Abstract：
The health, longevity, and performance of dairy cattle can be adversely affected by heat stress. This study evaluated the in-barn condition [i.e., temperature, relative humidity, and resulting temperature-humidity index (THI)] at 9 dairy barns with various climates and farm design-management combinations. Hourly and daily indoor and outdoor conditions were compared at each farm, including both mechanically and naturally ventilated barns. On-site conditions were compared with on-farm outdoor conditions, meteorological stations up to 125 km away, and NASA Power data. Canadian dairy cattle face periods of extreme cold and periods of high THI, dependent on the regional climate and season. The northernmost location (53°N) experienced about 75% fewer hours of THI >68 compared with the southernmost location (42°N). Milking parlors had higher THI than the rest of the barn during milking times. The THI conditions inside dairy barns were well correlated with THI conditions measured outside the barns. Naturally ventilated barns with metal roofs and without sprinklers fit a linear relationship (hourly and daily means) with a slope <1, indicating that in-barn THI exceeded outdoor THI more at lower THI and reached equality at higher THI. Mechanically ventilated barns fit nonlinear relationships, which showed the in-barn THI exceeded outdoor THI more at lower THI (e.g., 55-65) and approached equality at higher THI. In-barn THI exceedance was greater in the evening and overnight due to factors such as decreased wind speed and latent heat retention. Eight regression equations were developed (4 hourly, 4 daily) to predict in-barn conditions based on outdoor conditions, considering different barn designs and management systems. Correlations between in-barn and outdoor THI were best when using the on-site weather data from the study, but publicly available weather data from stations within 50 km provided reasonable estimates. Climate stations 75 to 125 km away and NASA Power ensemble data gave poorer fit statistics. For studies involving many dairy barns, the use of NASA Power data with equations for estimating average in-barn conditions in a population is likely appropriate especially when public stations have incomplete data. Results from this study show the importance of adapting recommendation on heat stress to the barn design and guide the selection of appropriate weather data depending on the aim of the study.
摘要：
健康，长寿，热应激会对奶牛的生产性能产生不利影响。这项研究评估了谷仓内的状况[即，温度,相对湿度,以及具有各种气候和农场设计管理组合的9个奶牛场的温度-湿度指数（THI）]。比较了每个农场的室内和室外的每小时和每日条件，包括机械和自然通风的谷仓。现场条件与农场室外条件进行了比较，距离气象站125公里,NASA的电力数据。加拿大奶牛面临极端寒冷时期和高THI时期，取决于区域气候和季节。与最南端位置(42°N)相比,最北端位置(53°N)经历的THI>68小时减少约75%。在挤奶时间内，挤奶厅的THI比谷仓的其他部分高。乳品谷仓内的THI条件与谷仓外测量的THI条件密切相关。具有金属屋顶且没有洒水器的自然通风谷仓符合斜率<1的线性关系（每小时和每天平均），表明谷仓内THI在较低THI时超过室外THI，而在较高THI时达到相等。机械通风谷仓符合非线性关系，这表明谷仓内THI在较低THI时超过室外THI更多(例如，55-65），并在更高的THI时接近平等。由于风速降低和潜热保留率等因素，谷仓内THI超标在晚上和晚上更大。建立了八个回归方程(4小时，4daily)topredictin-barnconditionsbasedonoutdoorconditions,考虑不同的谷仓设计和管理系统。使用研究中的现场天气数据时，谷仓内和室外THI之间的相关性最好，但是50公里范围内的气象站的公开天气数据提供了合理的估计。距离75至125公里的气候站和NASAPower集成数据给出了较差的拟合统计数据。对于涉及许多奶牛场的研究，使用NASAPower数据和方程式估算人口的平均谷仓条件可能是适当的，尤其是当公共站点数据不完整时。这项研究的结果表明，根据研究的目的，使对热应力的建议适应谷仓设计并指导选择适当的天气数据非常重要。
