Stress is common when temperatures exceed 90 F for several days in a row, humidity at 70% or more, and night temperatures no lower than 75 F; conditions that rarely occur in this area.
Indeed there are a number of studies looking at the relationship between heat, shade, stress factors and weight gain as well as milk production. Overall shade seems to improve weight gain. Animals pant less, feed more and have lower body temperatures in various studies. This then translates to improved weight gain or milk production [1, 2].
Most of the studies I found were conducted on cows in feedlots. One, of lactating cows on pasture, I found especially interesting. Cows were given access to shade (some with, some without) over ten day periods and then switched. Even with moderate high temperatures between 77 and 83°F, milk production was higher (and core temperature lower) with access to shade .
Interestingly, this response may vary depending on the breed. For example, in one study from a tropical area, cows with some Brahman blood had higher summer weight gain under hot conditions than European stock .
However, as a horticulture educator I am not an expert in this area. So I spoke with Penn State Animal Science Professor Dr. John Comerford. He pointed out that most studies on shade and stress have been done in the tropics, conditions very different than what we have in the Mid Atlantic. Stress is common when temperatures exceed 90°F for several days in a row, humidity at 70 percent or more, and night temperatures no lower than 75°F; conditions that rarely occur in this area. Additionally, since grazing animals do most of their eating just before or right about dawn and dusk, times that are usually cool in our area; the availability of shade may actually reduce total grazing intake because animals spend more time in the shade. An additional consideration is the concentration of waste that tends to build up in the shady areas.
It seems that shade definitely can affect weight gain in beef cows and milk production in dairy cows, but the affect is less likely to occur in the Mid Atlantic. The caveat may be for dairy cows whose response (drop in milk production) is greater.
- Blaine, K.L. and I.V. Nsahlai, The effects of shade on performance, carcass classes and behavior of heat-stressed feedlot cattle at the finisher phase. Tropical Animal Health and Production. 43(3): p. 609-615.
- Mitlohner, F.M., et al., Shade and water misting effects on behavior, physiology, performance, and carcass traits of heat-stressed feedlot cattle. Journal of Animal Science, 2001. 79(9): p. 2327-2335.
- Kendall, P.E., et al., The effects of providing shade to lactating dairy cows in a temperate climate. Livestock Science, 2006. 103(1-2): p. 148-157.
- Cartwright, T.C., Responses of Beef Cattle To High Ambient Temperatures. Journal of Animal Science, 1955. 14(2): p. 350-362.