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Walk through a dairy barn on a hot afternoon, and you’ll probably see more cows standing. Some are standing in their stalls instead of lying down. Others are hanging around the waterers, crowding into the areas with the most air movement, or standing at the bunk soakers without necessarily eating much. As the heat builds, you may see faster respiration, open-mouth breathing, and cows that just don’t look settled.
Most dairy farmers recognize those signs. It’s hot. Of course the cows are hot.
But why does a hot cow stand up? And more importantly, what is it costing you when she does?
A cow stands because she is trying to get rid of heat. Standing exposes more of her body surface to the air and gets her away from the stall surface. This isn’t just something we assume cows are doing. Researchers have measured what happens to core body temperature (CBT) while cows are lying and standing.
In a 2019 Journal of Dairy Science study, Nordlund and colleagues found that “During lying bouts, CBT increased at a mean rate of 0.50°C/h.” When the cows were standing in the freestall pen, CBT moved in the opposite direction, decreasing at an average rate of 0.25°C per hour.
Another study by Allen and colleagues found that as CBT increased, cows spent less time lying and more time standing. A CBT of 38.93°C marked a 50% likelihood that a cow would be standing.
In plain English, as the cow gets hotter, she becomes more likely to get up.
That matters because we normally work hard to encourage lying. We build comfortable stalls, manage bedding, address lameness, watch stocking density, and think carefully about barn design because lying time matters. Yet when a cow becomes hot enough, getting rid of heat can take priority over lying down.
The change can be substantial. In the Nordlund study, average daily THI increased from 68.5 to 79.0 over the six-day trial. During the same period, average lying time fell from 9.5 hours to just 6.2 hours per day.
The cows gave up more than three hours of lying time as the heat load increased.
Now the heat is costing you twice. The cow is heat-stressed, and she is changing productive behavior to deal with it.
Why is she getting so hot?
The obvious answer is that it’s hot outside, but that is only part of the story.
A high-producing dairy cow is a heat-producing animal. Feed intake, digestion, rumination, maintenance, and milk production all generate metabolic heat. The more productive the cow, the more heat she has to dissipate into the environment around her.
That is why temperature alone can be misleading. At 75°F (24°C) with low humidity, a cow has considerably more opportunity to lose heat than she does at the same temperature with high humidity. As temperature and humidity rise together, her ability to get rid of the heat she is producing becomes more limited.
She doesn’t stop producing metabolic heat just because the barn gets hotter, so she adapts. She stands more to expose more surface area. She breathes faster as respiration becomes an increasingly important way to lose heat. She may eat less because feed intake and digestion create additional heat. She changes when she eats, rests, and ruminates in an attempt to manage the heat load building inside her body.
Those are not just signs that your cow is uncomfortable. Those are things she is giving up to stay cool.
What does standing cost you?
This is where the things you see in the barn start showing up in the numbers you care about.
You’re shipping less milk. The cows aren’t eating like they should. You’re struggling to get cows pregnant. Those problems may show up at different times, but they can all be connected to what is happening during periods of heat stress.
Start with lying time. If a cow that would normally spend 10 to 12 hours lying down spends more of the hot part of the day standing instead, those hours have to come from somewhere. She may try to make some of them up overnight, but that only works if nighttime conditions actually allow her to recover. When temperature stays high or humidity climbs overnight, she may never get that opportunity.
Then there is feed intake. One of the most consistent responses to heat stress is reduced dry matter intake. A cow generating too much heat has a biological reason to eat less because fermentation and digestion add even more heat.
A 2024 Journal of Dairy Science meta-analysis by Chen and colleagues combined data from 31 studies and 34 trials. They found that heat stress reduced both dry matter intake (DMI) and energy-corrected milk (ECM). Their analysis found that “for each unit increase in THI, DMI and ECM decreased by 4.13% and 3.25%, respectively, in mid-lactation cows.”
The exact response varies with the cow, stage of lactation, severity and duration of heat stress, but the direction is clear: as heat load increases, feed intake and milk production suffer.
The dairy doesn’t get paid because the cow successfully reduced her metabolic heat production. It gets paid for milk.
Reproduction is another cost that can be harder to see. Heat stress can affect estrus expression, conception, and early embryo survival. You may not connect a cow standing in her stall on a hot Tuesday afternoon with a pregnancy that doesn’t happen weeks later, but they can be different pieces of the same heat-stress problem.
And then there is milk. When cows eat less, spend less time resting, and devote more of their biology to dealing with excess heat, production suffers. The milk loss may be what finally gets our attention, but it is often not the first thing that changed.
The cow changed first.
Maybe standing is telling us something
This is why standing cows deserve more attention during hot weather.
If you walk into the barn and cows that should be lying comfortably are standing instead, don’t just ask whether the stalls are comfortable. Look at the temperature and humidity. Look at respiratory rate. Look at where the cows are choosing to stand and what they are doing there.
Then ask a different question: Are these cows standing because they are trying to cool themselves?
If the answer is yes, the next question is even more important: Is our cooling system actually solving the problem inside the cow?
We usually talk about how much air a fan moves, how many degrees an evaporative system can lower the barn temperature, how often the soakers run, or how long cows spend in a cooling yard. Those things tell us what the cooling system is doing. They don’t necessarily tell us what is happening to the cow.
Take a day when the air temperature is 33°C and THI is around 82. If an evaporative cooling system lowers the air temperature by 5°C, that sounds impressive. The system has lowered the air temperature considerably.
But the air around the cow is still 28°C.
So now we need to ask the question that actually matters: At that temperature, that humidity, and with the available airspeed, can a high-producing cow dissipate the heat she is generating fast enough to maintain her core body temperature?
If she can’t, she is still accumulating heat.
We may have slowed the process. We may have extended the amount of time before her CBT rises. But if she is producing heat faster than she can get rid of it, we haven’t solved the underlying problem. We’ve delayed it.
Eventually, she still has to do something with that heat. She stands more, breathes faster, eats less, and changes when she rests and ruminates. As heat continues to accumulate, core body temperature rises, and eventually we see the consequences in milk production, reproduction, and health.
That brings us right back to the cows we saw standing in the barn.
Cooling the barn and cooling the cow are not the same thing
There is value in lowering barn temperature. There is value in air movement, evaporative cooling, soaking, and cooling yards. The question isn’t whether those technologies can provide cooling. Of course they can.
The question is whether they provide enough heat removal at the cow to keep her core body temperature where it needs to be.
If we lower the barn temperature five degrees but the cow’s core body temperature continues to climb, have we solved the heat-stress problem? If we move a huge volume of air through a barn but cows are still standing, panting, and reducing feed intake, what have we accomplished? If we cool cows intensively several times a day but they begin accumulating heat again when they return to the pen, what happens during all the hours between those cooling events?
Those aren’t questions about whether a particular fan, evaporative system, soaker, or cooling yard works. They are questions about what we are asking the cooling system to accomplish.
A high-producing cow doesn’t generate metabolic heat for twenty minutes and then stop. Milk production, maintenance, digestion, and rumination produce heat throughout the day. Her heat challenge is continuous, and our cooling strategy needs to recognize that.
Whether we are cooling the air around her or cooling her intensely at certain times of the day, we eventually come back to the same question:
Can the cow get rid of her heat as quickly as she is producing it?
If she can’t, heat is accumulating inside the cow.
And that means our target shouldn’t simply be cooler air. Our target should be maintaining core body temperature.
Help her get rid of heat before it builds
That is the thinking behind Core Cool Systems.
We aren’t trying to air-condition a dairy barn. We are trying to create the conditions immediately around the cow that help her continuously transfer the heat she is producing to the environment around her.
That means bringing focused, high-velocity air and low-volume evaporative cooling directly to the cow where she already needs to be: at the feed bunk and in the resting area. Instead of using energy and water primarily to change a huge volume of barn air, we focus those resources where the heat-transfer problem actually exists: at the cow.
And instead of waiting until the cow has accumulated enough heat that we need to bring her core body temperature back down, the goal is to help her continuously dissipate heat so her core body temperature doesn’t climb into heat-stress territory in the first place.
That changes how we measure success. A five-degree reduction in barn temperature is useful information. So is fan performance or the number of cooling sessions cows receive. But none of those measurements, by themselves, tell us whether we actually solved the heat-stress problem.
For that, we have to look at the cow.
Did she maintain her core body temperature? Did she keep eating and ruminating? Was she comfortable enough to lie down? Did she maintain milk production? Did she continue to perform normally despite the heat outside?
So the next time it’s hot and you walk through the barn, pay attention to the cows that are standing. They may be doing exactly what their biology is telling them to do: trying to get rid of excess heat. The bigger question is why they still need to.
When you evaluate your cooling system, start with the cow. Ask what happens to core body temperature during the hottest hours of the day. Ask what happens overnight. Look at lying time, respiratory rate, feed intake, and milk production. Don’t just ask how many degrees the system can cool the barn. Ask whether it can keep the cow from getting hot in the first place.
If your cooling system is working, don’t just show me what it did to the air. Show me what it did to the cow.
Core Cool Systems
Cool the Cow. Not the Barn.
Research
Nordlund, K. V., et al. (2019). Thermodynamics of standing and lying behavior in lactating dairy cows in freestall and parlor holding pens during conditions of heat stress.
Nordlund et al. — Journal of Dairy Science
Allen, J. D., et al. (2015). Effect of core body temperature, time of day, and climate conditions on behavioral patterns of lactating dairy cows experiencing mild to moderate heat stress.
Allen et al. — Journal of Dairy Science
Chen, L., et al. (2024). Effects of heat stress on feed intake, milk yield, milk composition, and feed efficiency in dairy cows: A meta-analysis. Chen et al. — Journal of Dairy Science