If you have a horse with hyperkalemic periodic paralysis (HYPP), you should know that your horse requires careful management. Hyperkalemic periodic paralysis, (HYPP) is an inherited metabolic disease of the muscle which is caused by a genetic defect. Prevalent in American Quarter horses, it is expressed in the muscles of afflicted horses. It is a “point mutation,” (a type of mutation that causes a single nucleotide base change, insertion, or deletion of the genetic material, DNA or RNA.) that exists in the sodium channel gene and is passed on to offspring. Characterized by sporadic attacks of muscle tremors (shaking or trembling,) weakness and/or collapse and excessive potassium concentrations in the blood, one of the most important ways to manage the horse is to make dietary adjustments.
Blood potassium levels cause many of the debilitating symptoms of HYPP. Limiting a horse’s potassium intake is one of the most effective management methods used for keeping HYPP-positive horses free of clinical symptoms.
The type of forage fed to a horse with HYPP is critical. Forage is typically the horses main dietary source of potassium. The amount of potassium in different types of forage varies significantly according to plant species, soil characteristics of the field in which forage was originally grown, rainfall during the growing period, length of time since cutting and stage of maturity at harvest. It is highly recommended that if you have a horse with HYPP, that you have your forage assessed through nutritional analysis. This can help you select hay with low potassium content and eliminate any which may be too high. If you are struggling to understand forage analysis results, ask your veterinarian for assistance.
Although an allowance should be made for natural variance, it is generally found that grass forages have lower potassium content than legume forages (alfalfa.) Bermuda grass, prairie grass, and timothy are the most suitable forage choices for horses diagnosed with HYPP, whereas alfalfa should be avoided. It is recommended that hay is soaked prior to use as this may help reduce the natural potassium levels. Unlike hay, grass at pasture does not generally threaten the health of the horse. Its higher water content helps keep potassium absorption low.
If you are feeding a manufactured mixture or extruded cube to your horse, the potassium content should be clearly listed on the bag. Ingredients such as soybean meal, soybean or canola oil, dehydrated alfalfa (Lucerne,) and molasses contain significant amounts of potassium and should be avoided by owners of horses with HYPP. Feed which contains oats, corn, barley, and “unmolassed” or rinsed beet pulp will generally be safer options.
When feeding an HYPP-positive horse, the daily rations should be broken down into two to three meals over the course of the day. Forage should be provided during these intervals in a large enough portion to last until the next meal. If grain is fed (where body condition cannot be maintained on forage alone,) this should be broken down into two or three small portions during the day. This benefits the horse because spreading out meals throughout the day will reduce fluctuations in blood insulin concentrations that in turn help maintain normal blood glucose and potassium concentrations. Insulin promotes the uptake of potassium by the muscle cells, thus reducing serum potassium concentrations.
It is not recommended to ever use supplemental electrolytes with HYPP-positive horse as these contain high levels of potassium. If rehydration is required, only plain salt or potassium-free products should be used.
HYPP (hyperkalemic periodic paralysis) is a complex condition, often seen in American Quarter Horses. With careful dietary management designed, you can help control symptoms in your horse.
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