When cattle are stressed by wind and cold, they seek shelter. If there are no natural windbreaks, stockmen can provide artificial wind barriers.
David Ames, a retired Colorado State University environmental physiologist, did early studies at Kansas State University on cold-weather effects on cattle. He developed wind-chill indexes for cattle and established critical temperatures.
“Realizing the value of windbreaks has come partly from understanding wind-chill factor. The impact of wind chill, in combination with energy requirements for cattle during cold weather, suggests there’s a lot of value in feed cost savings and well-being of the animals if animals are protected from wind when temperature drops below their thermo-neutral zone or critical temperature,” Ames says.
He says the wind-chill index for cattle is based off the index developed for humans by the U.S. Army. The difference between humans and livestock, of course, is the presence of a hair coat, which fluffs to create insulation and hold body heat in and keep cold out. Hair is effective in keeping a cow warm unless it gets wet and flattens, which allows moisture next to the skin. When cattle get wet, or if the wind blows hard enough to separate the hair, cattle are more vulnerable to cold.
“In those conditions, windbreaks become very important,” Ames says.
Variety of windbreaks
“In many parts of the country, there are no natural shelters. In Wyoming, we’ve used big round bales, letting cattle eat the windbreak during winter. This works well, if you move the windbreak each year. A windbreak collects cattle and they damage the grass and soil, so we put out bales in different areas the next year,” Ames says.
Windbreaks are a cost/benefit equation, he says. If cattle can shelter in a draw, the cost is low. When you start putting posts in the ground to hold a windbreak, and lumber on that frame, that adds up.
Windbreaks in feedlots show an economic advantage as well, he adds, but the value is more difficult to quantify than for cow-calf operators. However, several designs have been shown to lower energy feed costs in winter, he says.
“One popular type of windbreak is a half circle, because you don’t always know which direction wind will come from. Half circles catch a north wind, west wind, and even a southwest/northwest wind. In a half circle, you can protect from every direction except an east wind, which is normally not a direction from which we get wind,” Ames says.
Location is important, too. “Windbreaks pile up snow, and you don’t want snow to pile up somewhere you don’t want it,” he says.
He says engineers and animal scientists from North Dakota and Nebraska have fact sheets on engineering and building windbreaks (search “EC-94-1766-X” or “Windbreaks for Cattle”).
Steve Paisley, University of Wyoming Extension beef cattle specialist, explains there are many ways to create windbreaks. “You can buy fabric windbreaks and attach them with zip-ties or lace them to existing panels or fence. This is a short-term fix that works well. We’re putting some of these up in pens here at the university. We already have the pens and fences; we just need some type of wind protection.
Even though the fabric windbreaks are not a long-term structure, they endure well, Paisley reports. “My parents in western Nebraska have some in their calving pens that have been there for 10 years. So I’d guess these fabric windbreaks would have at least a five-year lifetime, depending on how well they’re attached and how much the wind can grab.”
In his travels around Wyoming, Paisley says he’s seen operators north of Cheyenne employ oilfield tires as windbreaks. “Up around Douglas and Gillette, you’ll see abandoned oil storage tanks on their sides. There’s probably a low-cost solution in your own area, using whatever is available and inexpensive.
“We have plenty of beetle-killed timber in our state, which some people are harvesting. Assuming it’s been harvested and treated properly to remove or kill beetles, this may be a cheaper source of lumber for livestock facilities,” he adds.
Windbreak design is important. “With a solid wall – such as a plywood sheet – wind goes up and over and dips right down behind it. You need openings creating at least 20% porosity. That gives a larger downwind effect, with greater area behind the windbreak providing protection,” Ames explains.
“All you need is about 80% wind blockage,” Paisley concurs. “Much of the research on this was done in the 1970s and ‘80s by Bob Jairell, a hydrologic technician with the Rocky Mountain Research Station in Laramie.”
“Wind goes right over a solid wall,” explains Ames. “If you use slats, some of the air flows through – at a much lower velocity, and protects animals much farther out,” he explains.
Lorne Klein, grazing/forage specialist with the Saskatchewan Ministry of Agriculture, says optimum protection is obtained with a fence porosity of 25-33%, which means only 75 to 66% of the windbreak is solid.
“For example, for 25% porosity, you could place 6-in. boards, 2 in. apart. For 33% porosity, 6-in. boards would be placed 3 in. apart. With a porous windbreak, the protected area behind it extends 8-10 times the height of the windbreak,” Klein says.
“If cows are standing right next to the wall to be out of the wind, this means the boards are too close together. A 30% porosity gives a much larger protected area; cattle can benefit from a proper windbreak even when they are 20 ft. behind it,” he says, giving more protection to more cows.
Diagrams showing how this works – and why a porous fence is more beneficial than a solid one – can be seen in his document “Portable Windbreak Fences,” available at www.agriculture.gov.sk.ca.
Klein says stockmen in western Canada are discovering the benefits of portable windbreaks, which enable producers to utilize pastures without natural shelter. The ability to move windbreaks with cattle offers a large advantage over building permanent structures.
Portable windbreaks must be constructed in such a way that they remain stable and won’t tip over in a strong wind, he says. They need a broad base, with a base width at least 1.5 times the height to counter the force of the wind. And they must be built sufficient to withstand movement to different locations.
“Whether a windbreak blows over or not is a function of three things – height of the wall, weight of the structure and width of the base. The mistake many people make is not having the base wide enough. Most windbreaks in our region are built of oilfield pipe and lumber,” Klein says.
For an 8-ft. wall, he recommends legs at least 7 ft. out. The total height is usually about 9 ft. because producers build them a little off the ground to keep the bottom from being buried in snow.
Some people think porosity in the structure will help prevent the structure from blowing over, but this isn’t true, Klein says. The force that results in tipping over a structure is a combination of pressure against the windward side and suction on the leeward side. Thus, a partially porous fence must withstand the same amount of wind force as a solid fence. Force reduction from reduced surface area is offset by increased suction when wind goes through the openings between the boards.
“Engineers tell me that the porosity (whether 10% or 50%) creates the same amount of air pressure. There is still suction on the leeward side,” Klein explains.
Ease of movement is just as important as not blowing over. “If you have to get off your tractor to move windbreaks, you may not take time to do it. I move mine weekly. I’m out with the tractor anyway, and I back up to a windbreak, lift it up, drive forward and drop it where I want it,” he says.
He uses a three-point hitch and says windbreaks should be designed for easy movement using available equipment. They can be lifted and carried from the side with a front-end loader, or towed from one end. The side-lift design takes less material in the frame because skids or wheels aren’t needed.
“It can be built with an elevated frame and legs, so only four corners touch the ground, eliminating the problem of skids or wheels lodging in snow or manure. Such windbreaks also can be placed end to end to form a long fence.
“When moving them from one field to another, however, gates must be wider than the length of the windbreak, or you have to be able to lift it higher than the fence. The end-tow design needs skids or wheels, but is easier to move through narrow gates,” Klein says.
Sidebar: Windbreaks for feedlots
Steve Paisley, University of Wyoming Extension beef cattle specialist, says feedlots have different requirements than cow-calf operations when it comes to windbreaks. He cites environmental stress studies done by Nebraska researcher Terry Mader that investigated windbreaks in feedlots.
“Mader found slight improvements in intake and performance in cattle that were provided windbreaks during winter. However, if windbreaks remain in the pens during summer, he saw a decrease in feed intake and performance because cattle got too hot. In warm weather, cattle need a breeze to help keep them cool,” Paisley says. Thus, removing windbreaks or altering them so they don’t obstruct wind for summer can be helpful.
“At our research station, we’ve been testing a lot of bulls, which are exposed to wind. The windbreaks we’re interested in are hinged metal panels that act as windbreaks when they’re rotated down; but, in summer, we rotate them up to provide shade for the cattle. In confinement feeding, this gives the best of both worlds. Several companies make these tall, solid windbreak panels that are hinged in the middle,” Paisley says.
Sidebar: Use some creativity
There is no one correct way to build a windbreak. Former Colorado State University environmental biologist David Ames believes anything that protects animals from wind during cold weather is helpful.
“You need to spread cattle out (not all bunched up behind one windbreak) and you don’t want them standing in cold water or mud. The windbreak should be on a high, dry, well-drained area,” he says.
Determine what might work best in specific pastures, regarding windbreak location and design.
Every ranch is different, regarding natural terrain and wind direction. Air currents may be different depending on whether you’re in a valley, on the plains, or on a mountainside.
“Wyoming, for instance, has a lot of information available regarding prevailing wind directions,” says the University of Wyoming’s Steve Paisley. “A lot of wind mapping is already done. If you know the direction of prevailing winds in your area, it may help.”