Antibodies to Pasteurella haemolytica somatic antigens in two models of the bovine respiratory disease complex

Serum samples obtained from feeder calves before and after entry into the market system (days 0 to 7) were assayed for antibodies to Pasteurella haemolytica biotype A, serotype 1 capsular polysaccharide (CPS) and lipopolysaccharide/outer membrane protein (LPSp) by isotype in a kinetic-augmented, antigen-capture ELSIA. These test results, plus indirect hemagglutination (IHA) antibody titers, and hemolysin-in-gel test (HIGT) findings were compared with clinical performance data during the initial 4 weeks in the feedlot (receiving period). High concentrations of HIGT antibody, at the point of initial assembly of feeder calves at weaning and during the subsequent 7-day marketing period, were associated with freedom from bovine respiratory disease (BRD) during the receiving period. High or rapidly increasing concentrations of anti-CPS IgG1 during the marketing period were also associated with less BRD. However, high concentrations of anti-LPSp IgG1 during the marketing period were associated with increased BRD during the receiving period. There was no correlation between the concentrations of antibody determined by IHA tests early in the marketing period and freedom from BRD during the receiving period. High concentrations of antibody determined by this test at entry into the feedlot (day 7) were associated with a high incidence of BRD. Calves vaccinated with a P haemolytica bacterin had significantly (P less than 0.05) higher HIGT values and concentrations of anti-LPPp IgG1 and IHA antibody than did nonvaccinated calves on entry into the feedlot (day 7). Vaccination appeared to have little effect on the amount of anti-CPS IgG1. Of all the tests used to quantitate antibody, the HIGT correlated best with clinical performance. High concentrations of HIGT antibody during the marketing period predicted freedom from BRD during the receiving period. When calves were vaccinated with tissue culture-derived and conventional P haemolytica bacterins in oil adjuvant at 28-day intervals and tested for antibody responses by isotype on days 0, 28, and 35, there were clear and highly significant increases in anti-LPSp IgG1 activity. Also, the amount of anti-LPSp IgM and the HIGT and IHA antibody titers increased significantly. In all tests, the antibody response was highest to the tissue culture-derived bacterin. High concentrations of HIGT antibody, as found in vaccinated animals, were correlated with resistance to transthoracic inoculation of virulent P haemolytica.