New approach for adaptation to high temperatures and its effect on the thermal resistance of broilers reared in western Algeria

Sahnoun Attou and Abdelkader Homrani

Faculty Sciences of Nature and Life, Department of Agricultural Sciences,
Abdelhamid Ibn Badis University, Hamadou Hossine Avenue BP 300 Mostaganem, Algeria
attousahnoun@hotmail.fr

Abstract

The objective of this work was to test an alternative approach of acclimatization of chickens to high temperature. Hubbard chickens were divided into 3 groups of 150 animals each. Different thermal environments to each group were applied from the 7^th day: thermo neutral temperature (NT: 25 ± 2°C) for the first group, moderately hot temperature (MT: 32 ± 2°C) for the second and very hot temperature (HT: 37°C) for the third. Simultaneously, the precocious acclimatization method for the chickens was also performed as a reference comparison. For this method, 2 groups of 150 Hubbard chickens (termed PA3 and PA5 respectively) were exposed for 24 hours at 39 ± 1°C for 3 or 5 days. After precocious heat treatment, all PA3 and PA5 chickens were placed at NT until the end of breeding (50 days). At 51 ^st day, broiler chickens of both acclimatization methods were exposed to a scorching temperature (40 ± 1°C) for 7 hours with greater water distributed.

A significant decrease (P˂0.05) in body weight (BW) of HT broilers was recorded at end of rearing compared to those of MT, NT, PA3 and PA5 broilers. The lower feed conversion ratio (FCR) recorded in HT broilers demonstrates the decrease in feed intake caused by HT. Precocious acclimatization of chickens (PA3 and PA5) allowed mortality rates (MoR) better than those of the NT chickens. No significant difference was found between MoR in PA3, PA5 and MT broilers. Finally, the precocious and continuous adaptation of HT broilers had generated a MoR significantly better than that of PA3 and PA5. Moreover, thermal shock of 7 hours caused a significant increase of rectal temperature (ReT) in HT and NT broiler chickens.

Keywords: acclimatization, heat wave, mortality rate, poultry

Introduction

In Algeria, especially in the western regions, poultry farming incurs heavy losses dues to adverse climatic conditions. These temperatures can cause significant economic losses due to higher mortality (Pereira et al 2010; Do Vale et al 2010).The absence of statistical data on economic losses to poultry caused by heat in Algeria warrants investigations to assess these losses. For example, in Morocco, a neighboring country of Algeria, high temperatures have caused considerable losses, nearly 15 and 10% mortality of broilers and turkeys, respectively (Baazi 2010). Several Algerian farmers prefer to avoid poultry farming, particularly of broilers, due to the summer heat and the associated losses (Alloui and Tlidjen 2001). It is important to note that over 90% of lower capacity buildings for rearing belong to small-scale farmers who cannot afford cooling equipments (Nouad 2011).

Fewer acclimatization techniques for chickens have been tested to adapt the birds from a younger age (De Basilio et al 2001; Temim et al 2009; Boudouma and Tefiel 2012). However, these tested temperatures are significantly lower than those recorded in the warm and unpredictable summer of western Algeria.

Compared to the already tested acclimatization techniques, it would be interesting to test another method of adaptation of chickens to higher temperatures that are appropriate to western Algerian climatic. The objective of this work was to evaluate the effectiveness of the adaptation of chickens to higher temperatures by a different approach of acclimatization. This approach is to raise chickens, from a younger age, in hot environments until the end of the breeding period.

Materials and methods

Broiler birds and their diets

The test was conducted in breeding workshop of Abdelhamid Ibn Badis University (Mostaganem). With 24 m² floor area, each of the buildings had static natural ventilation.

Non-sexed Hubbard chickens were used from the hatchery of west poultry group Mostaganem (WPGM) with an average weight of 37.1 ± 3.2g. Just after hatching, they were vaccinated against Marek’s disease and infectious bronchitis. After one, two and three weeks of age, they received vaccination against Newcastel disease through a triple vaccine (respiratory disease, infectious bronchitis and Gumboro), which was administered via drinking water.

Starter and grower diets were supplied by the WPGM industrial complex. Diets and drinking water were provided ad libitum. The diets characteristics are presented in Table 1.

Dietary analysis

Dietary fiber content was determined by the Weende method, which uses double hydrolysis of the non-cellulosic constituents, first in an acid solution and then in a basic solution (AOAC 1995). The content of lipids in the diets was determined by extraction in a dispositive Soxhlet apparatus using petrol ether (AOAC 1995). The crude protein of diets was determinate by the Kjeldahl method (AOAC 1995).

Experimental methodology

Mortality rates (MoR) were determined using two approaches to adapt the chickens to high temperatures. Rectal temperature (ReT) was recorded during heat stroke (7 hours) in all broilers. Production parameters of the broilers such as body weight (BW) and feed conversion ratio (FCR) were also recorded.

Former approach: Precocious adaptation of the chickens to heat

The 3-day or 5-day chickens (PA3 or PA5) were exposed to 39 ± 1°C for 24 hours. This heat treatment was to prepare the precociously grown chickens for possible heatstroke (i.e. sirocco), which are very common in western Algeria.

Hubbard chickens (150 per room) were stored in three rooms, each measuring 20m². The first two rooms were designed for the groups of 3-and 5-day chickens that were previously exposed to 39 ± 1°C for 24 hours. The third room consisted of the group of control chickens raised at normal temperature (between 35 and 36°C) during the first week.

To maintain constant temperature (39 ± 1°C for 24 hours), the 3- or 5-day chickens were placed in two isolated spaces of 4m2 each. For each space, a gas radian and oil heating (with adjustable temperature) were used.

After heat treatment (24 hours at 39 ± 1°C), all the chickens were returned to normal rearing temperature and reared for 50 days.

New approach: Precocious and continuous adaptation to heat

A total of 450, day-old Hubbard chickens were divided into 3 groups and reared for 50 days. From the 7^th day, different thermal environments were applied: a thermo neutral temperature (NT: 25 ± 2°C) for the first group, a moderately hot temperature (MT: 32 ± 2°C) for the second, and a very hot summer temperature (HT: 37°C) for the third.

Evaluation of resistance after heat stroke

In poultry farming, MoR is considered the best test to evaluate the resistance of a broiler to heat stroke. Economic losses are noticeable especially in late breeding i.e., in the finishing phase. This justifies the choice of the age (51 days) to submit broilers to scorching condition (heat stroke).

Thus, at the 51^st day of breeding, broiler chickens of both heat acclimatization approaches were exposed for 7 hours at a scorching temperature (40 ± 1°C) with greater water distribution. Exposure to such temperatures allows for a comparison of the difference in temperature resistance achieved with the two acclimatization approaches in broiler chickens. Adaptation results were evaluated as a percentage of mortality of chickens.

Statistical analysis

Mortality rates were compared by the Chi2test. The statistical software XLSTAT was used for analysis of variance of the rectal temperatures and zootechnical parameters. The Newman-Keuls test was used for comparing mean values.

Results

At the end of the rearing period, a significant decrease (P˂0.05) of BW was recorded in HT broilers than in MT broilers. This decrease of BW in HT broilers was more pronounced compared to those of NT, PA3 and PA5 broilers (Table 2).These differences in BW in NT, MT and HT broilers varied due to differing FCR values. Indeed, the low FCR recorded in HT broilers demonstrates the feed intake decrease caused by HT in the same broilers (Table 2).

Precocious acclimatization of chickens (PA3 and PA5) caused a significantly lower MoR than the NT broilers (Table 3). However, no significant difference was found between MoR in PA3, PA5 and MT broilers (Table 3). Finally, the precocious and continuous adaptation of HT broilers generated a MoR significantly better than that of PA3 and PA5.

During 7 hours of heat shock, significantly (P<0.05) higher ReT values were recorded in HT and NT broilers than the PA₃, PA _5, and MT broilers.

Discussion

For both acclimatization methods, the MoR decreased compared to that of NT chickens. However, MoR was better (i.e., lower) when the acclimatization was precocious and chronic, especially with the HT. Depending on the age of the broilers, exposure time, and temperature tested, several studies have been done on their acclimatization. Broilers exposed to 24–35°C for three days can resist heat stroke 40°C (Reece et al 1973). They can also develop resistance to thermal shock at 38°C when undergoing precocious acclimatization (5 days old) of 24 hours with 35-38°C (De Basilio et al 2001; Temim et al 2009). Other studies have already shown the relationship between the intensity of the ambient heat and MoR in broiler chickens (Wiernusz and Teeter 1996; Berrong and Washburn 1998; De Basilio et al 2001; Mashaly et al 2004; Al-Fataftah and Abu-Dieyeh 2007).

In non-acclimated chickens (in warmer environment or after heat stroke), higher MoR may be due to inefficient cooling by evaporation. This causes buildup of heat in the bird’s body. This could probably explain the higher mortality after seven hours of heat stroke in non-acclimatized chickens precociously or placed at NT. This buildup of heat inevitably causes an increase in rectal temperature, reaching or exceeding a lethal threshold at which the chickens die. In all dead chickens during heat stroke, symptoms and behaviors were similar. Just before death, the chickens looked exhausted and showed a rhythmic irregular panting. They then became immobile for about 10 minutes before dying. At that moment, their rectal temperature exceeded the mean rectal temperatures of the control chickens during the two thermal shocks (44 and 43.7°C).

Depending on the heat intensity and duration of its action, several anatomic changes may precede death in a non-acclimatized chicken having undergone a heat stroke. Indeed, death may be caused by cardiovascular failure or by blood ionic imbalance of sodium, potassium, calcium, phosphate, sulfate, and magnesium (Deaton et al 1984). In addition, when the body temperature increases (exceeds the thermo neutral), the parenchyma and endothelial cells start to deteriorate (Guyton 1966). This is followed by a rise in blood pressure which can cause circulatory failure followed by bleeding into organs, such as the kidney, lungs, liver, and heart (Aengwanich and Simaraks 2003; Aengwanich et al 2003; Aengwanich 2009). In this study, it is likely that the broilers that survived a heat stroke developed tolerance to high temperatures according to the two processes of acclimatization. This becomes evident from the limited MoR of acclimatized chickens, the survival time of >7 hours at 40°C, and large variations in rectal temperature of all chickens (acclimatized or otherwise).It has been reported that even with relatively warm temperatures (30 and 35°C), broilers can adapt to limit their mortality after a heat stroke (Al-Fataftah and Abu-Dieyeh 2007). This proves that with precocious and scorching temperatures used in our study, broilers acquired a better adaptation and increased tolerance to excessive heat intervening at a later age (late growth and / or finish) compared to a very early acclimatization of chickens (3 or 5 days). Heat stroke resulted in a significant increase in body temperature in non- non-acclimatized broiler, inevitably causing death of several broilers. Also, the body resistance at this temperature (40°C) probably exceeded the threshold tolerated of heat accumulation in those birds.

The body temperature caused by heat stroke was significantly lower in chickens acclimatized with HT. This could explain the HT broiler chickens to maintain this temperature below the critical threshold tolerated by the dissipation of a large amount of body heat through evaporative cooling (panting).This probably explains the observations made on acclimatized broilers that grouped around the water troughs and panting rhythm would have remained steady and constant during this heat stroke. Panting in birds is directly related to respiration rate which increases with the thermal stress.

El Hadi and Sykes (1982) noted a respiratory rate of 150 beats/min with a rearing temperature of 35°C. They also found that the panting begins 45 minutes after the beginning of exposure to 38°C. Some studies have shown that acclimatization to heat is generated by a decrease in production of heat rather than by an increase in heat loss (Sykes and Al-Fataftah 1986; Al-Fataftah and Abu-Dieyeh 2007).

To accurately assess the practical interest of this acclimatization technique, we suggest that further studies are required using higher bird count. Moreover, the use of this technique cannot be recommended only during seasons of extreme heat to allow for better use of solar energy elsewhere.

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Received 16 September 2016; Accepted 25 February 2017; Published 1 May 2017

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