Heat Stress in Dairy Cows

Ms. Morgan Westover, Senior, Department of Animal Sciences, The Ohio State University

At $900 million a year, heat stress has a large financial burden on the U.S. Dairy Industry (St. Pierre et al., 2003). Therefore, managing heat stress in dairy cows is an important challenge that all producers should be working to overcome. With summer rapidly approaching, it is important to prepare now for the high temperatures that will be seen throughout the next three to four months. Heat stress results when an animal can no longer keep their body temperature low and there is an accumulation of heat load within the animal (Tucker et al., 2019). Usually, this occurs when the primary means of cooling, radiation, conduction, and convection are no longer effective. Heat stress can be detected from elevated body temperature, respiration rate or panting, or environmental monitoring (Tucker et al., 2019). Although the exact threshold an animal becomes heat stressed may vary slightly, a cow with a high heat load will attempt to dissipate heat by sweating, seeking shade, increasing their respiration rate, increasing their time spent standing, consuming less feed, and drinking more (Tucker et al., 2019).

The temperature humidity index (THI) is one example of environmental monitoring for heat stress. THI is shown to have a large negative correlation with dry matter intake (DMI; West, 2003). Milk yield is also negatively impacted as THI rises. With each unit increase on the THI index, it is estimated that milk production drops 0.70 lb/day (West, 2003). This negative effect increases as relative humidity goes up. When relative humidity is 90%, yields from Holstein cows decreased to 69% of normal production (West, 2003). Aside from decreased DMI and lowered milk production, there are also other consequences for a heat stressed animal, such as lowered fertility, potential lameness, and longer calving intervals (Tucker et al., 2019). On the other hand, dry cows also experience negative effects from heat stress. Active cooling during the dry period not only decreases body temperature of the animal but leads to significantly higher milk production during the subsequent lactation, especially during the first 60 days of the lactation (Tao and Dahl, 2013). Like lactating animals, heat stress can also lead to decreased DMI (Tao and Dahl, 2013). In addition, cows that experience heat stress prepartum have reduced development of the mammary gland and less functional mammary cells (Tao and Dahl, 2013).

So, it is important to make sure that your farm is equipped to handle high temperatures this summer. Aside from shading cows, there are a variety of methods to cool cows. Evaporative cooling is one means of cooling cows that is very effective as long as the humidity is not too high (Tucker et al., 2019). Sprinklers are one option to complete this. When utilized every 15 minutes for 1.5 minutes, sprinklers can improve milk production by 11.6% (West 2003). Utilization of fans to increase airflow is also another way to cool cows (West, 2003). Utilizing a combination of both typically provides the most relief from heat and the best cooling (West, 2003). In addition to the types of tools available for heat abatement, producers should also consider where they are utilizing them. It is critical to make sure that heat abatement is utilized in the parlor holding area, along the feed alley, and over free stalls.

With that, it is also vital to make sure that the maintenance of fans and sprinklers is kept up. Debris around fans, belt wear, misalignment of pulleys, and dust accumulation are all signs that fans need some attention. Water lines and nozzles are important areas to check for wear on sprinkler systems. If the facility has a natural ventilation system, it is also essential to ensure that curtains are being opened. Routine checks of these can allow you to get ahead of the heat of summer, as it is important to make sure all fans and sprinklers are up and running and ready to go now before the warm days of June, July, and August are upon us.  


St. Pierre, N.R., B. Cobanov, and G. Schnitkey. 2003. Economic losses from heat stress by US livestock industries. J. Dairy Sci. 86:E52-E77.

Tao, S., and G. E. Dahl. 2013. Invited Review: Heat stress effects during late gestation on dry cows and their calves. J. Dairy Sci. 96: 4079-4093.

Tucker, C.B., A. Drwencke, J.M. Van Os, G. Tresoldi, and K.E. Schütz. 2019. Detecting and abating heat load in dairy cows. Proc. Tri-State Dairy Nutrition Conference. The Ohio State University, Columbus. Pages 11-16.

West, J. W. 2003. Effects of heat-stress on production in dairy cattle. J. Dairy Sci. 86: 2131-2144.