Genetic-diet interactions in the Hyperkalemic Periodic Paralysis syndrome in quarter horses fed varying amounts of potassium: Part II-symptoms of HYPP

Abstract

Six broodmares that were genetically tested to be heterozygous (H/N) and six broodmares that were tested to be homozygous negative (N/N) for Equine Hyperkalemic Periodic Paralysis (HYPP), that were descendents of the same stallion, were used in a replicated 3x3 Latin square experiment to determine the genetic-diet relationships in the HYPP syndrome. The mares were fed rations consisting of 65% pelleted concentrate and 35% Coastal Bermudagrass hay that provided 1.1 (diet A), 1.9 (diet B) and 2.9% (diet C) potassium in the total rations. Symptoms of HYPP, such as repeated yawning, muscle twitching, generalized muscle fasciculations, myotonia, irregular movement, prolapse of the membrana nicitans and involuntary recumbency, were recorded during each 14-day experimental period. There were no HYPP symptoms in the HYPP N/N horses fed any diet, or in the HYPP H/N horses fed the low potassium diet. Symptoms were observed after 52% of the horse-meal combinations when the HYPP H/N horses were fed the medium potassium diet and after 67% of the horse-meal combinations when they were fed the high potassium diet. The onset and longest duration of symptoms were on the head or shoulders 66% of the time. Bi-phasic symptoms were rare and were more frequent after diet C than diet B. Symptoms were twice as common in the day as the night. These results indicate that a genetic-diet interaction exists in the HYPP syndrome and that dietary control of HYPP symptoms is possible in genetically susceptible horses.