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Thermal preferences of chicks brooded at different air temperatures a

Huda Alsam & C. M. Wathes

a b


Department of Animal Husbandry , University of Bristol , Longford, Bristol, BS18 7DU, England b

AFRC Silsoe Research Institute , Wrest Park, Silsoe, Bedford, MK45 4HS Published online: 08 Nov 2007.

To cite this article: Huda Alsam & C. M. Wathes (1991) Thermal preferences of chicks brooded at different air temperatures, British Poultry Science, 32:5, 917-927, DOI: 10.1080/00071669108417418 To link to this article:

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British Poultry Science (1991) 32: 917-927

THERMAL PREFERENCES OF CHICKS BROODED AT DIFFERENT AIR TEMPERATURES HUDA ALSAM AND C. M. WATHES 1 Department of Animal Husbandry, University of Bristol, Longford, Bristol BS18 7DU, England

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Received for publication 19th November 1990

Abstract 1. The thermal preferences of small flocks of 400 chicks brooded under radiant heaters were determined at air temperatures of 21, 24 and 27°C from observations of behavioural thermoregulation. 2. At 1 d of age the upper limits of the preferred black bulb temperature increased with air temperature. Preferences for radiant temperature declined with air temperature. 3. Compensation for cold air temperature was imperfect because the chicks avoided zones of high radiant flux. The maximum tolerable radiant temperature was approximately 50°C. 4. Radiant heaters are preferable to convectors in poultry husbandry because the inherent lack of spatial homogeneity in thermal environments ensures that chicks can satisfy their individual thermal preferences. INTRODUCTION

The performance of broiler chicks at 2 weeks of age or older has been studied at different air temperatures by many workers (see review by Charles, 1986). There are fewer reports of the effect of brooding temperature on younger chicks (Barott and Pringle, 1949; Felton, 1974; Wathes et al., 1982ft). The overall conclusion from these studies is that bird performance is similar under quite different brooding temperature regimes, probably because the birds can practice behavioural thermoregulation. There are also few reports on the effect of light intensity on broiler performance where the treatments are applied at less than 2 weeks of age. For example, Wathes et al. (1982a) studied the growth of male and female broiler chicks under different light intensities and wavelengths, when the treatments commenced at 8 d. In the UK, current commercial practice is a light intensity of about 20 lux at 1-d-old. reducing to 1-0 to 2"5 lux by 4 weeks of age. This relatively bright intensity at 1-d-old enables the chicks to find their food and water. 1

Current address: AFRC Silsoe Research Institute, Wrest Park, Silsoe, Bedford MK45 4HS. 917



The accompanying paper (Alsam and Wathes, 1991) describes the preferences of chicks from 0 to 14 d for black bulb (environmental) temperature and light intensity at an air temperature of 24°C. The separate preferences were altered if the birds were both warmed under a radiant heater and illuminated with a spot light. This paper reports the results of two experiments. In the first, the effect of radiant brooding at three air temperatures on the performance and thermal preferences of broiler chicks was studied. In the second, the preferences for light intensity and temperature were examined in a flock of broiler chicks kept on a commercial farm.

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Many of the details of the materials and methods were similar to those used previously (Alsam and Wathes, 1991).

Experiment 1

A total of 2400 1-d-old male Ross broiler chicks were allocated at random to six environmental chambers in which radiant and air temperature, light intensity and photoperiod were controlled as before. The rooms were laid out in two blocks of three on either side of a central passageway. The minimum ventilation rate was the same in each room and was adjusted weekly. Two 1 kW electric radiant heaters were used as a supplementary source of heat in all the treatments and were hung at 475 mm height, side by side, and controlled by one thermostat placed at 395 mm from the midline of one heater. Air and black bulb temperature were recorded in each room at halfhourly intervals. The experimental treatment was air temperature, with three temperatures (21, 24 and 27°C) replicated twice. The spatial distribution of radiant and black bulb temperatures depended upon air temperature but the black bulb temperature at the location of the thermostat was similar in all rooms. At this site the black bulb temperature was controlled at 31°C at day 1, reduced by 0"5°C/d until the air temperature was reached. From then on the air temperature was reduced by 0-5°C/d until 20 d, at which point the temperature was similar in all the rooms. The spatial distribution of radiant temperature was measured with a miniature net radiometer and the mean radiant temperature was calculated from the average of the upwards and downwards radiant fluxes. A single incandescent lamp was placed in the centre of each room at a fixed height of 950 mm from the ground and equipped with a shade to produce a circle of light of intensity 34 lux beneath the lamp. The minimum intensity was 2 lux in the corners of the room. Other aspects of poultry husbandry were as described previously. Food and water were available ad libitum. A representative sample of 50 birds was



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weighed and the food intake of the birds in each room was measured at weekly intervals. Post-mortem examination was carried out on those birds which died. These data were analysed by a two-way analysis of variance with the two sides of the poultry house as a blocking factor and air temperature as the experimental factor. The behaviour of the birds was assessed at 5-min intervals for 1 h at 1 and 7 d of age, as described previously. The area occupied by the clusters of huddled birds was measured using an image analyser and related to the spatial distribution of black bulb and radiant temperatures for each treatment of air temperature. Contour intervals of 2°C and 10 or 20°C were chosen for the distribution of black bulb and radiant temperature, respectively. The mean occupancy of each zone was calculated from the individual observations at 5min intervals, and the black bulb and radiant temperature ranges preferred by 90% of the cluster were calculated.

Experiment 2

This experiment was carried out in a large poultry house belonging to a commercial poultry company. Approximately 14,000 1-d-old broiler chicks were housed in a building measuring 52 m long by 13-4 m wide with heights at the eaves and ridge of 1-5 and 2*8 m, respectively. Eight gas-fired radiant brooders (SRB3) of 5-7 kW capacity with a reflector diameter of 860 mm were hung at a height of 1-5 m at equal intervals along the centre line of the building. Eight fluorescent strip lights of 36 W capacity were mounted in the ridge about 2-1 m above the floor and faced upwards for the first few days. Food and water were available ad libitum from pellets scattered on cardboard strips resting on the litter and from chain feeders for the first few days and from chain feeders only thereafter, and from bell drinkers, respectively. All other husbandry followed current commercial practice. The preferences of the chicks for light intensity and temperature were recorded at 1, 7 and 14 d of age using a similar method to that described before (Alsam and Wathes, 1991). Briefly, a grid of 1 m X 1 m squares, made from string hung at a height of 200 mm, was placed in the centre of the building. It occupied two bays and had one brooder and one light at its approximate centre. The brooder was operated at full heat output during the behavioural observations. The distribution of light intensity and black bulb temperature was measured at every node and those within one quadrant, respectively, after each set of observations using the same instruments as before. Air temperature was measured with an Assman psychrometer. The locations of clusters of birds were recorded on a map at 5-min intervals for 1 h by two observers, but the first and last observations were discarded to discount any interference by the observers. The preferences were determined from a spatial analysis of the cluster distributions using contour intervals of 2°C and 10 lux (1 d) and 25 lux (7 and 14 d) for temperature and light intensity, respectively.

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Air temperature

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500 Distance, mm




FIG. 1.—The spatial distribution of black bulb and radiant temperature beneatli radiant brooders at air temperatures of 21, 24 and 27°C with thermostat settings at a fixed location of 31 (o) and 28°C (•), corresponding to bird ages of 1 and 7 d, respectively. Distance is measured perpendicularly to the heater's long axis.




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Experiment 1

Figure 1 shows the temperature profiles beneath the heaters in terms of black bulb and radiant temperature. The fall-off in radiant temperature with distance from the heater's midline was more marked than that of black bulb temperature and varied with both age and air temperature. The maximum mean radiant temperatures were 199, 140 and 67°C at 1-d-old and 127, 82 and 52°C at 7 d of age for air temperatures of 21, 24 and 27°C, respectively. The control of both air and black bulb temperature was satisfactory and the target regimes were met (data not shown). An analysis of variance of the performance of the chicks showed that there were no significant differences between treatments in terms of live weight, cumulative food intake, food conversion ratio and mortality during the periods 0 to 7 d and 0 to 14 d (Table 1). During the first 3 weeks there was a significant effect of air temperature on live weight with the lightest live weight occurring at the hottest air temperature, while the cumulative food intake, food conversion, ratio and mortality were not affected by the treatments. There were no differences caused by any of the treatments over the periods 0 to 28 d and 0 to 35 d. Figure 2 shows the spatial distribution of the chicks in one room at 2 d of age and an air temperature of 21°C. The chicks formed an annulus and avoided the central zone beneath the heater and spot light. Conversely, the chicks kept at an air temperature of 27°C formed an unbroken cluster at the same age, while those kept at 24°C had an intermediate pattern of distribution. Figure 3 shows the preference for radiant temperature at 1 and 7 d expressed on a cumulative basis. The majority of chicks preferred a radiant temperature of less than ca 50°C. A small minority (

Thermal preferences of chicks brooded at different air temperatures.

1. The thermal preferences of small flocks of 400 chicks brooded under radiant heaters were determined at air temperatures of 21, 24 and 27 degrees C ...
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