School is never out when it comes to cow cooling homework

Summer can be hard on a dairy herd, knocking the economic legs out from under an otherwise efficient operation. For higher management grades, complete your ‘assignments’ before it really gets hot.

By Ron Goble, editor, Western DairyBusiness

Whether grading milk production, reproduction or metabolic health, heat stress can send dairy herd performance standards plummeting. When economic times are tough, it’s even more important to make sure you are doing everything necessary to improve your dairy’s cow cooling systems.

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 found a delay of about two days between the onset of heat stress conditions and when cattle actually showed 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

Heat stress negatively impacts all aspects of dairy cattle management – and the economic potential at your dairy.

“The annual economic impact of heat stress 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 milk production reduction 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 it.

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 fans are working properly. Dust and debris accumulations on fan blades and grills can cause increased electrical load, diminished fan efficiency, reduced fan output and escalating electrical bills, according to Michael Tomaszewski, Texas A&M University.

It’s 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, replacing defective sprinkler nozzles and repairing leaky water lines before a heatwave hits.

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. Cows may double their water intake during the summer. If you’ve expanded your herd, verify the water supply system can keep up with the increased water demand. 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 producers to ask their nutritionist to check rations for changes to help maintain intake and/or milk production.

One key to reducing summer production drops is to provide a palatable diet, Tomaszewski added. Consider altering your feeding schedule so cows have fresh feed in front of them more frequently. Feed during cooler parts of the day and at night to encourage cows to come to the feed area.

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

Check to be sure cows are receiving adequate levels of vitamins A and E, and selenium. These nutrients help promote a strong functioning immune system, necessary to combat udder invading bacteria and elevating SCC values, Pritchard said.

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, water is still the most important nutrient of all. Make sure they have plenty, and easy access to it.

Manage water troughs to ensure they are clean and adequately sized for your cow numbers. Install water troughs so cows have access to water before and after milking, but be careful not to impede cow flow, Tomaszewski said. In addition, test your water quality.

Healthy hooves matter

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’re 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, said Bilby.

Other summer reminders

Tomaszewski offers other summer management reminders.

• Plan for fly control. Flies contribute to mastitis and impact cow comfort. Cows may not eat as often if bothered by flies, resulting in a loss in milk production. Consider new foam insecticide applicators. Install applicators in appropriate locations before fly season starts. Evaluate including a larvacide in the ration. Look for fly breeding areas and eliminate them. A little detective work to identify and clean up these areas reaps big benefits from reduced fly loads. Investigate introduction of parasitic wasps. Some dairies have been successful in including these natural predators, along with good farmstead sanitation, as effective fly control procedures. Don’t forget about fly control on the heifers and dry cows.

If you have dry lots, provide adequate shades. Orient them north-south so the sun can help dry wet spots as the shade moves.

Check that milking standard operating procedures are being followed. Evaluate whether milkers adequately cover the teats pre- and post-milking with an appropriate teat sanitizer.

Don’t forget about milker’s comfort in the parlor. Provide a fan or some other way to make it more comfortable in the pit during milking. Hot parlors are not conducive to proper milking procedures.


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

■ To contact Donald E. Pritchard at North Carolina State, phone: 919-515-8805, or e-mail:

To contact Michael Tomaszewski at Texas A&M, phone: 972-845-5709 or e-mail:

Sources & Resources: Heat stress and heifers

The Dairy Calf & Heifer Association offers a multi-part “Tip of the Week” addressing heat stress, by Roy Williams, 2010 DCHA Leadership Class member. Citing a study reviewed in the Journal of Dairy Science in 2003 (“Effects of Heat-Stress on Production of Dairy Cattle”, by J.W. West, vol. 86, pgs 2131-2144), Williams said heifers need not be severely heat stressed to suffer decreased growth rates.

Williams also reviewed on-line publications tackling some of the more complex components of heat stress. – Several suggestions for design/modification of confinement facilities that apply to both cows and heifers. – This 10-page paper from a dairy conference goes into some detail about the relationship between heat stress and the components of the feed ration. If you formulate your feed rations for your heifers, this will probably be worth your time to read. – This is another good, in-depth discussion of feeding strategies to reduce heat stress. This article discusses both feed ration issues and the timing of feeding. – This article discusses the impact of heat stress on breeding, and offers some strategies for improving breeding success during periods of heat stress. – This web page has photographs of cattle in various stages of heat stress. These may be useful in training your workers to recognize animals that are severely heat stressed. – For producers that raise heifers in a grazing system, this article discusses strategies for dealing with heat stress in grazing systems.

Visit; e-mail or phone 636-449-5077.

DAIReXNET resources

DAIReXNET offers publications and links to a wide variety of cow cooling and cow comfort information publications, including:

Evaluating and Selecting Cooling Systems for Different Climates. This report summarizes several studies documenting the negative effects of heat stress, concluding the combination of evaporative cooling, tunnel ventilation and feed line soaking were more effective in reducing respiration rates and vaginal temperature than tunnel ventilation and evaporative cooling alone. Even in high humidity environments created by the evaporative cooling systems, feed line soaking provided additional cooling for the cattle. The combination of evaporative cooling and feed line soaking is an effective heat stress abatement system.

Signs of Heat Stress. Some signs of heat stress in lactating cows are obvious, especially the reduced milk production and the lethargic behavior of the cows. If you have problems determining whether your cows are affected by heat stress, lock up 10 cows and take their rectal temperatures. If more than seven of the cows have temperatures above 103°F, the cows are probably exhibiting heat stress.

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