UNIVERSITY PARK, Pa. -- Dairy farmers shouldn't let the cool spring fool them -- summer heat will be here soon. They should plan now, according to an expert in Penn State's College of Agricultural Sciences, to provide their cows with relief from heat stress.

The highest producing cows are the ones most vulnerable to the damaging effects of heat stress, warns Dennis Buffington, professor of agricultural and biological engineering. Milk production decreases as heat stress increases. He points out that even greater economic loss results from the reduction in cows' conception rates as heat stress rises.

"First and foremost, the cows need to be protected from direct solar radiation," he says. "The shading system must be designed so that the animals have full access to quality feed and water while in the shade. Sufficient floor space needs to be provided under the shade structure so that the animals do not crowd together to stay in the shade.

"The underside of the roof needs to include insulation material to reduce the thermal radiation load on the cows. Finally the shade structure needs to be high enough and include a ridge opening so that natural ventilation will be enhanced."

Evaporative cooling systems to reduce heat stress levels on cows are common in the southern United States, but few are used by Pennsylvania dairy farmers, according to Buffington. He anticipates that evaporative cooling systems will become more popular in Pennsylvania as production levels of cows increase and as producers search for effective ways to reduce heat stress.

The evaporation of just one gallon of water per hour at 85 degrees F provides nearly the same cooling effect as a 3/4 ton air conditioner unit. "This amount of cooling can handle the heat produced by, on average, two lactating cows," he says. "The actual amount of water that can be evaporated depends on the humidity level of the air." Different approaches to providing evaporative cooling for dairy cows have been used over the past several decades. Buffington believes the use of a sprinkler or misting system in conjunction with forced ventilation is most effective. "It is not sufficient simply to cool the air with evaporative cooling and hope to significantly reduce the damaging heat stress effects on the cows," he says.

"It is essential to wet the cows and to provide forced ventilation to speed up the rate of evaporation," he adds. "The direct wetting of the cows cools them only a limited amount -- it is the rapid evaporation of the water that really does the cooling. The need for rapid evaporation is why it is essential to use fans in conjunction with sprinklers or misters. Natural ventilation is not sufficient, at least in the climates of the Northeast, to provide the quick evaporation."

During heat stressing conditions, cows must be wetted intermittently so that the water can evaporate from the surface of the cows. Effective evaporative cooling systems generally provide a spray of water for about a minute every three or four minutes with the fans running continuously. An evaporative cooling system should be developed with enough flexibility so that the wetting durations and intervals can be easily modified in the field.

The water spray should be directed onto the back and sides of each cow, Buffington explains. "Ideally, all the water should evaporate on the back and sides of a cow so that none of the sprinkler water comes down to the udder because of the danger of contaminating the teat openings with bacteria from the hide," he says. "It also is important to keep the floor surfaces and bedding materials dry."

Buffington contends that investments in effective systems to relieve heat stress for dairy cows will pay dividends in increased cow comfort, milk production and conception efficiency. "As the production levels of dairy cows increase, they become more vulnerable to heat stress," he says. "Therefore, it behooves dairy farmers to utilize evaporative cooling systems to reduce the effects of heat stress on their animals." EDITORS: Contact Dennis Buffington at 814-865-2971 or by e-mail at dbuffington@psu.edu.

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Contact:

Gary Abdullah gxa2@psu.edu Jeff Mulhollem jjm29@psu.edu 814-863-2719 814-863-9877 fax #174