J APPL POULT RES 2006. 15:362-366
© 2006 Poultry Science Association
Growth Responses of Male Broilers Subjected to High Air Velocity for either Twelve or Twenty-Four Hours from Thirty-Seven to Fifty-One Days of Age1
W. A. Dozier, III2,
J. L. Purswell and
S. L. Branton
USDA, Agriculture Research Service, Poultry Research Unit, PO Box 5367, Mississippi State, MS 39762-5367
2 Corresponding author: bdozier{at}msa-msstate.ars.usda.gov
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SUMMARY
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Heat stress contributes to increased late-mortality and decreased growth of broilers grown during hot weather. Tunnel ventilation is commonly used to alleviate heat stress by increasing sensible heat loss. As broilers approach heavy BW (>2.5 kg) in hot weather, operating tunnel ventilation continuously as opposed to only during times of high ambient temperature may improve growth rate and nutrient utilization. This study evaluated growth responses of male broilers subjected to high air velocity (2.79 m/s) for either 12 or 24 h from 37 to 51 d of age. The experimental treatments were 1) control (still air), 2) air velocity of 1.65 m/s (325 ft/min) for 12 h and 2.79 m/s for 12 h, and 3) air velocity of 2.79 m/s (550 ft/min) for 24 h. A cyclical temperature regimen of 25–30–25°C (77–86–77°F) was used with a constant 23°C dew point.
Providing continuous high air velocity of 2.79 m/s from 37 to 51 d of age led to a 112-g increase in BW gain and decreased feed conversion ratio by 15 points compared with subjecting broilers to high air velocity of 2.79 m/s for only 12 h. Broilers subjected to both high and low air velocity improved BW gain, feed consumption, and feed conversion over the control birds. These results indicate that continuous ventilation at high air velocity improves BW gain and feed conversion ratio of heavy broilers during the last 2 wk of the grow-out.
Key Words: air velocity • broiler • temperature • ventilation
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DESCRIPTION OF PROBLEM
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The production of broilers to heavy market weights has been increasing due to the demand of saleable white meat. Heat stress results in significant economic losses during hot weather grow-outs by decreasing growth performance and increasing late-mortality of broiler chickens [1]. The broiler produces approximately 3.2 W/kg of sensible heat. As sensible heat accumulates, body mass metabolic heat production can represent about 80% of the total heat load in the house as birds approach market weight [2]. Simmons et al. [3] reported that airflow at high velocity causes a proportional shift from latent to sensible heat loss. Sensible heat loss is more efficient for the bird because latent heat loss (panting) requires metabolic energy to remove heat. As the broiler progresses in body mass, surface area per unit body mass decreases, making heat removal difficult for heavy broilers.
High air velocity (3.0 m/s; 600 ft/min) is beneficial when broilers exceed 2.5 kg. Subjecting broilers to high air velocity flow (3.0 m/s) from 43 to 49 d of age has been shown to improve growth rate by 17% [4] and 13% [5] compared with broilers exposed to air velocity of 2.0 m/s. Dozier et al. [6] reported an increase in broiler growth with high air velocity (3.0 m/s) at 29 d of age when exposed to high temperatures (25–35–25°C) compared with birds subjected to an air velocity of 2.0 m/s. This response to high air velocity (3.0 m/s) occurred at a much earlier age than previous research, which has only shown benefits from high velocity (3.0 m/s) at 42 d of age when broilers are exposed to a moderate temperature cycle (25–30–25°C) [4, 5].
A strategy used by some broiler producers to reduce heat stress of heavy broilers is to tunnel-ventilate continuously (nighttime ventilation) during the last 2 wk of the grow-out to remove excess metabolic heat during the night [7]. Bottcher et al. [8] reported improved BW gain and feed conversion of broilers by increasing the use of mixing fans at night in naturally ventilated houses during the summer. However, to our knowledge, scientific information that evaluates the strategy of "nighttime ventilation" with tunnel ventilation as a means to improve growth performance of broilers approaching heavy weights during summer production is lacking. This study examined growth responses of male broilers from 37 to 51 d of age that were subjected to air velocities of 2.79 m/s for 24 h, or of 2.79 m/s for 12 h and 1.65 m/s for 12 h.
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MATERIALS AND METHODS
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Bird Husbandry
Four identical trials were conducted. In each trial, Ross [9] x Cobb [10] male chicks were purchased from a commercial hatchery and grown in a common environment and fed common diets until 36 d of age. Vaccinations for Marek’s disease, Newcastle disease, and infectious bronchitis were administered at the hatchery and infectious bursal disease at 14 d of age. At 37 d of age, 480 male broilers were weighed and allocated to 12 groups with BW being equated at the start of experimentation. Initial BW was 2,246 g and did not differ among the treatments (P = 0.17). Birds were randomly distributed to 2 wind tunnels (4 pens/tunnel) and 4 floor pens of a closed-sided environmentally controlled facility (40 birds/pen; 928 cm2/bird). A full description of the wind tunnel test facility construction and configuration is given by Simmons et al. [3]. The wind tunnels and floor pens were identical in floor space, feeder space, and waterer space per bird, and lighting (intensity and duration). Each pen (tunnel pens and floor pens) was equipped with a tube feeder, trough waterer, and fresh pine shavings. Birds had free access to feed and water for ad libitum consumption. Diet was formulated to meet or exceed NRC [11] nutrient recommendations and was presented in whole pellet form.
Treatments
Three experimental treatments were implemented: 1) control (floor pens with still air; 0.25 m/s); 2) wind tunnel with air velocity of 1.65 m/s for 12 h and 2.79 m/s for 12 h; 3) wind tunnel with air velocity of 2.79 m/s for 24 h. Ambient temperature was a diurnal cycle of 25–30–25°C (77–86–77°F) over 24 h with a constant dewpoint of 23°C. The temperature cycle followed a sine wave curve during a 24-h interval. Air velocity was calculated using fan speed as measured by voltage output from a DC generator coupled to the fan motor shaft; the system was calibrated using an anemometer array as described by Simmons et al. [12].
Measurements
Birds and feed were weighed by pen at 37, 44, and 51 d of age. Feed consumption was divided by BW on a bird basis to calculate feed conversion. The incidence of mortality was recorded daily. Air velocity and ambient temperature were measured at 30-min intervals. Air temperature and relative humidity were measured at the inlet end of each tunnel and the middle of the floor pens using a combination resistance temperature detector and thin-film capacitive humidity sensor [13] and recorded with a personal computer-based data acquisition system.
Statistics
Data were statistically evaluated by the GLM of SAS [14] in a randomized complete block design. Each of the 4 trials over time represented a block. The experimental unit was the average value of the 4 tunnels pens and the 4 floor pens because the air velocity treatments were applied to all pens within a tunnel. Treatment means were separated using orthogonal contrasts. In addition, a least significant difference comparison was used to test statistical significance. Statistical significance was considered at P 
0.05.
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RESULTS AND DISCUSSION
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Actual ambient temperature and air velocity for the 2 tunnels were in close agreement with the expected values (Table 1
). From 37 to 44 d, BW, BW gain, and feed conversion were improved by increasing the run time of high air velocity from 12 to 24 h (Table 2). Birds subjected to both high and low air velocity grew faster, consumed more feed, utilized nutrients more efficiently, and had less mortality compared with the control group.
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Table 2. Live performance responses of male broilers subjected to 2 air velocity durations under moderate cyclic temperatures from 37 to 44 d of age1
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Increasing the duration of exposure to high air velocity from 44 to 51 d resulted in heavier birds at 51 d of age (Table 3). Birds exposed to air velocity had improved BW, BW gain, and feed consumption over the control group. The cumulative effects of increasing the duration of high air velocity from 37 to 51 d led to advantages in BW gain and feed conversion, but feed consumption and the incidence of mortality were not affected (Table 4). The exposure to both high and low air velocity improved BW gain, feed consumption, and feed conversion over the control birds.
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Table 3. Live performance responses of male broilers subjected to 2 air velocity durations under moderate cyclic temperatures from 44 to 51 d of age1
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Table 4. Live performance responses of male broilers subjected to 2 air velocity durations under moderate cyclic temperatures from 37 to 51 d of age1
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Birds subjected to high air velocity (2.79 m/s) for 24 h from 37 to 51 d had an 8.8% increase in growth rate and a 15-point improvement in feed conversion compared with broilers exposed to air velocity of 2.79 m/s for 12 h. In a field study, Bottcher et al. [8] used a similar strategy by increasing the use of mixing fans at night in naturally ventilated houses during summer production. The treatments having increased use of mixing fans had thermostat settings 2.7 or 5.5°C below the control house. In the 11 field trials, growth rate was increased from 9 to 81 g and feed conversion improvements ranged from 1 to 4 points in houses with increased use of mixing fans over the control houses. The feed conversion benefit with use of mixing fans reported by Bottcher et al. [8] was less pronounced than the feed conversion response in the current study with airflow at high air velocity.
High air velocity (3.0 m/s) has been shown to be beneficial as birds approach or exceed 2.5 kg [4, 5, 6]. Increasing air velocity from 2.0 to 3.0 m/s from 42 to 49 d increased growth rate by 17% [4] and 13% [5] in 2 studies. In the current study, the benefit of increasing the duration of high air velocity may relate to sensible heat loss. As body mass increases, the surface area per unit BW decreases, making sensible heat loss more difficult. It has been shown that heat removal undergoes a proportional shift from latent to sensible heat loss when air is applied to the surface of the bird [3, 8]. One problem with latent heat loss is that the bird expends metabolic energy to remove the excess heat; thus, energy used for heat removal is not available for growth. As a result, growth rate can become impaired.
The economic benefit of using "nighttime ventilation" is justified to broiler growers. In an economic scenario, assuming an electrical cost of $0.09/kw·h, a fan efficiency rating of 28.8 m3/h·W [17 per cubic feet per minute (cfm)/W], and a fan output of 33,980 m3/h (20,000 cfm), the cost of power usage can be computed by: (fan output/fan efficiency) x electrical cost, which would equate to $0.106/h. If 11 fans were used to maintain 2.79 m/s for 336 h (14 d), the electrical cost would be approximately $391.77 for 1 broiler house. To achieve 2.79 m/s for 12 h and 1.65 m/s for 12 h, it would require running 11 fans for 12 h and 7 fans for 12 h for a total electrical cost of $320.54. Assuming that 1 fan supplied air at 0.25 m/s, 11 fans would have an output of 2.79 m/s. In the current study, a 112-g advantage in BW gain occurred when birds were subjected to the high air velocity (2.79 m/s) for 24 h from 37 to 51 d over applying high velocity for only 12 h daily during this same interval. Based on the broiler performance data from this study, a house having 20,000 broilers with a grower payment of $0.11/kg of BW would have a $200 increase in total revenue. It would cost an additional $71.23 per house to achieve the air velocity for 24 h vs. 12 h. This translates to a net return to the grower of $128.77 per house. If this had been a contract grower, their formula costs would have likely been lower, thus increasing the base pay, and further increasing return on investment.
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CONCLUSIONS AND APPLICATIONS
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- Subjecting male broilers to high air velocity (2.79 m/s) continuously from 37 to 51 d increased growth rate and improved feed conversion over birds exposed to high air velocity for 12 h, but feed consumption and mortality were not affected.
- Implementing continuous high air velocity (2.79 m/s; 550 ft/min) during the last 2 wk of the grow-out in hot weather can provide an estimated economic benefit of $128.77/house based on electrical cost and BW gain.
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FOOTNOTES
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1 Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA. 
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REFERENCES AND NOTES
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- Lacy, M. P., and M. Czarick. 1992. Tunnel-ventilated broiler houses: Broiler performance operating cost. J. Appl. Poult. Res. 1:104–109.[Abstract/Free Full Text]
- Reece, F. N., and B. D. Lott. 1982. The effect of environmental temperature on sensible and latent heat production of broiler chickens. Poult. Sci. 61:1590–1593.[Web of Science][Medline]
- Simmons, J. D., B. D. Lott, and J. D. May. 1997. Heat loss from broiler chickens subjected to various wind speeds and ambient temperatures. Appl. Eng. Agric. 13:665–669.
- Simmons, J. D., B. D. Lott, and D. M. Miles. 2003. The effects of high air velocity on broiler performance. Poult. Sci. 82:232–234.[Abstract/Free Full Text]
- Dozier, W. A., III, B. D. Lott, and S. L. Branton. 2005. Live performance of male broilers subjected to constant or increasing air velocities at moderate temperatures and a high dewpoint. Poult. Sci. 84:1328–1331.[Abstract/Free Full Text]
- Dozier, W. A., III, B. D. Lott, and S. L. Branton. 2005. Growth responses of male broilers subjected to increasing air velocities at high ambient temperatures and a high dewpoint. Poult. Sci. 84:962–966.[Abstract/Free Full Text]
- Czarick, M., B. D. Fairchild, and T. Hamrita. 2003. Are you cooling your birds at night? Poultry Housing Tips, Vol. 15, no. 6. University of Georgia, Athens.
- Bottcher, R. W., P. S. Bisesi, J. Brake, S. L. Pardue, and A. M. Etheredge. 1994. Reducing mixing fan thermostat setpoints in naturally ventilated broiler housing during hot weather. J. Appl. Poult. Res. 3:289–296.[Abstract/Free Full Text]
- Aviagen, Inc., Huntsville, AL.
- Cobb Vantress, Inc., Siloam Springs, AR.
- National Research Council. 1994. Nutrient Requirements of Poultry. 9th rev. ed. National Academy Press, Washington, DC.
- Simmons, J. D., T. E. Hannigan, and B. D. Lott. 1998. A portable anemometer to determine the output of large in-place ventilation fans. Appl. Eng. Agric. 14:649–653.
- Model # HMP 135 Y, Vaisala Woburn, MA.
- SAS Institute. 2004. SAS User’s Guide. Statistics. Version 9.1 ed. SAS Institute, Inc., Cary, NC.
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SUMMARY
DESCRIPTION OF PROBLEM
