Overheated cows can impact herd health and production

The summer sun shines rays of warmth helping grass pastures and hay fields grow. However, as the summer temperatures start to climb the excessive heat can create problems on dairy operations. In fact, heat stress poses a significant challenge for dairy producers nationwide.

Heat and Humidity: Detrimental Combination

The problem with heat stress is exacerbated in the Midwest, due to high temperatures combined with substantial humidity. The combination of elevated temperature and humidity adds additional stress to dairy cattle. Heat stress can lead to a decline in milk production and negatively impact a producer’s bottom line. 

There are tools producers can access to help them determine when their dairy herds may be at risk. “The temperature humidity index (THI) is a research-based tool to help producers identify when the weather will begin to take a toll on their herd,” Reagan Bluel, dairy field specialist with the University of Missouri Extension, said. “The color-coded chart shows that we should expect mild production losses as early as 74 degrees Fahrenheit when the humidity is 75 to 80 percent.” Bluel add. 

In June, most dairy operations throughout the Ozarks are well beyond those mild stress days. The negative effects of temperature and humidity continue to increase through the summer months. Producers anticipate severe heat stress to their herds through late June and July. During these high heat stress periods dairy herds experience a decline in production.

Heat’s Impact on Production

According to Bluel, data collected from researchers in Wisconsin shed light on the duration of heat’s effect on milk loss. “We expect a sliding scale of milk loss as exposure to stressful THI increases,” Bluel explained. “For example, they (researchers) reported a cow experiencing eight hours of 94 degrees Fahrenheit at 70 percent humidity will lose 20 pounds of milk that day.” 

Heat and humidity can have a significant impact on production. According to dairy specialists, it’s not uncommon for producers to see a 20 to 50 percent decrease in production on very hot days. The severity of production loss depends on how effective the manager is at providing a cool climate for the herd. Fans and sprinklers are common ways to keep dairy cows cool in the summer heat. 

Heat’s Long Reaching Effect

An often-overlooked class of cattle during this time, is the gestating or dry herd. According to Bluel, research completed in Florida revealed how hot days impact the fetus of pregnant cows and the profound effect it has in the milk production of the calf years later. 

The researchers discovered that heifers born from cows that were cooled during the dry period, produced 11.2 pounds per day more for the first 35 weeks of lactation, compared to the ones incubated in a hot uterus. “That’s more than a gallon of milk per day lower just for being born from a cow experiencing heat stress while pregnant,” Bluel added.

A more in-depth look at those numbers reveals 11.2 pounds more milk per day for 35 weeks would total a 2,744-pound increase in production for those heifers that were born to cooled cows. If producers assume 20 percent of the herd is first calf heifers and milk is $20, a 100-head dairy operation could lose up to $10,976 of revenue that year due to the heat stress that part of the herd endured while in utero.


Please enter your comment!
Please enter your name here