The Moos Room™

This episode examines how heat stress affects water intake in dairy cows—and why farms must prepare their watering systems for increasingly hot weather.

A review of studies from 1985–2024 found that Holstein cows producing roughly 65–70 pounds of milk averaged about 24 gallons of water per day under thermoneutral conditions. During heat stress, intake increased by approximately 10 liters, or 2–3 gallons, per cow per day. Each one-unit increase in the temperature-humidity index was associated with another 1.5 liters of water intake. Although heat-stressed cows produce less milk, they drink more because the additional water supports evaporative cooling and body-temperature regulation.

Data from the University of Minnesota’s dairy herd revealed a more complicated picture. smaXtec sensors showed that cows averaged around 23 gallons per day, but estimated intake declined during summer. Possible reasons include warmer drinking water, pasture water access, competition at waterers, and changes in drinking behavior. Cows generally drank only four or five times per day, consuming roughly 14–20 liters at each visit. Peak drinking also shifted from midafternoon in winter to around 7 p.m. in summer, often after milking.

These patterns highlight the importance of examining when cows drink—not just daily totals. Farms should ensure adequate water flow, tank capacity, access, and cool water during peak-use periods. Sensor readings are most valuable when compared with each cow’s normal behavior and interpreted alongside weather, milk production, rumination, health events, and management changes.
The central message is that water intake can be a useful indicator of heat stress, but unexpected changes should prompt investigation rather than an automatic conclusion. As extreme heat becomes more common, dairy water systems must be designed for peak demand rather than historical averages.

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Hosted by members of the University of Minnesota Extension Beef and Dairy Teams, The Moos Room discusses relevant topics to help beef and dairy producers be more successful. The information is evidence-based and presented as an informal conversation between the hosts and guests.

 Welcome to The Moo's Room. I'm just back from the World Congress of Genetics in Madison, Wisconsin, where I learned a lot about lots of different genetic stuff from calves to cows. I think the theme of the conference was methane. Obviously, a lot of people had been working on methane in the last four years.

Resilience was the other one that kind of was the resounding theme across all of the conference. So maybe we'll discuss some of those next week. I saw a lot of beef on dairy cross experiments going on, and I'll probably summarize some of those But kind of with the resilience thing, I wanted to talk about heat stress and water intake today.

And we're gonna be working on some of this heat stress stuff within the next couple years here at our research center. We've got sensors. I've put Smaxtec boluses in every single lactating cow now, so we can look at water intake and heat stress. And maybe we'll talk about some of the interesting things that I found in the last, just kind of some summaries on the Smaxtec boluses that I saw over the last couple years here.

But there was a interesting review that came out from Italy and Turkey that really wanted to look at the effect of heat stress on water intake in Holstein dairy cows. And this group looked at lots of different studies from 1985 to 2024, so 30 years worth of information on heat stress of cows. And basically, well, so livestock accounts for one-third really of the global water footprint.

So obviously there's lots of demand for water intake from global demand, from the US to Europe to Africa to Australia, New Zealand. Cows and livestock just need a lot of water. But as heat waves become more frequent, obviously animal drinking requirements become very highly sensitive to environmental variation.

There's a lot of different challenges that come from those animals related to thermal regulation, so dissipating the heat, and then it comes in operational efficiency. So what will a farm do if they need to increase water? And it's kind of we're in the middle of a lot of a heat wave here. At least in the US it's been really hot and humid, temperatures well into 90 to 95 degrees Fahrenheit a few days, and Wisconsin it felt like well over 100, so we're talking 32 to 35 degrees Celsius.

So very hot temperatures. And of course there's a lot of cattle, at least here in the Midwest, that were undergoing heat stress. We typically think of heat stress here in the US as being in the southern states, but obviously heat stress occurs up here in the M- Midwest as well. And there were numerous studies on heat stress at the genetics conference, so it's kind of a timely topic and I think a lot of people...

Uh, we always talk about heat stress when it gets really hot and

So what did this review kind of find? Well

They looked at a lot of different studies from all over the world. The average milk yield of these cows, about 33 kilos per day, so 65 to 70 pounds of milk that these cows had

And there was quite the shift that they saw in a cow. So if you think about thermal neutrality, so the average water intake for these cows

So the average water intake for cows in, in this review was 89 liters per day, so that's about 24 gallons per cow per day. And obviously the primary driver of that is milk production. So cows need to have milk production and they need to drink a lot of water to do that

And water intake was strictly coupled with feed composition and milk yield. Obviously, that is what is driving the water intake, is production. Now, under heat stress, the average intake of the cows was ninety-nine liters today, so an increase of ten liters per day, and that is about two gallons per cow, so two gallons more.

And the biggest driver there was evaporative cooling

So that is basically we're trying to cool the cows with water. So we increase their increasing water intake to cool themselves. That doesn't account for all of the other aspects that come around with it, cow cooling, sprinklers, you name it. Obviously, we're using a lot of water during heat stress times to account for that as well

But they also did Kind of a meta-regression, we'll call it, a fancy statistical term to trying to figure out what the relationship is of water intake and temperature humidity index. So basically, the thermal load dictated a linear response. So what does that mean? So every unit increase in THI, so that's temperature humidity index, the cow required an additional one point five liters of water to cope with that increase in heat stress.

So they're really gonna increase water intake when they're under heat stress. So under normal conditions, water intake is strictly coupled with feed and milk intake. Under heat stress, the relationship kind of breaks apart. So the cow produces less milk, but yet drinks significantly more water, which really proves that the extra volume of water intake is really dedicated to survival and thermoregulation.

So it's not going to milk production when the cows are heat stressed. It's going to survive and trying to regulate their body temperature So it's kind of interesting that as heat stress increases, more sweating, more respiration, they're trying to cool themselves, and they need more water to do that. So it's not just thirst that's driving that.

It's really trying to stay cool

So the biggest thing is can a farm handle that increase in water intake? If you have-- whether you have 50 cows or 500 cows or 5,000 cows, obviously water scales quite a bit. So if you have to have 10 more liters of water per cow, can you handle that flow? Is there enough waters on your farm? How are you watering the cows?

Do you have enough peak water for all of the other activities going on? Milking parlor, and now you need to have extra water for the cows. So it all comes down to do you have enough water, and we should have enough water for these cows to keep them cool

So kind of the conclusion of this study was water intake was certainly scalable, and it was an indicator of thermal load. But as we see temperatures increase, the dairy infrastructure really must evolve from supporting historical averages in temperature to really sustaining those extremes that are happening now that we see and that are gonna happen into the future

So let's talk a little bit about water intake that I've, I've seen on our, on our dairy and, and how that works

So we've been using the Smaxtec bolus in our herd since about 2019. We were doing some heat stress with grazing cows and grazing underneath solar panels, and we used these boluses to look at their internal temperature. So we've kind of been adding more sensors throughout time and in 2025 I had it in about 75 cows and in this year, this spring I put it in all 300 milking cows.

So every cow has a, a smaXtec bolus now. So we're really getting a lot of information now on, well, rumination, activity, body temperature and one of the interesting things that comes with this is water intake and drinking cycles and how we can really use this in our heat stress. So I've really been curious about water intake that's reported by the smaXtec system and how we can better use this for our herd management.

So the system reported daily water intake. So if I think about it from twenty twenty-five, we had these seventy-five cows. We had every day for these cows Average water intake across the whole time period in 2025 was 85 liters

So again, around that 23 gallons of, of water It kind of ranged from 75 to 90 really

So the cows averaged about 88 liters in the spring and about 74 liters in the summertime. So water intake actually went down in the summer. I was quite surprised why water intake may have gone down in the summer. Well, I think that's really related to heat stress and, and waters. You know, our waters are, are outdoors, sometimes in the pasture for some of the cows, and the water's getting hot, so they're just not drinking warm water either

But really at first glance, the lower water intake during the summer really surprised me. I think that generally you would think that cows are gonna need more water during the summer, but pasture waters for our cows, changes in water availability, and differences in drinking behavior for all the cows really influenced water intake.

So a lower sensor estimate of water intake doesn't necessarily mean they consumed less total water So really the water intake, and I found this quite interesting, changed by season. So peak drinking occurred about 2:00 in the afternoon during the winter, but 7:00 PM during the summer. So cows were really drinking water in the summertime about 7:00, and that's when they got done milking.

So after milking, cows were gonna be drinking more water, at least during the summertime. In the wintertime, it's quite variable, but it really peaked

During those evening hours. So these hourly patterns, they really may help us evaluate water access. You know, are enough cows available to drink during these peak periods? Do we have enough water tanks? Are cows returning from the pasture or leaving the parlor at the same time? Do we have enough water to handle all that?

Does competition develop around a limited number of waters? So really I think these daily totals provide part of the story, but the timing of the water intake really may reveal some of these management bottlenecks that we see in our operation

So about 40% of our drinking events occurred from 11 o'clock in the morning till about 3 o'clock in the afternoon, and that was the whole year. We're talking in 2025, what happened?

Well, I analyzed a little bit here the first six months in 2026 to really see what may have happened

And we kinda see the same thing. Water intake is right around 85 liters per day during the winter, drops by about 10 liters in the summertime. So again, cows are a little bit heat stressed, the water's probably higher, we have more competition

And an interesting fact is the cows are drinking about four to five times per day. That, that's all. You know, cows are drinking those times. We d- they don't drink a lot of times during the day, four to five on average, and that's throughout the whole year. So how much kind of water per cycle? Well, about 14 to 20 liters per cycle.

Average was about 18.8, so they're drinking about

20 liters per drinking cycle, about four times per day. So about 80 liters. Daily water intake, average 68 to 88. So it's kind of interesting to see what happens here during the first little bit of the season. Obviously, water intake may increase here. It'll be interesting to see what it's been doing over the summertime here with heat stress.

It's been really hot for the cows. If I look at the sensors, I've got numerous cows that are maybe had some slight temperature increases and lower rumination, so maybe they're not drinking as much water

But really our temperature in the reticular rumen, so these boluses are going into the reticulum and it's really affected by drinking behavior as well So the average temperature ranged from about 38 degrees Celsius in February to 39 in August. So the temperature readings from this bolus, they really must be interpreted differently from temperatures collected using other me- methods because they're inside.

They're inside the cow. So drinking cool water can temporarily lower the temperature surrounding the bolus. So as a result, we see a decrease in recorded temperature, and that can coincide with drinking events rather than illness or a true reduction in body temperature. So the most useful signal may be a departure from an individual cow's normal pattern rather than using a single high or low based on some temperature going on

So we really have to compare a cow with herself, and that's often m-more useful than really comparing her with a single herd cutoff. So some cows consistently drink more water, they ruminate at a higher level, or maintain a different temperature pattern than their herd mate. So a meaningful change for one cow may still fall within the normal herd range

So with this sensor systems, they're really valuable and-- but they take time. They take time to observe and connect with other farm records. So we have to look at weather, milk production, days in milk, lactation number, breedings, health treatments, ration changes, and these all help improve the interpretation of our data, especially from a heat stress standpoint.

So really monitoring technology, it can't explain every change that we see, especially in water intake or if our cows are under heat stress, but it can give us an idea of what's going on. So it can really show farmers when the herd's routine has shifted and help them decide where to look next. So the goal is really not to react to every single number that we have, and we know that there's so much data coming out of these systems.

But really the goal is to recognize meaningful changes early enough to ask better questions about cow health, comfort, management, and how to reduce heat stress that we're seeing in our cows, and do we have enough water for all of these cows?

So with that, hopefully you learned a little bit about water intake and that water intake is important. And as heat stress goes up, at least in all of these studies that we saw around the world from this research, showed that they need more water. Now, in our herd, we didn't see that. We saw less water intake, and maybe that's a management aspect that we need to look at and why our cows go down during the summer

So with that, I think we'll leave you today, and if you have any comments, questions, or scathing rebuttals, feel free to contact me at The Moose Room. That's T-H-E M-O-O-S-R-O-O-M @umn.edu.

Or find us on the web at University of Minnesota Livestock Extension or UMN WCROC Dairy. And with that, hopefully have a great week and try to stay cool. Bye