all regions in the two locations (P <0.01). In both locations, the neck had the highest average followed by the face and legs. In the two locations the feathered area had the lowest average.

Figure 2. The least squares means of TS for the interaction between
the different body regions and the locations studied

The different lowercase letters indicate a significant difference between the body regions in the same location. The different capital letters in the same body region indicate a difference between the locations (Tukey-Kramer P<0.01)


In general, the Brazilian semi-arid region (Bsh) is characterized by high solar radiation levels and temperature (Domingos et al 2013). The seasons are not well defined and are observed a dry season and a rainy season. Already the tropical climate with dry season (Aw) has high temperature and the rainfall is distributed throughout the year with higher values ​​in the coastal region.

In this study, the semi-arid had higher rainfall (305 mm) than the tropical region (51.2 mm), as was done during the rainy season in this region (Bsh in April-May). This meteorological event caused RH higher in Bsh, generating also decreased in TA.

The geographic regions studied have different climatic types, but have a latitudinal proximity (Mossoró= 05°11'S; Natal= 05°47'S). Thus, despite the significant difference in RHL between the two locations, the values are very close (Table 2). It is noteworthy that the RHL values ​​in this study were measured inside the sheds. Similar to higher values ​​of RHL were found Queiroz et al (2014) studying broilers in semi-arid environment (459-585 W.m -2) inside the shed throughout the day. Already Da Silva et al (2010) found RHL values ​​much higher (742 W.m-2) in three locations next to the present study, however these high values ​​were obtained with exposure to direct solar radiation.

The investigation of surface temperature by infrared thermography has been held in several species of poultry in recent years; among them are the broilers (Nääs et al 2010; Giloh et al 2012), quails (Souza et al 2013a), laying hens (Zhao et al 2013) and turkeys (Mayes et al 2015). Infrared technology is presented as an important measurement tool for thermal stress status at any given time. In addition to providing a thermal mapping of the body surface (Souza et al 2013a) can be used as tool to estimate of productive performance in production animals (Case et al 2012).

This thermal mapping has already been performed by Cangar et al (2008) and Nääs et al (2010) in broilers and Cook et al (2006) and Souza et al (2013b) in laying hens. Based on the findings of these studies, it has been found regional differences in surface temperatures. The feathered area has shown lower temperature than without feathers area.

In our study, we also found significant differences between the body regions in the two study locations and the feathered area also had the lowest value among the body regions studied. The temperature in the feathered area tends to be very close to the air temperature (Mutaf et al 2008). In this study, between body regions studied, feathered area was also closest to the air temperature, although there was difference between the locations ( Figure 2).

The temperature in the legs of birds also exhibit significant increase with increasing air temperature and act as thermal windows. A thermal window is a body surface region involved, partially or completely, in thermal exchanges. In these body regions occurs local vasodilation at high temperatures and local vasoconstriction at low temperatures in order to dissipate or maintain body heat, respectively (Mauck et al 2003; Nääs et al 2014).

In the present study, the higher air temperature in Natal caused a higher temperature in the legs of the hens when compared to Mossoró. Under these conditions the hens use their legs to dissipate excess heat gain of the environment, which was observed by the increasing temperature in this region. This may also be due to semi-intensive rearing system in Natal, where hens had access to an area with exposure to solar radiation direct.

The temperature of facial area was high in both locations (Mossoró= 36.0 °C; Natal= 38.5 °C). In this body part there is the presence of vision bodies, which are richly vascularized, besides the epidermis devoid of feathers in the periocular region. In this study TS facial area was high, but differs between the locations where the average difference of 2.0 °C in TA caused an increase of 2.5 °C in TS in this region. Dahlke et al (2005) also reported high values of TS ​​in the head of broilers at 42 days of age under heat stress. There are contradictions in the literature results for TS in the face when the birds are in lower TA. Cangar et al (2008) and Yahav et al (2008) found smaller values of TS in TA = 25.0 °C when compared to TA above 37.0 °C. These results differ from those found by Souza et al (2013b), who found that the TS in face did not change when TA ranged from 24.0 °C to 31.0 °C.

The hens strain used in this study presents the neck devoid of feathers. This feature is an advantage to these hens by to have an other pathway to dissipate excess heat in hot environments. Few studies have examined the temperature of this body region. Nääs et al (2010) found TS much lower in neck, but this result was found with a broiler strain that has feathers on the neck (Ross). Souza et al (2013b) studying Naked neck hens subjected to different TA found high TS and did not change with a variation of 7.0 °C in TA. This was justified to the effect of carotid arteries are located in the neck and supplies blood from the heart to all organs of the head. In our study the TS in the neck was high in both locations. High TA at Natal caused higher TS as compared to Mossoro, around 1.7 °C.


Conflicts of interest

We confirm that we have no conflicts of interest.


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Received 18 March 2016; Accepted 31 March 2016; Published 1 May 2016

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