Abstract In this study, we investigated the influence of a silvopastoral system on the thermal environment, behaviour and thermoregulation of dairy heifers in a subtropical climate. The experiment was conducted on a dairy farm in Southwest Paraná, Brazil, during the summer of 2014. Crossbred Holstein × Jersey dairy heifers (n = 10) were used in a split-plot design. The fixed effects in this study include time of day (9:00–10:00, 13:00–14:00, and 17:00–18:00 h) under silvopastoral or open pastures conditions, which were the main-plot and split-plot factors, respectively. To assess the environmental conditions in both systems, air temperature, relative humidity and wind speed were recorded. In addition, the temperature-humidity index was calculated based on the microcli-mate measurements. Respiratory rate and hair coat surface temperature of heifers were measured in both groups during time of day (30 days). Diurnal behaviour using focal observations with 0/1 sampling was observed. Data were analysed using Bayesian inference with a mixed effects model. The air temperature was higher (P<0.05) in open pasture conditions than the silvopasture system. Temperature-humidity index values for the silvopasture system were lower than open pasture during the hottest hours of the day. Regarding thermoregulation responses, there was an interaction between time of day and pasture environment (P<0.05). Heifers showed lower respiratory rates and hair coat surface temperature values (P<0.05) when access to shade was provided, mainly during the hottest periods in the afternoon. In addition, there was also an interaction between rumination and water intake (P<0.05), which indicates a higher rumination frequency for animals in the silvopasture system during the hottest period, as well as a higher water intake frequency for heifers in open pasture during midday. These findings imply that the arrangement of trees in a silvopasture system provides better thermal comfort conditions for dairy heifers raised in a subtropical climate.

中文翻译：

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亚热带气候下林牧系统饲养的奶牛的体温调节和行为反应

摘要 在本研究中，我们研究了林牧系统对亚热带气候下奶牛热环境、行为和体温调节的影响。该实验于 2014 年夏季在巴西巴拉那西南部的一个奶牛场进行。杂交荷斯坦奶牛 × 泽西奶牛（n = 10）用于裂区设计。本研究中的固定效应包括在林牧或开放牧场条件下的一天中的时间（9:00–10:00、13:00–14:00 和 17:00–18:00 h），它们是主区和裂区因子，分别。为了评估两个系统中的环境条件，记录了空气温度、相对湿度和风速。此外，温湿度指数是根据小气候测量值计算的。在一天中的某个时间段（30 天）测量两组小母牛的呼吸频率和毛皮表面温度。观察到使用 0/1 采样的焦点观察的昼夜行为。使用贝叶斯推理和混合效应模型分析数据。露天牧场条件下的气温高于林场牧场系统（P<0.05）。在一天中最热的时间里，林牧系统的温湿度指数值低于露天牧场。关于体温调节反应，一天中的时间和牧场环境之间存在交互作用（P<0.05）。当提供阴凉处时，小母牛表现出较低的呼吸频率和毛皮表面温度值（P<0.05），主要是在下午最热的时期。此外，反刍和饮水量之间也存在交互作用（P<0.05），这表明在最热时期林牧系统中动物的反刍频率较高，而开放牧场的小母牛在中午的饮水频率较高。这些发现意味着林牧系统中树木的排列为在亚热带气候中饲养的奶牛提供了更好的热舒适条件。