Social group disruption and maternal separation result when calves are abruptly weaned. This study evaluated the effects of these stressors on the physiology of the calves. Calves were either abruptly weaned or not. Plasma cortisol concentration and neutrophil:lymphocyte concentrations increased and leukocyte concentration and immune response decreased for calves that had experienced social disruption. The behavioural response to handling did not change as a result of weaning or sex. There was an interaction between weaning and sex and time and sex on plasma noradrenaline concentration. Male calves showed an increase at weaning and each sampling time after, but heifers did not show an increase due to weaning. Leukocyte concentration was not affected by weaning or sex. Following weaning, the neutrophil:lymphocyte ratio increased, and this was affected by sex. Immune response was weakened due to weaning. The alterations in physiological responses indicate that abruptly weaning suckler calves makes them sensitive to stress associated with social disruption and weaning. Some of the physiological effects of the stress were still apparent a week after weaning. Therefore, efforts should be made to reduce social stress, and allow the calves time to adjust before imposing other management stressors.