With heat indexes soaring over 100° this week, livestock need to be closely monitored to prevent health and production problems, warns Ted Funk, University of Illinois Extension ag engineer.

"Dairy cows will especially be impacted by a hot week," says Funk. "If producers don't anticipate problems in hot weather, cows could go off feed, produce less milk and even experience reproductive failure."

He says dairy producers should focus on three priorities: shade, airflow and water.

"Fortunately this week, despite the high air temperatures predicted in the mid-90s, the dew point is expected to remain around 68 or 69. Dew point, or the measure of moisture in the air, doesn't change very fast unless a weather front comes through. If you have a sustained period of stable weather like we should have this week, you can look at the morning dew point and determine if it's going to be a dangerous or manageable day."

Dairy producers should expect a manageable week if dew points stay under 70, Funk says. The most critical point of the day to monitor is when cows are in the holding pen. That’s when they’re under the most stress, making it even more important to provide shade, fans for airflow and sprinklers for water.

"By putting sprinklers on cows and drying off the water with increased air flow, we can keep cows fairly productive," he says. "As you move cows inside the barn, try to approach the ambient temperatures outside. Inside the barn, the dew point will be higher because you are evaporating moisture from the surfaces and cows are perspiring. You need enough airflow in the barn to approach what's happening outside. That's the best you can do."

Funk advises producers to use large drops of water to sprinkle cows, not misters or fog. For cows on pasture, provide shade structures when possible.

"Cows in the sun will absorb quite a bit more heat than cows in shade. Once cows overheat, it takes hours for them to cool off because they have more bulk. You need to keep the cooling going long after the sun goes down to get them back to normal temperatures."

Drinking enough water is important, too. Cows can double their intake of water in summer vs. the winter. High-producing cows may drink more than 30 gallons a day, so it's important to make sure the water system can produce, not only enough drinking water, but also enough cooling water.

"While this week may not be a really dangerous situation, producers should be aware that if the dew point increases during periods of high temperatures, they will have to work even harder to keep the cows cool," says Funk. "The higher the dew point, the less cooling potential you have with water evaporation. When we get dew points in the low to mid-70s, that's very dangerous. But at 68 or 69, we can handle it if we are prepared."