Managing Livestock Heat Stress

At least 2,000 head of cattle died during an extreme heat event in southwest Kansas during one weekend in June. The week started hot and only got hotter: 80º F on Thursday, Friday up to 90º with 66% humidity. But nighttime temperatures were still dropping below the 70º, the temperature ruminants need to recover. Saturday it was 101, Sunday 104º and 41% relative humidity with almost no wind. It was so hot that even soil 4” below the surface was baking at 90º.

The sharp increase in heat left the cattle little time to acclimate and because temperatures never dropped below 70º at night, they got none of the relief they needed to survive.

This video shows the damage done in Kansas this past June

 

Preparing for a warmer future

While heat stress kills some livestock every year, an extreme loss like this is both financially and emotionally devastating. It’s also a harbinger of things to come. As the climate continues to shift towards higher temperatures, and extreme weather events become more common, these kinds of situations are more likely to occur. In fact, an international group of researchers concluded that, because of climate change, the global cattle farming sector may lose between $15 billion and $40 billion each year by the end of the century, depending on how high greenhouse gas levels rise. Most of these losses will hit farmers in the tropic regions of South America, Africa and Asia. In the U.S. beef and dairy production will like decrease by almost 7%.

This week we’ll look at what to do about heat stress in the near term. I also have a few ideas of how the livestock sector can help prevent further warming and I’ll share those in this month’s Thinking Grazier.

Now, let’s get started preventing heat stress!

Animal Risk Factors

Pastured livestock are not as susceptible to heat stress as feedlot animals. If there is shade, water or a slight breeze, their risk is reduced. But no matter where they live, as temperatures rise above 80º F, ruminants begin to struggle. The fermentation process they use to process their food creates heat, compounding any heat load they take on during the day. They typically need nighttime temperatures of 70º and below to successfully dissipate heat.

Cattle

The U.S. Meat Animal Research Center breaks risk factors for cattle into four areas: Genetics, Health, Production Status and Previous Exposure.

The first three are pretty self-explanatory. The most problematic for many of us is removing dark colored animals from the herd. The great marketing of the Angus breed means that we’ve tilted to black for our cattle. This might be a time to start reconsidering that kind of marketing for something more environmentally friendly. When it comes to Previous Exposure, cattle that have not been preconditioned to hot weather will have a greater stress response and be in more danger of heat stress.

If you have dairy cows, keep in mind that high-producing cows eat more and generate more heat so they can begin to experience heat stress at temperatures as low as 65º.

Sheep and Goats

Sheep and goats tend to tolerate heat better than swine, cattle llamas and alpacas. Hair sheep are less susceptible than wooled sheep and goats tend to be more heat tolerant than sheep. Of course breed and color are factors, as are horns and ear shape. Horns are another way that some animals off-load heat, and goats with floppy ears, just like cows with floppy ears are better adjusted to heat.

Chickens

As with ruminant livestock, genetics, feather cover, and acclimation to heat all affect poultry heat tolerance. Older birds, heavy breeds, and broilers are typically more susceptible to heat stress.

Environmental Risk Factors

Weather is the top risk factor, so it’s helpful to know what’s coming at you. You can check your local forecast, or you can visit the USDA Agricultural Research Service’s Meat Animal Research Center’s forecast page. Their maps are color coded from blue (normal) to Red (Emergency) so you can get a quick look at what your animals are facing in your area. Once you’re at the site, you can click on your region for a 7-day forecast.

Other local conditions can contribute to higher than forecast heat. These include:

  • Saturated soils from recent rains, irrigated cropland or a leaking stock tank
  • Overnight lows that don’t drop below 70º
  • Danger or Extreme Danger conditions for 2 or more consecutive days
  • Minimal cloud cover
  • Low or no wind
  • High humidity
  • Natural variation in weather due to hills, valleys, and low points.

The tables below are also helpful in tracking the potential for heat stress. You can download and print all of these tables here.

Cattle Heat Index

Sheep and Goat Heat Index

Chicken Heat Index

From “Experiments on Energy-Efficient Evaporative Cooling Systems for Poultry Farm Application in Multan (Pakistan)“.

Swine Heat Index

Heat Stress Impacts

High temperatures are negatively affecting animals long before it becomes fatal. As heat increases, livestock forage less. According to the Lancet:

“Cattle reduce feed intake by 3-5% for every additional degree of temperature. Heat stress increases respiration and mortality, reduces fertility, modifies animal behaviour, and suppresses the immune and endocrine system, thereby increasing animal susceptibility to some diseases.”

We see the impacts of heat stress in reduced weight gain, reduced milk production, lower pregnancy rates, and reduced egg production and hatching rates along with thinner shells and poor internal egg quality.

Signs of Heat Stress

Living in Tucson where summer temps can reach 110º and higher, I’ve noticed that one of the first things that happens is it becomes harder to breathe normally. It’s not like panting, which is one way some animals have of dealing with heat. Heat just seems to elevate breathing rates. That’s also the first sign that your animals are feeling stress. As they breathe more quickly, they also become restless and stand around more. As stress grows, they begin to breathe more and more rapidly, turn to open-mouth breathing, drool or foam at the mouth, and become increasingly restless. At the final stages their tongues hang out, breathing becomes labored, and respiration rate may even decrease, they drop their heads and isolate themselves form the herd, and drooling may cease.

Keeping Livestock Safe

Shade and plenty of water are both critical to keeping livestock safe in high temperatures. Here are a few On Pasture articles with ideas for solving the shade problem. Depending on where you live, you might also consider silvopasture as an option for providing shade for your livestock. You can learn more here.

All animals will increase the amount of water they drink when it’s hot and salt consumption may also go up. According to the Maryland Small Ruminant website, ewes drank 9 to 11 percent of their body weight in the winter and 19 to 25 percent during the summer. In hot weather a dairy cow needs 25-35 gallons per day. These are just a few examples to remind us all that we need to provide LOTS of water for hot animals. Do your best to keep water cool as well. Animals drink less warm water.

Don’t work your livestock when it’s hot. If you must, do it early in the morning. Even in the evening, when it may seem a bit cooler, animals are still recuperating from the day’s heat. For example, cattle’s core temperature peaks 2 hours after peak environmental temperature. It also takes at least 6 hours for cattle to dissipate their heat load. Therefore, if peak temperature occurred at 4:00 pm cattle will not have recovered from that heat load until after 12:00 am and it will be later than that before cattle have fully recovered from the entire day’s heat load.

I hope this gives you a few tools to deal with heat now and in the future. Stay safe out there!

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