Social proximity in dairy calves is affected by differences in pessimism

Negative social interactions have been extensively studied in dairy cattle, but little is known about the establishment of positive (preferential) relationships. Adult dairy cows are known to spend more time at close proximity to specific social partners, indicating that they establish stronger bonds with these animals, but few studies have explored what happens in socially housed calves. In this study, we explored whether calves that spent their entire life in the same social group established social preferences (i.e. pairs of individuals that interact more) that are stable over time (two 48-h periods, separated by three days), across two types of behavior (standing and lying) and across contexts (change in environment and housing design). When housed in an open pack, calves showed consistent proximity patterns when standing (but not when lying). These preferential relationships persisted even after calves were moved into a new pen fitted with free stalls. At the individual level, calves varied in how selective they were in their social relationships, with some calves spending much more time with specific partners than did others. This degree of selectivity was not associated to Sociability, marginally associated to Fearfulness, but was associated with Pessimism (more pessimistic calves were more selective in their social relationships). In conclusion, calves can form selective relationships that appeared to be consistent over time and across context, and the degree to which calves were selective varied in relation to individual differences in Pessimism.

奶牛的负面社会互动已被广泛研究，但学界对其正向（偏好性）社会关系的建立过程却鲜有探索。已知成年奶牛会花费更多时间与特定社交伙伴保持近距离接触，这表明它们会与这些个体形成更牢固的社会联结，但目前鲜有研究探讨群养犊牛的社会互动模式。本研究旨在探究：终生饲养于同一社会群体的犊牛，是否会形成随时间稳定存在的社会偏好（social preferences，即互动更为频繁的个体配对）——该稳定性体现在两次间隔3天的48小时观测周期中，且在两种行为模式（站立与躺卧）以及两种环境背景（环境改变与饲养设施变更）下均保持一致。当犊牛饲养于开放式散养群时，其站立状态下的空间亲近模式具有一致性，但躺卧状态下则无此特征。即便将犊牛转移至配备自由栏的新圈舍后，这些偏好性社会关系仍持续存在。从个体层面来看，犊牛间的社会关系选择性存在显著个体差异：部分犊牛会花费远多于其他个体的时间与特定社交伙伴共处。该选择性程度与社交性（Sociability）无显著关联，与恐惧性（Fearfulness）仅存在微弱相关，却与悲观性（Pessimism）显著相关：悲观程度更高的犊牛，其社会关系的选择性更强。综上，犊牛能够形成具有选择性的社会关系，且该关系随时间与环境背景均保持稳定；犊牛的社会关系选择性程度，与其个体间的悲观性差异显著相关。