SELECTION OF QUARTER HORSES AFFECTED WITH HYPERKALEMIC PERIODIC PARALYSIS BY SHOW JUDGES

Thirty offspring of a Quarter Horse sire, affected by hyperkalemic per iodic paralysis (HPP), were examined electromyographically. On the bas is of the defection of or lack of spontaneous activity with high frequ ency myotonic or pseudomyotonic discharges, the horses were diagnosed as being affected (14 horses) or unaffected (16 horses) with HPP. The show performance of these horses was evaluated for the first 3 to 9 ye ars of their life by use of American Quarter Horse Association records . Horses affected with HPP performed significantly (P < 0.01) better i n halter classes than did unaffected horses; mean halter points for th e 2 groups were 11.9 and 0.4, respectively. The mean total performance points were not significantly different. None of the offspring had a successful racing record.