THE ASSOCIATION OF TITERS TO BOVINE CORONAVIRUS WITH TREATMENT FOR BOVINE RESPIRATORY-DISEASE AND WEIGHT-GAIN IN FEEDLOT CALVES

The association between bovine respiratory disease (BRD) and antibody titers to bovine coronavirus (BCV) was studied in 604 calves (19 diffe rent groups in 4 different feedlots from 2 provinces). Almost all calv es had antibody titers on arrival in the Alberta feedlot and 82% of th e calves had an antibody titer on arrival at the Ontario feedlots; tit ers in calves in Alberta were almost twice as high as those in calves in Ontario. The incidence of infection, in the first mo after arrival as judged by seroconversion, ranged from 61% to 100%; titer increases were much greater in calves in Ontario feedlots. Titer variables were not significantly related to BRD, except on a within-group basis (grou p was a confounding variable for BCV-BRD associations). Given control of group effects, calves with an antibody titer on arrival appeared to be protected against BRD for the first 28 d in the feedlot, and the a ssociation was reasonably linear over the range of titers. Each titer unit on arrival decreased the risk of BRD by about 0.8x (odds ratio). Titer change was not strongly related to the risk of BRD and the relat ionship was not linear over the range of titer changes. Titer change w as strongly and negatively correlated with titer on arrival, and titer change was not significantly related to BRD in the presence of arriva l titers. Arrival titer retained its relationship with BRD in the pres ence of titer data for other putative pathogens. Each higher unit of t iter to BCV on arrival increased the 28-day weight gain (controlling f or group, initial weight and the occurrence of BRD) by slightly more t han 1 kg. Titer change was associated with decreased weight gain, when initial titer was not in the model. The lack of a linear or multivari able association between BCV titer change and BRD, and weight gain, ma y indicate that BCV is not a major pathogen; or, its lack of significa nce may merely be due to its strong correlation with arrival titer. Gi ven the associations found in this study, particularly the interprovin cial differences in arrival titers, more and different approaches to s tudying the possible effects of BCV on BRD are in order.