Previous research found reflective hutch covers reduced hutch temperature during hot weather, but the biological significance is unknown. This study determined the effect of reflective covers on calves’ immune response, body weight, and respiration rate. The study was conducted from June to August, on 2 farms: one near Stanfield, Arizona (10,000 cows) and one near Plainview, Texas (6,000 cows). Agri-Plastic hutches were used in Arizona and Calf-Tel in Texas. Covers were 3.0 mil (aluminized on the external side) white LDPE overlaying the top, sides, and back of the hutches; leaving the front exposed. At each farm, 5 covered and 5 uncovered (control) hutches were also fitted with temperature loggers that recorded internal hutch temperature every 30 min. Calves were given a commercial IBR vaccine at 21-d of age and antibody titer differences at 21 and 42 d determined immune response. Titers were determined using virus neutralization with logarithmic transformation to normalize data. Treatment effects were analyzed with ANOVA and LSD. Calves in covered hutches in AZ (n = 50) had a higher (P < 0.05) titer responses (25%) than control calves (n = 54). Respiration rates taken during sunny conditions at 16:00 at AZ were significantly lower (8 bpm, P < 0.01) for covered calves (n = 43) than controls (n = 50). Body weight was not significantly influenced by treatments at either farm (P > 0.05). Covered hutches were 3.03°C cooler than controls at the hottest time of the day at AZ (P < 0.01) and 0.7°C warmer (P < 0.05) during the coolest 2 h period at night. TX was much cooler than average with cloud cover and rain, and daily highs averaged 7.9°C lower than AZ over the study period, so the cover were not advantageous in TX. In conclusion, the reflective covers were most effective during sunny and hot conditions, resulting in increased antibody response and decreased respiration rate.