一般在断奶后，牧场为便于生产管理，将来自不同群体大小的犊牛进行混群或重新分组，这种常规操作对犊牛的福利存在负面影响。混群前的社交经验可能会缓解混群应激，但仍需要更多研究验证这一假设，因此本文通过出生后单栏饲养或群养犊牛在混群后的生理和行为指标的变化，探究早期社会环境对犊牛抗应激能力的影响。将132头初生犊牛随机分为单栏饲养、3头群养、6头群养、12头群养，共4个处理组（S、G3、G6、G12组，每组6个重复）。60日龄时，将每个处理组(S、G3、G6和G12)每2个重复引入较大的围栏中，形成44头犊牛规模的新群体。分别记录重组前后生理参数，包括心率(HR)、唾液皮质醇（S-CORT）、唾液分泌免疫球蛋白A(SIgA)、白介素-2（IL-2）、白介素-6（IL-6）、肿瘤坏死因子-α（TNF-α）水平和行为反应。重组后，无论是单栏饲养还是群养组犊牛HR和S-CORT立即升高(P<0.05)，但与群养犊牛相比，单栏饲养犊牛差异更显著(P<0.05)。单栏饲养犊牛的SIgA和IL-2水平下降(P<0.05)，且IL-2在所有组中最低(P<0.05)。此外，犊牛混群后具有不同的行为表现，包括活动时间和休息时间的变化，与新环境应激引发的负面情绪有关。群居犊牛的互相修饰、玩耍、探索行为和趴卧时间较多(P<0.05)，而单栏饲养犊牛的自我梳理、攻击行为、站立和行走时间则显著增加(P < 0.05)。研究表明，单栏饲养犊牛可能比群养犊牛更易产生混群应激，从而对行为和神经生理产生影响，而出生后的群居经验则可能帮助犊牛缓解这种应激。

Mixing or regrouping of calves from different pens is a common animal management practice on the farm, which frequently occurs after weaning and has a negative effect on calve welfare.  Social integration before regrouping may relieve stresses, but more evidences are needed to verify this hypothesis.  The present study aimed to investigate acute physiological and behavioral variations of individually- or group-housed calves after being introduced into a mixed group.  A total of 132 postnatal calves were randomly divided into groups of 1, 3, 6 and 12 animals (S, G3, G6, and G12; 6 replicates in each group) until 59 days of age.  At 60 days of age, every two replicates from different groups (S, G3, G6 and G12) were introduced in a larger pen which containing 44 of the aboved experimental calves.  Before and after regrouping, physiological parameters of stress, including heart rate (HR), saliva cortisol (S-CORT), saliva secretory immunoglobulin A (SIgA), interleukin-2 (IL-2), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) levels, and behavioral responses were recorded.  After regrouping, HR and S-CORT increased immediately (P<0.05), and higher (P<0.05) levels of such molecules were found in S calves compared to those in group-housed calves.  Levels of SIgA and IL-2 were decreased (P<0.05), and the lowest (P<0.05) IL-2 values were found in S calves compared to those in group-housed calves.  In addition, the introduced calves displayed a distinct behavior, including altered active and rest time, which was associated with negative emotions triggered by the novel surroundings.  Allogrooming, play, exploration behaviors and lying time were increased significantly (P<0.05) in group-housed calves than those in S calves.  Conversely, self-grooming, aggressive behaviors, standing and walking time were increased (P<0.05) in S calves than those in group-housed calves.  These findings suggest that individually-housed calves may be more susceptible to stressors arising from regrouping than group-housed calves, which consequently negatively affected behavioral and neuroendocrine responses.  Furthermore, moving calves with previous social experience may help mitigate regrouping stress.