By Jeanne van der Veen, MS, PAS
Equine Hyperkalemic Periodic Paralysis (HYPP) is an inherited muscle disorder characterized by abnormal muscle movement or activity. The disorder is found primarily in Quarter Horses with a genetic link to the stallion ‘Impressive’. Impressive was used extensively as a sire in many breeding programs for over 25 years, leaving many descendants potentially affected with HYPP.
Symptoms of Equine HYPP include muscle rigidity, fasciculations (spasms), weakness, irregular movement, repeated yawning, prolapse of the third eyelid and involuntary recumbency (collapse). These symptoms may vary from mild to intense, depending on the horse. In extreme cases, if the heart muscle is affected, the disorder may lead to heart failure and death. Yet, many horses carrying the gene for HYPP may not show any signs of the disorder and lead normal lives. Given that Equine HYPP is genetic, however, future breeding of horses carrying the gene should be carefully evaluated.
For horses with HYPP, research at Texas A&M University has suggested that some horses can be managed to prevent the HYPP symptoms from occurring by feeding a low-potassium diet. In this study, horses with the gene for HYPP exhibited some degree of HYPP symptoms when total diet potassium levels were at 1.9% and 2.9%. The HYPP horses fed 1.1% potassium in the total diet did not exhibit any symptoms. Thus, recommendations are to keep potassium below 1.5% in the TOTAL diet.
Total diet potassium level includes not only the grain ration provided, but also the hay and/or pasture fed. All Kent Nutrition Group grain rations are below 1.2% potassium, with the sweet feeds being lowest, followed by low- to moderate-fiber pellets and nuggets, then the high-fiber pellets and nuggets. The hay fed along with these grain rations, however, may not be low. Typically, good-quality hay will contain between 1.8% – 2.5% potassium.
For horses exhibiting symptoms of HYPP, one viable alternative is to feed greater amounts of a higher fiber feed and reduce the amount of hay fed to keep potassium levels low. In addition, feeding a hay/fiber substitute type product in place of some of the hay would reduce potassium in the total diet. Even though the potassium level is higher in these higher fiber feeds, by reducing the amount of hay fed and feeding more high-fiber “grain,” the TOTAL potassium in the diet is reduced.
These researchers also suggested that managing horses with HYPP may involve more than just the percent potassium in the feed. Their recommendation was to feed smaller amounts more often (more ‘meals’) to reduce the amount of potassium absorbed in the blood at a given time. The use of pasture will further spread the intake of potassium over time as moisture and availability make it difficult for horses to eat large amounts at once.
Many other factors, such as exercise, may also trigger an episode of Equine HYPP. While further research is needed to fully understand all factors that may lead to an episode of HYPP, current recommendations are to alter feed management practices and provide less than 1.5% potassium in the TOTAL diet.