Big head is an inflammatory swelling of the head of sheep, usually young rams, caused by Clostridium novyi type A. Continual butting between young rams bruises the subcutaneous tissues of the poll and sets up suitable anaerobic conditions for entry and multiplication of pathogenic clostridia.
The head, face and neck become swollen with oedema. Differential diagnoses include photosensitisation, bluetongue and possibly actinobacillosis.
Specimens for laboratory confirmation are smears or swabs of exudate for bacteriology collected from live or freshly dead animals. In dead animals, also submit sections of affected tissue, collected aseptically, and submitted chilled for bacteriology; and in buffered formalin for histology.