The welfare benefits of shade in cattle operations have been documented, yet there are some inconsistencies between studies, particularly in behavior patterns in shaded and unshaded groups. Studies have shown reduced physiological responses to heat stress, performance benefits, and increased use of shade in cattle provided the opportunity to utilize shade in the weather outside of their thermoneutral zone. Common reasons for not providing shade on operations are often related to the cost of the investment paired with the assumed unclear benefits and the questionable need for shade in certain regions. 

Fraser’s framework for animal welfare was discussed, identifying the need for a holistic approach to welfare assessment when evaluating the impacts of shade on overall cattle well-being. Current research focuses on performance indicators in part due to the fact that if the economic value can be found with shade implementation, then the return on investment becomes extremely clear. It is important for stakeholders to expand their vision of animal welfare to include things such as cattle preference, mental state, and opportunity for choice in their environment when evaluating the value of shade to cattle welfare. Future research should focus on quantifying current shade provision across the supply chain, understanding producer perspectives of cattle shade need, including indicators of the affective state into studies, and assessing the economics of shade implementation.

Benefits of Shade Grown Livestock

One visible effect of including trees in pastures is the shady haven which they provide for livestock o­n hot summer days. The benefits of providing protection from the hot rays of the summer sun are obvious. After all, that is why we wear a hat! It easily follows that animals, which are unable to shelter from the direct sun during the heat of the day, will have to expend energy to deal with their discomfort and/or reduce their feeding activity. Their productivity should decline in proportion to the time spent under these unfavorable conditions. Increased livestock production during hot weather is often promoted by agroforestry as o­ne of the benefits of having trees. However, there is very little published research available to either verify or disprove this widely held belief.

Cattle may orient their pasture use to be near sources of shade. But how much does livestock performance really improve when summer shade is provided? This is a harder question to answer than you might think. Millions of cattle are successfully raised in the hot humid summers of the Midwestern and Southeastern states without shade. So, would shade increase their performance? Shade has generally been useful in increasing milk yields of dairy cattle and live weight gains of feedlot cattle in hot climates. This is especially true for European breeds of cattle in areas that are both hot and humid (Blackshaw and Blackshaw 1994). However, high concentrations of high-producing animals consuming relatively high-energy rations are somewhat different than the conditions typical of forage-based cattle production in pastures and rangelands.

Surprisingly few reliable studies of cattle productivity with and without shade have been done under realistic pasture conditions. I could o­nly find two controlled comparisons of cattle grazing in pastures with vs. without shade in the regularly published literature. The greatest effect of shade trees o­n summer weight change in free-ranging cattle was reported for European breeds of cattle in Louisiana (McDaniel and Roark 1956). Averaged over 4 years, cows grazing under scattered pines spent about half an hour more time grazing each day and gained 1.29 lb./head/day compared to cows grazing open pastures, who lost weight during the summer. Unfortunately, no pasture data are provided.

It is not possible, therefore, to completely separate shade effects upon forage quantity and quality from its effect o­n animal thermoregulation. Much more modest increases in summer weight gains were reported for cattle with access to artificial shade structures in Oklahoma (McIlvan and Shoop 1970). During 4 years, weight gains of Hereford cattle were increased 6, 9, 1, and 11% by artificial shades, with the greatest impact of shade seen during hot and humid weather.

Blackshaw and Blackshaw (1994) summarized the literature relating shade to heat stress in cattle. As they explain the situation, cattle receive heat directly from the sun when standing in the open. Dull, dark-colored hair absorbs most sunlight, which is converted to heat. White, shiny coats reflect much of the energy, and less is converted to heat. Shade can be very helpful in reducing heat loading from the sun’s rays, especially for dark-colored animals. However, quite a bit of heat can be received after being reflected from bare soil or nearby objects. Shade is not very effective in protecting cattle from reflected radiation. For example, a California study found that 33% of the heat load received by a shaded animal was reflected from the ground and 28% came from the overhead shade material. Total heat load was o­nly reduced by 30% under shade compared to out in the sun.

Metabolic heat generated from the digestion and use of energy contained in food can also be a significant source of heat. Approximately 35-70% of the energy which cattle extract from food is converted to heat. Active animals and those consuming large amounts offered can generate significant amounts of internal heat. Shade has no direct effect on this heat source. So, although shade may reduce the heat loading of cattle, it probably o­nly directly affects less than a quarter of the total heat energy cattle must deal with o­n a sunny day. This reduction may be important under severe heat conditions or when livestock is under stress because of other factors. It is less likely to be crucial for acclimated cattle that are otherwise well-fed, well-watered, and healthy.

Cattle lose heat primarily by transferring it to cooler air, and by evaporation of water from sweat and from moist tissues in the respiratory system. The cooler air temperatures under trees are very helpful in increasing heat transfer from animals. This is probably as important in the general cooling effect of shade as is protection from direct sunlight. It is less effective, however, for naturally well-insulated animals, such as some of the northern European breeds of cattle, which have thick coats of hair. Shade trees do not reduce air temperatures under windy conditions and still air under trees may be more humid as well as cooler than that out in the open pasture. Because of the major role that the evaporation of water plays in heat transfer, heat stress is much greater under humid conditions than under dry heat.

The issue of heat stress is further complicated by both physiological and behavioral adaptations which cattle make to reduce the effects of heat. Heat stress may reduce animal performance in two ways. First, it may depress grazing and food intake. And second, animals may resort to panting or other actions that consume energy. Cattle breeds differ markedly in their ability to tolerate heat. In general, Brahman-type cattle are more heat tolerant than are northern European breeds. However, much heat tolerance is behavioral. Cattle may successfully deal with lack of shade by restricting their grazing and traveling to the cooler hours of the day or night and by standing together in areas of good airflow.

So, where does all this leave agroforestry? There are many sound esthetic, ecological, and economic reasons for including trees in pastures. It makes intuitive sense to most of us that shade should increase comfort and improve animal performance. However, the factual basis for improved livestock production due to shade is very limited. We need to be careful about advocating shade as a means of reducing heat stress. Protection from sunlight o­nly reduces o­ne of several sources of heat which contribute to thermal stress in animals. Livestock has both physiological and behavioral mechanisms they can use to counter environmental stresses. Livestock performance is unlikely to be greatly improved by shade unless heat stress is sufficiently great and of adequate duration to overcome these coping mechanisms. Such conditions are probably less common under traditional range and pasture production systems than we think.

Literature Cited

Blackshaw, J.K., and A W. Blackshaw. 1994. Heat stress in cattle and effect of shade o­n production and behavior: a review. Aust. J. Exp. Agr. 34:285-295.

Cook, J.G., L.L. Irwin, L.D. Bryant, R.A. Riggs, and J.W. Thomas. 1998. Relations of forest cover and condition of elk: a test of the thermal cover hypothesis in summer and winter. Wild. Mono. 141:1-61.

McDaniel, A.H., and C.B. Roark. 1956. Performance and grazing habits of Hereford and Aberdeen-angus cows and calves o­n improved pastures as related to type of shade. J. Anim. Sci. 15:59-63.

McIlvain, E.H., and M.C. Shoop. 1970. Shade for improving cattle gains and rangeland use. J. Range Manage. 24:181-184. 

Ockenfels, R.A., and D.E. Brooks. 1994. Summer diurnal bed sites of coues white-tailed deer. J. Wildlife Manage. 58:70-75.