A QUANTITATIVE FLUOROMETRIC ASSAY FOR THE MEASUREMENT OF ANTIBODY TO PASTEURELLA-HAEMOLYTICA IN CATTLE

Abstract

A rapid simple fluorometric method is described for measuring antibody to P. haemolytica in sera of cattle. Various antigen preparations were compared for the test including live formalin-killed and phenol-killed P. haemolytica. A preparation composed of formalin-killed organisms from a 22 h culture gave consistent results and was used in the studies. The test was reproducible with percent coefficients of variation for fluorescent signal unit values on .gtoreq. 10 replicate samples ranging from 5.7 to 28.0. Sera from calves vaccinated by aerosol exposure to live P. haemolytica had up to a 5-fold increase in antibody titer as measured by the fluorometric method test during a 21 day period. Fluorometric method titers were comparable to those obtained by the indirect bacterial agglutination test. There was no seroconversion to P. haemolytica in calves vaccinated by aerosol exposure of P. multocida. The major advantages of the fluorometric method test over conventional methods and the assay does not require serial dilutions of serum samples, and thus limits time and effort to determine antibody titers.