The Moos Room™

 Welcome to The Moos Room. It's been a hot one here in the Midwest of the US. Hot temperatures and 90 degrees Fahrenheit. It's been hot for the last few days. Finally starting to cool off, but I think we're gonna get hot again We have gotten first crop done. We've been chopping some oatlage here at our research center for the cows as well, kind of in between some rains.

It's been hot, but it's been rainy here as well, and I know there's lots of places in the US that are in a drought, and we were early on in the spring, but not anymore. We've got some timely rain, so it's been nice. But with all of this heat comes my thought about heat stress. So we're gonna talk a little bit about heat stress today and some of the studies I actually saw from calves and heat stress at the dairy science meetings that I was at a few weeks ago in Milwaukee.

And it's really not been on my mind at all, and I don't think many of us really think about heat stress in calves. Yes, we, we maybe do a little bit when it's 100 degrees and we're trying to feed them and they're not really interested in that, and they're out in these super hutches or individual calf hutches outside.

And we don't really do much about it or think much about it. But there were some interesting studies that showed heat stress effects of dairy calves at the research meetings, and we'll talk about some of the results that these researchers saw. It was kind of interesting, and I've really never thought about much on behavior of calves and how that all works.

We always think about growth all the time, but we never really think about behavior. So let's kind of dissect a few of these and see what they actually found So there was one study done at the University of Guelph in Canada. Lydia Ben was the, the student that was involved in it, and they were really looking at the effects of heat stress or THI, temperature humidity index, on lying behavior of pre-weaned calves.

You know, their thought was dairy calves obviously in Canada are exposed to wide ranges of temperature and humidity levels during the summer And their thought was we really didn't know much about lying behavior, and it's not really well established what can happen in some of these climates. So it's really just like the US here, Canada has wide ranges of temperatures, humidity during the summer.

And so their thought was, can we look at lying behavior and if some of these summer conditions affect lying behavior of pre-weaned dairy calves? So they went to two commercial dairy farms in Ontario. So the study was done in Ontario, and they looked at 140 Holstein heifer calves from two to nine weeks of age to look at heat stress So this temperature humidity index kind of takes into account temperature, humidity, and the average THI was about 65, and it ranged from 49 to 74.

And there were some max THIs as well, the maximum about 74, but ranged from 59 to 83, so from cool to really hot heat stress conditions

So they put loggers on calves and looked at lying time, lying bouts and see what really happened

Well, the average lying time in these calves was about 1,125 minutes per day. So that's most of the day, 20 hours plus per day of lying time, and that ranged from 840 to 1300 for calves. So every calf is different. Not everybody's the same. So how did THI affect l- lying time? Well, as THI increased, lying time decreased.

So if we went from a THI of 50 and lying time 1,170 to THI of 75, now we're down to 1,080 minutes of lying time. So we've lost almost 200 minutes per day of lying time for calves as THI goes up. So that could be three hours per day less lying time as THI increases. So what about lying bouts? Well, kind of lying bouts increase as THI goes up.

So as heat stress happens, calves get more stressed, number of lying bouts increases from about 16 to 20. So not a lot, but they have a few more lying bouts during the day. So that means more up and down, up and down. So these calves are kind of stressed trying to be comfortable and trying to find times to, to lay down and their lying bout length went down, decreased by about 30 minutes from a THI of 50 to 75.

So calves just laid a lot less and spent less time laying. So with greater THI or greater heat stress, they had less lying time with more frequent and shorter lying bouts So as calves got hot and heat stressed, they had less lying time. And I never really thought about that. Seems like you go in there, a calf, if they're heat stressed, they would just be lying there and not doing anything.

Instead, they're standing up. They're up and down, up and down. They're just stressed. So trying to find a way to reduce heat stress obviously will help calves increase lying time as well

So we want to be able to reduce heat stress in the summertime for these calves. Well, there was another study

from The Ohio State University that looked at heat load on commercial dairy farms

So the goal was to really look at calves and respiration rates and shade use on farms. So they went to six commercial dairy farms in Ohio, and they looked at calves over three consecutive days to look at observations of calves' intensive movement. So they looked at calves that were panting, standing, idling, and using shade

So they kind of compared this with THI as well Most of these dairy farms had calf hutches, so 62% of the farms had calf hutches. About 27% had indoor pens, and 11% of the farms had outdoor pens for their calves

Basically, they found ambient air conditions. They varied across the dairies, which we would expect, and they were quite warm. Average THI was 76, ranged from 65 to 83 The climate inside the calf housing was warmer than the outside. So calves that are inside individual hutches, pens, you name it, tend to be much warmer.

The climate inside is much warmer than what it is outside, which is kind of interesting. You think we'd go inside to get out of the shade, but seems like sometimes those calf hutches can be like ovens just with the heat beating down on them. They just heat up. The air inside is much warmer than what it is outside.

I found THI to be slightly higher, not much inside than what it was outside

So what did they find? Most of the calves were observed using shade. They were lying down and idling. So as it got hotter, they were trying to find some shade. Panting was observed in a very small proportion of the calves, about 3%. So some of the calves do pant when it gets hotter. And they looked at some focal heifers, so focused on some heifers for respiration rate and other things.

But they found that higher THI caused increased drinking, grooming, and tucked lying positions and reduced idling, which meant standing time increased for those heifers. So they weren't laying down. And respiration increased with THI, which you would expect, and had higher increases for calves that were housed in hutches versus calves that were housed in pens.

So if they were in an individual hutch, respiration rate increased at a much higher rate than what they did in pens. So kind of another study that found that calves that have heat stress, they're not lying down. They're kind of up and down and standing time increased. So if they're hot, they're standing probably in a group.

I've seen this in our auto feeder barn. Calves are hot, heat stressed, flies are potting. They're all standing in a corner, really, all together bunched up, so causing more heat stress than what they could. And this is indoors, indoors. So I think these results from the Ohio study found that there's a need for summer heat abatement strategies for dairy calves.

And certainly it's not going to be the same whether you have an individual housing effect or whether you're in pens.

So one study actually with calves looked at shade and looked at growth performance and response in pre-weaned beef on dairy calves. So this was kind of a beef on dairy calf. So they had Angus Holstein and Angus Jersey crosses And their goal was to evaluate the effects of shade on growth performance for these calves.

And they used, basically they used shade cloth over individual hutches. So they were in individual hutches for eight weeks. Some had shade cloth, kind of a 70% shade cloth, so obviously gonna let some sun through, and then some that had no shade. And they measured growth, so body weights. They also measured They also measured rectal temperature, respiration rates, and then they looked at environmental metrics, obviously temperature, humidity, and looked at THI again as a measure of, of heat stress

So what did this study find? It was in, done in, in Mississippi at Mississippi State University And basically it found that the shade calves was less THI environmental conditions than what it was in the sun, which you would expect. But actually, as the study went on, it got hotter during the summer, THI was still quite high for the shade calves.

So not much difference. The mean THI for the shade was 75, the mean in the sun was 78. So still means of heat stress when they were under shade What about internal body temperature? So they looked at rectal temperatures of these calves. Calves that were in the shade had less internal body temperature than what calves that were in the sun, which you would expect.

Respiration rate, same thing. Less respiration rate. Breaths per minute, 76 for the shade, 84 for the calves in the sun. So less respiration rate, less breathing heavy, I would say, for calves that were in the shade versus the sun

What about weights? If you look at wither height, they found that calves that were in the shade were taller by about one and a half centimeters compared to calves that were in the sun at eight weeks of weaning. Final body weight, so this would be weaning weight, was 64 kilos for the

calves that were in the sun

So that was about 141 pounds and 72 kilos, about 158 for calves in the shade. So almost 20 pounds more body weight at weaning for calves that were in the shade versus in the sun. So they just were, were bigger with a 70% shade cloth over their hutches

So interesting that providing this artificial shade during pre-weaning improved growth performance and they had calves that were 15 to 17 pounds heavier at weaning. And the shade reduced sort of indicators of heat stress which included body temperature and respiration rate. So decreased body temperature, decreased respiration rate in the shade.

So these are kind of some simple environmental things that we can do just by putting some shade cloth over calf hutches and it really helped reduce heat stress and it increased body weight at weaning

And one last study, this one was actually from a milking cow study. I found it interesting. Actually, it was done with one of my former graduate students, Maddie Bacon. She's now at Texas A&M in College Station, Texas, working on heat stress of cows, and she looked at drinking behavior and robot behavior in dairy cows under heat stress.

So they went to a dairy in, in Texas, and about 125 cows on the study milking in Lely robots. They also had smaXtec boluses, so they looked at rumen temperature, water consumption, drinking behaviors, and she broke out the stages of lactation by early lactation, mid-lactation, so 100 to 200 days in milk, and then late lactation cows, 200 to 300 days in milk, and kind of looked at THI and what all happened Almost 70% of the herd was Holstein, about 30% was crossbred in this study.

Mean THI was 65, so not terribly high, but that's maybe when you start to see some heat stress. At least there's some thought that it's not 72 like, um, many people have thought. And the THI range here was from 33 to 83, so we had a wide range in temperature swings and humidity str- swings

So water intake across lactation, about the same, whether you're early lactation or late lactation. It goes up a little bit, but then it kind of plateaus around 60 to 70 days in milk and doesn't go down a lot. It decrease a little bit by 300 days in milk. Cows are still drinking about 90 liters per day, so 50 gallons maybe of water per day.

And we see about the same, maybe a little bit more, 50 to 60 gallons in early lactation, but water intake tends to be the same

Well, what I found most fascinating was looking at heat stress for these individual cows across lactation and when they experience heat stress. Early lactation cows, heat stress goes up sharply at about 65. Really when heat stress is over 80 THI, they're probably getting into two to three hours of really bad heat stress during the lactation.

Now, the mid-lactation cows, late lactation cows, not much heat stress. As THI was at 80, they're maybe experiencing a half hour, mid-lactation cows maybe 50 minutes of severe heat stress, but not like the early lactation cows. So it appears that mid and late lactation cows are experiencing less heat stress compared to early lactation cows.

Now, she found obviously the early lactation cows had higher production, so higher milk yield, higher protein yield They didn't necessarily drink more water. Water intake was about the same, but not crazy. Maybe the early lactation cows drank a little bit more water than mid and late lactation cows, but again, not as much.

110 liters versus 105 liters for mid lactation, so about five liters less, maybe a gallon less per day compared to the early lactation cows. Number of drinking events, about six. So cows are only drinking about six times during the day to get their full water intake, and they drink about 20 liters per drinking event, which is kind of interesting

Rumen temperature pretty much similar across time. Maybe the early lactation cows a little bit warmer compared to mid and lacta- late lactation cows, but not terribly. Rumination minutes about 30 minutes more for early lactation cows compared to late lactation cows. So kind of what did this study find?

What was their summary? Well, early lactation cows had obviously higher milk production. They had greater m- water intake, higher rumination, and greater heat stress than cows in mid and late lactation. So obviously heat stress increased with THI, and they saw the strongest response in early lactation cows.

But there's considerable cow-to-cow variation that happens when THI goes up, obviously, so there's definitely meaningful differences that we see among individual cows. But I think their kind of conclusion was they can use these precision life tech- technologies to monitor obviously production and behavior, as well as identify the cows that are more prone or more resilient to heat stress and how to effectively manage heat stress.

But it looks like early lactation cows seem to have the most heat stress, so maybe we need to maybe focus on those cows first from a heat stress perspective instead of the late and mid-lactation cows, which really don't have as much heat stress So kind of some interesting things that we saw based on heat stress in calves and cows, and I think as the summer goes on here, we're only mid, early July, so heat stress is only gonna increase as the summer goes on, especially here in the upper Midwest.

So we probably need to look at ways that we can alleviate heat stress and especially in those calves, you know, probably using some shade over them. Individual hutches seem to be kind of a cooker, and I know that's hard to get away from the individual hutches, but maybe some shade cloth over those can certainly help.

We've actually done some-- put some calves underneath our solar panels in individual hutches, and that's helped reduce heat stress in those calves. So I think there's lots of different ways, and we maybe need to be a little more cognizant and thoughtful about ways to reduce heat stress, 'cause maybe that heat stress as young calves affects their growth throughout the rest of their life and maybe milk production.

We don't know that, but certainly could be plausible that heat stress early in life is affecting those calves as well. So I think there's things to think about when we think about heat stress, and maybe we should think about that a little bit more. I never really thought about calves would be standing more in heat stress.

You'd think that they'd be lying down feeling miserable, but they're actually not. They're lying and stand-- They're standing more than they are lying So with that, I think, uh, hopefully you learned a little bit about heat stress and maybe it gives you pause and you can think about it a little bit more as you go to farms or if you're on your own farm, think about heat stress for those calves and how to alleviate that.

So 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 July week. Bye.