Between Aug. 24 and Aug. 29 temperatures are predicted to be higher than normal and in the 90s for parts of eastern South Dakota. Temperatures like these, when combined with relative humidity will result in high temperature humidity indexes which are going to affect beef and dairy cattle, said Alvaro Garcia SDSU Extension Dairy Specialist.
"The expectation is that this week the humidity indexes will be in the 80s which is considered severe heat stress for dairy cattle," Garcia said. "This is because during hot weather it's difficult for dairy cows to regulate their body temperature."
Garcia explained that body temperature regulation in dairy cows is constantly challenged by a combination of environmental heat and the heat produced during rumen fermentation and nutrient metabolism.
"Heat stress occurs when cows cannot dissipate enough heat to maintain their core body temperature below 101.3 °F. Air velocity also increases the maximum threshold, suggesting cows housed in facilities with forced air can tolerate higher ambient body temperature," he said.
When temperatures exceed 75 °F however, intake drops considerably even at 50 percent relative humidity. Intake is reduced at higher intakes and/or productivity.
Garcia said that close-up and early lactation cows are the most sensitive to heat stress and need more stringent cooling strategies. One strategy he suggests is soaking them with water.
"Heat loss through the skin can be improved when both skin and coat are soaked," Garcia said. "Cows can tolerate greater body temperature during the day when ambient body temperature during the night drop below 70 °F. Keep soaking them in the evening to help accomplish this."
He added that intake and production are more closely associated with the temperature of the two previous days than those of the present one.
"Whenever necessary it is important to have strategies that reduce temperature at night," Garcia said.
Cooling affects milk yield
In order for soaking to be effective, Garcia said sprinklers must soak coat and skin and should work intermittently to allow time for water to evaporate before the next soaking cycle.
"Fans alone are not enough," Garcia said. "Treating cows under severe heat stress with sprinklers or fans alone is not enough. Both strategies need to be combined."
He added that the effectiveness of the cooling system depends on the number of rows of cubicles; four rows, then the sprinklers over the feed bunk and two rows of fans, one over the cubicles, one over the feed bunk, if working with two rows, then one row of sprinklers over the feed bunk and one of fans over the cubicles.
He warned dairy producers about the risks associated with high-pressure misters.
"High-pressure misters reduce the amount of water used, but eject very small droplets and when incapable to soak completely the coat and skin," he said. "They create an air space between the skin and the water film which insulates and impairs heat dissipation. To achieve cooling they must work with a minimum water flow of 3.4 gallons per hour with 5 minute cycles."
He explained that if the temperature is 86 degrees, the soaking cycle frequency needs to be every 8 minutes, (1 minute on, 7 minutes off.) When body temperature exceeds 68 degrees, the fans should work continuously.
"Supplemental fan cooling, in combination with low pressure feed bunk sprinklers can reduce the effects of heat stress on milk production and intake," Garcia said. "Providing clean and fresh water, enough shade and adequate air circulation is critical to maintain production. These systems should be accompanied of key nutritional management strategies suggested for hot weather."
Garcia along with other members of SDSU Extension and University of Minnesota Extension staff will discuss this topic during the Aug. 27, 2013 workshop on Evaluating Heat Stress and Energy Use on Dairies from 10 a.m. to 3 p.m. at the Hammink Dairy located at 200th Street and 469th Avenue, Bruce.
This workshop is a joint effort between SDSU Extension and University of Minnesota Extension, and is based upon work supported by USDA/NIFA under Award Number 2012-49200-20032. Registration for this event is $15 and includes lunch and ice cream.
To register for this event call Candy Rogness at 605-688-5141. An online registration option is also available through iGrow.org. If you have questions or require special accommodations to attend this workshop, contact Erin Cortus at 605-688-5144, or Alvaro Garcia, SDSU Extension Dairy Specialist.