Feed Lot

NOV 2018

Feedlots and cow/calf operations in the beef industry who feed 500 or more has annually on grains and concentrates; maintain 500 or more beef cows; backgrounder, stocker/grower, preconditioner; veterinarian, nutritionist, consultant

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14 FEED•LOT November 2018 Constructed windbreaks or planted windbreaks have their corner in the northwest." Density/porosity is the ratio or fraction of solid space relative to total space. This impacts the effectiveness of a windbreak by controlling how much wind blows through it versus over it. "The denser the windbreak the greater the initial reduction in wind speed, but wind speed increas- es faster on the downwind side, which decreases the protected area. Dense shelterbelts and solid fences create a larger negative pressure area just behind them, causing snow to build up in drifts. The target for livestock windbreak density is 60-80%," he says. Constructed windbreaks are generally made with boards (often placed vertically), leaving spaces between them rather than a solid barrier. "The target porosity, ac- cording to several studies, is from 20% porosity (open) and 80% solid, down to 65 or 70% solid. If you have more than 35% porosity (more than 65% density/solid) or closer to 50-50, you lose some benefits In climates where wind chill is an issue during colder months, windbreaks can reduce feed costs, illness and health costs, with less loss of body condition in cows— and better gains on young animals. If there are no natural windbreaks available, constructed wind barri- ers can give protection from wind and drifting snow. Dr. Joseph Darrington, Assis- tant Professor and Extension Specialist-Livestock Environment Engineer at South Dakota State University says some shelterbelts of trees don't have much foliage in winter/spring to stop the wind. "If you plant a shelterbelt, have a cou- ple rows of tall trees and a couple rows of smaller trees. If you want more protection, include some evergreens," he says. Constructing windbreaks Main considerations when build- ing windbreaks include height, orientation, length, and density/ porosity. "Height is the highest point on the structure or tallest row of trees. Generally, the protected zone will extend out 10-15 times the height of the windbreak with a 50% reduction in wind-speed. Wind- break length is the uninterrupted distance of trees or total length of a constructed windbreak. Ide- ally the ratio of windbreak length and height is 10:1, which means a 10-foot-tall windbreak should be 100 feet long," explains Darrington. Orientation of the windbreak is ideally perpendicular to win- ter wind; windbreaks are usually constructed to face the prevailing wind direction. If wind tends to come from several directions, some people create a curved or cornered windbreak. "In our region the pre- dominant cold wind comes from the northwest, about 60 to 70% of the time. The best position would be to run a windbreak from south- east to northwest, to be perpendic- ular to prevailing wind. If ranchers want a larger protected area, they sometimes run another windbreak from northwest to southeast, cre- ating an arrowhead shape pointing to the north to give the greatest protection," says Darrington. "When planting shelterbelts we situate them north-south and east-west. COW/CALF CORNER WINDBREAKS FOR CATTLE BY HEATHER SMITH THOMAS

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