Date of Award
Doctor of Philosophy
Theses & dissertations (Interdisciplinary)
James A. Roth
Many organisms which cause bovine mastitis are opportunistic pathogens. Opportunistic bacterial infections occur when the integrity of native host defenses is breached and often are indicative of predisposing immunosuppression in the host animal. The prepartum mammary gland is highly susceptible to new infections. The two studies presented here support the hypothesis that immunosuppression occurs during the periparturient period and therefore, predisposes the dairy cow to new infections and may result in the progression of subclinical mastitis into clinical disease. Neutrophil and lymphocyte function data from these studies of periparturient dairy cows showed marked impairment of various neutrophil functions (adverse changes in migration and oxidative killing mechanisms) and lymphocyte blastogenesis;In the first study, peripheral blood neutrophils from eight Holstein heifers were evaluated for function during the periparturient period. Random migration, ingestion of bacteria, superoxide anion production, native (non-enhanced) chemiluminescence, iodination and antibody-dependent cell-mediated cytotoxicity by neutrophils were determined. Significant (P <.05) increases in random migration of neutrophils, iodination, and chemiluminescence were evident 2 weeks before parturition and then decreased dramatically by the first week after parturition. Lymphocytes were also evaluated during the periparturient period for mitogen-induced lymphocyte blastogenic responses. Phytohemagglutinin P- and concanavalin A-induced lymphocyte blastogenesis increased 2 and 3 weeks before parturition, respectively. However, by the first week after parturition, lymphocyte blastogenesis was markedly impaired;In the second experiment the effects of hypocalcemia at parturition on the immune status of dairy cows was investigated. Ten healthy, multiparous Holstein cows were fed a high calcium diet prepartum to induce hypocalcemia at parturition. Five of these cows received intramuscular parathyroid hormone (crude synthetic N-terminus 1-34) to prevent hypocalcemia at parturition. All cows exhibited significant loss of immune cell function in the weeks surrounding parturition. Hypocalcemia or the development of parturient paresis did not exacerbate the immune cell dysfunction.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Marcus Eugene Kehrli, Jr.
Kehrli, Marcus Eugene Jr., "Immunosuppression in periparturient Holstein heifers and cows in the pathogenesis of mastitis " (1989). Retrospective Theses and Dissertations. 9208.