Warm summer episodes have a significant effect on the overall health and well-being of young cattle; however, it is not known which temperature measure should be used for estimating heat stress in dairy calves. In this study, generalized linear mixed-effects models were used to estimate the relationships between thermal comfort indices and animal-based heat stress indicators in sixteen Holstein bull calves that were housed in individual calf hutches. Data were collected under continental weather characteristics over a 5-day period: day 1 (lower-temperature day), days 2 and 3 (heat stress days), and a 2-day post-stress period. Relative humidity, ambient temperature, the heat index, the humidex and five different temperature–humidity indices (THI) were used as thermal indices. Physiological variables monitored included respiratory rate, rectal temperature, ear skin temperature and heart rate. The heat index and the humidex measuring human thermal comfort were more closely associated with physiological measures than were the ambient temperature or the THIs (in case of heat index: R² = 0.87 for respiratory rate, R² = 0.63 for rectal temperature, R² = 0.70 for ear skin temperature, and R² = 0.78 for heart rate, respectively; in case of humidex: R² = 0.85 for respiratory rate, R² = 0.60 for rectal temperature, R² = 0.68 for ear skin temperature, and R² = 0.75 for heart rate, respectively). Based on our results, parameters of human outdoor comfort seem better to estimate heat stress in dairy calves in a continental region than those of THIs or ambient temperature.

夏季温暖的天气对幼牛的整体健康和福祉具有重要影响；但是，尚不清楚应采用哪种温度测量方法来估算乳牛犊的热应激。在这项研究中，使用广义线性混合效应模型来估算单个小牛箱中饲养的16头荷斯坦公牛犊的热舒适指数与基于动物的热应激指标之间的关系。在5天的时间段内，根据大陆性天气特征收集了数据：第1天（低温天），第2天和第3天（热应力天）以及应力后2天。相对湿度，环境温度，热指数，湿度指数和五个不同的温湿度指数（THI）用作热指数。监测的生理变量包括呼吸频率，直肠温度，耳朵皮肤温度和心率。与环境温度或THIs相比，热指数和衡量人类热舒适度的湿度指数与生理指标之间的关系更为紧密（在热指数的情况下：对于呼吸频率，R ² = 0.87，对于直肠温度，R ² = 0.63，对于耳朵皮肤温度，R ² = 0.70，对于心率，R ² = 0.78；在使用湿润剂的情况下：呼吸频率R ² = 0.85，直肠温度R ² = 0.60 ，耳朵皮肤温度R ² = 0.68 ，心率R ² = 0.75）。根据我们的结果，与THIs或环境温度相比，估计大陆地区奶牛犊的热应激似乎更好地达到了人类户外舒适度的参数。