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Lockjaw in Horses
A stiff gait, rigidity of the extremities sawhorse" stance, inability
to eat and overreaction to sounds are signs of lockjaw. They
appear about two weeks to a month following infection, but
can be seen earlier depending upon the amount of toxin
The microbe Clostridium tetani is responsible for causing the
characteristic muscle rigidity often seen in lockjaw, more
commonly known as lockjaw. The organism is found in most soils
and enters an animal’s body through dirty, neglected wounds and
especially via punctures. The exotoxin which C. tetani produces
binds to the nerves at the site of the injury and then travels to
the spinal cord and brain.
The toxin prevents muscles from relaxing, so once a muscle
has been stimulated to contract, such as to close the jaw, it
cannot return to its original relaxed state, thus creating the
rigidity seen with the disease. Death results from either an
inability to breath or due to seizures.
Horses and humans are the species most susceptible to the toxin’s
effects. The best way to treat lockjaw in horses is to prevent it. Lockjaw
toxoid (vaccine) is given initially as two doses three to six
weeks apart followed by an annual booster. It provides strong,
long-lasting protection against the toxin itself, not C. tetani.
Lockjaw antitoxin (serum) also works against the toxin, but is
only effective for two to three weeks. Antitoxin is best used
when the vaccination history of an injured animal is unknown, in
unvaccinated mares at foaling and for newborn foals born to
unvaccinated mares. The first lockjaw toxoid injections should be
given at three to four months of age. Horses that are vaccinated
yearly should be given toxoid if they are injured or undergo
surgery more than six months since the last booster.
Treatment of lockjaw is limited to providing muscle relaxation,
killing any bacteria still in the body using antibiotics
(penicillin), neutralizing the toxin with serum antitoxin, and
administering nutritional supplementation. Full recovery takes
weeks to months, but even with treatment up to 80% of cases in
horses are fatal.
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