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Be ready for summer!

Marcia Endres

Extension Dairy Scientist
May 20, 2011

As I write this article, the temperature is in the high 70's for the first time this year. It was a long winter in Minnesota, so we are all looking forward to the warmer weeks ahead. However, this also means the eventual arrival of very hot and humid weather.

Cows suffer more than we do during the warm and humid summer days. They are most comfortable around 50 F. When it is 70 F they are already feeling stressed. Recent research by Collier and his group at the University of Arizona have suggested that the new temperature-humidity index (THI) threshold for today's dairy cows is 68 rather than the traditionally suggested 72. Dairy cows today are more productive and more sensitive to heat than cows used for the research back in the 1960s that suggested THI of 72. In addition, Cook and his group at the University of Wisconsin reported changes in cow's lying behavior when THI reached 68.

So, does this new threshold mean that fans and sprinklers should be turned on sooner? Probably yes, but the additional cost of water and electricity must be considered. Some experts recommend starting fans at 65 F and the wet-dry cycle for sprinklers at 70 F (every 15 minutes; on for 2 minutes). As temperature increases, sprinklers need to cycle at shorter intervals. Sprinkling systems should apply water in large droplets to the cows' backs, wetting them to the skin. Fans blowing on the cows help evaporate the water which cools the cows. Research shows a possible improvement of 4 to 5 lbs of milk per cow per day if cooling begins at THI 68 vs. 72. Other advantages of reducing heat stress include improved reproduction and reduced lameness prevalence.

Some producers in the Midwest have been implementing cross ventilation in order to provide a more comfortable environment for their cows. My graduate students and I conducted a study comparing cross-ventilated freestall barns with naturally ventilated freestall barns in Minnesota and eastern South Dakota. Herd sizes ranged from 400 to 1700 cows. All herds had stalls bedded with sand, so our comparison would not be affected by comfort of stalls. All naturally ventilated barns used fans and sprinklers (so they had good heat abatement) and all cross-ventilated barns had evaporative cooling pads. We collected hourly temperature and humidity data for one year inside the barns using data loggers. In the summer, we measured respiration rates on 75 cows from the high production pen. Three times during the summer visit, we also calculated the cow comfort index (CCI) in each pen. This index is calculated as the number of cows lying down in stalls divided by the total number of cows touching a stall (lying, standing with two feet in the stall, or standing with four feet in the stall).

The summer barn THI was lower in cross-ventilated than naturally ventilated barns (65.9 vs. 68.5, respectively). However, respiration rates were not different between the two barns (about 56 breaths per minute). The outside THI (73.7) was similar for cross-ventilated and naturally ventilated barns during respiration rate measurement. The cross-ventilated barns had higher CCI (85.4) than the naturally ventilated barns (75.9) during the summer, a possible indicator of improved cow comfort. In addition to the slightly lower THI in cross-ventilated barns during the summer, those barns had basically no flies, which could be another reason for cows lying down more in the stalls.

An 'out of the box' approach to cooling down cows is being tested at the University of Arizona. Using the concept of geothermal climate control, they found that adding passive cooling in the form of a heat exchanger system installed beneath the cows bedding area in dairy barns worked as well as traditional cooling methods of fans and sprinklers. A passive system would reduce electricity and water cost. However, installing this system would need to be cost effective.

During summer, make sure cows have easy access to plenty of water. Water can help cool down their large fermentation vat (i.e. the rumen). Ideally, if cow flow would not be affected negatively, an extra water trough should be added where cows exit the parlor area. In addition, providing additional potassium and bypass fat in the ration can be helpful to cows fighting heat stress.

Finally, make sure your fan blades are clean, sprinklers are working, evaporative cooling pads are clean and free of mold or debris, enough clean drinking water is available to the cows, holding pen has cooling mechanisms in place, ration is properly balanced for the summer, and your cows are not overcrowded (especially transition cows). Managing dairy animals during hot weather and high humidity can be challenging but hopefully these suggestions will help you have a productive summer.

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