Signs and Symptoms of Heat Stress in Dairy Cattle

Learn about the warning signs and symptoms of heat stress in your dairy herd. Part two of this four-part podcast series covers what to look for when managing heat stress. UW-Extension and industry continue their talk about summer management of dairy cattle.


Liz Binversie, UW-Extension Brown County Agriculture Educator


Mark Mayer, UW-Extension Green County Agriculture Agent
David Kammel, UW-Madison/UW-Extension  Biological Systems Engineering professor
Dr. Vicky Lauer, Professional Services Veterinarian, ANIMART



Time: 5:42 minutes

Liz Binversie: Greetings. I’m Liz Binversie, Agriculture Educator for UW-Extension in Brown County, Wisconsin.  Today we will continue our discussion on heat stress and talk about the warning signs to watch out for so we can maintain a healthy and productive herd.

On the panel today is David Kammel, Biological Systems Engineer and Professor for UW-Madison and UW-Extension; Mark Mayer, Agriculture Agent for UW-Extension in Green County; and Dr. Vicky Lauer, Professional Services Veterinarian for ANIMART.

Some of the signs of heat stress are completely obvious but others are more subtle.  The earlier you can detect heat stress the better so you can do what is needed to keep those cows cool.  Dr. Vicky, when monitoring for heat stress what signs should producers look for?

Dr. Vicky Lauer: On a herd level, one of the first things we will see when there is heat stress is cows will start to drop in milk. Even with mild heat stress we can lose about 5 lbs. per cow per day. That is one of the first things you will see. Also on the herd level there will be lower fat and lower protein in the milk, and then herd level again, lower fertility due to poor conception and then increased early embryonic loss.  On an individual animal level, cows or calves will have an increased rectal temperature, usually above 103°F. They will be breathing faster, breathing harder; 75 breathes per minute is pretty typical. Once you get to 100 breaths per minute you’re looking at pretty serious heat stress where you need to deal with those cows immediately, otherwise they can die from the heat stress. Some cows with heat stress will be more lethargic and not want to move around as much. Other cows will actually be more restless; they will kind of be pacing, wandering around. Usually they’re hanging out around the waterers. Unfortunately cows with heat stress will usually group together and often by the waterers, and that’s just going to increase that heat with all those bodies standing together. Most of the time the cows won’t want to lie down, they’ll just be standing around.  Their appetite is very poor which is what will cause the decrease in milk production. As you get more severe heat stress,  those cows will start to sweat, they will be drooling, and then they  start to pant with open mouth breathing and their tongue hanging out. At that point it is very serious heat stress; those cows need to be cooled immediately before they die.  Then another side effect of heat stress is it will lower their immune function so cows are more likely to get sick from things like pneumonia, mastitis, metritis, and will also have an elevated  somatic cell count. Mark, do you have anything to add?

Mark Mayer:  Yes, the only thing I’ll mention is to look at feed intakes if you are using TMR and weighing everything, you can obviously start to see if they are not cleaning up the feed. That feed intake right away is going to be a good indicator of some stress because the digestion process creates more heat and they are just like us, they eat food and feed, it creates body heat, so you’ll see  the feed intakes go down and as you mentioned, that obviously will affect the milk production. And you’re going to certainly see cows standing more and that’s when we see problems with acidosis and feet and leg problems. They can actually dissipate more heat when they’re standing than lying down. So if you start to see some of those symptoms, I would just add those as well. David, do you have anything to add?

David Kammel:  Yes, Mark, Vicky did a pretty good job of covering all those bases.  Probably another thing you will probably observe, and we get calls like this quite often, about the cows bunching. You would normally think the cows would prefer to go towards the windward side of the barn where maybe the air is blowing through that area of the barn on the south side or the east side or  the west side of the pen. But in fact when they  get under heat stress, they are a herd animal, and  their instinct is to group together because  they are stressed, and that heat caused that stress, so  their  tendency is to go towards low light levels. Now under a barn roof we’ve already got that shade but there’s certainly differences that cows can discern and we don’t know exactly all the nuances of how that animal decides when it needs to move to low light, but what they’re  going to do probably is move to the north side of the pen or the east side of the pen or the west side of the pen of whatever pen they’re in to get away from that higher light level because  they want to get into the shade. So even though we think they’re under shade, they still realize that under stress they want to get into as low a light condition as possible and that might be in the worst possibly location for ventilation purposes, even if we’re running fans or the wind is blowing from the south. They might be towards the north and east end of the pen on the north pen of the barn and not getting any benefit from that wind, but that’s the lowest light level of that particular pen.

Liz Binversie: Thank you again to our wonderful panel today. If you have questions or would like to reach any of our panelists, you can reach them by email.

Tune in next time for part 3 “Ventilation Strategies.”