Clostridium tetani, the bacterium that causes tetanus, can live in soil and manure can infect horses and livestock through breaks in the skin, including small cuts, surgical wounds and umbilical attachment points. Infected horses can develop life-threatening muscle stiffness, difficulty breathing and digestive issues. Annual vaccinations and boosters after surgery or injury prevent tetanus in horses, cattle and small ruminants, says veterinarian Kallie Hobbs.