The Moos Room™

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Dr. Joe Armstrong: What's up, everybody? This is Dr. Joe Armstrong. Today on the Moos Room, we are answering a listener question about temperature in barns and what temperature is good, what temperature is bad, how do we decide what should be happening in our barn for different age groups. This is definitely a dairy-focused question and we're focusing on the dairy side with this one. Our listener has to be anonymous on this one. That's totally fine. We love getting questions either way. Love giving shouts as well, but if you want to stay anonymous, that is totally fine.
The first question that started all this is what is up with the different thermo-neutral zone requirements and recommendations out there for different age groups of cattle? They just don't seem to make sense. How could a thermo-neutral zone for a cow be between 5 and 25 degrees celsius, which is roughly 40 to 75 degrees fahrenheit? How could that recommendation be the exact same for a cow and then turn around and say pretty much the same thing is allowed for calves when they're not ruminating, they don't have that ruminant to depend on for heat production, all of these things?
The real question in all of that was, what is the ideal temperature for indoor house cattle at different ages, regardless of breed? What are we supposed to do? Where do we set our upper limit and our lower limit? Well, of course in true extension fashion, my first answer is it depends and I need to have a big question answered before I can move on and provide any help. What I really need to know is when we say indoor-housed dairy cattle, what does that mean? Are we talking 100% mechanical ventilation or are we talking natural ventilation or some kind of mix of the two?
That's a big deal to me when we say indoor-housed dairy cattle, is that a roof and we're depending on natural ventilation to make things happen? Or are we truly totally enclosed with mechanical ventilation providing everything that we need on that end? With a naturally vented barn, you really only have control of so much. The temperature outside's going to be the temperature outside. There's not a whole lot of barriers to changing the temperature in the barn other than providing shade. Then whether you add mixing fans or something to cool the cows in addition to the natural ventilation, that all comes into play.
With mechanical ventilation, we have a little more control if it's done properly, of what the temperature and humidity in the barn are going to be. For the purposes of today, we're talking about a fully mechanically ventilated barn. We're going to make our decisions based on this barn being fully mechanically ventilated. This barn, in my understanding, has all different age groups in this one barn. We're pulling air in and through the calf and heifer area and where the hay storage is, and we're pushing that all the way through and it's exiting on the cow side.
Now, from a biosecurity standpoint, that's good. We want that air to come in and go from calves or younger animals to older animals rather than the other way around. The challenge with that setup sometimes is that now you're pulling your coldest air in the winter in on top of your calves, and it doesn't have a chance to warm up before it gets to them. From a biosecurity standpoint, makes a lot of sense from pulling cold air in on top of calves, depending on how you do it and where that air goes first, we don't have a whole lot of opportunity to warm it up before it gets to the calves.
Enough beating around the bush and trying to do all this other stuff. The question is, what is the upper limit and lower limit that you would set for a mechanically ventilated barn in this situation housing all different age groups that would make it work for all the different age groups? Now, to me, summer is a little easier in this case. We're going to start there. Summer, the short answer is take care of the ventilation parameters and then see what else you need to do. Let's focus on ventilation and then see what else we have to do to keep cows cool.
In the summer, we need a minimum of 60 air exchanges per hour for the entire barn. That means all the air in the barn has to leave and be replaced by fresh air at least once every minute. That's the first step in controlling humidity and keeping cows cool. If that's not enough, then you have to start adding measures in. Mixing fans or putting air directly on the cows would be my first choice. I'm not a huge fan of fogging or misting, at least in our environment. Depends on the situation. The barn, how it's set up. I'm not a ventilation expert. That's someone we can call and talk to together and we can both learn.
In my experience, in our high-humidity environment in the summer, fogging, and misting, maybe not the best idea. Soaking cows, very dependent on the type of barn as well. If you're talking a tie-stall barn, I don't think you should be soaking cows. You've created a huge mess in that barn. If you're a freestall barn and you've got your ventilation really on point and you can reliably soak cows and soak them well to the skin, then soaking is a good option. As we've talked about before on this program, temperature, and humidity go together. Especially in the summer, we need to talk about the temperature humidity index.
You can control one or the other or both or try to figure out how to make those work together. My solution usually is let's focus on ventilation, get as many air exchanges as we can reasonably with numbers of fans in a mechanically ventilated barn, and balancing cost of operation and all of these things. Let's get as many air exchanges as we can with at least 60 air exchanges per hour for the entire barn, and then see where we're at. If we don't have those air exchanges and we don't have that focus on ventilation, you're not going to have any chance at controlling temperature and humidity in that barn.
If we go midsummer moderate to high humidity, let's call it 75% humidity, and we use that and we say, okay, we're going to keep humidity constant at 75%, what's the maximum temperature we can have in the barn before we start to impact cow performance? Well, we know that heat stress starts at a temperature humidity index of 68. That's the cutoff, that's the threshold for dairy cattle. If we want to keep that temperature humidity index at 68 or below with a 75% humidity, that barn has to be 70 degrees max, 21 degrees C in that barn to keep our temperature humidity index at 68 or lower.
Now, some days it's just unavoidable to experience some level of heat stress and cows are different. Each one is different. Some experience heat stress at a different level, and some are more tolerant just like people. In general, we're looking to keep them out of heat stress, obviously, but it's not reasonable to say we're never going to experience any heat stress. That's not reasonable in my mind, especially if you get that day where it's 95 degrees out and it's 100% humidity, you're going to have trouble keeping all of your cows in the barn from experiencing heat stress regardless of your ventilation system.
Now, I've got a friend, maybe he listens to this, who is a ventilation expert. He might argue with me on that because I feel like he probably has designed some facilities that do accomplish that feat, especially when we talk about leaving our country and going to places where it's extremely hot and extremely humid. That all comes at a cost. In a reasonable world where we're controlling for cost, I think it's unreasonable to think that you're going to keep cows out of heat stress all the time, every single day of the year. You're going to experience some that's just the way it works.
We need to be conscious of that and make sure that we're minimizing the numbers of those days as much as possible so we don't impact performance of these cattle, both from a milk production standpoint or a health standpoint overall when we consider health events. Now, in an effort to appease Dr. Bradley J. Hines PhD, tenured professor, we have to talk sensors for a second. If you're trying to figure out what's going on, are these cows' heat stressor sensor is a great option? Putting a smack stack [unintelligible 00:09:01] in these cows and saying, "What is body temperature doing on these days? Are we getting to a point in the day where it's unacceptable?"
It's a great way to do it. Now, playing devil's advocate to that, if you need to prove this point where you're saying, my cows are heat stressed and I think they're heat stressed, sensor's a great way to do that. Very passive way to do that. Collect the data. You've got everything ready to go, but you can do this without a sensor. You can count respiratory rates in barns. That gives you a snapshot of what's going on at that time point.
We know that cows are in mild heat stress when their respiratory rate gets above 60 breasts per minute. If we have respiratory rates above 60 breasts per minute, we know that our cows are in heat stress. If you take certain times of the day and you go out there and you count respiratory rates on cows, and you do it on more than one. Cows are different, so we need to get enough cows counted so that it matters. Ten is a great number.
Just check 10 depending on the size of your herd. If we're talking a pig guy math here, then we would go 30. That would give you a 95% confidence interval, pretty much regardless of herd size, but I don't know if anyone has time for that so 10. Ten animals, respiratory rates, are they heat stressed or not? Just based on that, take it at different time points. You can see if it builds throughout the day and they experience heat stress at different time points throughout the day, it's a way to do it without a sensor. I'm not saying don't get a sensor, just saying there's other options in case you don't have the money to put a sensor in everything.
I've apologized already for giving you a very extension answer where I'm saying it depends. Well, it does. If we're going to figure this out, we need to focus on the ventilation, get at least 60 air exchanges every hour, and then see where we're at. If you fix the ventilation side and make sure you've got 60 air exchanges every hour, everything else might work out. You might not have to do a whole lot else, but if you can't get there, you need to fix that first, and once you're there, we can address all the other options that are available.
If we're going to count on humidity being a thing, what's the proper goal for what we should have in the barn? I'd have to talk to somebody and say, "It probably is dependent on the outside temperature." If we have an outside temperature of this and the humidity outside of this, really the appropriate measure is probably how much different can we be from outside to inside? That's a more appropriate figure to do this. I don't know that answer, so I'd have to reach out to a friend to figure out what is that answer.
The goal in this case when we're answering this question, what's reasonable? I think that most days we can have a relatively good humidity control inside at 75%, which means that you should probably keep the barn between 70 and 75 degrees max inside. That would be a reasonable thing to do, in my opinion. All right, let's get to the winter side of this. That's a very different question and I told you that it's a little trickier to figure out what to do, especially when we have all these different age groups in the same barn.
If we're going to have that many different age groups, we're going to have calves in the mix, how do you accomplish a right temperature for that calf that's pretty much still wet and that cow that's at peak milk? How do you figure out what's the right temperature for both those animals? You're not going to find the right temperature for both those animals.
I don't think that's probably possible, but when we're talking winter, again, it comes back to ventilation.
If we're going to have proper ventilation in the winter, we need four air exchanges of that entire barn, every hour at a minimum. The goal really, when we're talking proper ventilation in the winter is, let's get as much as possible without causing the barn to freeze. We can't have waters freezing. We can't have it being crazy slippery because that's dangerous for the cows and it's dangerous for the people. We need our workers to be somewhat comfortable, but we need to balance that with cow and calf health as well.
What's the answer? The answer is let's get ventilation figured out. Again, the focus is ventilation and then see where we are. Four air exchanges minimum per hour in the winter, all the air leaves, fresh air comes in at least four times every hour. If that's happening, we can assess how much we can push it. We just can't let the barn freeze. Now, in the winter, calves are the most susceptible to the cold. That makes sense, but it all comes back to how you feed them.
We've talked extensively on this show about how to feed calves on the dairy side and our opinions on it and the data behind it. We don't need to get into that today, but if you're going to feed calves a 20/20 milk replacer, and you're going to give them four liters or four quarts a day total, you better have your barn warm or they're not going to grow at all.
If we go back to feeding the appropriate amount, the appropriate milk replacer, or whole milk at eight liters per day or nine liters per day if you feed three times, you can still get optimal growth for those calves at a pretty cold temperature.
If I'm feeding the appropriate amount of the appropriate thing to these calves, I can get away with a temperature of 15 degrees Fahrenheit or -10 �C and still achieve optimal calf growth just under two pounds per day of gain. Again, my answer comes back to that old extension answer of it depends, and it does. If you feed your calves correctly, you can let that barn get pretty cold. Is 15� reasonable for the barn if you want to keep waters open and things comfortable for people? Maybe not.
Again, I think the way to ride this in the winter is to maximize your ventilation as much as possible without making the barn freeze. That's a trial and error game in a lot of cases, trying to figure out how to make that work, but ideally, we would let that barn ride just above freezing so that everything still works, everyone's still safe, and both the cows and the people are reasonably comfortable.
I don't know if I answered any questions today or if I just rambled for 15, 20 minutes and maybe you're not even here listening to me still, totally understandable, but we covered a few things we haven't touched on in a long time, just about heat stress and cold stress, and how much we feed our calves, and what are we really looking for when it comes to ventilation. Really the goal is, let's start with ventilation.
The more I visit different places and I work on different issues that people have. I come back to focusing on ventilation in a lot of cases, and really, when we talk barn design or people starting to work on building a building or finding a new way to put cows somewhere, the first question for me and how you design that whole thing really comes down to ventilation because it's really, really expensive and difficult to fix after the fact. There's just certain things you can't get around if you design things incorrectly right away with the ventilation.
Enough rambling. I will move on. Let's wrap this episode up. If you have comments, questions, scathing rebuttals to this episode, please email themoosroom@umn.edu. That's T-H-E-M-O-O-S-R-O-O-M@UMN.EDU. Catch us on Twitter @UMNmoosroom and @UMNFarmSafety. Catch Bradley on Instagram @umnwcrocdairy. Thank you for listening, everybody. Catch you next week.
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