Impacts of an additional cooling event during the night on physiological and productive parameters of two breeds (B) of dairy cows under severe heat stress conditions were determined. Fifteen Holstein (H) and 15 Jersey x Holstein (JxH) cows were assigned to one of the two cooling strategies (CS), where the difference was an added 1 h cooling event during the night (i.e., 3X and 4X cooling events) with the 4X group having the added night cooling event. Maximum and minimum average temperature/humidity indices during the study were 86 and 77 units, respectively. There were no CS x B interactions for any response variable. Body condition score (BCS) was similar between CS, but H cows had higher (P<0.05) condition than JxH. There were no differences in rectal temperature due to CS or B. Respiration rate between breeds and cooling strategies were similar throughout the day. However body surface temperatures of head, thurl, right flank, and udder were higher (P<0.05) in 3X versus 4X cows, and H cows maintained a higher (P < 0.05) temperature in thurl and right flank than JxH during PM hours. Metabolites and hormone concentrations were not affected by CS, but H cows had lower (P < 0.05) triiodothyronine and higher (P < 0.05) thyroxine, than JxH. The 4X cows had higher (P<0.05) milk yield and milk energy output than 3X cows. While H cows produced more milk than JxH, the latter had higher (P < 0.05) milk component levels. In general, JxH cows were judged to have to demonstrate a more desirable physiological response and milk composition outcome than H cows. An additional night cooling event was judged to result in more desirable physiological and productive responses than in cows without this extra night cooling event under the extremely hot and dry environmental conditions during the study.

确定了夜间额外降温事件对两个品种 (B) 奶牛在严重热应激条件下的生理和生产参数的影响。15 头荷斯坦奶牛 (H) 和 15 头泽西 x 荷斯坦奶牛 (JxH) 被分配到两种降温策略 (CS) 中的一种，其中不同之处在于夜间增加了 1 小时降温事件（即3 倍和 4 倍降温事件） 4X 组增加了夜间冷却事件。研究期间的最大和最小平均温度/湿度指数分别为 86 和 77 个单位。任何响应变量都没有 CS x B 交互作用。CS之间的身体状况评分（BCS）相似，但H奶牛更高（P <0.05) 条件比 JxH。由于 CS 或 B，直肠温度没有差异。品种之间的呼吸率和降温策略全天相似。然而，3X与4X 奶牛的头部、臀部、右侧和乳房的体表温度较高（P<0.05），并且 H 奶牛在下午时间保持较高（P<0.05）的 thurl 和右侧腹部温度（P<0.05）。代谢物和激素浓度不受 CS 影响，但与 JxH 相比，H 奶牛具有较低 ( P < 0.05 ) 三碘甲状腺原氨酸和较高 ( P < 0.05 ) 甲状腺素。4X 奶牛有更高的 ( P<0.05) 产奶量和产奶量比奶牛高 3 倍。虽然 H 奶牛比 JxH 产奶更多，但后者的奶成分水平更高（P < 0.05）。一般来说，JxH 奶牛被认为必须表现出比 H 奶牛更理想的生理反应和牛奶成分结果。在研究期间，在极端炎热和干燥的环境条件下，与没有这种额外夜间降温事件的奶牛相比，额外的夜间降温事件会导致更理想的生理和生产反应。