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Beating the Summer Slump— Keeping Your Cows Cool (part 1 of 2)

Paul Porter, Ph.D, Land O’Lakes

Before the dog days of summer arrive, think about how you can minimize the milk production loss and poorer reproductive performance that inevitably comes with warmer temperatures. A lactating cow starts feeling heat stress much sooner than you and I (for example, 75 F with moderate humidity). This week we’ll explore the management side. Knowing just a few basics of cooling cows and a little creativity at your dairy can yield thousands of dollars in returns: 5 pounds milk/day X 60 days X 100 cows X $8/cwt IOFC = $2400.

While researchers using use rectal temperature to quantify how severely a cow is heat-stressed, another simple observation is to watch their respiration rate. Normally a cow breathes less than 60 times per minute. When you see respiration rates in the 60 to 80 breaths per minute, your cow is heat stressed. So what do you do? As Dr. Dennis Armstrong pointed out at this year’s Western Dairy Management conference, there are 3 ways to effectively cool your cows: 1) Wet the cow to the skin then blow air across her. 2) Wet the cow to the skin then blow air across her. 3) Wet the cow to the skin then blow air across her.

Before going into the details of some recent research, let’s cover 2 fundamentals: ventilation and water. If your barn does not have adequate air exchange and movement, you are coming to home plate with two strikes against you. This means either tunnel ventilation, curtain sidewalls (natural ventilation) or fans. Additionally, cows’ water intakes can increase by 50%. Is your water system (pipe size, pump capacity, well depth) up to the task? For cows milked in a parlor, find a way to add a few stock tanks of water on their return trip to the feed alley and free-stall.

Let’s be clear about "misting" versus "sprinklers". Remove "misting" from your vocabulary. In theory, misting cools the air around the cow. In practice, our humidity levels limit the effectiveness of adding water to the air to cool it. In addition, a fine layer of mist on a cow’s hair coat actually can act as insulation and reduce the amount of heat she can dissipate through her skin. Consider the following data: Smith and Armstrong measured the increase in respiration rate of cows under different cooling systems from morning to afternoon. Over 40 herds from the Southwest were involved (proceedings of the 1999 Western Dairy Management Conference).

Type of cooling Increase in respiration rate

No cooling 23%

Spray and fan (feed alley) 14%

Feedline spray (no fan) 18%

High Pressure Foggers (mist) 42%

The good news about cooling cows is that it can frequently be done without a large investment. Simple garden sprinkler hose or small PVC pipe with nozzles strategically located and attached to a timer often is all that is needed. A common cycle is 1 to 2 minutes of water followed by 15 to 20 minutes of fans. The first priority area is the holding pen for parlors. Exit lanes and feed alleys would be the other areas to consider.

Consider these real life examples: I worked with a 500 cow herd during the summer of ‘95 that typically lost 5 to 10 pounds of milk during extended heat stress while their neighbors lost 10 to 20 pounds of milk. How’d they do it? All cows exited through one doorway from their triangle parlor. As they exited, they were drenched with water. The natural ventilation did the rest. In 1997, a client took my suggestion of using a garden backpack style sprayer and wetted their cows twice daily. It was a 100 cow, tunnel ventilated tie stall barn. During short periods of heat stress, they maintained their bulk tank average (compared to a typical 2 to3 pound loss) and felt the barn was at least 5 degrees cooler. Last year, a client with a 3-row barn and covered feed alley installed a spray system over the feed alley. Every time I visited the barn, the feed bunk was full of cows. Production and reproduction didn’t miss a beat.

Finally, don’t forget the cows outside! Florida research has documented a 1000 pound milk loss in the following lactation for dry cows kept outside with no shade during the summer. Providing shade might be easier than you think: set a 12-foot post inside a tire and pour concrete in it. Place them strategically, using 80 to 90% shade cloth. Provide 50 to 75 square feet per cow.

In the next installment, we’ll review the common ration practices to help hold intake and production. A little preview: if your corn silage inventory is going to run out in June or July, start figuring out now how to make this the last year this happens.