Conditions affecting sheep. The major acute pneumonic
condition of sheep is pasteurellosis caused by Mannheimia
haemolytica serotype A2 and infection with this organism is
susceptible to the same antimicrobials used for its treatment
in cattle. Pasteurella trehalosi infections may present as
pneumonia and may be treated in the same way but are less
sensitive to penicillin. New and effective vaccines against
these two infections mean that passive protection of the
lamb and active protection of the growing and adult sheep
are now routine. These vaccines are available alone or in
combination with vaccines for clostridial infections (see
section 18.2).