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Preventing & Treating Heat Stroke in Cattle Herds

By Hubert J. Karreman, V.M.D.

Signs of heat stroke are very consistent among animals, but it’s just that some are more at risk than others: those that are clinically ill, those tee­tering on becoming ill, and especially those right around calving time.


What is heat stroke? The condition involves the increase of body temperature to an extreme point. Unreasonably high temperatures in an animal that seemed completely healthy a few hours ago would be above 106ºF–107°F. Therefore, on a very hot and humid summer day, it would be wise—indeed, necessary—to check an animal that is down or otherwise depressed to see what her temperature is. Most times, a typical heat stroke will be 106°F–108°F. If the temperature is above 108°F, like 109°F–110°F, the cow (or horse) will either not recover fully or recover at all since that level of temperature causes brain damage. Check the temperature of the worst-affected animal to know where she is on the temperature spectrum. On the worst days, normal cows will have elevated temperatures in the range of 103°F or so when they are coming in from pasture or when in the barnyard congregated together. Simple heat stress can deteriorate into heat stroke in animals that have had pneumonia at some point in the past (look in the health record) or in just-fresh older cows with low blood calcium levels.

heat vs yield

Difference Between Heat Stress and Heat Stroke

heat-stressed cow (or horse) will show signs of open-mouth panting with quick, shallow breathing but can still stand, while a heat-stroke cow will usually be down and not rise. A heat-stroke cow will have shallow, rapid respirations and usually appears depressed or even co­matose—much like a milk fever cow. The pupils of the eyes will be dilated. The animal will feel hot to the touch. She may or may not be sweating. If you do a rectal on her, she will feel like she is burning up internally (which she basically is). Heat-stroke animals tend to not drink water, while a heat-stressed animal will. Basically the difference between a heat-stressed cow and a heat-stroke cow is that the heat-stroke cow will have lost control of normal functions (cannot stand, won’t drink, nonresponsive, or comatose). Unfortunately, milk-fever cows and coliform-mastitis cows show these signs as well, so you must check the quarters for watery secretions and take into account if she is just fresh and an older cow (suspicious for milk fever/low calcium). The older fresh cows sometimes get “caught” in the sun and can’t get out of the area since they are too weak to get up from the milk fever. Treat the milk fever first. It is entirely possible that a cow that started with milk fever or coliform mastitis also develops heat stroke.

Treatment of Heat Stroke

While milk fever and coliform mastitis are treated in the vein with electrolytes and medicines, heat-stroke and heat-stress animals are primarily treated by hosing down the animal with cold water con­tinuously for twenty to thirty minutes, head to tail, with special atten­tion paid to hosing the back of the head since this is where the cow’s temperature regulation center is. (If treating heat stress in pigs, do not hose the back of the head.) Heat-stressed cows will often stand still to be hosed down with no need of tying them to anything. Intravenous fluids (five or more liters of lactated ringers solution, 500cc dextrose, and 200cc 8.4 percent sodium bicarbonate) are definitely indicated for heat stroke but are secondary to using a hose. If a hose is not avail­able, quickly move the cow on a four-by-eight-foot plywood board or a tractor bucket to an area where a hose is. Although your intentions may be good, a sponge bath or lugging out a few buckets of cold water and dumping them over the cow will be ineffective. If a cow is deemed to have both milk fever and heat stroke, treat IV for the milk fever (do not put oral liquids into the mouth of an animal that is weak and down). When an overly hot animal is hosed down for a good twenty to thirty minutes, the temperature will often drop to about 103°F (just above nor­mal), which is an excellent sign that your hydrotherapy treat­ment worked.

HEAT-STRESSED COW (or horse) will show signs of open-mouth panting with quick, shallow breathing but can still stand, while a heat-stroke cow will usually be down and not rise. A HEAT-STROKE COW will have shallow, rapid respirations and usually appears depressed or even comatose—much like a milk fever cow.

Four-Seasons Cow Care

Prevention of Heat Stroke

While there’s not much you can do about the weather, there are things you can do to prevent an­imals from getting heat stroke. More and more people are misting their cows to cool them, either in the cow yard or at the feed rack. And while I don’t think allowing cows in streams is generally a good idea, on the most oppressive hottest days it seems reasonable to let them enjoy some wading time in the water. Allowing cows into the woods is another option. But making them wait at the gate until milking time to come in from a baking pasture is simply being foolish.

We all know how cows can look on a very hot and humid afternoon when they come in to be milked. They can appear rather withered in a sense. Of course they tank up on water. If you see this, you might ask yourself why they are drinking so much all at once. Possibly not enough water is being delivered to them while outside at other times of the day, and/or the water quality available to them is not desirable. It is under these circumstances that animals may be drinking highly objectionable water from little puddles outside in the pastures or from small creeks that slowly wind their way through the landscape and may carry potentially harmful bacteria and parasites. Make sure your cows always have access to fresh, protected water sources.

cattle in pond
Cattle will find cooler areas if you provide them on your property during hot days.

Some other things to keep in mind are shade and ventilation. For some reason, cows like to bunch together when hot. But if there is enough shade, they will at least disperse into small groups. There is nothing worse for a group of cows than one lone tree they all try to stand under. A mucky area under one or a couple trees will create more health problems than no shade at all. On the worst days, in barns with good tunnel ventilation (whether free stall, bedded pack or tie-stall), it is more beneficial to keep the cows in during the day and let them out to graze or exercise at night. It’s no sin to keep cows indoors during oppressively hot days. Cows will graze much better in the early morn­ing and cooler evenings than during bright daylight hours when it’s steaming. Reduce feeding of high carbohydrate/starchy rations (i.e., grains) during hot spells since they tend to “heat up” the rumen gener­ally and replace grains with haylage/grass silage, hay, and evening graz­ing. Oats are a cooler grain to feed if interested in trying that.

Without doubt, tunnel ventilation provides a much more comfort­able environment for both the cows and the workers. Keeping cows in all day without either tunnel ventilation or something nearly like it can make for very uncomfortable cows. Also, having really big cows (heavy body weight and over-conditioned) can make for problems in the summer because of the heat generated internally from metabolism produced from very rich rations. These cows really need tunnel ventila­tion and/or big fans.

Most intensively grazed cows are not burdened by excess body con­dition (usually they are too lean if anything), but if they are to get most of their nutrition from pastures, then attention must be paid to their comfort out in the pastures. Cross-bred cows and leaner cows tend to be resilient in the heat compared to big fat ones. It does not matter what the breed is, if an animal is fat, she will suffer in the heat. Many graziers will easily point a finger at Holsteins as being inferior grazing animals, but I take exception to that. One herd I know has about ten out of forty animals of ages twelve and up—the oldest being eighteen and still in the milking herd. The herd is all Holstein. The trick to getting longevity in cows is in their conformation and especially their legs. If you want cows that will last a long time, breed for legs rather than production. And keep them exercised.

Tunnel ventilation, if you have it, also keeps flies from being a problem as they cannot fight the air current. Even if you don’t have tunnel ventilation, it may be better for your animals to be taken off pasture during those blazing midday hours, keeping them around the barnyard out of direct sunlight if possible. Most people have a large box fan or overhead fans to help animals keep cool. Since I’ve driven between farms a lot, I tend to keep my windows down and not use air conditioning, so I get acclimated to the heat in general. Almost universally, getting out of the truck and going into a barn with fans running (whatever sort) always beats no fans or no shade or no breeze. Curtain barns are excellent at catching whatever breeze may be avail­able. Keeping the animals in for the least amount of time is the goal of most graziers. However, keeping animals cooler by keeping them in during the day with whatever fans and practicing nighttime grazing is smartest during the hottest stretches. Portable shades in pasture are helpful as long as there are enough square feet of shade provided for the amount of animals.

A handy hint for calves in hutches is to raise the back of the hutch off the ground during hot days by placing a cinder block there to prop up the back. This will give nice ground flow of air circulation, which will greatly help keeping the animal cool. Simply prop up the back for the rest of the season until it starts cooling down.

Farms that like to graze animals on pasture also need to keep in mind what folks driving by may see in relation to a down cow. The large animal protection officer in my area has gotten in touch with me to treat ailing animals that have been seen by people driving by. As long as the animal receives prompt veterinary attention, the officer will not levy a fine. Preventing any down cows in a field on very hot days is reason enough to bring in the cows in late morning when they are finished grazing so they can be cooled by fans or lots of shade.

Environmental management is a very important skill for farmers to hone. Although we cannot control the weather, we certainly can control the areas our cows inhabit to help prevent potential disasters in the heat of summer.

Source: Four-Seasons Cattle Care