The objective of this study was to evaluate the effects of heat stress (HS) on: i) time and daily pattern of rumination and ii) in situ degradability in Holstein-Gyr crossbred dry cows. Nine cows, weighing 556.2 ± 97.1 kg were housed in a climate chamber (average THI=83.1) or a freestall barn (average THI=66.5) randomly assigned to treatments in a crossover design. Cows were fed corn silage ad libitum and 1 kg of concentrate as a maintenance diet. To measure rumination, we used a sensor attached to a collar. The in situ ruminal degradability was evaluated by incubation of concentrate, silage, and diet samples into the rumen of a fistulated cow for 6, 24, 48 and 96 h. The RT was affected by HS (P<0.001) and time of the day (P<0.001). The rumination pattern for control and HS cows had a first peak at approximately 04:00h and the magnitude of this peak in HS was 22.9% less than controls. The second RT peak occurred in the evening (~20:00h), when RT in HS was 27.8% less compared with controls. We observed a reduction in dry matter digestibility (DMD) of concentrate (85.1% vs 77.8%, control and HS, respectively; P<0,05) and also in the slow-degradable fraction of concentrate (93.9% vs 85.1%, respectively; P<0,05). Finally, DMD of the diet reduced from 73% to 70% for animals exposed to HS compared to controls. In conclusion, HS negatively affected e rumination time and in situ ruminal degradability in dry dairy cows.

这项研究的目的是评估热应激（HS）对以下方面的影响：i） Holstein-Gyr杂交干奶牛的时间和日常反刍模式以及ii）原位降解性。将九头重556.2±97.1 kg的母牛圈养在一个气候室（平均THI = 83.1）或一个自由饲养的谷仓（平均THI = 66.5）中，以交叉设计随机分配给处理。母牛自由饲喂玉米青贮饲料和1千克浓缩饲料作为维持饲料。为了测量反刍力，我们使用了连接在衣领上的传感器。在原位通过将浓缩液，青贮饲料和日粮样品孵育到有瘘口的母牛的瘤胃中6、24、48和96小时来评估瘤胃的可降解性。RT受HS（P <0.001）和一天中的时间（P <0.001）的影响。对照和HS母牛的反刍模式在大约04：00h出现第一个峰，并且HS中此峰的大小比对照少22.9％。第二个RT峰出现在晚上（〜20：00h），与对照组相比，HS的RT降低了27.8％。我们观察到精矿的干物质消化率（DMD）降低（分别为对照和HS，分别为85.1％和77.8％； P <0.05）以及精矿的可缓慢降解级分（分别为93.9％和85.1％） ； P <0.05）。最后，与对照组相比，暴露于HS的动物的日粮DMD从73％降低至70％。结论，干奶牛的原位瘤胃降解性。