Sometimes called “lockjaw,” tetanus is caused by toxin-producing bacteria present in the intestinal tract of many animals and found in abundance in the soil where horses live. The spores can exist for years and they enter the body through wounds, lacerations, or the umbilicus of newborn foals.

Therefore, although not contagious from horse to horse, tetanus poses a constant threat to horses and humans alike. Symptoms include muscle stiffness and rigidity, flared nostrils, hypersensitivity, and the legs stiffly held in a sawhorse stance. As the disease progresses, muscles in the jaw and face stiffen, preventing the animal from eating or drinking. More than 80 percent of affected horses die.