Effects of supplemental shade on thermoregulatory response of calves to heat challenge in a hutch environment.

Holstein (n = 12) and Guernsey (n = 6) calves, housed in hutches, were used to evaluate the complex relationships among external environment, housing microclimate, and thermal status of calves. The study was conducted during the summer; 9 calves were housed in hutches under supplemental shade, and 9 calves were maintained in hutches under direct sunlight. Environmental and calf temperatures were measured twice daily at 0700 and 1500 h, which included determinations of air temperature, inner and outer surface temperatures of the hutch, rectal and skin temperatures of the calf, and respiration rate. Outer and inner surface temperatures of the hutch were lower under supplemental shade. Hutch air temperature was highly correlated with inner surface temperature and therefore was lower in the shaded environment. During the p.m. period, when heat stress was highest, calves housed in a shaded hutch environment had lower skin temperatures and respiration rates than did unshaded calves. Body temperature and respiration rates increased less for calves in shade than for calves in sun. These data define the relationship between the calf and the environment. Supplemental shade diminished the severity of heat stress experienced by calves that were housed in hutches during the summer.