The interruption of the maternal-filial bond in young calves can alter the physiological responses due to increased stress at this moment. Therefore, we aimed to analyze the association between age at weaning and the immune responses of 64 beef calves weaned abruptly. The animals were distributed in three weaning (W) treatments: hyper-early (W30), early (W75) and conventional (W180). The treatments agree with the weaning ages used in cow-calf systems in South America. Blood samples were collected of all experimental animals on the day of weaning and days 1, 2 and 7 post-weaning day of the three treatments. Blood samples were used to analyze hematological variables, total plasma proteins (TPP), fibrinogen, serum amyloid A protein (SAA) and cortisol. The variables analyzed were influenced by the sampling day (P < 0.001) and the calf gender (P < 0.05), and an interaction between treatment x sampling day was observed. Over the study period, high serum cortisol levels were observed for W30 calves. The serum amyloid A protein was significantly influenced by sampling day. When compared to W180 calves, W30 and W75 animals showed prolonged concentrations in plasma fibrinogen. In addition, they presented neutrophilia and lymphopenia during the 180–187 days period, which resulted in a greater neutrophil:lymphocyte ratio (N:L ratio). Calf gender resulted in changes in the number of blood leukocytes (P < 0.05). This result provides an alert for weaning at an early age, indicating that different management strategies must be tested to minimize physiological instabilities in critical periods of the life of animals.

由于此时压力增加，幼崽母子关系的中断会改变生理反应。因此，我们旨在分析断奶年龄与 64 头突然断奶牛犊免疫反应之间的关系。动物分为三种断奶 (W) 处理：超早 (W30)、早 (W75) 和常规 (W180)。这些处理与南美洲牛犊系统中使用的断奶年龄一致。在断奶当天和断奶后第 1、2 和 7 天收集所有实验动物的血样。血液样本用于分析血液学变量、总血浆蛋白 (TPP)、纤维蛋白原、血清淀粉样蛋白 A 蛋白 (SAA) 和皮质醇。分析的变量受采样日的影响（P < 0.001) 和小牛性别 ( P  < 0.05)，并观察到处理 x 采样日之间的相互作用。在研究期间，观察到第 30 周小牛的高血清皮质醇水平。血清淀粉样蛋白 A 受采样天数的影响显着。与 W180 犊牛相比，W30 和 W75 动物的血浆纤维蛋白原浓度延长。此外，他们在 180-187 天期间出现中性粒细胞增多和淋巴细胞减少，这导致中性粒细胞：淋巴细胞比率（N:L 比率）更高。犊牛性别导致血白细胞数量的变化（P < 0.05)。这一结果为早期断奶提供了警告，表明必须测试不同的管理策略，以最大限度地减少动物生命关键时期的生理不稳定性。