Impact of exposure to cold on layer production

Impact of exposure to cold on layer production

Alves FMS; Felix GA; Almeida Paz ICL; Nääs IA; Souza GM; Caldara FR; Garcia RG

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ABSTRACT

Infrared thermographic images were used to evaluate the effect of the exposure of layers to cold. In this trial, 540 Isa Brown® layers with an average age of 69 weeks were housed in a conventional layer house typically used in Brazil during a period of cold environmental temperatures. Environmental and heat-transference data were recorded between July 13-16, 2010. It was verified that layers under cold stress conditions lost four times more energy that the recommendations trying to maintain their body temperature. Due to their reduced feed intake capacity, hens are not capable of increasing the availability of the metabolic energy required to maintain their body temperature and egg production, consequently resulting in economic losses.

Keywords: Infrared image, housing environment, heat exchange, economic evaluation, egg production.

INTRODUCTION

During the last decade, there has been an increasing concern with animal welfare, particularly when associated with physiological responses used as indicators of animal comfort (Silva, 2001). Studies have determined a thermal comfort zone, within which livestock present higher and better production (Teeter & Belay, 1991; Barbosa Filho, 2007). However, the determination of this thermal comfort zone involves the knowledge on the many parameters, such as air temperature, air humidity, radiation, and wind, as well as their interactions (Paludo, 2002). It is difficult to determine the exact combination of these parameters that triggers heat stress, as it depends on the animal and specific environmental conditions (Azevedo & Souza, 2007).

Few studies were published in Brazil on the effect of cold on the behavior of layers, trying to identify the factors that cause cold stress, despite its tropical climate with wide temperature and humidity ranges (Nääs et al., 1995). One of the main problems related to low environmental temperatures when poultry are maintained in open-sided poultry houses is the increase in feed intake, which is a natural response to try to increase the intake of the energy required to maintain essential body functions.

Infrared thermography (IRT) has been used in many studies to determine thermal responses on several animal species (Phillips & Heath, 2001). The IRT technique is not invasive and it is capable of detecting the heat emitted by a surface (Van Hoogmoed & Snyder, 2002). It has been used to provide a more precise image of surface temperature variations compared with other methods available for this type of evaluation. Therefore, this study aimed at evaluating the effect of the exposure of layers to cold on the cost of egg production using infrared thermography.

MATERIALS AND METHODS

This study was carried out in an experimental facility located at latitude 22º 11’48.8", longitude 54º 56’11.7" W, and altitude of 450 m. The predominant climate in the region is tropical with mild Summer, dry in Winter and humid in Summer.

Birds and housing

In total, 540 Isa Brown® layers, with an average age of 69 weeks, were used. Six hens were housed per cage. During the experiment, the following average environmental parameters were recorded: 8.97 ºC environmental temperature, 66 % relative humidity, 23.43 lx luminosity, 13.91 ºC bird temperature, and 0.38 km h^-1 air velocity.

Environmental data were collected in six random locations inside the house (Figure 1) and were recorded on July 13-16, 2010, always at the same time (15 h:30 min), during the incidence of a wave of cold temperatures in the area.

Experimental procedure

Thermographic images of groups of birds were collected from the frontal and lateral positions to evaluate heat exchange. Images were collected using an infrared thermography camera with ± 0.1 °C precision and 7.5-13 μm series of the infrared spectrum.

The infrared thermography camera was placed approximately 1 m from the target in order to obtain the complete image of the group. Images were evaluated using a specific software program (Testo®, 2009), and a 0.95 coefficient of emissivity was used for the entire bird body surface. Average surface temperature (Ts) and standard deviation of a determined body area were calculated using the temperature measured in different randomly chosen points inside the birds’ body (Figure 2), according to the methodology proposed by Nääs et al. (2010).

Sensitive heat loss was considered as heat loss by radiation. Surface area was calculated using the geometric shape of layers, which is 0.372 m² according to Curtis (1983). Based on that datum, the theoretical estimate of heat loss by radiation (Qs=Qr) was calculated to measure the amount of heat lost by birds to the environment. Qr was calculated using Equation 1 (Meijerhof & Van Beek, 1993; Yahav et al., 2004).

Qr = ε σA(Ts⁴ - Ta⁴) Eq.1

Where: Qr = heat loss by radiation (W), ε = emissivity of the biological tissue, σ = constant of Stefan Boltzmann (5.67 10^-8 W m^-2 K^-4), A = bird surface area (m), Ts = bird surface temperature (°C) and Ta = air temperature (°C).

Egg production cost was evaluated using egg production percentage at 69 weeks of age, which was obtained by daily counting and weighing eggs produced and comparing the data with the recommended value for the genetic strain (Isa poultry, 2007), as well as average feed cost and egg price during the experiment. Feed intake was daily calculated by subtracting the weight of the feed residues from the weight of the feed offered. Economic and production losses were calculated taking into account average feed price and average fresh egg price, as shown in Equations 1, 2, and 3.

PL = Pc2 – Pc1 Eq. 2

where: PL = production loss, Pc1= production cost with stress, and Pc2= production cost with no stress.

Cp was calculated as:

PC = [(FI x n) tne] Fp Eq. 3

where: Pc = production cost, FI = feed intake per bird per day (g), n = number of birds, tne = total number of eggs, Fp = feed price (g)

PL = (Pd + Lshell) Eq. 4

Where PL = production loss, Pd = egg production drop, Lshell = egg loss due to soft eggshells.

RESULTS AND DISCUSSION

During data collection days, average environmental temperature in the experimental house was 10.5 ºC and air relative humidity 66%, which as different from UBA’s recommendations (2008) of temperature range at bird height of 20-27°C and 40-65% relative humidity. House temperature and ventilation must be provided according to rearing system, age, weight and physiological status of the birds to allow them to easily maintain their normal body temperatures (Curtis, 1983).

According to literature reports (Bridi, 2005; Pereira & Nääs, 2008; Pereira et al., 2008), the thermoneutral zone of mature layers in lay is between 21 and 33°C. Similarly to mammals, poultry use mechanisms of sensitive heat loss, non-evaporative by radiation, conduction, and convection, as well as latent heat exchange by evaporation. Poultry lose heat by evaporation through breathing.

Metabolizable energy (ME) intake was calculated based on Equation 1, indicating that birds consumed around 443 kcal day^-1. According to the NRC (1994), layers lose 15.7% of this energy as heat increment (69.51 kcal ME), but in the present study, heat increment was four times higher (287.71 kcal day^-1 ME). Part of ME intake is lost as heat (heat increment) and part is retained in the body, which is then called net energy and represents the efficiency of the conversion of dietary ME into protein, egg production, etc. (Sakomura et al., 2004). Heat increment depends on dietary energy source, and may be manipulated according to environmental temperature. At low temperatures, feeding diets rich in carbohydrates and proteins increase heat increment, consequently increasing body temperature. On the other hand, lipid-rich feeds should be used at high environmental temperatures, as lipid heat increment is low and does not contribute to increase body temperature. Rabello et al. (2004) reported that, when birds are submitted to low environmental temperatures, feed intake increases due to higher energy requirements, as observed in the present study.

Layers older than 65 weeks commonly consume around 122 g of feed with the composition shown in Table 1 (Isa poultry, 2007). However, in the present study, layers had a feed intake of about 160 g per day, possibly due to the requirement for maintaining thermal balance. However, despite the increase in feed intake, production losses were 6.63%, as estimated by Equations 2 and 3, which may also be related to the attempt to maintain homeothermia when exposed to discomfort caused by cold. The calculated economic loss (Equation 4) was of approximately 10.4% of the production.

The percentage of eggs with soft eggshells increased in 1.50%, further increasing the economic loss caused by the exposure of layers to intense cold and consequent thermal discomfort. On the other hand, average egg weight remained around the recommended value of 64 g (Table 2).

CONCLUSIONS

The use of thermographic images showed that, under cold stress conditions, layers spend four times more energy than that reported in literature. Due to its limited feed intake capacity, even if the bird increases feed intake, this is not sufficient to supply the ME required to maintain both body temperature and egg production, resulting in economic losses.

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Submitted: February/2011

Approved: October/2012

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Publication Dates

• Publication in this collection
  03 Dec 2012
• Date of issue
  Sept 2012

History

• Received
  Feb 2011
• Accepted
  Oct 2012