HYPP, Hyperkalemic Periodic Paralysis, Impressive Syndrome
HYPP is a genetic disorder seen in some horses with Quarter Horse breeding. Any horse whose pedigree traces back to the sire "Impressive" should be tested for HYPP. Theses horses have an inabilty to regulate electorlytes such as sodium, chloride and pottasium. The electrolyte imbalance in the blood causes impaired nerve function that can lead to muscle termors and eventually paralysis.
Weakness, especially in the hindquarters, trembling, abnormal perspiring, unusual appearance of the third eyelid (nictitating membrane), collapse, distorted vocalizations. During an attack the horse remains alert. Attacks can occur at rest and during work. The horse appears normal after an attack.
An attack can range from mild to severe. During a mild attack a horse may tremble, have muscle cramping, and respiratory distress. Death can occur if the potassium levels become too elevated.
Horses with HYPP can be maintained on a low potassium diet, moderate outdoor daily exercise, and strict feeding schedule. The only way to eliminate HYPP is to not breed horses that carry the HYPP gene. Genetic testing should be done on any horse suspected of having Quarter Horse bloodlines tracing back to the sire "Impressive".
A mild attack can be dealt with by exercising the horse very lightly and feeding a low potassium/ high carbohydrate feed to drive the potassium levels in the blood down. More severe attacks require veterinary care.