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Management-Intensive Grazing: Grazing System Design: Grazing System Infrastructure

Heat Stress Mitigation

Substantial research at UGA and elsewhere has shown that heat stress can drastically reduce forage intake and, as a result, animal performance. Some mechanism for mitigating heat stress is necessary to maximize the performance of grazing animals. Of course, the most important method for reducing heat stress is to provide grazing animals with an ample supply of cool, clean water (for more on this, see the Water Systems page). However, this may not be sufficient to mitigate heat stress, especially for highly-productive animal classes like lactating dairy cows or goats.

Significant amounts of heat are evolved by the grazing animal as the result of the mere ingesting and digesting of forage.  Add this to standing in the sun on a hot and humid day in Georgia, and the effect of heat stress can become apparent.  It is, therefore, not surprising to learn that research has shown that animals provided natural shade spend more time grazing and less time standing than those without shade. Of course, artificial shade will also reduce heat stress.  However, the cooling effect that evapotranspiration provides can further reduce heat stress for animals shaded by large, well-canopied trees.  In fact, this is one of the fundamental advantages of silvopasture systems.

Unfortunately, silvopasture systems or MIG systems that have too many trees will require a lower stocking rate, since the trees will compete with the forage species for light, water, and nutrients.  As a result, artificial shade or cooling systems may need to be considered in non-silvopasture grazing systems.

When constructing artificial shade, there are several factors that need to be considered. First, consider the materials being used.  Ensure that the top surface reflects heat but the bottom surface does not.  Covers that are white on top and black underneath will help reflect the heat from the sun and absorb any heat given off by the animals being shaded.  Second, ensure that there is sufficient square footage given the number of animals that will congregate under the shade. According to NRCS guidelines, stocker calves require 32 ft2/head and mature beef and dairy cows require 40 and 50 ft2/head, respectively. Finally, the benefits of portability should also be considered.  Shades built on skids can easily be moved with a tractor, truck, or an ATV. The benefit to this is the prevention of excess hoof traffic on the forage stand and reduced nutrient deposition near fixed sources of shade.

Certainly, there are many other ways to mitigate heat stress including cooling ponds, misting systems, and shade cloths. In fact, many of the grazing dairies in S. Georgia run a second hose down the length of their center pivot irrigation systems for a high-pressure mist system that serves both as a method of cooling the grazing herd, but also as a way of influencing their grazing patterns.

Resources for More Information
"Cooling Systems for Georgia Dairy Cattle" – This article by Dr. John W. Worley (Extension Engineer, Dept. of Biological and Agricultural Engineering) describes various options for cooling dairy cattle.

"Interim Standard: Livestock Shade Structure" – This is a technical brief that describes the NRCS's standard for a livestock shade.

"Shade Options for Grazing Cattle" – This is an Extension publication from Extension Engineers at the University of Kentucky that presents specifications and plans for portable shade structures.