Expert Interview: Nicolaas Vreeburg on Heat Stress in Dairy Cows

In this Expert Talk video, Dr Nicolaas Vreeburg answers our questions about heat stress signs and mitigation strategies for dairy operations.

What is the temperature and humidity index (THI)?

It’s not only about temperature because humidity is as important as the temperature itself. When humidity is high, cows suffer a lot more from heat stress, and that’s why we call the combination the temperature-humidity index or THI.

How much can the cows lose during heat stress?

Well, the first thing farmers see is, of course, the loss of milk production, which can be 4, 5, 6 liters (9-13 pounds) of milk, but the worst I’ve seen was that cows lose 10 liters (22 pounds) of milk during a heat stress period.

In addition, what are the other major signs?

The first thing you can see with the cows is that the respiration rate goes up. Normal respiration rate is only 10, 20, maybe 30 breaths per minute, but if the cows are panting, it goes up to 60 or even higher. Which is what we call panting.

The second thing is that cows eat fewer, but bigger meals.

The third thing you can see is that they stand more, so they lay (down) less, and they stand more in the barn.

What are the longer-term consequences?

When cows change their eating behavior, there is a higher risk for ruminal acidosis. The second thing is that because cows stand longer, there are more hoof problems, and the third thing is that when heat stress occurs, there are more fertility problems.

All farmers know that, but what people don’t know is that the offspring of cows that suffered from heat stress also have production loss during their lifetime.

What are practical tips to succeed?

One: make a really good customized plan to avoid the negative consequences of heat stress.  

Number two is to design a well-ventilated barn, a good functioning cooling system, smart management, and make your ration work more for you by using an active dry yeast probiotic, such as LEVUCELL SC.