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Following discovery of acute bovine respiratory syncytial virus (BRSV) infection enhancing Histophilus somni (H. somni) clinical disease in calves, further understanding of the safety and efficiency of live-attenuated BRSV vaccines is important. Our objective was to determine the safety, efficiency and immunomodulation of an intranasal (IN), trivalent (infectious bovine rhinotracheitis virus [IBRV], parainfluenza-3 virus [PI3V], and BRSV) respiratory vaccine with parenteral, bivalent bovine viral diarrhea virus (BVDV) and a parenteral, pentavalent (BVDV type I and II, IBRV, BRSV, and PI3V) respiratory vaccine. High-risk beef calves (n=525) were received in 5 truckload blocks and stratified by body weight (213 ± 18.4 kg), sex, and presence of a pre-existing ranch ear-tag. Pens were spatially arranged in sets of 3 and randomly assigned to treatment with an empty pen between treatment groups. Treatments included: 1) no viral respiratory vaccination (CON), 2) cattle intranasally administered a trivalent, modified-live virus (MLV) respiratory vaccine with parenteral BVDV type I and II vaccine (INT), and 3) cattle administered a pentavalent, MLV respiratory vaccine (INJ). Pen was the experimental unit, with a total of 15 pens per treatment and 11 or 12 calves per pen in this 70-d receiving study. Performance, morbidity, mortality, BRSV, H. somni, Mycoplasma bovis (M. bovis), Mannheimia haemolytica (M. haemolytica), and Pasteurella multocida (P. multocida) prevalence and cycle time in nasal swabs via rtPCR on d 0, 7, 14, and 28 was determined, and BRSV-specific antibody titer and serum IFN-γ concentration via ELISA were evaluated on d 0, 14, 28, 42, 56, and 70. Morbidity (P = 0.83), mortality (P = 0.68) and average daily gain (P ≥ 0.82) did not differ; however, feed efficiency from d 0 to 56 was improved (P = 0.05) for CON. Serum antibody against BRSV increased with time (P < 0.01), and was numerically greatest for INT. There was a treatment × time interaction (P < 0.01) for H. somni present in nasal swabs; on d 14 and 28, INT (21.1 and 57.1%) more frequently (P < 0.01) became H. somni positive than CON (3.6 and 25.3%) or INJ (3.4 and 8.4%). Also, INT had reduced (P = 0.03) cycle time of H. somni positive samples on d 28. There was a tendancy (P = 0.06) for a treatment effect for BRSV cycle time; CON had a reduced mean (30.80) than INT (33.53) and (32.93). No treatment × day interaction (P ≥ 0.17) existed for M. bovis, M. haemolytica, or P. multocida prevalence and cycle time. No treatment differences (P = 0.55) were detected for serum IFN-γ concentration. There was a treatment effect (P < 0.01) for the rate of M. haemolytica positive culture from lung tissue specimens; INT had less (0.0%) M. haemolytica positive lung tissue cultures than INJ (45.5%) or CON (74.0%). These data indicate MLV vaccination of high-risk calves, either parenterally or intranasally, did not clearly impact health or growth during the feedlot receiving period. However, INT caused increased prevalence of H. somni in the naris and resulted in less M. haemolytica cultured from lung tissue samples upon necropsy. The intranasal administration of MLV vaccines may alter the microbial community in the upper respiratory tract of cattle; specifically, we observed that MLV IN increased the prevalence of H. somni in high-risk feedlot calves.

bovine respiratory syncytial virus, Histophilus somni, intranasal, vaccination