Variation in available shaded area changes behaviour parameters in grazing dairy cows during the warm season

ABSTRACT The objective was to investigate the effects of available shaded area on behavioural characteristics of lactating cows during the warm season in the subtropics. Twelve Holstein cows were divided into groups, with 2 (SH2) or 10 m2 (SH10) of available shade per cow (six cows per treatment). The behaviour was recorded when animals were grazing from 09.00 to 16.00 h (GMT −02.00 h) throughout the trial. Data considered in the statistical analysis were restricted to the five days when the maximum temperature was ≥ 25 °C. Cows in the SH10 group had lower panting score, but higher proportions of time in shade and lying down and stayed more time per visit in the shaded area than cows in the SH2 group. Cows in the SH10 group had less events of competition near the water trough and in the shaded area than cows in the SH2 group. The solar radiation threshold that triggered the use of the shade was lower in SH10 than in SH2 group. Hourly proportion of time spent grazing or ruminating differed between shaded areas at specific times. The 2 m2 of available shaded area per cow is sufficient for all cows to enter the shaded area at the same time. In spite of that, 2 m2 of available shaded area per cow negatively affects the proportion of time spent lying and in the shaded area; in addition, it enhances agonistic behaviours between cows when compared with 10 m2 of shade per cow.摘要 本研究旨在探究亚热带暖季条件下，可利用遮阴面积对泌乳奶牛行为特征的影响。试验选取12头荷斯坦奶牛（Holstein），按每头奶牛可获得的遮阴面积分为两组：SH2组为2平方米/头，SH10组为10平方米/头，每组各6头奶牛。试验期间，于每日09:00至16:00（GMT-02:00）奶牛放牧时段记录其行为。本研究统计分析的数据仅选取最高气温≥25℃的5天数据。与SH2组相比，SH10组奶牛的喘气评分更低，但其在遮阴区域的停留时间、趴卧时间占比更高，且单次进入遮阴区域的停留时长更长。SH10组奶牛在饮水槽附近及遮阴区域内的竞争行为发生频次低于SH2组。触发奶牛进入遮阴区域的太阳辐射阈值，SH10组低于SH2组。不同遮阴面积组的奶牛，其放牧或反刍的小时时间占比在特定时段存在差异。每头奶牛2平方米的可利用遮阴面积，已足够所有奶牛同时进入遮阴区域。尽管如此，与每头奶牛10平方米的遮阴面积相比，每头奶牛2平方米的可利用遮阴面积会对奶牛趴卧时间及遮阴区域停留时间占比产生负面影响，同时会加剧奶牛间的攻击性行为。