PS12-9. Effects of a pentavalent, modified-live virus vaccine administered during initial antimicrobial treatment for bovine respiratory disease in high-risk feedlot cattle.

It was reported that 39.3% of U.S. feedlots include a respiratory vaccine as part of initial BRD treatment (NAHMS, 2013), yet the effects of this ancillary therapy (ANC) are largely unknown. Our objective was to evaluate effects of a pentavalent modified-live virus (MLV) respiratory vaccine as ANC, given concomitantly with antimicrobial treatment, in high-risk feedlot calves with BRD. Five truckloads of high-risk crossbred beef calves (n = 515; initial BW = 222 ± 16 kg) were processed, housed by truckload in a dry-lot pen, and monitored daily for BRD after a 7-d post-metaphylactic interval. Calves meeting the BRD case definition (BRD1; n = 203; BW = 219 ± 3 kg) included bulls (n = 167) and steers (n = 36) at arrival; were randomly assigned to 1 of 2 treatments: 1) control (CON), antimicrobial only; or 2) VAC, antimicrobial with a pentavalent MLV respiratory vaccine. Study-eligible cattle were moved to treatment pens (5 to 12 calves/pen; 10 pen replicates/treatment). A 48-h allocation period existed for each pen; once a pen reached capacity (n = 12) or 48 h elapsed, d 0 began. Body weight and blood were collected on d 0, 35, and 70 to assess performance, bovine viral diarrhea virus (BVDV) type 1a antibody titers, and immune status using a gold nanoparticle-based assay (D2Dx assay). Initial BRD treatment cost was increased for VAC (P < 0.01). The proportion of calves requiring a second (BRD2; P = 0.81) or third (BRD3; P = 0.85) antimicrobial treatment did not differ. The percentage of chronically ill cattle did not differ (P = 0.45) but was numerically greater in VAC (4.3 vs. 2.1%). Likewise, mortality was not different (P = 0.69) but numerically increased for VAC (4.0 vs. 2.9%). Days to BRD2 (P = 0.95) and BRD3 relapse (P = 0.45) did not differ. From d 0 to 35, ADG tended to be greater for CON (1.59 vs. 1.44 kg/d; P = 0.08), and G:F was 0.126 vs. 0.116 for CON and VAC (P = 0.27). Dry matter intake did not differ (P = 0.33) but remained numerically greater for CON over the 70-d study. A day effect was detected for the D2Dx immunity score (P < 0.01), but no treatment or treatment × day effects were observed (P ≥ 0.94). The BVDV serum antibody titer increased over time (day, P < 0.001), but a treatment × day interaction (P < 0.001) existed such that VAC calves had greater BVDV titers than CON at d 35 and 70, with no difference at d 0 (P = 0.40). Administering a pentavalent MLV vaccine as ANC during initial BRD treatment increased BVDV antibody titers and treatment cost but did not improve health outcomes and transiently reduced performance.