When to call the vet: nervous system problems
Problems with the nervous system can arise due to trauma, organ problems or infections. Call your veterinarian immediately if your horse has abnormal behavior, muscle twitching that persists, difficulty walking, head tilt, bite wound plus change in behavior, or seizure activity (abnormal motion followed by dullness).
While you wait, put the horse in a stall with minimal objects or in a small area by itself, make sure everyone leaves the stall or area to avoid injury, and decrease stimulation (other horses moving by, noise, lights).
A horse that seems to have problems with the urinary system can have a urinary stone, colic or a severe muscle disorder. Call your veterinarian immediately if your horse is straining to urinate, can't seem to move his/her back end properly, or has brown urine. While you wait, take a heart rate, collect urine if he/she urinates, and don't exercise the horse.
Horses may develop breathing problems with pneumonia, or with problems in the head that prevent them from breathing well through the nose. Horses cannot breathe through their mouths. They can also develop problems in the head that can lead to severe blood loss. Call your veterinarian immediately if your horse makes noise while breathing at rest (not exercising), flares his/her nostrils while at rest, has rapid breathing after a wound or after an illness, or has bloody nasal discharge. While you wait, minimize exercise and stress. If it could be strangles, try to isolate the horse, their gear and caretakers, take the horse's temperature if it is used to it, and if the barn or horse is hot, put cold water along the horse's backbone.
Due to the environment, horses can injure their eyes relatively easy. Injuries need to be treated aggressively to prevent loss of vision. Call your veterinarian immediately if your horse is squinting, suddenly blind, or there are cuts or tears to the eyelid. While you wait, put your horse in a dark stall.