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HYPERKALEMIC PERIODIC PARALYSIS 

ETIOLOGY 

  • Hyperkalemic periodic paralysis (HYPP) is an inherited (autosomal dominant trait) muscle disease. It is caused by a genetic defect that disrupts a protein that forms the sodium ion channel, a tiny gateway in the membrane of muscle cells. 
  • The genetic defect disrupts the channel’s normal opening and closing such that uncontrolled sodium influxes occur. These influxes in turn change the voltage current of muscle cells, causing uncontrolled muscle twitching or profound muscle weakness. 
  • High levels of potassium in the blood usually are present when the disruptions in the sodium ion channel occur. At the same time, potassium leaks out of the cell, affecting the voltage current after contraction. The potassium remains in the extracellular fluid, preventing the muscle cell from relaxing. 
  • The condition is found in Quarter Horses, or other breeds like Paints and Appaloosas, where Impressive AQHA #0767246 is found in the pedigree. 

Note: Acetazolamide is now approved by AQHA as a therapeutic medication, subject to specific rules. 

SYMPTOMS 

HYPP is characterized by muscle weakness, sporadic tremors and twitching (fasciculation), difficulty chewing and swallowing, collapse/recumbency, paralysis, and death in severe cases. 

FOR MILD EPISODES 

  • Exercise the horse either by walking or longeing. Exercise stimulates adrenaline, which helps replace potassium inside the cells. 
  • Use caution because the horse could stumble and fall while sustaining muscle tremors. 
  • Supplement diet with grain (oats, dry corn-oats-barley (COB)or light corn syrup) as a source of glucose. Glucose stimulates the release of insulin and promotes potassium uptake by cells. 

FOR SEVERE ATTACKS 

  • Instruct horse owners to seek immediate veterinary attention. 

MANAGEMENT RECOMMENDATIONS 

  • A DNA test should be used to confirm the status so that appropriate treatment can be administered. 
  • The horse should be turned out as much as possible and/or placed on a regular exercise program. 
  • Do not train or work the horse during peak post-prandial plasma K+ concentration times (usually about 2-5 hours after a large meal). 
  • Other factors such as sleep, resting after exercise, physical stress, weaning, transport, surgery, anaesthesia, fasting, and dietary changes have been associated with HYPP symptoms. 

DIETARY RECOMMENDATIONS 

  • A horse suspected of being N/H or H/H should be on a low potassium diet (less than 1% in total diet and no more than 30 g potassium in any given meal). More realistically, we aim for 1.1% in total diet (with a range of 0.6 to 1.5%) or 138 grams of potassium per day, without exceeding 33 grams per meal to avoid an overload. 
  • In most horse diets, forage is the major dietary source of potassium. 
  • Feed grass hay but NOT orchard grass hay, which is high in potassium. Focus on 2nd and 3rd cuts and avoid 1st cut hay as it has a tendency to be richer in potassium, especially in cases of cold and humid springs. Avoid feeding legume hays (alfalfa and clover). 
  • It is recommended to have forage tested for actual potassium content. Soaking the hay may be beneficial to leach out some of the potassium when dealing with higher potassium hays. 
  • Do not feed electrolytes containing potassium. 
  • Avoid feeding high levels of cane molasses, soybean meal or bran mashes as these may contain high levels of potassium. 
  • Small, frequent meals should be provided at equal intervals throughout the day to help maintain more consistent potassium levels. At the very least, serve three meals a day with 8 hours between meals (this means 6 AM, 2 PM, and 10 PM). Slow hay feeders will help to spread out the daily forage intake. Non-molasses beet pulp can be used as a hay replacer when limited to high potassium hays. 
  • Avoid fasting or long intervals between meals as this can precipitate clinical symptoms. 
  • Horses fed a greater than 1.1% potassium diet over time (14 days) appear to adapt and have less severe symptoms after meals. Change diet components slowly, especially when the new diet consists of a higher potassium hay. Take at least 14 days to make the change. 

SUGGESTED PURINA PRODUCTS 

FEED NOTES 

  • Control circulating levels of potassium by limiting potassium intake. 
  • Increased nonstructural carbohydrate intake will stimulate insulin release, which promotes potassium uptake by cells. 

Equilibrium Pro Plus (0.85% potassium) 

ALTERNATIVES 

Hulless Oats with Easy Balance (1% potassium) 

Simplici-T Concept 

SUPPLEMENT 

Consider using Pur-Athlete as a high calorie source. 

FEED RATE PROTOCOL NOTICE 

This feeding protocol described here pertains only to Cargill Limited Horse Feeds. There is not established feeding protocol that all feed companies must follow. Purina provides two feeding rates on their tag a “Minimum” and a “Purina Superior”. The “Minimum” meets the levels established by the NRC Nutrient Requirements of Horses (2007), which will prevent all classic nutritional deficiencies. The “Purina Superior” is a greater level of fortification that promotes an optimal level of performance and immunity. By no means does that imply “Minimum” is subpar, and for the non-competitive horse, that stays home year-round and has no health issues there is probably no need to exceed this level. However, if you are feeding a truyear-roundthlete, with all the immune stresses associated with that level of competition, then the “Purina Superior” level is paramount to ensure an optimal level of performance and immunity. 

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