Tetanus can be caused by a small entry wound from a sharp object. Especially, enclosed wounds, where airless conditions are ideal for these anaerobic bacteria are most dangerous. - Thomas
Bacteria and dirt are driven deep into the wound by the offending sharp object. After the toxin reaches the central nervous system by traveling along nerve trunks, muscle spasms begin.
The spores of C. Tetani are commonly presented in the soil and can contaminate puncture wounds, crushing wounds, open lacerations, surgical incisions, and the umbilici of foal.
In some cases, death is usually by suffocation because the muscles used in breathing become paralyzed.
Antitoxin are made by special cells and circulate in the blood serum. An antitoxin is created in a laboratory by injected a healthy animal with a particular bacterium.
An other type of medicine to help build a horses immunity to tetanus is Toxoid. Toxoid consist of inactivated toxins used to immunize against tetanus.
These two medicines appear to be very safe and induce a long-lasting immunity.