Preweaning calf immunity is the sum of positive and negative impacts that include the peripartum cortisol surge associated with the onset of parturition, the concentration of passively acquired antibody from colostrum, the age of the calf, calf nutrition, concurrent stresses such as new introductions, castration/dehorning, and transport; concurrent disease, and the rate of exposure to infectious agents through natural infection or vaccination. The net effect of these impacts is dependent on the timing at which they occur. To optimally manage calf immunity, the goal is to allow exposure to infection or vaccination that induces maximal immune stimulation with minimal disease.