July 16, 2003

 

Use Multiple Methods to Cool Confined Livestock, Ag Engineer Advises

Though the early part of the summer has been cool, late July and August likely will bring hot days when livestock producers will need to use all the cool-off tools available to protect livestock from heat stress, according to a North Dakota State University agricultural engineer.

Heat related ills for mature livestock include poor reproductive performance and low feed intake. Symptoms of heat stress include elevated respiration rates, abnormal body temperatures, feed avoidance, playing with waterers, and crowding into shaded areas are common signs that animals are overheating.

To combat heat stress, Ken Hellevang, engineer with the NDSU Extension Service recommends a four-pronged approach that focuses on heat load, evaporative cooling, air speed, and body thermal capacity. First, reduce the heat load on the animals. "One essential strategy for reducing heat load on the hottest days is to provide shade from the sun in the midday and afternoon hours. This is especially critical for high-producing dairy animals," he says

For confined animals, the western exposure of a building must provide adequate shade for animals in late afternoon. Shade cloth or other materials that do not block airflow may need to be placed to block late sunshine, or the animals in that part of the building may have to be relocated.

The second strategy Hellevang recommends is to use evaporative cooling wisely. "Evaporation of water from wetted skin is one of the most powerful methods available to remove heat from the body of an animal," he notes. The technique, to be effective, relies on fairly dry air (less than 65 percent relative humidity) and high air speed over the wetted area of the animal’s body.

Hellevang recommends that a producer use a thermohygrometer to measure relative humidity hourly to know when to activate the evaporative cooling equipment. Look for Thermohygrometers or "relative humidity instruments" in farm and industrial supply catalogs. They are available for about $60. Electronic units available for home use can be used, but will need to be protected from the elements.

The third factor to consider is air velocity. To effectively cool a cow or a pig requires a sustained wind of at least 300 to 500 feet per minute (3.5 to 5.5 miles per hour) over much of the animal’s body. Circulation fans typically throw air effectively about ten times the fan diameter, and producers should install fans accordingly.

"Frequently a building will have enough exhaust fans and air inlets to get the heat out of a building, but inadequate air speed at the animal level to get a good cooling effect," Hellevang notes. "Adding water for evaporative cooling will increase the animals’ misery in that situation."

He cautions that producers must pay attention to air speeds and recommends using a smoke stick or an inexpensive anemometer to help find areas where air speeds are not adequate.

The final step is to learn to use the animals’ body thermal capacity to advantage. "Humans can heat up and cool off fairly quickly compared to a 400 or 1,400 pound animal. It can take several nighttime hours for an overheated dairy cow to get her body temperature down to normal," he says. "On days when conditions make it very difficult to cool animals in midday, it is vital to cool them aggressively with fans in early evening when temperatures moderate. Use every opportunity to remove body heat and get the animal back to normal."

To avoid neglecting an area where conditions are less than optimal, Hellevang recommends observing animals throughout the building and suggests using outdoor cooling pens, with good sky exposure to obtain radiant cooling, for nighttime cooling of grouped animals. A warm roof will block the radiant cooling to the cool sky.

For more information on cooling livestock, get a copy of Heating, Cooling and Tempering Air for Livestock Housing, MWPS-34, which can be purchased online at www.mwpshq.org , by calling (800) 562-3618, or by sending email to mwps@iastate.edu. 

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Source: Kenneth Hellevang, (701) 231-7243, kjh-eng@ndsuext.nodak.edu
Editor: Tom Jirik, (701) 231-9629, tjirik@ndsuext.nodak.edu