Exploring dairy heifers' consistency in social motivation in the absence or presence of conspecifics

We examined the consistency of heifers’ (n=36) sociability in the absence and presence of conspecifics. We applied standard animal personality tests to measure social motivation during social isolation. Additionally, we developed two novel test paradigms designed to quantify heifers’ willingness to trade off access to conspecifics in exchange for feed, thus measuring social motivation within a social context. In our distribution test, groups of three dairy heifers (n=12) could freely move between two feed troughs where grain was provided at two rates, with one providing twice as much feed as the other. Time feeding alone in the distribution test varied among heifers from 0 to 56.6 % of the time; this variation was weakly associated with differences in sociability as assessed by the time animals took to return to peers following social isolation, but not with heifers’ willingness to leave peers to access grain when tested in an alternative social-feed trade-off test. Our findings suggest that different measures of social motivation are not necessarily consistent, challenging the assumption that sociability is a stable personality trait in cattle. Instead, we propose to regard sociability as a ‘behavioural consequence’ resulting from the combined effects of internal characteristics (e.g., other personality traits such as fearfulness) and external factors (e.g., testing environment) at the time of evaluation.

本研究探究了36头奶用青年母牛（heifers）在同种个体（conspecifics）存在与缺失两种情境下的社交性一致性。我们采用标准动物性格测试，以评估社交隔离状态下的社交动机。此外，我们开发了两种全新的测试范式，用于量化青年母牛以接触同种个体换取饲料的权衡意愿，从而实现在社交情境中测量其社交动机。在分配测试（distribution test）中，12组（每组3头）奶用青年母牛可在两个饲槽间自由移动，两个饲槽分别以两种速率投放谷物饲料，其中一个饲槽的饲料投放量为另一个的两倍。该测试中，个体单独进食的时长占总测试时间的比例范围为0%至56.6%；这一比例差异与通过社交隔离后动物返回同伴群体的时长所评估的社交性差异呈弱相关，但与另一项社交-进食权衡测试中，青年母牛离开同伴以获取饲料的意愿无显著关联。本研究结果显示，不同的社交动机测量方式未必具有一致性，这对“社交性是牛只稳定性格特质”的既有假设提出了挑战。据此我们提出，应将社交性视为评估当下内部特质（如恐惧性等其他性格特质）与外部因素（如测试环境）共同作用所产生的“行为结果”。