Eighty crossbred feedlot heifers were used during Summer, 1999 to assess the impact of heat stress and its relief by shade and (or) water misting on behavior, physiology, performance, and carcass traits. Treatments were: (1) no shading or misting (CONT); (2) only misting (MIST); (3) only shading (SHADE); and (4) shading and misting (SHMI). Head in feed bunk, head in/or above waterer, walking, standing, and lying behaviors were observed using a 10-min scan sampling method and analyzed on a daily and hourly basis. Rectal temperature and respiration rate were measured as well as DM intake, total live weight, ADG, gain:feed, and dietary NEm and NEg concentrations calculated from performance data. After slaughter, actual and adjusted preliminary yield grade, kidney pelvic and heart fat, longissiumus muscle area, marbling score, hot carcass weight, and final yield grade were measured or calculated. Lying and walking behavior did not differ among treatments, but CONT cattle spent less time (P < 0.01) standing than SHADE and MIST cattle. Cattle in the MIST treatment performed less (P < 0.05) head-above-waterer behavior than CONT control. Rectal temperatures did not differ among treatments, but respiratory rate was lower in shaded than in unshaded heifers (P < 0.05). Shaded compared with unshaded heifers had higher DM intake (9.46 vs. 8.80 ± 0.14 kg/d, P < 0.01) and ADG (1.6 vs. 1.4 ± 0.1 kg/d, P < 0.01). Heifers provided with shade reached their target weight 20 d earlier than the unshaded heifers and differed in final live weight (547 vs. 520 ± 6 kg, P < 0.01). Gain:feed, and calculated NEg and NEm concentrations were similar among treatments. Carcass traits were similar among treatments except actual and adjusted preliminary yield grade and hot carcass weight, which were greater for the SHADE heifers (P < 0.05). In conclusion, CONT cattle had a physiological and behavioral stress response to heat that negatively affected productivity. Providing shade was a suitable solution to decrease heat stress and lower the negative effects of heat on performance, whereas misting was largely ineffective.
Keywords: Cattle, Heat Stress, Shade, Mist
J. Anim. Sci. Vol. 78, Suppl. 1/J. Dairy Sci. Vol. 83. Suppl. 1/2000, pg. 34