We all enjoy spending time outside on warm summer days, but what about our cows? Animal productivity and health is negatively affected by heat stress. As a result, it costs American agriculture over $4 billion per year, and almost $900 million is lost by the U.S. dairy industry alone.

During hot weather humans can seek air conditioning, grab an ice cream cone or take a dip in the pool to cool off. Our cows need these same luxuries in the form of shade, fans, and sprinklers. Without adequate heat abatement dairy cows may negatively respond to a heat wave by changing their natural behavior and physiology.

Most research focuses on how healthy cows respond to heat stress, often measuring feed and water intake, respiration rate, body temperature, lameness, and milk yield. Until recently, very little research has evaluated a cow’s chance of recovery from illness during heat stress.

A 6-year study investigating the mortality of dairy cows during heat waves was recently published in the Journal of Dairy Science. The study defined a heat wave as one or more days where the temperature humidity index (THI) exceeded 77.4, and the ambient temperature was approximately 90°F — an unpleasant temperature for a cow without proper heat abatement! While this study was conducted in Italy, the Northeastern U.S. and Canada have similar mild to moderate climates where dairy cattle are exposed to intermittent heat waves.

The data included dairy cows that died on the farm due to illnesses which were exacerbated by heat stress.

Dairy producers prioritize treatment and care of their sick animals. While the study didn’t indicate the heat abatement systems used on these farms or whether the cows were grazing, it’s safe to say that keeping sick cows cool is just as important as other aspects of their care. This research discovered that sick cows are more likely to recover on non-heat wave days. A heat wave decreases a cow’s chance of recovery not only during the heat wave itself but also for the three days following.

Heat waves had the largest effect in June, demonstrating the importance of proper heat abatement even in the beginning of the summer.

In addition, the cow’s chance of recovery decreases as the length of heat exposure increases, especially when the heat wave lasts for three or more consecutive days. It is also important to consider the age of the animal. The study found that the chance of recovery for late term pregnant heifers was not affected by heat wave. Lactating cows generate more body heat than heifers and therefore have a more difficult time recovering from an illness during a heat wave.

So what can dairy producers do to improve their cow’s chance of recovery? Most barns use fans to cool the environment, but research has shown that fans alone may not lower a cow’s body temperature during a heat wave. Fans are more effective when paired with a sprinkler or misting system which cools the cow through evaporative cooling.

Fans should be placed about 10-blade diameters apart and tilted towards the bottom of the next fan in the line. Sprinkler systems are often installed over the feed alley and in the milking parlor holding area. New misting technology, paired with fans, can be placed over the stalls which cools the cow without soaking their bedding.

Keeping our cows alive, healthy, and happy is the number one priority. It’s beneficial for dairy producers to pay careful attention to their cows’ environment during a heat wave, especially when cows are recovering from an illness. Limiting dairy cow exposure to heat stress will improve animal welfare and decrease economic losses, making happier cows and happier farmers!