Reducing Heat Stress in the Holding Pen
By Barry Steevens and Joe Zulovich, University of Missouri
During the summer months dairy cows spend two to six hours a day in a "hot box" called the holding pen. Any time the temperature humidity index (THI) exceeds 72 cows experience heat stress. A THI of 72 could be 76 degrees at 65% humidity or 72 degrees at 80% humidity. Stress level goes up quickly when the temperature is 85 degrees. The average cow gives off about 4500 btu's /hour. This is similar to a 1500 watt hair dryer blowing at high speed. (That's a lot of heat!)
Heat stress reduces feed intake which in turn reduces milk yield and affects reproduction. Research data reported by Harner et. al., 2,000 showed when an overhead spray system with fans were installed, the cows body temperature dropped 3 degrees F. within 20 minutes and the cooled cows produced 1.8 lbs more milk than cows not cooled. Another trial showed an increase of 5 lbs. milk/ cow/day when cows were cooled 5 times/day for 30 minutes in the holding pen.
Cows should be grouped so they do not stand in the holding pen more than one hour for 2X milking and 45 minutes for 3X milking. Altering the milking schedule may avoid the hot part of the day from 1:00 to 7:00 P.M. A grazing dairyman switched to a 10:00 A.M. and 10:00 P.M. milking schedule. The cows were observed to better utilize the A.M. cool morning for grazing and milking was avoided during the hottest part of the day.
Holding Pen Comfort
- Shade. Some holding pens are still open. Shade can easily be accomplished with installation of a nylon mesh cloth (90% sunlight blockage).
- Open sidewalls. At least 60 % of the sidewalls should be open to allow for natural ventilation. Curtains or doors can enclose the area during the winter.
- Ridge ventilation. Heat rises. Remove the ridge cap or create an opening to allow excess heat escape. Provide at least 2" per 10' of holding pen width.
- Fans. Install fans to blow over the cows. Thirty-six inch fans should be placed 6 to 8 feet apart and provide a throw distance of 24-30 feet. Fans should be 8- 9 feet above the floor and tilted at about a 30 degree angle down towards the cows. Electrical service should be addressed. The typical three foot fan will use 5-6 amps at 120 volts and 2.5-3.0 amps at 240 volts. Be sure to balance the loads to avoid any potential stray voltage problems.
- Sprinklers. Sprinklers should be sized to provide 0.45 gal/15 square feet or "one cow". If the nozzles have an 8 foot spray diameter, then they are placed at an 8X8 foot grid. The nozzle should have a 25 gallon/ hour rating in order to deliver 0.03 gal./sq.ft. Suggested cycle timing is 1 minute spray and 6 minutes off. Caution; Always install fans first. Excessive humidity without fans could cause severe stress on the cows.
- Water access. Open water troughs available to cows upon exiting the parlor are recommended. Several dairies installed a water trough accessible in the holding pen. Water access from the holding pen can be helpful for the "one group" dairy especially if the cows are waiting more than one hour.