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It does not have to be 100 degrees for heat stress to occur in dairy cows.

Edstrom Spray CoolingStudies have found that dairy cows will begin to reduce feed intake and lose body weight at temperatures as low as 79°F. Milk production falls. Reproductive performance and health are affected. Heat stress will continue to affect performance even in the cooler months ahead, as cows struggle to rebound from complications such as rumen acidosis. High yielding cows are most susceptible to heat stress. All of this quickly impacts your profits!

The degree of heat stress suffered by the cow will depend on the combination of environmental conditions - air temperature, relative humidity, air movement, and radiation from the sun. Dairy farmers use shades, fans, and ample fresh drinking water to help herds beat the heat, but often shade and ventilation are just not enough.

Dairy farmers are also using soaker systems to provide added cooling effects. Research on dairy cooling has shown that shade in combination with intermittent showering and forced air movement is a very effective method of cooling dairy cows, thereby reducing the production losses experienced during hot, humid weather conditions. Recent research at Kansas State University has shown that the application of water with low-pressure sprinklers cools cows more efficiently than fans alone. If you cannot install both fans and sprinklers, start with installing sprinklers before fans. (KSU Cow Comfort Consortium 2001 - Brouk, M.J., J.F. Smith and J.P. Harner, III)

Disadvantages of Misting and Fogging

By using a high capacity, coarse droplet soaker nozzle, enough water can be applied to fully wet the cows to the hide. The water is then allowed to evaporate, which pulls heat from the animal, just like sweating. Increased air movement across the wet hide, provided by fans, makes this system most efficient. Proper control is critical to ensure that the cow gets soaked to the hide along the topline, while not getting wet to the point of having water running off her sides (see photo "Proper Degree of Wetting Cattle").

Mist and fogging nozzles have been used to cool dairy cows, and have proven advantageous in dry climates. They work by cooling the air around the cows. The disadvantage is the mist can be easily blown away under windy conditions or when used with fans. If a mist or fog builds up on the cow's hair, it can trap a layer of air between the skin and the water, which holds in body heat. Respiratory problems can also arise if proper ventilation is not provided. In addition, mist and fogging nozzles usually must be operated at high pressures and require regular maintenance, especially when poor water quality conditions exist.

In comparison, soaker nozzles produce a coarse droplet spray, which penetrates the hair and wets the cow's hide. To avoid formation of a mist, the soaker nozzles operate at reduced water pressure of 10 to 15 psi.