Vol. 12, No. 6. University of Georgia, Cooper- ative Extension Service, Athens, GA. Duncan, D. B. 1955. Multiple range and multiple F tests. Bio- metrics 11:1â42.
Ventilation, Sensible Heat Loss, Broiler Energy, and Water Balance Under Harsh Environmental Conditions1 S. Yahav,*,2 A. Straschnow,* D. Luger,* D. Shinder,* J. Tanny,† and S. Cohen† *Institute of Animal Science, and †Institute of Soil Water and Environmental Sciences, ARO, the Volcani Center, Bet Dagan 50250, Israel der these conditions, suggesting the ability to direct a sufficient amount of energy to control body temperature, while maintaining relatively high growth rates. Convective heat loss increased significantly with increasing AV, whereas radiative heat loss was not affected. Sensible heat loss, expressed as a percentage of energy expenditure for maintenance, was significantly higher at 2.0 m/s compared with 0.8 m/s but significantly lower than that of 3.0 m/s. The high level of heat loss observed at 3.0 m/s probably affected body water balance, as supported by significantly higher plasma osmolality, arginine vasotocin concentration, and the hyperthermic status of these birds. It can be concluded that AV of 2.0 m/s enables broilers to maintain proper performance together with efficient thermoregulation and water balance under harsh environmental conditions.
ABSTRACT Air velocity (AV) is one of the main environmental factors involved in thermoregulation, especially at high ambient temperatures. To elucidate the effect of AV on performance and thermoregulation of 4- to 7-wk-old broiler chickens, an experiment was conducted using 4 different AV (0.8, 1.5, 2.0, and 3.0 m/s) at constant ambient temperatature (35 ± 1.0°C) and RH (60 ± 2.5%). BW, feed intake, and fecal and urinary excretions were monitored in individuals and were used to calculate the amount of energy expended for maintenance. Infrared thermal imaging radiometry was used to measure surface temperatures for the calculation of heat loss by radiation and convection. Brachial vein blood was collected for plasma osmolality and arginine vasotocin analysis. Broilers performed optimally at an AV of 2.0 m/s. Energy expenditure for maintenance was significantly higher un-
(Key words: air velocity, arginine vasotocin, body temperature, broiler, sensible heat loss) 2004 Poultry Science 83:253–258
energy cost pathway for heat loss than sensible heat loss, and it further affects blood acid base balance and body water balance, thus adversely affecting the ability to maintain body temperature (Tb) in a normothermic range. Any shift from evaporative to sensible heat loss may reduce maintenance energy and thus increase the amount of energy available for growth. Sensible heat loss can also prevent hyperthermia caused by dehydration, which results from severe panting. Unbalanced energy and water budgets are detrimental to performance. At high Ta optimal AV may enable cooling to be partially shifted from the evaporative to the sensible pathway (Timmons and Hillman, 1993; Simmons et al., 1997) and so to improve both water and energy balances. One of the main impediments to quantifying sensible heat loss was the inability to accurately measure animal surface temperature distribution and to differentiate between the contributions of different surface regions to heat loss. Recently, infrared thermometry has been used successfully to measure surface temperature in mam-
INTRODUCTION The main environmental factors affecting performance of broiler chickens are ambient temperature (Ta), RH, and air velocity (AV). Whereas the first 2 factors have been extensively studied (reviewed by Yahav, 2000), only limited information is available on the effect of AV on broiler performance (Lott et al., 1998; Czarick et al., 2000; Yahav et al., 2001). The importance of AV at high ambient temperatures lies in its effect on body energy and water balance. Birds, as homeotherms, can balance body energy by reducing heat production, increasing evaporative heat loss (via panting, which is recognized as the main pathway for heat loss, and cutaneous heat loss), increasing sensible heat loss (convection and radiation), or a combination of these (Hillman et al., 1985). Panting is a much higher
2004 Poultry Science Association, Inc. Received for publication July 14, 2003. Accepted for publication September 9, 2003. 1 Contribution No. 436/03 from the Agricultural Research Organization, the Volcani Center, Bet Dagan, Israel. 2 To whom correspondence should be addressed: yahavs@agri. huji.ac.il.
Abbreviation Key: AV = air velocity; AVT = arginine vasotocin; Qr = radiative heat loss; Qc = convective heat loss; Ta = ambient temperature; Tb = body temperature.
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maintained constant temperature at ±1.0°C, RH at ±2.5%, AV at ±0.25 m/s, and continuous fluorescent illumination. During the acclimation period (wk 5), Ta, RH, and AV were changed by equal increments to attain the target environmental conditions of the experiment: 35°C, 60% RH [the optimal RH for raising broiler chickens at high Ta (Yahav et al., 1995)], and AV of 0.8, 1.5, 2.0, and 3.0 m/s. Water and food in mash form were supplied ad libitum. The diet was designed according to National Research Council (1994) recommendations. At weekly intervals, BW and feed intake were recorded on individual and group bases, respectively. In each treatment 8 birds (2 from each replicate) were selected randomly for physiological analysis. The local Animal Care Committee approved the use of animals and all experimental procedures in the present study (IL 15-02). FIGURE 1. Thermal image of a broiler chicken exposed to 35°C. The blue frame on the leg demonstrates a section of surface area for which minimum, average, and maximum surface temperatures were determined.
Physiological Analysis
mals (Mohler and Heath, 1988; Klir et al., 1990; Klir and Heath, 1992; Phillips and Heath, 1992) and in birds (Phillips and Sanborn, 1994; Yahav et al., 1998). This technology provides better accuracy of surface temperature measurement than thermocouples (Mohler and Heath, 1988); and thermal imaging (Figure 1) was used in this study to evaluate the rate of sensible heat loss in broilers exposed to different AV. In the present study, the effect of AV on the amounts of sensible heat loss and maintenance energy was determined. The effect on thermoregulation and body water balance was elucidated, and the influence on performance was evaluated.
Energy Balance
MATERIALS AND METHODS Experimental Design The effect of AV on energy and water balance was studied in fast-growing male Cobb chickens. All birds were obtained from a commercial hatchery and raised for 4 wk in battery brooders in a temperature-controlled room at 26°C. At the age of 4 wk, 240 male chickens were selected by weight from a population of 280 birds. Birds with extreme weights were omitted. The birds were divided among 4 treatments × 4 replicates of 15 birds each, with equal average BW. The birds were housed in cages (40-cm length; 28-cm width; 45-cm height; 2-cm wire mesh), one bird per cage, situated in 4 computer-controlled environmental chambers that
3 Newtron TM 5007, CHY Firemate Co. Ltd., Jen-Te Hsiang, Tainan Hsien, Taiwan. 4 Model 1108, Parr Instrument Company, Moline, IL. 5 Model 760, Inframetrics Inc., North Billerica, MA. 6 Thermoteknix Systems Ltd., Cambridge, UK.
After acclimation to the targeted environmental conditions, blood samples, Tb, energy balance factors, and thermal images were recorded for each of 8 randomly selected birds per treatment. Blood samples drawn from the brachial vein were centrifuged, and the plasma was stored at −20°C pending further analysis. Tb was measured in 8 birds of each treatment by a digital thermometer.3
Energy balance was measured in 8 individuals from each treatment on 4 consecutive d at the age of 6 and 7 wk. Chickens were weighed, feed intake was monitored, and excretions were collected on a daily basis. Weight gain and feed intake were calculated. Diet and excreted samples were homogenized, dried, and analyzed calorimetrically with an oxygen combustion bomb- calorimeter.4 Energy requirement for maintenance (M) was calculated using the equation M = energy intake − (excreted energy + retained energy). Retained energy was evaluated from daily weight gain, using the assumption that at high Ta 85% is retained as fat and 15% as protein (Boekholt et al., 1994).
Heat Loss by Radiation and Convection To determine heat loss by radiation and convection, an infrared thermal imaging radiometer5 was used to measure the chicken’s surface temperature (Figure 1). The infrared thermal imaging is characterized by longwave (8 to 12 µm) thermography, high resolution of 0.05°C, and accuracy of ± 2%. A computer program, Thermonitor-95,6 was used to translate the color spectrum into temperature and to measure the surface area and temperature in each surface area. Heat loss by radiation was calculated according to the following equation (Monteith and Unsworth, 1990): Qr = eσA(Ts4 − Ta4),
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SENSIBLE HEAT LOSS IN BROILERS TABLE 1. The effect of air velocity on performance of broiler chickens exposed to 35°C and optimal RH Air velocity (m/s) Variable Body weight (g, age 7 wk) Feed intake (g/21 d) Feed efficiency (g/g)
0.8
1.5
2.0
3.0
1,878 ± 54c 1,193 ± 54c 0.23 ± 0.04b
2,071 ± 91b 1,489 ± 88b 0.30 ± 0.04ab
2,308 ± 39a 1,708 ± 42a 0.36 ± 0.02a
2,164 ± 61ab 1,653 ± 81ab 0.30 ± 0.04ab
a–c In rows, values (means ± SE) with different letters differ significantly (P ≤ 0.05); n = 4 replicates of 15 birds each.
where Qr = radiative heat loss (watts), ε = emissivity for biological tissue, σ = Stefan-Boltzman constant, A = surface area, and Ts and Ta = surface and ambient temperatures, respectively. Heat loss by convection was calculated from the following equation: Qc = ρcp(Ts − Ta)/ rh, where Qc = convective heat loss (watts), ρ = air density (kg/m3), cp = air specific heat (J/kg per °K), and rh = resistance to heat transfer. To calculate rh, each body organ was represented by a corresponding geometrical shape. Resistance to heat transfer was estimated using available (Holman, 1989) or derived heat transfer relationships (Tanny et al., unpublished).
Arginine Vasotocin Analysis Plasma samples were extracted according to the method of Arnason et al. (1986). Extracts were reconstituted in 0.15 mL (factor 3) of RIA buffer7 immediately prior to assay. One milligram of synthetic arginine-vasotocin acetate salt was dissolved in 0.1 N acetic acid to prepare standards for the assay. Standards were prepared in concentrations of 256, 128, 64, 32, 16, and 8 pg/ mL with RIA buffer. Plasma arginine vasotocin (AVT) concentrations were measured using a commercial kit, [Arg8]-Vasopressin.7 The kit antibody has cross-reactivity: [Arg8]-vasotocin, 100%; ACTH, 0%; oxytocin, 0%. Sensitivity of the method is: IC80, 10 pg/mL; IC50, 50 pg/mL; IC20, 190 pg/mL. Intraassay variation estimated on the extraction and assay of 6 control plasma samples averaged 6.6%. Interassay variation estimated in triplicate over 3 assays averaged 8.7%. Recovery (91%) was determined by evaluating the extraction of 6 control samples paired with the same samples spiked (1:1) with standards of 32 and 64 pg/mL.
Ta. All 3 parameters exhibited a bell-shaped response to AV, with maximum response at 2.0 m/s (Table 1). Broilers exposed to AV of 2.0 m/s exhibited significantly higher BW and feed intake than broilers exposed to lower AV (0.8 and 1.5 m/s). Feed efficiency in this treatment was significantly higher only when compared with that obtained in broilers exposed to 0.8 m/s. Body temperature was significantly lower in broilers exposed to 1.5 and 2.0 m/s (Table 2). In broilers exposed to 0.8 m/ s, Tb was significantly higher than that found in broilers exposed to 3.0 m/s. Plasma osmolality and AVT concentration were significantly lower in broilers subjected to 2.0 m/s AV in comparison with values recorded in broilers exposed to 0.8 or 3.0 m/s (Table 2). Heat loss by radiation did not differ among treatments. However, Qc significantly increased with the increase in AV, as expected, reaching significantly higher values of loss at 3.0 m/s (Table 3). Total sensible heat loss was significantly higher in broilers exposed to 2.0 and 3.0 m/s compared with that for broilers at 0.8 and 1.5 m/s. Total sensible heat loss as a percentage of energy used for maintenance was similar in broilers exposed to 0.8 and 1.5 m/s and was significantly higher at 3.0 m/s (Table 3). Energy expended for maintenance was significantly higher in broilers exposed to 2.0 m/s compared with that of 0.8 m/s (Figure 2).
Statistical Analysis All 4 AV treatments were subjected to one-way ANOVA (Snedecor and Cochran, 1968) and Duncan’s multiple range tests (Duncan, 1955). Means were considered significantly different at P ≤ 0.05.
RESULTS Air velocity significantly affected BW, feed intake, and feed efficiency of broiler chickens exposed to high
7
RIK8103, Peninsula Laboratories Inc., San Carlos, CA.
FIGURE 2. The effect of air velocity on energy expended for maintenance in broiler chickens exposed to 35°C and 60% RH. Columns with different letters differ significantly (P ≤ 0.05); n = 8 for each treatment.
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YAHAV ET AL. TABLE 2. The effect of air velocity at high ambient temperature on body temperature (Tb), osmolality, and plasma arginine vasotocin (AVT) concentration in broiler chickens Air velocity (m/s) Variable Tb (°C) AVT (pg/mL) Osmolality (mosM/L)
0.8
1.5
43.9 ± 0.08 25.3 ± 1.7ab 324 ± 3.0a
2.0
42.9 ± 0.08 22.4 ± 2.4bc 317 ± 2.1bc
a
3.0
42.8 ± 0.09 19.2 ± 1.5c 314 ± 2.2c
c
43.2 ± 0.1b 28.0 ± 1.8a 323 ± 1.4ab
c
In rows, values (means ± SE) with different letters differ significantly (P ≤ 0.05); n = 8.
a–c
temperature gradients between the bird surface and the environment. However, increasing AV did not always positively affect broilers. Body weight, feed intake, and feed efficiency increased with AV up to 2.0 m/s. But why did these factors decline at 3 m/s despite the increase in sensible heat loss? This study suggests that body water balance is the main reason for the deterioration in performance. Two factors support this idea: plasma osmolality and AVT concentration. Both responded to the increase in AV with bell-shaped patterns, characterized by a nadir at 2.0 m/s AV. AVT is a hormone important in regulating water balance. It is well documented that water deprivation results in increased plasma osmolality and plasma AVT concentration, and both factors are positively correlated (Arad et al., 1985; Koike et al., 1977; Tanaka et al., 1984). However, whereas Saito and Grossmann (1998) agreed with the previous statement, they did not find a significant positive correlation between the 2 factors. The results of this study do show a significant positive correlation between plasma osmolality and plasma AVT concentration (R2 = 0.84). The significant increase of these 2 factors in broilers exposed to high AV suggests problems in balancing body water. High AV may significantly increase cutaneous water loss (Webster and King, 1987) and thus contribute to body water imbalance. Another reason may be the inability of broilers to drink sufficient amounts of water under extreme environmental conditions. Yahav et al. (1995) suggested that broilers exposed to high Ta and low RH were not able to balance body water as a result of insufficient drinking capacity. Thus, it can be suggested that, at high AV, both a high degree of water loss from the surface together with insufficient drinking capacity lead to some degree of dehydration associated with an increase in plasma osmolality and AVT concentration.
DISCUSSION This study indicates the important role that AV can play in thermoregulation of broiler chickens at high Ta. Optimal AV can positively affect energy and water balance and thus improve chicken performance. The intensive genetic selection of broilers for fast growth rates apparently leads to major difficulties in coping with suboptimal environmental conditions (Emmans and Kyriazakis, 2000; Yahav, 2000). Therefore, the effect of each environmental factor on the whole animal response is of great importance. Heat flow from and to the environment is a function of the temperature of the exposed surface (Prosser and Heath, 1991). Insulation plays a major role in impeding heat transport and therefore in thermoregulation (Scholander et al., 1950). It is well documented that sensible heat loss does not play an important role in the domestic fowl when Ta is above the upper limit of the thermoneutral zone (for review: Hillman et al., 1985). In fully feathered birds on which only limited areas are unfeathered (i.e., legs, head, wattle, and comb), the role of sensible heat loss in thermoregulation at high Ta was found to be negligible (Tzschentke et al., 1996). Thus, latent heat loss by panting was considered to be the main route for heat dissipation (Marder and Arad, 1989). Although AV did not affect Qr over a wide range of air velocities, a significant and linear increase of Qc (r2 = 0.998) with AV was observed. The increase had a dramatic effect on the ratio of sensible heat loss to maintenance energy. Although the ratio was only 29% in broilers exposed to 0.8 and 1.5 m/s AV, it exceeded 44% of the energy expended for maintenance in broilers subjected to 3.0 m/s. This finding demonstrates that sensible heat loss (i.e., Qc plus Qr) may have a major role in heat loss depending on AV, despite the small
TABLE 3. The effect of air velocity at high ambient temperature on heat loss by radiation (Qr), by convection (Qc), and by radiation plus convection (Qt) as a percentage of energy expended for maintenance in broiler chickens Air velocity (m/s) Variable Qr (kcal/d) Qc (kcal/d) Qt (kcal/d) Qt (% of energy expended for maintenance)
0.8 21.7 47.9 69.6 24.1
± ± ± ±
1.5 2.9 6.0d 8.8b 3.7b
21.9 67.3 90.2 29.1
± ± ± ±
2.0 3.1 6.4c 9.4b 4.4b
27.4 90.2 117.6 36.8
± ± ± ±
3.0 2.9 6.0b 8.8a 2.2ab
In rows, values (means ± SE) with different letters differ significantly (P ≤ 0.05); n = 8.
a–d
27.2 114.0 141.2 44.7
± ± ± ±
2.9 6.0a 8.8a 4.7a
SENSIBLE HEAT LOSS IN BROILERS
Imbalances of total body water are usually reflected in panting rate. Yahav et al. (1995) demonstrated a decline in broiler panting rate despite increases in Tb. It was speculated that mild dehydration depressed panting rate and reduced water loss, which led to increased Tb. In this study hyperthermia was observed in both extreme AV. In both cases it may be speculated that hyperthermia developed as a result of body water deficit. However, although the deficit at high AV resulted mainly from passive skin loss, the deficit observed at low AV most probably resulted from a high panting rate. The effort to control Tb and total body water directed a large amount of energy toward maintenance in broilers exposed to the optimal AV, which prevented the hyperthermia that can develop in broilers exposed to 35°C (Yahav et al., 1997) and precluded a deleterious effect on performance (Yahav et al., 1996). It was expected, however, that unbalanced broilers would expend a larger amount of energy for maintenance, especially when energy consumption was reduced (0.8, 3.0 m/s). The results obtained in this study suggested an opposite response, namely, a decline in energy invested for maintenance. It can be speculated that the genetic selection for growth is so dominant in these fowls that even hyperthermia and dehydration do not significantly alter the amount of energy invested in maintenance. It can be concluded that 2.0 m/s is the optimal AV for raising broilers at high Ta. The association between AV and body water balance reflects the optimization of AV. It can be further speculated that genetic selection for growth dominates, to some degree, physiological responses.
ACKNOWLEDGMENTS This study was supported by the Chief Scientist of the Ministry of Agriculture (356-0360) and the Egg and Poultry Board of Israel (356-0345). We thank M. Rusal, B. Gill, and P. Shudnovsky for technical assistance.
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