The frequency, distribution and effects of antibodies, to seven putative respiratory pathogens, on respiratory disease and weight gain in feedlot calves in Ontario.

During 1983-85, 279 calves requiring treatment for bovine respiratory disease and 290 comparison (control) animals from 15 different groups of feedlot calves were bled on arrival and again at 28 days postarrival. Their sera were then analyzed for antibodies to seven putative respiratory pathogens. On arrival, the prevalences of indirect agglutination titers to Pasteurella haemolytica, P. haemolytica cytotoxin, Mycoplasma bovis and M. dispar were greater than 50%, the prevalence of titers to bovine virus diarrhea virus (BVDV) was approximately 40%, and the prevalences of titers to infectious bovine rhinotracheitis virus (IBRV), bovine respiratory syncytial virus (RSV) and parainfluenza virus type 3 (PIV3) were all below 25%. Seroconversion during the first month after arrival occurred in more than half the calves to P. haemolytica cytotoxin, PIV3 and RSV. Seroconversion of agglutination titers to P. haemolytica, Mycoplasma and BVDV occurred in about 40% of calves, and seroconversion to IBRV was infrequent (less than 5%). Initial titers were negatively correlated to subsequent titer changes within organism. Initial titers, and titer changes between organisms were essentially independent. Light calves had an increased risk of being selected for treatment for respiratory disease. Seroconversion to P. haemolytica cytotoxin, RSV and BVDV were predictive of respiratory disease cases, explaining approximately 69% of all respiratory disease cases in the feedlots. It was not possible to accurately predict weight gain or relapse from the serological data.