Remember the first warm day of spring? Sixty-eight degrees can feel downright heavenly.

But if you’re a high-producing dairy cow, 68 degrees F is beginning to get uncomfortable. In fact, recent research shows that it’s at this threshold — not the previously thought 72 degrees F — that cows can begin to experience the effects of mild heat stress.

Since heat stress zaps $5 to $6 billion in lost production and animal performance from U.S. dairy farmers annually, new ways to combat this serious challenge are worth a second glance.

Here’s why you need to take a look at cooling cows sooner, rather than later.

Different cows, different times

For years, the dairy industry has relied on a temperature- humidity index (THI) to help determine when cows begin to experience heat stress and to calibrate cooling programs.

According to the traditional THI, cows can begin to show the effects of mild heat stress at 72 degrees F, depending on humidity.

But, cows today produce a lot more milk than they did when these tables were first introduced.

The original THI was developed from analyses of milk production and cow response to thermal stress between 1955 and 1965, says Robert Collier, professor of environmental physiology in the Animal Science Department at Arizona State University. “Cows then averaged between 35 and 50 pounds of milk per day,” he explains. “That’s much different from the cows in our study that averaged around 80 pounds of milk per day.”

Since increases in production increase a cow’s sensitivity to heat stress, it’s easy to see that it’s time to update this concept.

The THI is also criticized for its timing. Collier and his colleagues note that the time interval between stress initiation and milk yield measurement in the original THI analysis was two weeks, and there was no clear definition of the time required at a given THI to induce milk yield loss, other than two continuous weeks of heat stress. That lack of data or clear-cut parameters just doesn’t fly in today’s competitive dairy environment.

Furthermore, the original THI does not account for radiant energy and any cooling by convection.

Positive impacts

So, researchers took all of these factors into account and followed the effects of heat stress on today’s modern dairy cow.

They found that cooling high producing cows at 68 degrees F makes cows more comfortable and more productive than following the original THI. And it makes economic sense. That is, the milk production gained (or losses limited) at this temperature compensate you for the cost of cooling.

For example, you can reasonably expect to gain about 4.8 pounds of milk per day if you cool high-producing cows at 68 degrees F rather than at 72 degrees F. Even if you gain half of that, for 100 cows, you’re still increasing daily production by about 200 pounds.

Using a milk price of $17 per hundredweight for those 200 pounds and a feed cost of $14 per cwt., your income over feed cost is $6 (34-28=6).

Using a variable cost of $0.14 per cwt. and assuming each cooler would cool 10 cows, the total cooler variable cost is $1.40, or a cost of about $0.045 per cow per day for 100 cows. Of course, you’ll need to use figures from your operation to determine whether this makes financial sense for your dairy, but these numbers give you the general idea.

In addition, Collier notes that cooling cows at 68 degrees F, or even 65 degrees F, has positive effects on reproduction.

“Since high-producing cows are generally early-lactation cows, these are the animals you’re trying to breed,” he notes. “It makes sense that cooling them would have a reproductive benefit.” Additional research currently under way should bring some more definitive answers as to the total reproductive impact.

Future strategy

In the meantime, these findings mean you have the potential  to target cooling strategies within your facilities — or at least begin thinking about how you can improve your cooling program.  For instance, you can cool your high-producing cows down to 68 degrees F, but then use the original THI for their lower-producing herdmates to further reduce cooling cost.

In addition, researchers are working to learn more about how to best accomplish this cooling. That is, how should you time your cooling strategy. “If we started cooling early in the morning, some cows stayed away from feed,” Collier notes. “So, should we wait until later in the day? Or should we wait until it hits 68 degrees F to begin cooling? These questions all have to be worked out.”

And, Collier and his colleagues are working on a new THI chart for high-producing cows that should be available sometime later this year.

Therefore, while not all the answers are yet available, the concept of cooling high-producing cows at a lower temperature looks like a real opportunity for dairies, he concludes.