Abstract
Individual respiration rates of 188 calf-fed Holstein steers (591 ± 43 kg) was observed over a 4-d period (July 10 through July 14, 2017). Steers were provided 7.2 m(2)/hd pen space with 3.7 m(2)/hd overhead shade). Respiration rate for each steer was measured at 0800, 0900, 1000 and 1100 h (2, 3, 4, and 5 h following the morning feeding). Ambient temperature averaged 32.9 ± 0.7, 34.9 ± 0.7, 36.6 ± 0.5, and 37.8 ± 0.5 C for the respective time intervals (corresponding to THI of 82.5 ± 1.1, 83.1 ± 1.2, 83.4 ± 0.9, and 83.8 ± 0.6, respectively). Although increasing (P < 0.01) with ambient temperature, respiration rates among steers at each time interval was highly variable, averaging 71.5 ± 10.3, 81.3 ± 10.4, 86.1 ± 11.4, and 87.1 ± 12.1 breaths/min, respectively. Individual respiration rate at 1100 h was not associated with live weight (r(2) = 0.009, P = 0.22). Daily weight gain during the 28-d period prior to respiration measurements averaged 1.07 ± 0.41 kg and was likewise poorly associated (r(2) = 0.012, P = 0.13) with respiration rate at 1100 h. We conclude that individual respiration rate is highly variable, and alone, may be an unreliable indicator of animal comfort based on growth performance.