Editor’s note: The following article is the first in a series of articles regarding current heat stress research and heat abatement techniques. Winter in Minnesota, as usual, was very cold this year, especially in January. On one especially frigid day, the wind chill was -35ºF.

With temperatures like those, the thought of cow cooling may seem out of place, but this is exactly the time to start thinking about heat stress in your herd and ways to mediate this problem on your dairy operation. This article will discuss a few heat stress research points to consider well before the summer swelter arrives.

When approaching the topic of heat abatement, make sure to prepare early, and also make a point to review the current research available.

The University of Arizona’s re-evaluation of the impact of the Temperature Humidity Index (THI) on a dairy herd indicates that heat stress begins to take its toll on animal health and milk production when temperatures reach 68ºF. Heat stress begins to have negative effects on reproduction at temperatures as low as 55ºF.

Preparedness is the first step in heat abatement and protecting your dairy investment against heat stress. Cow comfort is a great investment, and having a heat abatement plan in place can lead to dramatic increases in milk production and conception rates, as well as reducing abortions and improving herd health.


The academic world has conducted many studies and has evaluated many systems for cooling animals including shades, cross-ventilation and tunnel ventilation, as well as other cooling options in freestall and pack barns.

Currently, manufacturers, universities and other institutions have conducted independent tests to determine which cow cooling methods and techniques yield the best results. This research has been performed in labs and on some of the best dairies in the U.S. and abroad.

The academic world is constantly looking for the best systems for the dairy producer. Manufacturers then join in to learn and apply these best practices. All of this information is available to you online, presented at conferences, from your dealers, manufacturers and nutritionists, as well as your fellow producers.

Winter and summer ratio comparisons on feed intake, milk production and conception rates are great places to look to determine how your operation may be impacted by heat stress.

Use these tools, along with advice from industry experts, to help you determine your operation’s heat stress-related losses and to decide the best places to start addressing heat abatement on your dairy.

Heat-stressed cows experience a reduction in dry matter intake and a higher percentage of the dry matter is utilized for maintenance to abate heat. Changes in resting behaviors occur, such as an increase in standing bouts and decrease in resting bouts.

Another indication of heat stress is an increase in panting, respiratory rates and body temperatures. When respiration rates exceed 60 breaths per minute (BPM) at about 68 degrees, the rectal temperature begins to exceed 101.3ºF(38.5ºC) and reproduction losses will become detectable.

At 70ºF, mid to moderate stress will occur as respiration rate increases to 75 BPM and rectal temperature exceeds 102.2ºF(39ºC). Moderate to severe stress occurs at 80ºF when respiratory rate reaches 85 BPM and rectal temperature exceeds 104ºF(40ºC).

Severe heat stress begins at 90ºF with respiration rates over 120 BPM and a rectal temperature of above 106ºF(41ºC). A third indication is a decline in summer conception rates. These are all good starting points to begin your research and evaluation.

A dairy cow exchanges heat with the environment through evaporation (panting and sweating), convection, radiation and conduction. As temperature rises, one of the most effective ways to increase heat loss is by increasing the surface area of an animal that is wet and increasing air velocity. Start looking for issues in the holding pen.

Cows increased their activity by walking to the pen, which caused a heat build-up. Heat build-up is further increased because the animals are jammed together in the holding pen. Once the core body temperature of the animal rises, it could start costing you profit.

Providing high-velocity fans around the cows in a crowded holding pen is one of the most critical applications and the first place one should focus on to reduce heat stress issues.

Some of the latest studies indicate that higher-velocity fans, when placed correctly with the correct amount of water to create evaporative cooling, yield better results than moving a large volume of rising hot air back down slowly onto the animals as seen on composite velocity pattern tests for high-volume low-speed (HVLS) fan applications.

Furthermore, place fans over beds where your cow should spend 80 percent of her time resting and ruminating. Studies at the University of California – Davis on resting behaviors is a great tool in assessing the severity of heat stress and its effects on resting behaviors.

According to a study at Kansas State University, velocity aided by the correct amount of water to create evaporative cooling is very effective over feed lines.

Some of the most recent studies have been conducted on cooling shades at the University of Arizona, Kansas State University and the University of California – Davis, all working together by looking at the core body temperature (CBT), resting behaviors, fan placement, velocity and the application of water and mist.

The studies and their results provide the most recent insight on ways to prevent heat stress from impacting your bottom line. They have incorporated the latest in testing technology and techniques to monitor results.

The data and results from this kind of research can help you with your dairy’s heat stress issues. There are also many dairy operations you can visit to learn what has worked for them and might work for you. There are many additional resources, such as studies that support the economic loss of heat stress, and many tested applications.

It may only be April, but still start developing a plan to mitigate the effects of heat stress on your herd. The next article in this series will further discuss how a cow’s core body temperature and overall herd health is affected by heat stress. Start on the right foot and win the battle against heat this summer. PD

References omitted due to space but are available upon request. Click here to email an editor.


James Kleinke
V.P. of Agricultural Sales
Schaefer Ventilation Equipment