Shade and wind barrier effects on summertime feedlot cattle performance

In each of three summertime trials conducted over consecutive years, approx imately 110 predominantly black and black-white-face steers were blocked by weight and randomly allotted to one of 16 pens in a 2 x i factorial arrang ement of treatments. Factors consisted of cattle being fed in facilities wi th or without wind barriers and with or without shade. Steers were fed dry- relied corn-based diets (1.43 Mcal/ kg, NEg). Mean starting date and days o n feed were June 26 and 79, respectively. I;I unshaded areas, temperature a nd humidity averaged 21.6 degrees C and 77.9%, and the blackglobe-humidity index (BGHI) at 1500 averaged between 84.0 and 89.1. Each of four 6.1- x 6. 1-m structures (mean height = 3.4 m) with white steel roofs provided shade (2.65 m(2)/steer) for two pens. In facilities with wind barriers provided, airflow was reduced from the north and northwest by a 25-m-wide shelterbelt containing six rows of trees. For cattle fed in pens with wind barriers, s hade increased(P < .05) gain from 0 to 56 d and decreased (P < .05) DMI/ADG from 0 to 28 d. Differences (P < .05) in performance were not found betwee n shaded and unshaded cattle in any portion of the feeding period for cattl e fed in the pens without wind barriers and over the entire feeding period in either type of facility. The shade response in pens with wind barriers s eemed to be greater the Ist yr than in subsequent years. Differences in wea ther patterns among years, especially air temperature, humidity, and solar radiation, may partially explain this interaction. Also, in yr I, cattle te nded to have greater fat thickness at finish than in yr 2 and 3. Correlatio ns between BGHI and DMI tended to be greater during the early portion of th e trial(0 to 28 d) than over the entire trial. Correlations between the dif ference in BGHI under shade vs no shade and percentage of shade use had the greatest magnitude and were significant only in the first 28 d vs over the entire feeding period. Although no heat-related cattle deaths occurred in this study, results suggest that shade improves cattle performance in the s ummer when they are fed in facilities with winter wind protection available and have not become acclimated to hot conditions. Once cattle are acclimat ed or hot conditions subside, compensation by unshaded cattle offsets much of the initial benefits of providing shade.