Experimentally induced infectious bovine keratoconjunctivitis: relationship of vaccination schedule to protection against exposure with homologous Moraxella bovis culture.

Calves were intramuscularly vaccinated with a formalin-killed Moraxella bovis culture. They were given 3 doses of the vaccinal culture at 3 different intervals between injections, as follows: 7-day intervals (group I), 14-day intervals (group II), an21-day intervals (group III); 14 days after the 3rd vaccinal dose was given, calves in all groups were challenge exposed to virulent homologous M bovis. The challenge bacterium became established in all (100%) of the control (group IV, N equals 8) and group I (N equals 8) calves, in 7 (87%) of the group II calves (N equals 8), and in 5 (62%) of the group III (N equals 8) calves. Signs of infectious bovine keratoconjunctivitis (IBK) developed in 8 (100%) of the controls, in 6 (75%) of the group I calves, in 1 (12%) of the group II calves, and in 2 (25%) of the group III calves. These results indicate that at least 14 days should be allowed between successive doses of this experimental vaccine.