Seroepidemiology of undifferentiated fever in feedlot calves in western Canada

The relationships between 4 bacterial and 3 viral antibody titers and morbi dity (undifferentiated fever (UF)) and mortality were investigated in recen tly weaned beef calves. Blood samples from 100 animals that required treatm ent for UF (Cases) and 100 healthy control animals (Controls) were obtained : upon arrival at the Feedlot (Arrival), at the time of selection as a Case or Control (Selection), and at approximately 33 d of the Feeding period (C onvalescent). Seroconversion to Pasteurella haemolytica antileukotoxin was associated with an increased risk of UF (OR = 2.83); however, seroconversio n to bovine herpesvirus-l G-IV glycoprotein was associated with a decreased risk of UF (OR = 0.43). Higher Arrival bovine viral diarrhea virus antibod y titer was associated with a decreased risk of UF (OR = 0.83). Increases i n Mycoplasma alkalescens antibody titer after Arrival were associated with an increased risk of UF (OR = 1.10). Higher Arrival Haemophilus somnus anti body titer and increases in Haemophilus somnus antibody titer after Arrival were both associated with a decreased risk of UF (OR = 0.76 and OR = 0.78) . The odds of overall mortality (OR = 5.09) and hemophilosis mortality (OR = 11.31) in Cases were significantly (P < 0.05) higher than in the Controls . Higher Arrival bovine herpesvirus-1 antibody titer was associated with an increased risk of mortality (OR = 1.30). Protective immunity to Pasteurell a haemolytica antileukotoxin, Haemophilus somnus, bovine herpesvirus-1 G-IV glycoprotein, bovine viral diarrhea virus, and Mycoplasma spp. may be nece ssary to reduce the occurrence of UF. Animals with UF are at an increased r isk of overall and hemophilosis mortality.