Minimizing Heat Stress in the Dairy Facility

Dr. Mike Brugger, Extension Livestock Housing Specialist, The Ohio State University

As I right this article, it is 92 ºF and 42% relative humidity and a light breeze in Wooster. Thanks to the air conditioning in my office, I am comfortable and can be productive. Are you providing an environment in your dairy barn so that the cows can be productive? While it is not economical to air condition your free stall barn, there are some things you can do to reduce heat stress. Here are some points to help you evaluate your facility and plan for improvements as needed.

The combination of soaking and blowing air across the cow gives the maximum cooling. Use a spray nozzle that will quickly wet the cow and not one that provides a fine mist. If you have a system installed, be sure that it is working properly. Clean fans provide the most airflow for the cost of operation. Keep them clean. The spray nozzles should provide about 0.33 gallons per cow per wetting cycle. The on time for a cycle will depend on the nozzle flow rate and spacing. A properly sized nozzle may not be getting the desired wetting effect if the water supply line limits the flow.

In adding cooling, the first place to look is the holding pen. Here the cows are crowed together and the natural airflow can be limited by other buildings. Fans blowing down on the cows will reduce the heat stress. Provide one 36-inch diameter fan for each 150 sq ft or one 48-inch diameter fan for each 300 sq ft of holding area. Place the first row of fans right outside the holding area for blowing toward the back of the holding area. Add another row of fans every 20 to 24 ft for 36-inch diameter fans and 30 to 36 ft for 48-inch fans. Mount fans as low as possible without interfering with equipment. Use a thermostat to turn the fans on when the holding pen temperature reaches 72ºF.

A soaker system for the holding area should supply about 1 gallon per 150 sq ft of holding area. The soaker should have an on-off cycle of 1 minute on and 5 minutes off. Turn the soakers on when the temperature reaches 72 ºF.

In the free stall barn, a combination of fans and soaker system at the feed line and fans over the free stalls is the best approach. Use the same fan spacing recommendation as for the holding area. Adding soaker nozzles to wet the cows will improve the cooling affect. A recommended flow of 0.33 gallons per cow per cycle will produce the desired effect. The one time per cycle will depend on the nozzle size and spacing and will generally be one to two minutes. Increase the soaking frequency with temperature according to the chart below:

  • 70 - 80 ºF; every 15 minutes,
  • 81 - 90 ºF; every 10 minutes, and
  • > 90 ºF; every 5 minutes.

Size the water line to the nozzles based on the number of nozzles and flow per nozzle. For example, a 1.5-inch diameter pipe can supply 60 nozzles that supply 0.5 gpm but only 30 nozzles that supply 1 gpm. If the nozzles are spaced 8 ft center to center, the allowable length is 480 ft with the 0.5 gpm nozzles and 240 ft for the 1 gpm nozzles. A 2-inch diameter line can handle 50 nozzles at 8 ft spacing for a total length of 400 ft. These examples are based on limiting the maximum flow velocity in the pipe to 5 ft per second.