ABSTRACT
The objective was to measure effects of cooling technique (shade vs. water sprinklers) on performance, behavior, physiology, and the environmental effect of 40 Holstein heifers housed in drylot corrals during the hot summer months. The experiment was a replicated crossover design with four 21-d periods and 2 treatments: 1) shades installed in the front half of the pen or 2) sprinklers, which applied water to the pen surface at 2-h intervals from 1100 to 1900 h. Animal performance measures were dry matter intake, average daily gain, and feed efficiency (gain:feed). Behavioral measures, elimination patterns, and corral spatial distribution were measured in 5-min scan frequencies over four 24-h periods. Physiological measures were rectal temperature, respiration rate, urinary urea N, and blood urea N. Environmental measures were corral soil surface temperature and moisture, particulate matter, and surface NH(3) volatilization; meteorological measures were also collected. Shaded compared with sprinkled heifers had increased dry matter intake (3.4%), increased average daily gain (14%), and increased feed efficiency (11%). Heifers in shaded vs. sprinkler treatments had decreased respiration rates (13%). Behavioral differences between the treatments varied by time of day. Heifers spent most time in either the shaded or sprinkled areas of their corrals (65.9 and 64.2%, respectively). Elimination behavior occurred predominantly at the front of the corral in close proximity to the feed bunks and additionally at the water trough in sprinkled corrals. Sprinkler treatment had a 31.7% greater average corral surface moisture than the shaded treatment. Corral surface temperature varied based on areas of surface moisture, shade location, and elimination concentration within the corral. Sprinkled corrals had less particulate matter emissions than shaded (25%), but NH(3) emissions were 46% greater in sprinkler vs. shaded treatment. Overall, the use of shade in heifer corrals improved heifer performance and physiological measures, but sprinkler treatment had less PM [corrected] emissions from corral surfaces under heat stress conditions. Both cooling techniques affected spatial distribution and behaviors of the heifers, which affected pen usage and surface characteristics.
