Heat stress during summer negatively affects animal performance. During summer months in the south, cattle are exposed to not only high temperatures and humidity but also direct sunlight. Although grazing cattle can't escape the heat completely, they instinctively will use natural shade to escape the radiant heat of the sun and may also immerse themselves in ponds or stream pools for cooling. Management for reduced heat stress has production, environmental and welfare implications. While small acreage, extensive grazing systems in the southeastern U.S. usually offer natural shade, more intensive systems using rotational grazing or drylot confinement may not provide natural shade.
From a production perspective, access to shade may neither improve nor hinder growth compared to cattle in a similar environment without access to shade. Research has demonstrated that in feedlot confinement, shade may be beneficial early until cattle become acclimated to summer heat. Breed type and coat color can influence heat tolerance. Brahman influence and tropically-adapted beef breeds such as Senepol and crosses that express slick hair traits tolerate the summer's heat better than dark-colored beef breeds and cattle that retain a thicker hair coat into summer. Research with cattle of different coat colors at the USDA Meat Animal Research Center indicated that solar absorption was greater in cattle with darker hair coats (dark red and black) and black cattle spent more time in the shade than white cattle. Cattle with dark coats also pant more than cattle with light-colored coats.
Heat stress can increase body temperature, but this response is not observed in all studies. Research in Thailand observed greater oxidative stress and increased ratio of neutrophils to lymphocytes, which is also an indicator of greater stress among cattle without shade compared to cattle with shade access.
Cattle with access to shade may exhibit less time grazing. This observation was recently reported in a study out of Uruguay. Although cattle without shade were observed spending more time grazing, the weight gain response among cattle with or without shade was similar.
The challenge to providing shade to cattle managed under intensive grazing is overcome by using shade cloth to construct an artificial shade. Shade cloth comes with different levels of sun blockage (40 to 80 percent) and will cost approximately $3.20 per square foot. The Uruguay study compared activity with different amounts of sun blockage and found that 80 percent shade increased lying time, but even the 35 percent block provided relief from the sun. Research with 80 percent artificial shade in feedlot pens has demonstrated improved weight gain and feed conversion response compared to pens without shade. In a recent grazing study, Guillermo Scaglia at LSU observed similar performance among heifers that had access to artificial shade with 80 percent blockage compared to natural shade. Research with permanent artificial tin roof shade was compared to tree shade and no shade at the University of Arkansas, Livestock and Forestry Research Station. During early summer, natural shade demonstrated the greatest benefit, but over the entire observation period, there were no differences in cow weight gain among treatments of shade and no access to shade.
To cool themselves, cattle may also immerse themselves in water when accessible. This is commonly observed with cattle on toxic fescue, even when the temperature should be comfortable for cattle. Researchers in Brazil observed that cattle naturally preferred shade over water immersion. During a recent farm visit in Arkansas during early afternoon, there were only a couple of cows in the pond whereas the majority of cows were standing under shade trees.
While access to shade may not always improve cattle performance due to their ability to acclimate to their summer environment, from a welfare perspective cattle instinctively seek relief from the radiant solar heat of the sun during summer, and providing shade affords this opportunity. Use of shade cloth can provide shade to cattle in more intensively managed systems such as rotational grazing or confinement feeding systems. Since cattle seem to spend more time using shade to seek relief from the sun than immersing themselves in water for cooling, speculatively thinking, strategic placement of shade may provide opportunities to reduce environmental damage to stream banks or ponds.
When constructing shade, approximately 15 to 20 square feet is recommended per 400-pound calf, 20 to 25 square feet per 800-pound feeder calf and 30 to 40 square feet for beef cows. University of Kentucky publication AEU-91, Shade Options for Beef Cattle, provides additional detail on artificial shade construction.