These plants contain cells known
as idioblasts. Inside the cells are
sharp, needle-like crystals of calcium
oxalate that are packed in a gelatinous
material. When the plant material is
chewed, saliva or plant sap can enter
the idioblasts. The gelatinous material
swells and this causes the calcium
oxalate crystals to shoot out of the
idioblasts. The crystals can penetrate
the tongue, throat and the inside of the
mouth to cause severe irritation. Some
of these plants also contain chemicals
that aggravate the symptoms by causing
an inflammatory response. Signs (can
appear immediately or within hours
of ingestion): head shaking, salivation,
mouth and tongue swelling, depression.
In very rare cases the swelling can cause
airway obstruction. Affected animals
may take days to fully recover. If
poisoning is suspected, rinse the horse’s
mouth with water and seek veterinary
attention.