Heat Stress Part 2 with Dr. Marcus Kehrli

This episode explores the physiological effects of heat stress on dairy cattle, its long-term impacts, and nutritional strategies to mitigate these effects. Dr. Marcus Kehrli shares insights on managing heat stress to improve animal health and productivity.

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Transcript

Chris Radke (01:37)
Hello and welcome to AK Podcasts, where we explore science and nutrition behind livestock care and management with the best and the brightest in the business. I'm your host, Chris Radke, part of the sales department here at Agri-King and with me today is the Director of Field Services and a member of the Sales Management Team, Mr. Mike Downson. Mike, this is part two with the amazing Marcus, but what are we going to continue talking about today?

Mike Donaldson (01:59)
We're going to keep delving into these long, not only the short term, but especially the long term impact that's being discovered that heat can have on, we're primarily talking about dairy cattle, but as Marcus said in part one, beef enters into this too. So to kick off this second part, this epigenetic effect is absolutely fascinating.

Could you do a quick review of some of the physiological changes in heat stress cows that lead to that decrease in milk production as well? part one dealt very heavily with that long-term aspect, but we do see the short-term problems as well.

Dr. Marcus Kehrli (02:41)
Absolutely we do Mike and there is a lot of good information on heat stress physiology that particularly targets you know the real time effects of this heat stress. So I'm going to just hit the high points today because there's a lot of information that's been out there but it kind of helps tie all of this together and then we'll bring in some of the nutritional approaches that do give the opportunity to help the cow. So

Core body temperature of a cow is somewhere between 101 and a half to 102 degrees Fahrenheit. For those in the metric world, that's 38.6 to 39.2 Celsius. So these temperatures are a range because they're buried with the amount of activity that the animal has been experiencing, their size, their age, even breed defects. So cows will begin experiencing heat stress when that temperature humidity index, the THI, exceeds 68 to 72.

It can get much higher. But some of the responses of the cows, they will vary depending on the breed. And it's important too, if you can, to acclimate the cow to those changes. So it's not a dramatic sudden shift like what happened with transportation of cows between herds across states. So I'm sure many producers have seen what are called psychrometric charts. And these are used to depict

how hot weather feels to the body, to your skin, and how that humidity can accentuate the fields like temperature. So we all get these news reports, many of on our phones these days, of what today's feel like temperature is. And with the elevated humidity, that number can be considerably higher than the number you read on your thermometer. So Mike, these weather reports are also applicable for livestock. And in fact, as we've mentioned before, cows have less ability to deal with

with ⁓ the temperature and humidity index than what we do as humans. So some animals are far more affected by this index than we are. We usually get to come indoors at night where it's cooler if we're out working on the farm. And that helps us a lot in adjusting. But livestock, they're only going to benefit if the temperature cools off at night. And that doesn't always happen in certain geographic locations where humidity may remain very high.

and or the temperature remains elevated throughout the night. cows, you know, it's important to understand that they maintain their core body temperature through only a few mechanisms. One is sweating. In Holsteins, there's actual estimates that they can only sweat about 200 to 600 grams of sweat per square meter of body surface area per hour. Some of the Boss Indicus breeds, they can actually do a little better than that, but

Overall, the effectiveness of sweating is very limited in cattle and it's only about 10% as effective it is for us as humans. The other thing that cows can do is they can breathe more. Their respiration rates will begin to rise depending again on their activity level, what their resting respiration rate is. It can go from 20 to 50 per minute, but when that heat stress starts affecting them, they're going to raise their respiration rate up to

60 to 80 or even up to 120 or more and when a cow start breathing about 150 breaths per minute, they're in severe stress and the back to the effort of cooling from the lungs is only about 20 or 25 percent as effective as the sweating is in the cows. So they're losing that mechanism when it gets really really hot. So they're going to reduce their feed intake ⁓ at least 10 to 30 percent when the index gets above 75 and

they're going to increase their water intake. may double it, trying to keep cool and deal with the effects. ⁓ One of the things that they will do to help them cool off is they shunt their blood flow into the skin. And we do this as well, ⁓ but that has an effect where it reduces blood flow into the gut and the uterus. So these are things that you can imagine are starting to affect the environment of the gut.

and the ⁓ environment that that fetus that we talked about the epigenetic effects is sitting in inside the uterus. So a lot of things are going on and that's how that fetus is likely getting its environment changed to cause some of those epigenetic changes. So shunting of the blood into the skin ⁓ is going to reduce the efficiency of the gut when it comes to digestion of food and uptake of nutrients.

That cow can have things really get devastating for her when she can no longer ⁓ lose heat, body heat ⁓ when it's hot outside. So that can be very devastating. So these cows are going to depend a lot on evaporative cooling. That's why sweating and panning helps. But when the humidity is so high that it blocks that type of evaporation, they have no backup mechanism. And that's why producers have learned to use sprinklers, fans, and shade, which are absolutely critical.

in helping these cows. And that will help reduce the milk production losses. It's going to help reduce the impact on milk fat and protein levels. The feed efficiency will improve once they get some of these accommodations. It'll help with the conception rate reductions that you see. It may actually have a big impact on the immune health of those cows. So I want to point that out because the transition cows

As they go through the end of the dry period and end of early lactation, this comes back to the work that I did for a big portion of my research career. Those transition cows are immune suppressed. Mother Nature does this by design, I believe, but it makes those cows very vulnerable to infectious diseases, everything from mastitis, mitritis, it affects routine placenta.

will also increase their susceptibility to diarrhea and respiratory diseases after calving. All of those diseases occur at a high frequency in the early parts of lactation. So heat stress is only going to further exacerbate that. ⁓ Certainly heat stress is well documented to increase cortisol, one of the stress hormones, and that ⁓ we know is immune suppressive. It will also have effects

on your antibody production capacity and so how cows respond to vaccinations under heat stress can be compromised. Overall though, the scientists have come to realize that heat stress induces an oxidative stress in the body of the cow. And I'll touch on this just a little bit, but that disrupts a lot of the functions of the cells that are important for both milk production and immunity and as well as digestion.

That will raise the level of inflammation in the body and that chronic stress is going to have a lot of impact on energy consumption by the cow because they are already reducing their dry matter intake when they get out of their comfort zone. But scientists and research have shown that the decrease in milk production only accounts, you know, the dry matter intake reduction only accounts for about half of the reduction in milk yield in these heat stress cows. So they've actually, guess,

calculated how much reduction in lactose production there is. And we know that you need a glucose for every lactose that that cow puts into milk. the glucose consumption does seem to be being used in the cow in places other than the mammogram when the cow is heat stressed. And that's about half of the explanation for the reduction there.

We know that these cows are also not able to mobilize body fat when they're heat stressed as a source of energy and the non-esterified fatty acids that you see under normal low intake, they don't go up under heat stress. So this is evidence that's been recognized in several different animal species. And one of the effects of this change in blood flow in the gut is that it appears that the intestinal tract becomes leaky.

And this results in some of the endotoxins and other toxins that are in the gastrointestinal tract begin entering the body from those locations when the gut is leaky. Why is this happening? Well, as I mentioned that vasodilation of the skin normally allows some of the blood to be getting partitioned between the skin and the gut. But if you increase it for the blood going into the skin, less of it's going to go into the gut. And that results in low oxygen.

levels in the gut and causes some tissue damage in the lining. And that is what is in turn leading to the uptake of some of these toxins. And in some cases when it gets severe enough, you can get some of the bacteria in the gut to actually get into the bloodstream and cause what we call a bacteremia. And all of that will activate the immune system in that cow, triggering inflammation. And this can all happen within a matter of a few days and actually even measured in hours. ⁓ And that

endotoxemia, that chronic inflammation, that's what's going to be adding to the consumption of the cow's blood glucose levels that would otherwise go into milk production. in short, heat stress causes an unhealthy gut and immune activation in turn consumes more glucose than normal.

Mike Donaldson (12:32)
Marcus, it sounds like getting in front of heat stress and being able to maintain a healthy gut is absolutely important to minimizing these long-term harmful effects. Is that accurate?

Dr. Marcus Kehrli (12:48)
Yes, it would be.

Mike Donaldson (12:50)
So what are some of the things that our nutrition consultants are doing to help our Agri-King clients, dairy herds, deal with this ⁓ by being in a position to maintain instead of treat?

Dr. Marcus Kehrli (13:07)
Well, I think there's ⁓ a lot of evidence that support what we're going to discuss here, Mike. We've known a long time that you got basically three strategies to minimize the effects of heat stress. First and foremost, physical modifications, the environment that cows in. Farmers know this shade, adequate ventilation, misters and soakers where you can use them to aid in the evaporative cooling of those cows, ⁓ especially in regions like in the holding pen where cows are crowded and overheat very frequently.

In addition, don't overcrowd the barns, don't work the cows during the heat of the day. And then the third prong of this is there are improvements in our nutritional management practices that we can make. And planning ahead goes a long ways to making sure that we aren't behind the eight ball when the heat begins to get to the point of the cows discomfort. So managing the environment of our cows for optimal comfort is extremely important.

We always need to be monitoring our cows. We need to use various indicators and a lot of our, ⁓ if you will, our technology that we use with cows today, many places can track things like feed intake and room and temperature and respiration rates, cow movement and so forth. And some of that data that people can analyze gives you a hint of what's going on, but it's always good to be out there looking at the cows in the herd.

But utilize the technology that you have available for, if you will, real time monitoring and invention and establish your thresholds where you got to get in there and make sure that everything's working right. making sure you got good clean water. When these cows get overheated, you're going to see them trying to seek out shade if it's available. You may see in severe situations, open mouth panting and drooling, their tongue out. You're going to see reduced rumination rates. The cows are going to be crowding the water trough. ⁓

They're just, they're not comfortable. not, they prefer to stand cause maybe there'll be a slight breeze if they don't have a good fan, that'll cover more of their body to help them cool, but, they don't like to lie down. So a lot of wasted energy there for the cow. There are high risk groups that we need to focus on. Certainly the higher producers, they're going to generate more metabolic heat from digestion, ⁓ late gestation, dry cows and transition cows.

I believe they're among the most vulnerable and of course we have the aforementioned fetal programming effects of the epigenetics. Certainly cows with black hair coats or heavy cows, they're going to absorb more radiant heat from the sun. And certainly Holsteins are more susceptible, for example, than Jerseys who are a smaller breed size and have some better heat tolerance. But there are nutrition factors to keep in mind. Don't need to remind this audience, but the heat of digestion or the heat increment

That's the heat that's produced during digestion of the feed. And this is especially important in ruminants because this mainly comes from the microbial fermentation of the diet in the rumen. And the breakdown of some of these products is a little less efficient and it will release a lot of energy in the form of heat, especially when you're breaking down a lot of the ⁓ forages.

So feed stuffs that require extensive room and fermentation, they actually produce the biggest heat increment. we need, I mean, that's the advantage of ruminants is that they can break down a lot of feed stuffs that you and I as monogastrics don't have the capacity to gain nutrient benefit from. But for a cow, it's important to pay attention to this during heat stress. And certainly the highest heat increment feed stuffs

There are your low quality high fiber roughages. So if you can avoid low quality roughages in the times of heat, that's extremely important. Next are your good quality forages, ⁓ which you're still going to be feeding it because the cows need them. But we need to make sure that they're as digestible as possible. Some of your protein rich feeds with crude protein supplements, for example, if you overfeed those, they can cause some extra heat.

Your starches, grain concentrates would be more moderate in their heat increment, followed by some of your bypass feeds that have the ability to get past the rumen. And then of course, the lowest of your heat increment energy sources are bypass fats. So think of adjusting your rations in that way. And certainly the AgriKing nutrition consultants are all fully aware of these points and they're going to do everything they can to manage your diet, to

Mike Donaldson (17:30)
Ahem.

Dr. Marcus Kehrli (17:57)
Increase the energy density. ⁓ I also recommend that you feed your cows during the cooler hours of the day. Try to get 60 to 70 % of the dry matter intake to happen at night when it is a little bit cooler. Provide plenty of clean, cool water with plenty of space at the water trough for the entire herd. And then adding electrolytes, buffers, and yeast products which will improve the room and pH and dry matter intake.

Chris Radke (18:19)
Thank you.

Dr. Marcus Kehrli (18:24)
Feeding a very highly digestible roughage such as silage that can be made with AgriKing SiloKing, that will greatly improve the digestibility of those forages and help that cow by reducing the metabolizable heat increment. So in summary, avoid low quality high fiber roughages, Mike. In heat stress management, AgriKing nutritionists, they know how to minimize heat increment on your farm with the feed stuffs you use on your farm while maintaining energy intake.

It's always best to plan ahead to acclimate the cows to these rations before heat stress takes over. Another point, Mike, Agri-King's bovine replete, a lot of research went into that. And it's a vitamin trace mineral supplement that it's specifically designed to support dairy cattle during periods of stress, including heat stress. And it targets some of the oxidative stress that we talked about with the chronic inflammation with a leaky gut. So a key issue in those animals.

is that very fact and addressing that as a nutritional intervention for heat stress, it has a lot of antioxidant focused components. So that will help reduce a lot of the tissue damage. It's got a lot of vitamin E, it's got organic bioavailable selenium, zinc, copper, manganese in bioavailable forms, vitamins A and D, selected B vitamins, and it also has room in protective methionine.

These are all very good ⁓ antioxidants that will help protect ⁓ the oxidative bursts of chronic inflammation that's happening in these cows. So all aligned with proven nutritional strategies for heat stress. So I think bovine replete is a very effective tool for herds experiencing summer heat stress, inflammation, or even other oxidative challenges that are often recommended alongside the use of Trilution for rumen support.

Those are just some of my final thoughts here on Micon. Heat stress, it's always important to pay attention now that we know about it in late pregnancy. Avoid those smaller born calves ⁓ that are less immune, have less utter tissue with these long-term transgenerational effects of epigenetics. That's important. We need to manage that to the best of our ability. Heat stress in these transition cows, that transition cows liver is always overworked.

She's got to deal with the additional stress of the rapid growth of the fetus in the last few weeks of pregnancy. But she's also got to ramp up that udder for milk production and then the rapid onset of milk secretion after calving. That's a lot of stress on her. And sometimes we don't give enough attention to the quality of the rations we're feeding our dry cows. And we need to make sure we're not feeding them some of our lower quality feed stuffs. ⁓

mainly because we need to avoid the mycotoxins that may be there. We need to avoid that heat stress. So focusing on how well that transition cow gets started, that's extremely important because that impacts the remainder of that lactation for that cow. If she doesn't get off to a good start, you're going to be paying for it that entire lactation. So prevent the effects of heat stress by all means possible. Shade, fans, plenty of clean, cool water, sprinklers for all cows that ⁓

you can use in your area and remember include the dry cows prior to calving. line replete to support the room and health. A stressed liver is always going to be a difficult thing for the cow and you need to help maintain a healthy gut. So minimizing the mycotoxin burden because some of the mycotoxins will cause direct damage to the gut and you can use product like Agri-Kings AKMC

which will help against some of these challenging feeds.

Mike Donaldson (22:22)
I think the whole topic of heat is really getting long overdue attention. Marcus made the observation to me one time when we were putting this together that the discomfort a person feels in the 90s for temperature. I didn't mean age. I'm getting close to that. at 90 some degrees, the discomfort a person feels, a cow starts to feel in the 70 degree range.

And it's easy not to look at the situation from their perspective. Even little things, know, relatively, we've used fans and sprinklers for years, but people realizing that it's one thing if you want your fans to kick on at a certain temperature, when it gets to the evening, when things start to cool down, they should run to a little lower temperature before they shut down to help the cow completely recover.

So if you've got them kicking on at 70, don't have them turn off till 65. And all those little things make so much difference. And June and July is not the time to start addressing that from a facility standpoint. You do it when you've still got to wear gloves and car hearts to do some of this stuff and be ahead of the game. And that even applies, I mean, I know our nutrition consultants in April are looking forward, okay, what feeds do I have?

Where's my best quality forages? What do I need to do? When do I want to introduce replete into a diet? What do I need to do? Maybe change the energy content to go towards a more heat friendly source. I just think it's, I think we continue to learn about taking better care of animals and this far reaching impact of heat stress is a good example of how something can have a bigger impact on farms than we ever would have guessed it would just a few years ago.

Dr. Marcus Kehrli (24:18)
Absolutely, Mike. And I greatly appreciate the opportunity to discuss some of these long-term impacts of heat stress with you on cattle.

Mike Donaldson (24:28)
Thank you, Marcus. Well, Chris, now you can give us a final, what did you learn and even include part one and part two. Where are you coming away with, big guy?

Chris Radke (24:38)
My big takeaway is simplification of it what Marcus said because I would never really spit out what he just said honestly But as heat stress goes up cow comfort goes down and as cow comfort goes down those beautiful milk making machines are just not unable to keep up with what they're typically do so ⁓ kind of what ⁓ Dr. Marcus ended up with prevent heat stress even in your dry cows and something my coach used to always tell me it's better to proact than to react instead of

So get ready, even like Mike said, when you're putting on your gloves in the winter, because heat is going to come. All right, if you like what you heard, please leave us a review. If you'd like us to talk about anything else or if you have some suggestions, can email us at podcast@agriking.com
. Dr. Marcus, thank you so much for your wisdom and thank you so much for everything you do for Agri-king. And thank you so much, Mike. Have a good day.

Mike Donaldson (25:33)
Thank you guys, have a good one.