The relationship between the occurrence of undifferentiated bovine respiratory disease and titer changes to bovine coronavirus and bovine viral diarrhea virus in 3 Ontario feedlots

Serological evidence of previous viral exposure (titer at arrival) and curr ent viral exposure (titer increase) during a 28-day study period, was used to determine if bovine coronavirus (BCV) or bovine viral diarrhea virus (BV DV) was associated with the occurrence of undifferentiated bovine respirato ry disease (UBRD) in feedlot calves. Neutralizing antibody titers to BCV an d BVDV were determined for 852 animals from 3 Ontario feedlots. Calves at 2 of the 3 feedlots (n = 753) received a modified live 4-way viral vaccine c ontaining BVDV. On arrival at the feedlots, 90% of animals were seropositiv e for BCV, while 39% of animals were seropositive for BVDV. This evidence o f previous exposure to both viruses was associated with reduced subsequent UBRD risk. Evidence of exposure to BCV during the study period was common, as 50% of animals showed a 16-fold or greater titer increase; however, trea tment for UBRD was not associated with titer change. Although the majority of animals were vaccinated for BVDV at arrival, within a feedlot, animals t reated for UBRD had larger titer increases to BVDV than non-treated animals . Based on our findings we infer that BCV was not causally related to UBRD occurrence, however consistent with other literature, BVDV may be causally related to UBRD occurrence.