The heat is on: Dairies need to prepare

By Ron Goble

Summer time is hard on dairy animals. Whether a producer is looking at his herd reproduction program, or his milk production performance, heat stress can knock the economic legs out from under an otherwise efficient operation.

When times are tough it is even more important to make sure you are doing what is necessary to improve inadequate cow cooling systems on your dairy.

Under extremely dry conditions – 10 to 20% humidity – cows may not show signs of heat stress until temperatures are in the mid to upper 80s. In very humid conditions, however – above 75% – heat stress can start with temperatures as low as 70 degrees.

Research from the University of Georgia has found a delay of about two days between the onset of heat stress conditions and when cattle actually showed the signs of heat stress. Indicators that cows are experiencing heat stress are:

• Feed intake is reduced

• Milk production declines

• Cows are less active and stand more

• Cows often crowd together, especially around water tanks

• Panting and open mouth breathing

• Rectal or milk temperature increases

Impacts bottom line

Dairy specialists point to the fact that heat stress negatively impacts all aspects of dairy cattle production. Milk production decline and reproduction losses during the summer months substantially impact the economic potential at your dairy.

“The annual economic impact of HS on animal agriculture in America has been estimated at $2 billion, with the dairy industry alone accounting for $900 million of this loss,” according to Todd Bilby, dairy specialist at Texas A&M. “Heat stress occurs over a wide combination of solar radiation levels, ambient temperatures, and relative humidity This is further aggravated by metabolic heat production (generated by the cow herself).”

Herds with inadequate cooling systems can experience a reduction in milk production of 20% or more when the temperature-humidity index begins to rise above 72. It may be time  to take inventory and possibly alter the cows’ environment.

It’s time for fresh look

It never hurts to take a fresh look at your cow comfort and cooling systems. It might be time to evaluate the cooling system in your holding pen. Does a roof provide shade? If not, add shade.

If you don’t already have soakers and fans to cool cows while they wait to be milked there is still time to install them. Fans should be mounted at a 30-degree angle so air blows downward around the cow. Install parlor exit lane sprinklers to increase cooling beyond milking time.

Maintenance is also critical to assure that your fans are working properly. Don’t be surprised, but they may require cleaning to be operating at peak efficiency.

It is also important to have sprinklers or soakers at feed bunks to encourage cows to maintain their dry matter intake levels. Put the sprinklers and soakers on a timer so cows are soaked to the skin and then allowed time to air dry.

Test your system early and replace defective sprinkler nozzles and repair leaky water lines before a heatwave hits your neighborhood.

Not just for milking herd

Although shade and cooling for the milking herd might be your first priority, cooling is just as important for dry cows and heifers. At a minimum, provide dry cows, heifers and calves with shade.

Check water availability for your cows. Dairy Extension specialists say cows may double their water intake during the summer. If you’ve expanded your herd, verify that your water supply system can keep up with the increased water demand this summer. Provide baby calves with water as well. Milk isn’t enough, especially when temperatures climb into triple digits.

Humidity and diet

Extension dairy specialist Donald E. Pritchard, at North Carolina State University, who works with dairies in both hot and humid conditions, suggests that you ask your nutritionist to check rations for changes that will help maintain intake and/or milk production.

While the two main responses to heat stress are eating less and producing less milk, Pritchard says an elevation in the somatic cell count also can be problematic.

He says to check and be sure your cows are receiving adequate levels of vitamins A and E, and selenium. These nutrients help promote a strong functioning immune system which is needed to combat udder invading bacteria and elevating SCC values, Pritchard points out.

Researchers at the University of Minnesota say cows lose potassium through sweating and sodium is excreted in their urine in response to heat stress. Increasing potassium and sodium in their diet dry matter is recommended. Balancing for dietary cation-anion differences (DCAD) is one way of accounting for these two elements.

All that said, dairy specialists emphasize that water is still the most important nutrient of all. Make sure they have plenty and easy access to it.

Sure, healthy hooves matter

Even hoof trimming can make a big difference in how a cow survives the effects of high temperatures. Cows usually stand more in the heat of summer in an effort to cool themselves. If their claws are properly trimmed and balanced they are better able to handle the increased standing time under sprinklers and soakers.

Heat stress also can significantly decrease pregnancy rates with impacts lingering well into the fall months. Designing strategies to reduce negative effects of summer temperature on fertility; such as enhanced cooling, ration adjustments, and reproductive protocol changes, will improve your dairy farm profitability, says Bilby.


■  To contact Todd Bilby at Texas A&M, call 254-968-4144 or e-mail him at,

■  To contact Dr. Donald E. Pritchard at North Carolina State University, call 919-515-8805, or e-mail,