The objectives of the study described were to (1) compare environmental temperature-humidity index (THI) with the THI measured within two different calf housing systems and (2) determine how THI affects Holstein heifer calf body temperatures, serum cortisol concentrations, and serum thyroxine concentrations. At 24 to 48 h of age, calves were assigned to one of two individual housing treatments: (1) stalls in a three-sided barn (n = 8) or 2) hutches placed outside (n = 8). Calves were observed until 42 days of age during the summer months. Ambient temperature and relative humidity within housing systems were recorded hourly. Calf body temperatures were measured hourly using devices attached to the underside of each calf’s tail. Blood samples were collected at 7, 21, and 42 days of age via jugular venipuncture. Blood serum was analyzed for cortisol and thyroxine concentrations using enzyme-linked immunosorbent assays (ELISAs). Overall average THI was higher in hutches than in stalls (P < 0.0001). Calves housed in hutches had higher body temperatures (39 ± 0.18 °C vs 38 ± 0.15 °C, P = 0.005). No differences occurred in serum cortisol concentrations (P = 0.89) but at 21 days of age, calves housed in hutches had higher serum thyroxine concentrations (16.55 ± 0.51 μg/dl vs 13.91 ± 0.54 μg/dl, P = 0.0006) than calves housed in stalls. Although both housing systems in this study were located on the same dairy, calves housed in hutches were exposed to higher THI values, had higher body temperatures, and at 21 days of age had higher serum thyroxine concentrations than calves housed in stalls inside a three-sided barn.

中文翻译：

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荷斯坦牛犊对炎热天气条件的生理反应

所述研究的目的是 (1) 将环境温度 - 湿度指数 (THI) 与在两种不同的小牛舍入系统中测量的 THI 进行比较，以及 (2) 确定 THI 如何影响荷斯坦小母牛小牛体温、血清皮质醇浓度和血清甲状腺素浓度。在 24 至 48 小时龄时，小牛被分配到两种单独的饲养处理中的一种：（1）三边牛舍中的隔栏（n = 8）或 2）放置在外面的笼舍（n = 8）。在夏季的几个月里，小牛被观察到 42 日龄。每小时记录一次鸡舍系统内的环境温度和相对湿度。使用连接到每头小牛尾巴下侧的装置每小时测量一次小牛体温。通过颈静脉穿刺在 7、21 和 42 日龄时收集血液样本。使用酶联免疫吸附测定 (ELISA) 分析血清的皮质醇和甲状腺素浓度。笼舍的总体平均 THI 高于畜栏（P < 0.0001）。饲养在笼子里的小牛体温较高（39 ± 0.18 °C vs 38 ± 0.15 °C，P = 0.005）。血清皮质醇浓度无差异 (P = 0.89)，但在 21 日龄时，饲养在笼舍中的小牛的血清甲状腺素浓度（16.55 ± 0.51 μg/dl vs 13.91 ± 0.54 μg/dl，P = 0.0006）高于饲养的犊牛在摊位。尽管本研究中的两个饲养系统都位于同一个奶牛场，但饲养在笼舍中的小牛暴露于更高的 THI 值，体温更高，并且在 21 日龄时的血清甲状腺素浓度高于饲养在三边的谷仓。