45 - Vaccine Protocol Influences Immune Phenotype of Weaned Beef Calves

Abstract: Vaccination is one mechanism used as a preventative measure to decrease morbidity and mortality due to bovine respiratory disease (BRD), but vaccination efficacy is inconsistent. Therefore, the objective of this study was to compare the effect of inactivated (INA) vs. modified live (MLV) viral vaccines on the immune phenotype of weaned beef calves. Mixed-sexed pens with equal numbers of heifers and steers were randomly assigned to receive either INA (Vira Shield 6) or MLV (Titanium 5) treatments at d 0 (initial) and a booster (28 d). A subpopulation of heifers (n = 28) and steers (n = 18) were identified from these treatment pens and balanced for treatment. Samples were obtained prior to vaccination and 14 and 28 d post-initial vaccination and again at 14 and 28 d post-booster. All animals were weighed on collection days. Data were analyzed using either GLM or MIXED procedures of SAS with repeated measures. A treatment × day interaction occurred on cortisol at 14 d post-initial vaccination; the MLV calves had greater (P = 0.05) cortisol than INA calves. At 28 d post-initial and 14 d post-booster, MLV calves had greater (P < 0.05) total IgG and isotypes IgG1 and IgG2. MLV had greater (P < 0.05) cytokine concentrations associated with either humoral or cell-mediated immune responses. Conversely, serum neutralizing antibodies for antigens associated with the vaccine were significantly greater in INA calves than in MLV (P < 0.05). Calves receiving MLV were heavier (P < 0.05) at the end of the study. These data imply that vaccination protocol resulted in differential immune phenotypes. More specifically, calves receiving the MLV vaccine phenotype indicated stimulation of both the humoral and cell-mediated response. In contrast, the INA phenotype was indicative of a bias towards a humoral response. Further research should be done to determine the protective value of these phenotypes.