D
A I R Y I n i t i a t i v e s N E W S L E
T T E R |
Holy Cow? Is It Hot or What? |
Engineering Options for Reducing Heat Stress KEVIN JANNI |
|
It may not be here yet, but hot and humid weather is coming. When the average temperature exceeds 70° F, dairy cows -- particularly higher-producing cows -- begin to experience heat stress. They reduce feed intake, milk production, and reproductive efficiency. In other words, your profits drop as the temperature climbs. Fortunately, there are things you can do now to help minimize heat stress during the inevitable hot and humid weather coming this summer. Consider the costs and benefits of each option, then make the changes that make economic sense to you. Provide shade Shade reduces heat stress by reducing the amount of sun that reaches cows. Naturally ventilated curtain-sided barns make good shade. If you build shades, make them 12 feet tall or higher and leave room for good airflow underneath. A white or light-colored roof will increase shade effectiveness. Cows often lie down in the shade, so maintain some of the shaded area for good cow comfort. Shades over feed bunks encourage eating but do not provide an appropriate place for cows to lie down. Improve ventilation Ventilation picks up heat the cows produce and carries it away. The faster the air moves, the easier it is for animals to get rid of their heat. However, as air temperature approaches body temperature, ventilation loses its effectiveness for removing heat. Increase air exchange in mechanically ventilated barns by cleaning fans and inlets. Dirty fans with rusty and dirty louvers can reduce airflow by up to 39%. Plugged or dirty inlets reduce airflow further. You can also increase air exchange by installing more fans and inlets. Hot-weather ventilating systems should provide 500 cubic feet per minute (CFM) per 1,400-pound cow. Use rated fans to ensure that you get the necessary flow rate. Inlet location and adjustment affect ventilation. Distribute slot and ceiling inlets uniformly throughout the barn so every cow gets fresh outside air. Adjust them so inlet air velocity is 600 to 800 feet per minute (FPM). In naturally ventilated barns, increase air exchange by opening up the sidewalls as much as possible, having adequate sidewall height, and minimizing obstructions (e.g., silos, trees, other buildings, equipment, and hills) that reduce wind flowing past and through the barn. Make sure the ridge is as open as possible and not obstructed. Use tunnel ventilation in stall barns Tunnel ventilation provides air exchange and airflow past animals in a stall barn. Large exhaust fans are located at one end of the barn. Outdoor air enters at the other end and is pulled through by the fans. The ventilating rate is based on the cross-sectional area (height times width) of the animal area and the average air velocity (minimum of 220 FPM). Typical flow rates are 60,000 to 90,000 CFM. The inlet needs to be big enough to handle the airflow. Long barns with 110 cows or more need extra fan capacity. Tunnel ventilation is not used in cold weather. It generally requires more airflow than a slot inlet ventilated barn. Some producers report fewer flies in tunnel ventilated barns. Use mixing fans Mixing fans create a draft across or past an animal. They can be used in mechanically and naturally ventilated barns and milking parlor holding areas, and can be controlled with thermostats. Mixing fans provide a draft but no air exchange. Air exchange is needed to exhaust the air heated by the cows and to bring in fresh outdoor air. In stall barns with low ceilings, mixing fans blow air along the length of the barn across the cows' backs. Fans are usually located around the barn. The distance between fans depends on how far the draft from a fan can be felt, but 20 feet is common. In naturally ventilated barns, mixing fans are normally installed at a height of about 12 feet and angled downward at about 20 degrees. The goal is to create air velocities around 200 to 300 FPM across the cows' backs. The recommended distance between fans is 30 feet for 3-foot diameter fans and 40 feet for 4-foot diameter fans. All of the fans should blow air in the same direction in naturally ventilated barns. Use a sprinkling system Sprinkling systems can be used along feed bunks and in holding areas to wet the cows periodically. The sprinkling must be intermittent to permit evaporation, which is what helps cool the cow. Adequate air exchange is also critical to remove the warm, moist air. Use water droplets rather than a fine mist so the system wets the hair and skin. Irrigation nozzles and solid-cone coarse droplet spray nozzles with flow rates between 0.2 and 0.5 gallons per minute work very well. Locate sprinklers so they don't wet feed in the feed bunk or bedding in the freestalls. Wet bedding can lead to an increase in mastitis. Sprinklers are typically on for 1 to 3 minutes every 10 to 15 minutes. Excess sprinkling wastes water and does not reduce heat stress. Mixing fans should remain on during sprinkling. Sprinkler systems can be automatically controlled using a thermostat and 30-minute cycle timer in series. Don't overcrowd the milking herd Overstocking freestall barns increases the amount of heat that must be removed. It also reduces airflow past the cows, which reduces their ability to get rid of heat. Some experts suggest having less than 100% occupancy to allow more airflow past the remaining cows. In summary, elect a cooling system that fits your management and facilities. Make sure it works before the hot weather arrives and monitor cow performance to make sure the system is doing its job. |
For More InformationChastain, J. P., 1993. Improving Mechanical Ventilation in Dairy Barns. (AEU-3) Biosystems and Agricultural Engineering, University of Minnesota. http://www.bbe.umn.edu/extens/aeu/aeu3.html. Also available in printed form from University of Minnesota Department of Biosystems and Agricultural Engineering, 612/625-9733. Turner, L. W., R. C. Warner, and J. P. Chastain. 1992. Micro-sprinkler and Fan Cooling for Dairy Cows: Practical Design Considerations. (AEN-75) Biosystems and Agricultural Engineering, University of Kentucky. http://www.bbe.uky.edu/~lturner/dairyeng.htm. Dairy Freestall Housing and Equipment Handbook (MWPS-7) $22 plus tax and Tunnel Ventilation for Dairy Tie Stall Barns (NRAES-120) $4 plus tax, University of Minnesota Department of Biosystems and Agricultural Engineering, 612/625-9733. |
D A I R
Y I n i t i a t i v e s N E W S L E T T E R |