Technical Abstract: Stress in livestock can be broadly defined as situations in which normal homeostatic conditions of an animal are disturbed or threatened. This disturbed state can be triggered by various environmental factors to which an animal must respond physiologically to maintain equilibrium with the environment. Release of ACTH which induces synthesis and secretion of glucocorticoids is one response to stress. Recent studies of the effects of glucocorticoids on the immune system of cattle have identified alterations in leukocyte adhesion molecule expression that affect the normal trafficking pattern of neutrophils by causing the shedding of L-selectin. In addition, circulating gd T-cell numbers decline in response to glucocorticoid administration. Additional microbicidal functions of neutrophils are also suppressed by glucocorticoids, as well as the ability of cultured mixed populations of lymphocytes to produce interferon-g. Glucocorticoid administration will also suppress antigen specific immune responses to vaccines. Virtually identical changes in leukocyte trafficking patterns, cytokine and immunoglobulin secretion, and adhesion molecule expression on leukocytes have been reported in periparturient cows. These recognized compromises induced by glucocorticoids and parturient stresses on the immune system should be considered when planning vaccination protocols for management of herd health.