The effect of dexamethasone on some immunological parameters in cattle

Immunosuppression as a consequence of acute and chronic stress can increase the susceptibility of cattle to a range of infectious diseases. In order t o develop a panel of immune function assays for investigating the effects o f potential stressors on immune competence in cattle, the effect of treatme nt with short- and long-acting preparations of the synthetic glucocorticoid dexamethasone was examined. Short-acting dexamethasone (dexamethasone sodi um phosphate 0.08 mg/kg) followed 37 h later by long-acting dexamethasone ( dexamethasone-21 isonicotinate 0.25 mg/kg) was injected intramuscularly and blood was collected to assess immune functions at intervals over the subse quent 11 days from 6 treated and 6 control Hereford steers. Dexamethasone i nduced leukocytosis (neutrophilia, eosinopenia, lymphopenia, monocytosis), an increased neutrophil:lymphocyte ratio, an elevated percentage of CD4(+) lymphocytes, a decreased total CD8(+) lymphocyte count, decreased total and percentage WC1(+) lymphocytes, an elevated percentage of IL-2 receptor alp ha (IL-2R alpha)(+) lymphocytes, and an elevated percentage of B lymphocyte s. In vitro chemotaxis of peripheral blood neutrophils to human C5a and ovi ne IL-8 was increased by dexamethasone treatment. Lymphocyte proliferation in the presence of phytohaemagglutinin, and serum concentrations of IgM, bu t not IgA or IgG1, were suppressed by dexamethasone treatment, whereas mito gen-induced production of interferon-gamma (IFN-gamma), neutrophil expressi on of CD18, neutrophil myeloperoxidase activity and natural killer (NK) cel l activity were not influenced by dexamethasone treatment. The results indi cate the potential for haematology and immune function assays to reflect el evated activity of the hypothalamic-pituitary-adrenocortical axis in cattle . Immunological parameters may thus provide a useful adjunct to cortisol an d behavioural observations for assessing the impact of stress on the welfar e of cattle.