EVALUATION OF A MULTIVALENT PASTEURELLA-HAEMOLYTICA VACCINE IN BIGHORN SHEEP - SAFETY AND SEROLOGIC RESPONSES

We examined effects of a multivalent Pasteurella haemolytica vaccine ( serotypes Al, A2, T10) on humoral immune responses and El haemolytica isolation rates in bighorn sheep (Ovis canadensis). Thirty captive big horns, divided into groups of three on the basis of age, sex, and prev ious history of pneumonic pasteurellosis, received 0, 1, or 2 vaccine doses. Mild, transient lameness in most bighorns 1 day after initial v accination was the only adverse effect observed. Oropharyngeal (greate r than or equal to 75%) and nasal (less than or equal to 50%) isolatio n rates for P. haemolytica did not differ among treatment groups. Ten of 36 distinguishable biogroup variants accounted for about 87% of the 464 P. haemolytica isolates from bighorns, but prevalences of specifi c biogroups were not affected by vaccination. Bighorns receiving 1 or 2 vaccine doses showed marked elevations in leukotoxin neutralizing an tibody titers beginning 1 wk after vaccination. Agglutinating antibody titers to serotype A1 and A2 surface antigens were also elevated in v accinated bighorns within 2 wk after vaccination; agglutinating antibo dy titers to serotype T10 surface antigens were relatively high in all three groups but appeared unaffected by vaccination. Vaccination 7 to 14 wk prior to parturition elevated leukotoxin neutralizing antibody titers in colostrum, but neither leukotoxin neutralizing nor serotype A1 surface antigen agglutinating antibody titers differed through 16 w k of age among lambs born to dams from different vaccine dose groups. Our data demonstrate that this multivalent P. haemolytica vaccine is s afe and stimulates marked antibody responses in bighorn sheep. Further evaluation of this vaccine as a tool in preventing and managing paste urellosis in bighorn sheep appears warranted.