Farm Technology Group, Wageningen University and Research, 6700 AH Wageningen, the Netherlands.
Farm Technology Group, Wageningen University and Research, 6700 AH Wageningen, the Netherlands; Wageningen Livestock Research, Wageningen University and Research, 6708 WD Wageningen, the Netherlands.
J Dairy Sci. 2022 Feb;105(2):1701-1716. doi: 10.3168/jds.2021-21164. Epub 2021 Nov 17.
This study determined the effects of increasing ambient temperature (T) at different relative humidity (RH) and air velocity (AV) levels on the physiological and productive responses of dairy cows. Twenty Holstein dairy cows were housed inside climate-controlled respiration chambers, in which the climate was programmed to follow a daily pattern of lower night and higher day T with a 9°C difference, excluding effects from sun radiation. Within our 8-d data collection period, T was gradually increased from 7 to 21°C during the night (12 h) and 16 to 30°C during the day (12 h), with an incremental change of 2°C per day for both nighttime and daytime T. During each research period, RH and AV were kept constant at 1 of 5 treatment levels. A diurnal pattern for RH was created, with lower levels during the day and higher levels during the night: low (RH_l: 30-50%), medium (RH_m: 45-70%), and high (RH_h: 60-90%). The effects of AV were studied during the day at 3 levels: no fan (AV_l: 0.1 m/s), fan at medium speed (AV_m: 1.0 m/s), and fan at high speed (AV_h: 1.5 m/s). Effects of short and long exposure time to increasing T were evaluated by collecting data 2 times a day: in the morning [short: 1 h (or less) - exposure time] and afternoon (long: 8 h - exposure time). The animals had free access to feed and water and both were ad libitum. Respiration rate (RR), rectal temperature (RT), skin temperature (ST), dry matter intake, water intake, milk yield, and composition were measured. The inflection point temperatures (IPt) at which a certain variable started to change were determined for the different RH and AV levels and different exposure times. Results showed that IPt under long exposure time for RR (first indicator) varied between 18.9 and 25.5°C but was between 20.1 and 25.9°C for RT (a delayed indicator). The IPt for both RR and RT decreased with higher RH levels, whereas IPt increased with higher AV for RR but gave a minor change for RT. The ST was positively correlated with ambient T and ST was not affected by RH but significantly affected by AV. For RR, all IPt was lower under long exposure time than under short exposure time. The combination of higher RH levels and low AV level negatively affected dry matter intake. Water intake increased under all treatments except RH_l-AV_l. Treatment RH_h-AV_l negatively affected milk protein and fat yield, whereas treatments RH_m-AV_m and RH_m-AV_h reduced milk fat yield. We concluded that RH and AV significantly affected the responses of RR, RT, ST, and productive performance of high-producing Holstein cows. These responses already occurred at moderate ambient T of 19 to 26°C.
本研究旨在确定不同相对湿度（RH）和空气流速（AV）水平下环境温度（T）升高对奶牛生理和生产性能的影响。20 头荷斯坦奶牛被安置在气候控制呼吸室内，气候按照夜间较低、白天较高的每日模式进行编程，不考虑太阳辐射的影响。在我们为期 8 天的数据收集期间，T 逐渐从夜间（12 小时）的 7°C 升高到 21°C，白天（12 小时）从 16°C 升高到 30°C，夜间和白天 T 的每日增量均为 2°C。在每个研究期间，RH 和 AV 保持在 5 个处理水平中的 1 个恒定。RH 呈昼夜节律，白天水平较低，夜间水平较高：低（RH_l：30-50%）、中（RH_m：45-70%）和高（RH_h：60-90%）。在白天，AV 的影响通过在 3 个水平下进行研究：无风扇（AV_l：0.1 m/s）、中速风扇（AV_m：1.0 m/s）和高速风扇（AV_h：1.5 m/s）。通过每天采集数据 2 次来评估短时间和长时间暴露于升高的 T 的影响：早上（短：1 小时（或更短）-暴露时间）和下午（长：8 小时-暴露时间）。动物可以自由进食和饮水，并且都可以自由采食。测量呼吸率（RR）、直肠温度（RT）、皮肤温度（ST）、干物质摄入量、水摄入量、产奶量和组成。确定了不同 RH 和 AV 水平和不同暴露时间下特定变量开始变化的拐点温度（IPt）。结果表明，RR（第一个指标）的长时间暴露时间的 IPt 范围为 18.9 至 25.5°C，但 RT（延迟指标）的 IPt 范围为 20.1 至 25.9°C。RR 和 RT 的 IPt 随 RH 水平的升高而降低，而 RR 的 IPt 随 AV 的升高而升高，但 RT 的 IPt 变化较小。ST 与环境 T 呈正相关，ST 不受 RH 影响，但受 AV 显著影响。对于 RR，所有的 IPt 在长时间暴露时间下都低于短时间暴露时间。高 RH 水平和低 AV 水平的组合对干物质摄入量有负面影响。除 RH_l-AV_l 外，所有处理均增加了水的摄入量。RH_h-AV_l 处理会降低乳蛋白和脂肪产量，而 RH_m-AV_m 和 RH_m-AV_h 处理会降低乳脂产量。我们得出结论，RH 和 AV 显著影响高产荷斯坦奶牛 RR、RT、ST 和生产性能的反应。这些反应已经在适度的环境温度 19 到 26°C 下发生。
