Green Prairie Animal Hospital · Large Animal & Equine Care · Mason County, IL
Your horse is stiff. Won’t open his mouth to eat. His third eyelid — the membrane in the inner corner of the eye — is prolapsing across the eye in a way you’ve never seen before. His ears are pulled back and his tail is slightly elevated. If you’re seeing this combination of signs, tetanus — commonly called lockjaw — needs to be at the top of your list until proven otherwise.
This is a call-the-vet situation. Not a wait-and-see situation. Here’s what you need to know about tetanus in horses — how it happens, what it looks like, and why speed matters when it does.
What Tetanus Actually Is
Tetanus is caused by a neurotoxin — a poison that attacks the nervous system — produced by the bacterium Clostridium tetani. The organism lives in soil and in the intestinal tract of animals, including horses. It is present in virtually every pasture and barn in central Illinois.
Clostridium tetani is an anaerobic organism — it thrives in environments without oxygen. Deep puncture wounds, lacerations with tissue damage, surgical sites, and wounds that close over on the surface before healing internally all create the low-oxygen conditions where the organism can multiply and produce toxin.
The toxin travels from the wound site along nerve pathways to the spinal cord, where it blocks the inhibitory signals that normally regulate muscle contraction. Without those inhibitory signals, muscles contract continuously and cannot relax. That’s what produces the characteristic rigidity of tetanus — not the bacteria itself, but the toxin it releases into the nervous system.
Horses are among the most susceptible animals to tetanus toxin. The lethal dose for a horse is far lower than for cattle or most other species. That susceptibility is exactly why vaccination is so important and why an unvaccinated horse with a wound is a genuine emergency.
Early Signs of Tetanus in Horses
Tetanus does not appear instantly after a wound. The incubation period — the time between infection and the appearance of clinical signs — is typically one to three weeks, though it can range from a few days to more than a month depending on the location and nature of the wound and the amount of toxin produced.
Early signs are easy to miss or attribute to something else. Watch for:
Stiffness and a stilted gait — the horse moves with an unusual rigidity, placing his feet carefully, reluctant to turn or flex. This is often the first thing owners notice and the first thing that gets written off as a muscle strain or soreness.
Prolapse of the third eyelid — the nictitating membrane, a pale membrane in the inner corner of the eye, slides partially or fully across the eye. In a normal horse at rest this membrane is barely visible. Prominent third eyelid prolapse in a horse that isn’t sedated is an abnormal finding that warrants immediate attention.
Hypersensitivity to stimuli — the horse overreacts to sound, touch, or sudden movement. A noise that wouldn’t normally cause concern produces an exaggerated startle response. This hypersensitivity is caused by the nervous system losing its ability to modulate input normally.
Difficulty eating and swallowing — the classic lockjaw presentation. The masseter muscles — the large chewing muscles along the jaw — go into spasm, making it difficult or impossible to open the mouth. A horse that is dropping feed, taking unusually long to eat, or refusing grain he would normally eat eagerly warrants a closer look at jaw mobility.
Elevated tail head and erect ears — the tail is held slightly away from the body and the ears stand rigidly forward or back. Combined with the other signs, this posture is characteristic enough that an experienced large animal veterinarian can make a strong clinical diagnosis without laboratory confirmation.
How Tetanus Progresses Without Treatment
Tetanus in horses progresses rapidly once clinical signs appear. What starts as stiffness and difficulty eating becomes full-body rigidity within days in untreated or inadequately treated animals.
As the toxin spreads through the nervous system, muscle spasms intensify and become continuous. The horse assumes a characteristic sawhorse stance — all four legs spread wide and braced, neck extended, body rigid. Spasms can be triggered by any external stimulus — a loud noise, bright light, touch — and become increasingly violent as the disease progresses.
Respiratory muscles are eventually affected. When the muscles controlling breathing go into spasm, the horse suffocates. This is the most common cause of death in tetanus cases — not the initial infection, but respiratory failure caused by uncontrolled muscle spasm.
Survival rates for horses with clinical tetanus vary significantly based on how early treatment begins, how severe the signs are at presentation, and the quality of supportive care provided. Mild cases caught early and treated aggressively have better outcomes than severe cases treated late. There is no good outcome in a horse that reaches the stage of continuous whole-body spasm before treatment begins.
When to Call the Vet — Don’t Wait on This One
Any horse showing signs consistent with tetanus needs a large animal veterinarian called immediately — not at the end of the day, not tomorrow morning. Same hour.
While you’re waiting for the veterinarian to arrive, move the horse to a quiet, darkened stall if possible. Reduce stimulation — keep noise low, minimize handling, limit the number of people around the animal. Every stimulus triggers spasm. Reducing stimulation reduces the frequency and intensity of those spasms while the horse waits for treatment.
Do not attempt to force feed or water a horse you suspect has tetanus. A horse with compromised swallowing ability is at high risk of aspiration — inhaling feed or water into the lungs — which adds aspiration pneumonia to an already serious situation.
If you can identify the wound site — and sometimes you can’t, particularly with small punctures that have already closed — do not probe or manipulate it before the veterinarian arrives. The wound will need to be debrided — cleaned and opened to allow oxygen in and reduce the anaerobic environment where Clostridium tetani thrives — but that debridement should be done properly under veterinary guidance.
Treatment — What the Veterinarian Will Do
Tetanus treatment in horses is supportive and aimed at neutralizing toxin that hasn’t yet bound to nerve tissue, eliminating the source of ongoing toxin production, controlling muscle spasms, and keeping the horse alive while the nervous system recovers.
Tetanus antitoxin — antibodies that neutralize circulating tetanus toxin before it binds to nerve receptors — is administered as early as possible. Antitoxin cannot reverse the effects of toxin that has already bound. This is why early treatment matters so much — the window during which antitoxin can meaningfully reduce the course of the disease is the early stage before significant toxin has reached the spinal cord.
Penicillin — the antibiotic of choice for Clostridium tetani — kills the bacteria at the wound site and stops ongoing toxin production. Wound debridement opens the wound to oxygen, directly disrupting the anaerobic environment the organism requires.
Muscle relaxants and sedatives — diazepam, acepromazine, and others depending on severity — reduce the frequency and intensity of muscle spasms and keep the horse calm enough to prevent the stimulus-triggered spasm cascades that exhaust and injure an affected animal.
Supportive care — IV fluids, nutritional support through a nasogastric tube if the horse cannot eat, sling support if the horse goes down — is the labor-intensive component of tetanus management that determines whether a horse that survives the acute phase recovers fully. Recovery from tetanus takes weeks to months. It is not a short illness even in horses that survive.
Prevention Is Straightforward — Vaccination Works
Tetanus is almost entirely preventable. The tetanus toxoid vaccine — a core vaccine for horses in Illinois — produces reliable, durable immunity against the toxin. A properly vaccinated horse that receives a booster at the time of a significant wound is extremely unlikely to develop tetanus.
Core vaccination protocol for Illinois horses includes tetanus toxoid annually, with a booster administered any time a horse sustains a significant wound, undergoes surgery, or foals — foaling mares receive a pre-foaling booster to pass maternal immunity to the foal through colostrum.
Foals from vaccinated mares receive maternal antibody protection through colostrum that lasts several months. Primary vaccination for foals typically begins at four to six months of age with a series of two to three doses. Foals from unvaccinated mares or mares with unknown vaccination history should receive tetanus antitoxin at birth for immediate passive protection while the active vaccine series is started.
An unvaccinated horse with a wound — any wound — should receive tetanus antitoxin immediately for short-term protection and begin the primary vaccination series at the same time. Do not wait for signs of tetanus to consider protection in an unvaccinated horse with a wound.
Green Prairie Animal Hospital Serves Mason County Horse Owners
For horse owners in Mason County and across central Illinois, Green Prairie Animal Hospital’s San Jose location handles all equine care — wellness exams, core and lifestyle vaccines including tetanus toxoid, wound management, farm calls, and emergency response.
The San Jose team does farm calls throughout Mason County. A horse showing signs of tetanus does not need to be hauled — and hauling a horse with active tetanus, with the stress and stimulation that involves, is likely to worsen the situation. Call San Jose and the team comes to you.
As an AAHA-accredited clinic, the treatment protocols behind every emergency call and every farm visit at Green Prairie Animal Hospital meet the highest standards in veterinary medicine. When your horse needs help fast, that standard matters.
Call San Jose for Equine Emergency Care in Central Illinois
Green Prairie Animal Hospital’s San Jose location is our large animal and equine center for Mason County and central Illinois. Our team handles horses, cattle, and livestock — and we do farm calls.
