Summertime in Minnesota can get pretty warm. Daytime highs in the 90's and above are not uncommon. Since we have a lot of dairy farms in Minnesota, we have to be aware of what it takes to keep cows comfortable and producing during the warm summer months. Why the concern? Dairy cows are most productive at temperatures between 41 and 77 degrees F. At temperatures above 77 degrees, cows begin to use energy to rid themselves of heat generated by digestion and metabolism - energy that could be used to produce milk or grow a calf if pregnant. As relative humidity increases at temperatures above 77 degrees F, the combined heat and humidity increases the heat stress that cows experience.
There are several effective cow cooling practices that you can use to help your cows get through a period of hot and humid weather.
Shade cuts solar heat gain for cows on pasture. Cows in barns have shade. Roof overhangs provide more shade near the barn sidewalls.
Barn ventilation cools cows by providing air exchange between outside and inside. Ventilation can be by either natural or mechanical means. In hot weather, provide as much ventilation as you can.
Tunnel ventilation brings air in at one end of the barn and exhausts it out the other. Size fans and inlets correctly and make sure the fans are well maintained and inlets are open.
Mixing fans hung from rafters or trusses create air movement during hot weather to help keep cows by blowing air past the cows. Mixing fans do not provide air exchange between inside and outside but they supplement the cooling effect of ventilation.
Low pressure sprinklers along feed bunks or in holding areas wet the cows' backs to provide cooling. Wet the cows' backs to the skin. Low pressure sprinkler systems must turn on and off. Cow heat evaporates the water and cools the cows when the sprinklers are off. Mixing fans enhance the effect.
High pressure misters cool the air by creating a fine mist or small droplets. The droplets need to evaporate before they hit the stalls or bedding. Place misters near inlets. Misters are not as effective when ventilation blows the mist out of the barn before the air cools.
Evaporative pads cool and humidify the inlet air in low-profile cross-ventilated barns. The pads nee to be uniformly moist for best benefit. Fresh water needs to be added, and check for mineral accumulation and algae growth.
More information about these cooling methods is available at the University of Minnesota's Dairy Extension website at www.extension.umn.edu/dairy/management/facilities.htm. There are several Extension fact sheets from different land-grant universities that describe different cow cooling systems.
There are several common cooling system problems to be on the lookout for as you prepare for hot weather.
Poorly maintained fans can lose 40-60 percent of the fans capacity. Check for slipping belts, and corroded and dirty louvers.
Mixing fans improperly mounted may not point downwards towards the cows. Make sure that you can feel the air at cow level.
Low pressure sprinkler systems must cycle the sprinklers on and off. Sprinkling all of the time wastes water, adds water to the manure system and does not help cool the cows the way that it should. Cows are cooled when the sprinklers are off and the water evaporates.
Piping for low pressure sprinkler systems have to be sized large enough to provide water to the sprinkler the farthest away from the water supply.
High pressure misters can become plugged with dirt or accumulated mineral. Most systems have a filter; check the filter.