Expert’s view: Dr. Nico Vreeburg about heat stress signs and mitigation strategies for dairy operations

Nico Vreeburg, DVM, joined Lallemand Animal Nutrition in 2021 as a Technical Services Manager for ruminants after working in veterinary practice for 15 years and 20 years in the Cows Signals company, which he founded in the Netherlands. Nico has unrivaled expertise in dairy cow behavior and management. A self-proclaimed real “cowboy”, he shares his experience about heat stress can negatively affect animals as well as some management tips for farmers.

Nico, since you are based in the Netherlands, it may be a surprise to readers that you are concerned with heat stress. Is heat stress a problem in the Netherlands too?

Well, in fact, there is heat stress in most countries in the summertime. You know, unlike human beings, the optimal temperature for a cow is 10°C. Even in cooler climates, in the summertime, it can easily reach 25-30 C° these days. The other thing is that dairy cows are mostly kept inside, even in the Netherlands where grazing is still the standard. The climate inside a barn can be different from outside, with sometimes even a higher temperature.

Finally, let’s not forget that humidity plays a big role in heat stress (i.e., at the same temperature, cows will suffer more from heat if the humidity is high. The indicator to monitor is called the Temperature and Humidity Index, or THI). Under our climate, it is becoming a bigger problem every year.

So yes, farmers and farm advisers have to be aware of heat stress and the associated losses and consequences for dairy production. It is a growing concern in almost all countries now and farmers notice it more and more. Not only in the countries with warmer climates but also in the UK, the Netherlands, Germany, Denmark, Sweden, Finland…everywhere!

As an expert in cow behavior, or cow signals, can you tell us what are the first visible signs of heat stress?

There are some common signs of heat stress that can be easily observed in all farms.

1. First, the biggest change we observe is an increase in respiratory rate. You have to look very carefully because it is not something we typically monitor, and a lot of people don’t have a clue that a normal rate for a cow is only 10 to 30 breaths per minute. A cow is considered panting if 60 breaths or higher occur.
2. Another thing that is easy to see is that cows are standing more often. During heat stress, cows are more apt to stand in the barn with fewer cows lying down in the stalls.

These are the two, most visible signs that you can immediately observe in a barn.

3. Then, taking a closer look, you will see that cows are drinking more, and spending long periods at the water trough. A water meter for each pen is a good idea to help monitor heat stress exposure by the upward fluctuations in water intake per day.
4. Another, very often reported sign is that cows are gathering and crowing together at cooler places in the barn, such as places with more ventilation and fresh air.

If you take a longer and better look, you can also see differences in eating behavior.

5. Cows are eating fewer, but bigger meals. Consequently, the percentage of cows with a rumen score of 2.5 or lower goes up. Again, to see the signs of stress, you need to have a good reference of what is normal.

What are the consequences of heat stress? Can you give us some figures?

The first and most visible consequence that farmers see, of course, is the loss of milk production. That’s the easiest thing to see, and it can go up to 4 to 6 liters a day. With severe heat stress, I have seen cows losing 10 liters a day on average.

Longer-term impacts for the herd can be lowered fertility, and fewer cows getting pregnant. That impacts the calving pattern or interval of the herd. A drastic reduction in pregnancy rates can have lasting effects and can take upward of 2 years to recover from.

Another long-term issue is overall health. During and after heat stress, you can see an increase in poor foot health, lameness, and even laminitis. There are several reasons for that. First, cows are standing more to try to escape the heat and uncomfortable feeling, which can add more pressure on the foot and hooves. Even if everything is done correctly on a nutritional level poor rumen health can occur.  The erratic eating and meal patterns of the cows leave the cow more prone to ruminal acidosis during or after a period of heat stress. Cows prefer to eat when the day is coolest, so they often overcompensate by eating bigger meals in shorter periods of time. This disrupted feeding behavior will affect rumen health, and digestion and often increases the risk of sub-acute acidosis or bouts of clinical acidosis. For both these reasons, there is a higher risk of poor hoof health and locomotion in the herd with more hoof ulcers, white line lesions, and even laminitis.

Finally, there is data that now shows an even longer-term impact of heat stress on a dairy operation. Offspring born to heat-stressed dams have lowered immune function at birth, are more vulnerable to illness, and are less productive during the first lactation.

There are huge consequences of heat stress in dairy cows, and farmers report it more and more. Farmers are concerned and are willing to invest in preventive solutions to ease the stress on the herd.

Talking about solutions, which one would you recommend in practice?

Make a customized plan with your team of advisors to help avoid the negative consequences of heat stress. You cannot affect the weather, but you can prepare your herd for it. There are three types of solutions: environmental, nutritional, and management solutions.

Starting with management, it’s simple, you minimize moving cows during the hottest times of the day, think about your milking, vaccinating, and pregnancy and herd check times and see if you can adjust. That is something that is important and doesn’t cost anything but good planning.

Then there are animal environment measures. Here I distinguish between measures to cool down the cows, which are more effective and require less investment and measures to cool down the barn (misting systems, which are not recommended under humid climates, water curtains, air conditioners, tunnel ventilation, etc.).

I’ll focus on cooling down the cow, which is, in my mind, the most affordable and a must-do. The first step is to ensure good natural ventilation in the barn. An insulated roof with open ridges and wide-open sidewalls works well for maximal natural ventilation. When the THI goes up to 68, mechanical airflow should cool the cows.

Above a THI of 74-75, a shower or water misting system can help cows cool down. Big droplets on the cows along with ventilation and air movement will cool them down. It is important to cool cows down as they are lying, since they tend to stand in heat stress situations, and this is bad for their hooves and rumination. I always suggest putting fans above the stalls rather than the walking alleys, to encourage the cows back toward their natural behavior. If you look closely during heat stress periods, the dominant cows stand in the wind and the timid cows do not get the ventilation, so they suffer more from heat stress than their dominant herd mates. To avoid this, I prefer to start by putting fans above the stalls and installing a shower over the cow’s backs along the feed bunk. Cows are soaked when they eat and then they cool down because there’s wind in the free stalls. This way you stimulate the normal behavior of cows and profitable because lying time is rumination time, and rumination time is when milk is made and what keeps a healthy rumen.

Environmental solutions are the most discussed and one thing, which is often forgotten, is the feed. One solution to avoid the negative consequences of heat stress is to bring stability to the rumen since changing feeding behavior due to heat stress impairs the rumen function and decreases the ruminal pH. With the live yeast feed additive Saccharomyces cerevisiae CNCM I-1077 (LEVUCELL^® SC), the rumen pH can be stabilized at a higher level. Feeding live yeast will also support normal feeding behavior, helping cows to have more frequent and smaller meals even if they are under heat stress (Perdomo et al., 2020).

The other lever is to improve the digestibility of the ration. Feeding live yeast can also help improve the digestibility of the ration. Along with adding a rumen modifier, it’s good to check in with your nutritionist to ensure the diet includes more easily fermentable feedstuffs, for example, beet pulp or cotton seeds, etc., so the cow is receiving the most nutrient-dense bite she can during heat stress.If we talk about feeding, let’s remember that the starting point is to have good quality and cool silage, which starts much earlier during the previous harvest season. So again, it is all about planning and using a high-quality and proven silage inoculant at harvest! It is important to make sure to have cool and clean forages, especially during the summertime. Moldy or poorly fermented silage, have a negative influence on feed intake, metabolic energy, and nutrient availability.

A well-ventilated barn, well-designed cooling system, smart management, and investing in your ration with additions like LEVUCELL SC and MAGNIVA forage inoculants are the keys to success in the summertime, when the living is easy — for us, not for our cows.