This is what I found on Tetanus...
Tetanus in Horses
Horses are highly susceptible to tetanus, a condition caused by bacteria called Clostridium tetani. Humans receive vaccines to protect against this disease, and horses should receive an equine version of a tetanus vaccine also on a regular basis. Though many species can contract tetanus, next to horses, humans are the most susceptible. Another name used sometimes to describe this condition is "lockjaw" because frequently the muscles that control the ability to open and close the mouth are affected.
The bacteria live in soils and infection often follows a puncture wound or burn. A typical situation would be a horse that steps on a dirty nail in a barnyard, and the soil goes into the deep tissues of the foot along with the sharp object. These bacteria must be injected deep away from air (oxygen) to reproduce. Bacteria that need to be out of air to thrive are called anaerobic bacteria. This disease is much less common now because of modern, effective vaccines. Careful husbandry is still important to minimize exposure to dirty sources of this powerful bacterium because they are still in the farm environment.
The disease signs result from the liberation of powerful toxins from the infection site. This toxin affects the nervous system. Usually the first sign noted is that the eyes have a staring appearance and the third eyelid that normally sits inside the eyelids on the eyeball at the inner angle of the eye becomes partially drawn up over the eye. The horse will experience powerful muscle spasms that set the muscles in tight contraction leading to stiffness—but noises, movements, and light exposure will trigger very pronounced spasmodic movements. It can take a few weeks for these symptoms to appear after the wounding episode. Back and neck spasms tend to make the horse hold the head out forward. The combination of muscle spasms of legs, back and neck produces a typical posture referred to as a "sawhorse" or "rocking horse" stance. The tail also does not move normally because of muscle stiffness. Ears will be pricked up, mouth drawn back to appear to "grin" and nostrils dilate giving the horse a hyper-alert look.
It is a serious condition and up to three quarters of horses will succumb once the infection has become established and advanced clinical signs develop. This is why your veterinarian will emphasize yearly protection against this disease using tetanus toxoid vaccine. If your horse should get a puncture wound anywhere on the body, even a very small one, call your veterinarian promptly because they may recommend a booster for the patient to help bolster immunity. Sometimes an unprotected horse is exposed, and an antitoxin will be given also because vaccines do not provide protection immediately. It is very important to keep the horse's boosters up-to-date. Mares should be vaccinated to ensure that their foals are protected until they are old enough to be vaccinated.
During clinical illness, veterinary care may include sedation, pain therapy, antibiotics, wound care, nursing care (dark, quiet stall, elevated or nasogastric tube feeding) and direct antitoxin injections.
