Cool it! Cows can’t stand the heat

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UNIONTOWN, Ohio – The temperature outside the Northeast Ohio Dairy Management Conference was 20 degrees, but inside the conference the focus was on summer’s intense heat.

Heat stress is a hidden thief of milk production, reproductive health and dairy profitability, said Ohio State dairy specialist Normand St-Pierre.

Unfortunately, too few dairymen do anything about it.

“We haven’t realized that our cows are as stressed as they are, so we’re lagging in cooling them,” St-Pierre said.

Today’s dairy cow is an efficient milk machine – one that also produces a lot of heat. A cow producing only 40 pounds a day still generates 4,400 British thermal units/hour; a cow producing 120 pounds of milk generates 6,650 Btu/hour.

By the numbers. If no cooling measures are taken and dairy cow housing is only naturally ventilated, production losses can total as high as 706 pounds per cow per year. Couple that with breeding losses and culling costs and that’s a loss of $122/cow/year, St-Pierre said.

That may not seem like very much, but when you consider the average income per cow is approximately $400, it is a lot.

“We’re leaving a whole pile of money on the table,” St-Pierre said.

Related losses. The slower trickle into the bulk tank is the most obvious loss when cows are hot, but other things are happening with the herd that also steal profit.

Cows under heat stress are more susceptible to mastitis and other diseases. They’re also harder to get bred back during hot weather, which means culling rates because of poor reproductive performance will add to higher herd costs.

Cows also eat less when they’re hot, which throws a feed ration off kilter. Minerals are also easily depleted during hot weather.

And heat-stressed cows will also eat less frequently, then gorge themselves during cooler times of the day. This “slug feeding” can cause acidosis, which is considered a major cause of laminitis.

St-Pierre estimates Ohio dairymen are losing $18 million each year to heat stress and he pegs the annual economic cost of heat stress on all Ohio livestock to be $30 million.

No free lunch. Reducing heat stress isn’t free, so producers need to weigh whether the benefits justify the expense.

St-Pierre, however, calls the payback “quite obvious.”

“Look at it as an investment, one that gives you a 3.5 to 1 return on investment.

Water availability is a dairyman’s first line of defense. Providing enough water to cows when they leave the milking parlor and in housing should be a priority.

Secondly, make sure cows have access to shade, whether out on pasture, in a holding pen or in a barn.

Holding pen. Milk producers should pay special attention to the holding pen, because of the amount of heat generated in that small space – and the amount of time cows are forced to stay in the holding pen until moving into the parlor.

St-Pierre estimates that 40 percent to 50 percent of the total heat load in an average herd in Ohio occurs in the holding pen.

He recommends adding sprinklers, not misters, to the holding pen and fans to improve evaporation. He would also like to see improvement ventilation (open sidewalls) in the holding area.

Cooling the exit lane and making sure cows don’t have to walk too far to water, feed and housing are also critical.

Make sure your fans are positioned correctly (see related story) and in extremely hot weather, adding water through sprinklers is the only way to cool cows, St-Pierre said.

“You may have fans, you may be moving a lot of air, but you don’t have cooling.”

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Cooling cows: It helps if there’s water blowin’ in the wind

You may think you have good ventilation in your dairy barn, but is the air moving at “cow level?”

By Susan Crowell

UNIONTOWN, Ohio – You may think you have good ventilation in your dairy barn, but is the air moving at “cow level?”

Rick Stowell, an extension ag engineer at the University of Nebraska who spent part of the 1990s working at Ohio State, spends a lot of time walking around barns. He can tell just by looking at the cows where the air is moving and where the “dead spots” are in a barn.

Stowell returned to Ohio last week to share information at the Northeast Ohio Dairy Management Conference March 6 in Uniontown.

“Having a lot of air flowing through a barn doesn’t always mean the air is moving past the cows that are in the barn,” Stowell said.

Fan fare. Fan output (cfm) isn’t as important as the air velocity at cow level, Stowell said. “Cfm really doesn’t tell me what’s happening where the cows are.”

Instead, look for “throw” of air, or how far the fan’s output extends. Some fan manufacturers will talk about throw and “spread,” Stowell said, but there’s not a lot of unbiased research data.

Get a fan that will maintain air velocity, which also can be misleading when looking at fans, Stowell said. Less fast-moving air will slow down quicker than a larger mass of air at a lower discharge velocity.

Make sure you place and position your fans to direct the air where the cows should be, like over the freestalls or feed bunk and not over the alley.

Poor fan placement may do more harm than good, Stowell stressed.

Get wet. Although thoughts of sprinklers in the barn may create visions of puddles in the feed bunk and damp bedding, Stowell said water can do wonders to cool cows.

He cited several studies that found supplemental evaporative cooling (sprinkling) improves cow health and performance. And when using a fan and sprinkler, about two-thirds of the total cooling benefit actually comes from the sprinkling.

Sprinkling is different from “misting,” where tiny droplets are released to evaporate before hitting the cow. Sprinkling means using big enough drops to soak the cow’s hair coat, and then the cow’s body heat evaporates the moisture. Stowell recommends using low-pressure nozzles (10-20 psi) to get a large enough droplet.

The sprinkler is typically set on a timer to apply water (0.05 inch) every 15 to 20 minutes.

Air movement is essential in order to carry the moist air away so evaporation can continue, Stowell said.

High-velocity fans. Stowell presented details about nozzles and water pressure needs, and also briefly looked at a new fan design, the high-volume, low-speed fans. These are a big paddle-type fan that is installed at ceiling level parallel to the floor.

Stowell said these fans create lots of air flow at the floor level, but only about 25 percent of the air velocity at cow level are greater than 350 fpm (feet/minute), when 400 fpm is the critical range.

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Priorities for reducing heat stress


*      Adequate water


*      Provide shade


*      Reduce walking distance to parlor


*       Reduce time in holding pen


*      Improve holding pen ventilation


*      Improve freestall ventilation


*      Add holding pen and exit lane cooling

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