The objective of the present study was to evaluate the productive performance and grazing behavior of 25 primiparous and 44 multiparous Holstein cows in a pasture-based automatic milking system (AMS) while experiencing heat stress (defined as a temperature-humidity index-THI ≥ 68). Productive traits were analyzed according to the THI from days 0, -1, -2, and -3 in relation to the milking day, and grazing behaviors (expressed as the % of daily observation time) were related to the average THI only on the day of observation. Milk yield was not associated with the THI on day 0, but a significant linear relationship was found with the THI on the three previous days, decreasing approximately 0.18 kg (primiparous) and 0.40 kg (multiparous) per THI unit increment. In contrast, for multiparous cows only, the milking frequency was positively associated with the THI on the day of evaluation but not on the previous days, increasing 0.01 milking/THI unit increments. Additionally, for each unit of THI increment, cows spent 0.14% more time standing, whereas they exhibited a decrease in grazing, lying, and ruminating behaviors time by 0.30%, 0.04%, and 0.70%, respectively, for both parities. In conclusion, milk loss was related to heat stress conditions from the previous days, but not milking frequency, which increased with the THI of the same milking day. Lower grazing, lying, and ruminating activities and greater standing behavior were observed due to heat stress.

中文翻译：

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简短交流：热应激对自动挤奶系统挤奶的荷斯坦奶牛产奶量和放牧行为的影响

本研究的目的是评估牧场自动挤奶系统 (AMS) 中 25 头初产和 44 头经产荷斯坦奶牛在经历热应激（定义为温度-湿度指数 -THI ≥ 68）时的生产性能和放牧行为。 ）。根据与挤奶日相关的第 0、-1、-2 和 -3 天的 THI 分析生产性状，放牧行为（表示为每日观察时间的百分比）仅与平均 THI 相关。观察日。产奶量与第 0 天的 THI 无关，但与前三天的 THI 存在显着的线性关系，每增加 THI 单位，产奶量减少约 0.18 千克（初产）和 0.40 千克（经产）。相比之下，仅对于多产奶牛来说，挤奶频率与评估当天的 THI 呈正相关，但与前几天无关，增加 0.01 挤奶/THI 单位增量。此外，对于每胎次的 THI 增量，奶牛的站立时间增加 0.14%，而放牧、躺卧和反刍行为时间分别减少 0.30%、0.04% 和 0.70%。总之，牛奶损失与前几天的热应激状况有关，但与挤奶频率无关，挤奶频率随着同一挤奶日的 THI 的增加而增加。由于热应激，观察到放牧、躺卧和反刍活动减少，站立行为增加。而两组的吃草、说谎和反刍行为时间分别减少了 0.30%、0.04% 和 0.70%。总之，牛奶损失与前几天的热应激状况有关，但与挤奶频率无关，挤奶频率随着同一挤奶日的 THI 的增加而增加。由于热应激，观察到放牧、躺卧和反刍活动减少，站立行为增加。而两组的吃草、说谎和反刍行为时间分别减少了 0.30%、0.04% 和 0.70%。总之，牛奶损失与前几天的热应激状况有关，但与挤奶频率无关，挤奶频率随着同一挤奶日的 THI 的增加而增加。由于热应激，观察到放牧、躺卧和反刍活动减少，站立行为增加。