Abstract
Mannheimia haemolytica is responsible for considerable economic losses to sheep, goats, and cattle and other livestock industries in Egypt. This study aimed to evaluate the effectiveness of a newly developed gamma irradiation vaccine against Mannheimia haemolytica in comparison to a formalin-killed vaccine. Three groups of rabbits were used in this study. Group 1 animals were inoculated with 4 x 10(9) bacterial cells per dose of the formalin-killed vaccine. Group 2 was inoculated with 2 x 109 bacterial cells per dose of gamma-irradiated vaccine. Group 3 (control group) was injected with 2 mL of sterile PBS. The vaccines were injected subcutaneously into experimental animals twice with 3-week intervals between inoculations. Three weeks after the second vaccination dose, the animals in all groups were infected with M. haemolytica twice with 1-week intervals between inoculations. Blood samples were collected weekly after the first vaccination until one week after the second M. haemolytica infection challenge. ELISA results revealed that the gamma irradiation vaccine developed in this study provided protective effects that reached high levels at the time of challenge. Furthermore, the second dose of gamma irradiation vaccine could act as a booster dose resulting in increased antibody production.