"Could you please bring me a
tall lemonade?" I beg Sue, my wife, "With lots of ice?"
I'm in my usual midsummer repose, immobile in the hammock under the big oak. The most activity I can muster is to pray for a breeze. My chores can wait until after sunset or before it heats up in the morning. Meantime, Sue has been joyously weeding the garden. She loves hot weather, while I wilt as soon as it hits 80 F.
When the mercury climbs, I start to sweat. I eat less and drink more. If that doesn't cool me off, I begin to breathe faster. Then I start panting, even though romance is the last thing on my mind. I lie down in the shade and wait for a breeze. If Sue would let me, I'd flood the garden and wallow in a comforting mudbath.
Livestock react to heat a lot like I do. Their bodies go into survival mode. They seek shade, eat less, drink more and breathe faster. Blood flow shifts to the skin, away from developing muscles and, in females, away from reproductive internal organs such as the uterus and mammary glands. This helps dissipate internal heat to the surface, where sweat evaporating from the skin further cools the animal.
under shade trees to help sows and piglets keep cool.
These physiological changes come at the expense of meat, milk and wool production. Heat-stressed males produce fewer viable sperm, and females have smaller and weaker offspring. Add it all up and you'll find that, in most parts of the U.S., heat stress is the most costly and insidious environmental factor affecting livestock. (See sidebar "heat Takes Its Toll." below) Your best response takes into account factors such as the breed, age, condition and activity of your livestock, and makes effective use of shade, water and evaporative cooling.
Heat stress can reduce feedlot
cattle's rate of gain by 30 percent compared with cattle provided
with adequate cooling systems. In Midwest trials, lack of shade
reduced average daily gains by 4 to 22 percent and increased
feed costs by 4 to 28 percent.
It's Not Just The Heat
All animals have a thermal neutral zone the temperature range in which they are comfortable and productive.
Individual animals of the same species may have different comfort zones and responses to heat, just as Sue and I do. Species vary in their heat tolerance, with hogs being the most likely to suffer. Fat sows are especially sensitive. This is trite but worth emphasizing: It's not just the heat, it's the humidity. As the relative humidity rises, moisture evaporates more slowly. When it reaches 100 percent, the air is saturated and evaporation ceases. So sweating just makes you wetter, not cooler. Other evaporative cooling systems, such as foggers, misters, sprayers, ponds and wallows, are also less effective when it's humid. Wind and dry air speed evaporation, making such systems more effective.
Weather forecasters combine heat and humidity into the temperature-humidity index (THI) – sometimes referred to as the "misery index." In major livestock-producing areas, they sometimes issue heat-stress warnings based on the THI.
Animal scientists hesitate to pinpoint a particular temperature, humidity or THI number where animals are threatened. Far too many other factors are involved. But in general, if the temperature is above 80 F and the relative humidity is more than 50 to 70 percent, conditions are right for heat stress. A good rule of thumb is to observe your own response to the heat and humidity. If you're hot in the ham and find the breeze outside refreshing, chances are the cows will too.
Animals can adapt to heat. They become acclimated as the season progresses. So a hot day in September takes less of a toll than a sudden heat wave in June. Hairy and wooly animals have the best adaptation of all. They gradually shed their insulating coat as the temperature rises. In the case of sheep, we help them to prepare for the heat by shearing them in spring.
Adaptation can take place over the course of several seasons. A cow raised in Florida may tolerate the heat and humidity quite well, while an import from Montana may take several years to get used to the conditions. Some (like me) may never totally adjust.
The factors that determine how well animals can take the heat include:
Newborn and young livestock are less tolerant of heat than are
acclimated adults. Compounding the problem, overheated mothers
are more restless and less likely to stay still for nursing duties.
Newborns may not get any colostrum, which is critical to the development
of their immune systems. Young animals grow more slowly and are
easily dehydrated when they miss meals. This is a big problem
in farrowing houses where distressed sows are constantly up and
down, often crushing piglets in the process.
Metabolic rate. As you'd expect, livestock with higher metabolic activity – not just draft animals but those working hard to produce meat, milk or a fetus – are more stressed by heat than an animal that can idle the day away. For example, a thick-coated feedlot steer may be burning enough grain in its belly that its wintertime comfort zone may be in the 20 to 30 F range or even lower. It may become heat stressed when an early-spring thaw drives the temperature up into the 40s.
Body condition. Lean livestock tolerate heat better. Fat is a great insulator. A thick surface layer makes it harder for an animal to cool itself.
There are many strategies to help
keep your stock cool. Remember that the best heat-stress solutions
ones tailored to your management, breed and site. Be sure to consider existing buildings and shade, daily and seasonal temperature ranges, sunlight, humidity and prevailing winds in your plans. Extension staff and fellow farmers are good sources of ideas. Your main considerations should include:
Drinking water. It's often overlooked, but the best, most cost-effective feed you can provide your animals is
plenty of clean, cool water. This is especially true when they're trying to cope with heat. All livestock will have increased fluid loss during periods of heat stress. Their water intake may increase by 30 percent or more. For example, studies show dairy cows can lose two and a half times more water from their body surface when the temperature rises from 68 to 86 F.
Water should be readily available in a place where animals don't have to travel far to get it. The closer the better. Heat-stressed animals also need plenty of electrolytes, either via feed or salt blocks. Sodium, potassium and magnesium are particularly important to ruminants.
Shade. After water, shade is the best heat-fighter for outdoor animals. Trees are a natural choice. They're environmentally sound and the evaporation of water from their leaves provides more of a cooling effect than just shade alone. But trampling can destroy understory vegetation, damage roots and trunks and eventually kill the trees. Manure accumulates under the trees, instead of out in the pasture where you want it.
You can fence livestock out of groves and fencelines, but then the trees provide shade for only part of the day -and usually not the hottest part. Locate adjacent tree plantings along the south and west edges of grazing areas for maximum shade benefit. If you use groves to shade livestock, rotate them so they have time to recover.
cattle. He parks it where he feels the extra manure and animal impact will do the most good.
Portable or permanent artificial shade structures are another alternative. Keep in mind the following factors:
- Animals won't venture far from the structure during the heat of the day. So put feed and water under the structure or nearby.
- To provide maximum shade to animals
confined under a structure orient the long axis east to west.
But a north-south orientation may be best where animals are free
to come and go. This allows morning and evening sun to dry out
the ground under the structure.
- To take advantage of breezes.
allow at least 50 feet of clearance between shade structures
and adjacent buildings or other obstructions.
- Check with local Extension staff
for construction specifications (such as space allocations, roof
slopes and eave
heights) for your species and location. They can tell you if practices like painting roofs white or adding insulation make sense in your area and provide rough cost-benefit analyses. Don't forget to factor manure management into your design.
Many graziers think providing shade
makes livestock lazy, particularly in areas of the Dairy Belt
where there are only a handful of days each summer when it's too
hot and humid to graze. To keep cows grazing, these graziers acclimate
them to heat and provide plenty of water. When it's too hot during
the day cows can do the bulk of their grazing at night and in
Evaporative cooling. On a hot day livestock enjoy taking a dip as much as we do. Ponds and mud holes are pure summertime bliss for cattle and hogs. Some farmers who use cooling ponds have nothing but good things to say about them. But wallowing areas carry the risk of diseases such as leptospirosis, cryptosporidiosis, algae toxicosis, and a variety of agents that may cause mastitis and G.I. tract infections. To reduce disease risk, make sure ponds have a constant inflow and outflow. Drain small ponds and scrape them clean every year or so.
Foggers and misters spray fine droplets
of water that quickly evaporate and cool adjacent air. Such systems
are expensive and often take a mechanical genius to keep them
operating. They don't work very well when it's windy or humid,
and the moist air can be an ideal breeding ground for diseases.
Sprinklers spray larger drops that don' t cool the surrounding air very much. Rather, the water bath provides animals with more evaporative fluid than they can generate from sweat alone. Sprayers are usually located overhead, but dairy operations sometimes use high-pressure sprayers at entrances to milking parlors and holding pens. Plan ahead how you will handle manure and runoff, which can be as much as 50 to 100 gallons a day per cow with some systems.
Hog sprayers are used in farrowing and gestation areas. Directing water toward the sow's face near feeders makes more efficient use of water, because when a sow has a cool head, she feels cool all over. Kansas State University animal scientists have modified horticultural drip-irrigation systems that use only half a gallon of water per sow per hour – considerably less than most other methods. This and other swine-cooling options are detailed in the Swine Farrowing Handbook.
The downside of many confinement systems is that sometimes your only option is to keep the animals inside and run the fans. To cut power costs, consult an ag engineer to see if your buildings can be modified to improve ventilation.
" When you consider all the natural, low-cost ways to help livestock beat the heat, you start to wonder why we sometimes lock ourselves into systems that can keep them cool only at great expense. A better strategy is to carefully match breeds and management practices to your climate to prevent heat stress in the first place. Does It make sense to crowd a lot of big, high-producing animals under one roof in a hot climate? Sure, it can be done. But you'll likely pay big vet and utility bills trying to keep up production.
Editor's Note: Randy Kidd is a consuIting veterinarian based in Kansas City, Mo.
Reproduced with permission of the publisher. The New Farm, July/Aug. 1993, p. 8-12.