Effects of delivery method on serological responses of bighorn sheep to a multivalent Pasteurella haemolytica supernatant vaccine

The safety and efficacy of a remotely delivered multivalent Pasteurella hae molytica supernatant vaccine (serotypes A2 and T10) were examined in captiv e Rocky Mountain bighorn sheep (Ovis canadensis canadensis). Twenty bighorn sheep were grouped according to baseline leukotoxin neutralizing antibody titers (less than or equal to 2 or >2 log(2)(-1)) and vaccination history ( previously vaccinated or unvaccinated). Within these groups, animals were r andomly assigned to one of two delivery treatments: hand injection (control ) or biobullet implantation. All bighorns received a single dose from the s ame lot of vaccine (n = 10/treatment); four additional animals were injecte d intramuscularly with 0.9% saline as unvaccinated sentinels. Mild, transie nt lameness one day after hand injection or biobullet implantation was the only adverse effect. Serum neutralizing antibody titers to P. haemolytica l eukotoxin differed between delivery treatments (P = 0.009) and among baseli ne titer/vaccination history groups (P = 0.013). Neutralizing titers were h igher among hand-injected bighorns. Although neutralizing titers were lower among implanted bighorns than hand-injected controls at 1 wk (P = 0.002) a nd 2 wk (P = 0.021) after vaccination, seroconversion rates in response to implantation (6/10) and hand injection (9/10) did not differ (P = 0.303). A gglutinating antibody titers to T10 were high and did not vary over time or between delivery treatments. Agglutinating antibody titers to A2 in the ha nd-injected controls were not different (P greater than or equal to 0.07) t han those in bighorns vaccinated with biobullet implantation. These data de monstrate that although hand injection elicits higher absolute titers, biob ullet implantation may also stimulate effective antibody responses to P. ha emolytica supernatant vaccine. Further evaluation of biobullet vaccination against pneumonic pasteurellosis in free-ranging populations of wild bighor n sheep is warranted.