Soaker Nozzle Type Affects Water Use, But Not Cow Cooling
Adapted by Jennifer Chen and Dr. Cassandra Tucker, UC Davis
Heat stress costs US dairy producers as much as $1 billion annually. These costs come in many forms. When cows are hot, they eat less, milk production drops, and pregnancy rates fall. In extreme cases, cows can even die in hot weather. Dairy producers clearly recognize the importance of managing the environment to reduce heat stress. A USDA survey found that 94% of US dairies use either shade, fans, or sprinklers (soakers or misters).
When it comes to deciding how to reduce heat stress, soakers cool cows more efficiently than shade alone. The intermittent spray from soakers draws heat away in 2 ways: water dripping off the body, and evaporation from wet skin and hair. Although soakers are effective for cooling, they use potable water – a limited resource. In light of the ongoing drought, conserving water becomes more important. So, how much water should soakers use?
A common recommendation for how much water to apply each time the spray is activated is that the hair coat should be wet through the skin, but excess water should not drip from the coat; we’ve found that it takes about 1 gallon to wet a cow in such a manner. However, there is little science to support this recommendation. In practice, many operations – including the UC Davis dairy – use more than that: last summer, we found that Central Valley drylot dairies used between 1.2 to 11.4 gal/h/cow.
In order to determine how much water is needed to cool cows, last summer, we compared soakers that delivered 2.6 gal/h/cow (TeeJet TF-VP2 nozzle) vs. 9.8 gal/h/cow (TF-VP7.5) vs. no soakers at all. The amount of water sprayed didn’t matter. When cows had soakers, body temperature was consistently lower than when they had no soakers (only shade), regardless of the amount of water used. Furthermore, both 2.6 and 9.8 gal/h/cow maintained cooling effectiveness even in hotter weather. Because these soakers differ more than 3-fold in water usage, but were equally effective for cooling, this tells us that there is an opportunity for water savings on many dairies.
We have also found that cows prefer to use soakers that spray less water. Why does it matter what the cows think? In freestalls and drylots, cows can choose when and how they use soakers. If cows avoid standing directly under the spray, then water is wasted. Currently, we are studying which soaker setups cows are most willing to use. We’ll use this information to help conserve more water while maintaining cow comfort.
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