Etiology:

• Bacteria: P.aviseptica, Erysipelothrix rheusopathie
• Phytotoxins of certain plants
• Foreign bodies: Sharp objects, dust, encysted larvae
• Constant and repeated mechanical irritation (trauma); saddle and collar galls

Microscopic findings:

• Infiltration with mononuclear cells
• Tissue destruction due to inflammatory cells
• Repair: proliferation of small vessels