During hot weather it's difficult for dairy cows to regulate their body temperature, says Alvaro Garcia, SDSU Extension Dairy Specialist.
"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," Garcia said. "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."
Despite the recent cool temperatures of the early spring, temperatures in South Dakota can turn warm very quickly, says Dennis Todey, SDSU Extension Climate Specialist. He says this situation is expected during the next couple days.
"As warm air from the south combines with locally dry conditions it will allow temperatures to reach the 80s statewide," Todey said.
Because of the cooler spring overall; the rapid shift may produce stressful conditions for livestock.
"The heat this week was preceded by unusually cool days and nights. At this point, cows have not had the chance to acclimate. Cattle usually need two to four weeks of gradual temperature built-up to adapt to changes. Temperatures above the mid-80s can be very stressful, particularly if there is little air movement and humidity above 50%," Garcia said.
Temperature, humidity, and stage of lactation
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 says 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 adds 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 says 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 adds 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 warns 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 explains 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."
Todey says near average temperatures will prevail later in the week. But warmer temperatures will return in coming weeks. For more information on keeping dairy cows cool, visit iGrow.