Feeding the HYPP Horse
Dr. Martin Adams, PAS – Equine Nutritionist for Southern States
Hyperkalemic Periodic Paralysis (HYPP) is an inherited genetic defect that affects muscle function in the horse. This genetic defect interferes with a protein that disrupts the natural opening and closing of a sodium ion channel in the membrane of muscle cells. This disruption changes the voltage current of muscle cells, causing uncontrolled muscle twitching and weakness, and leakage of potassium of the cell. Potassium leakage from the muscle cell affects the voltage current of the cell after contraction. The potassium remains in the extra-cellular fluid and prevents the muscle cell from relaxing. Symptoms of HYPP in the horse include muscle weakness, twitching (fasciculation) and paralysis.
Symptoms can vary widely among horses, from mild muscle tremors to death from cardiac arrest or respiratory failure. A test is available to identify horses that carry the defective gene. HYPP horses are sensitive to high levels of potassium in their diets, as well as sudden changes in potassium levels that can be brought on by stress or pregnancy and dehydration
Acetazolamide is a prescription diuretic that is often recommended by veterinarians for the horse with HYPP, especially young horses fed higher protein diets for growth, since these feeds usually contain higher levels of potassium. Salt and water are especially important for these horses, since a lack of salt or water reduces urination, which is how the horse secretes potassium. Provide continuous access to a clean source of water and loose salt or a pure salt block (white) to a horse with HYPP. Some mineral blocks can contain added potassium, so be sure to read the guaranteed analysis and ingredient list before providing them to an HYPP horse. Most electrolytes contain added potassium, so avoid their use as well.
Most veterinarians recommend having a bottle of Karo Syrup on hand to treat the HYPP horse if it is showing mild symptoms. Oral administration of Karo Syrup lowers the potassium level by providing a source of sugar in the circulating bloodstream to allow an increased glucose and potassium absorption by raising the insulin secretion rate in the horse.
Symptoms of HYPP:
- Muscular fasiculations (tremors) down the rib cage and under the flank.
- Eversion of the third eyelid.
- Horse exhibiting signs of colic or “tying-up”.
- Elevated blood serum potassium levels, 3-4 milliequivalents per liter (mEq/L) is a normal serum potassium, but can be as high as 12 mEq/L with a severe episode.
- Tetany, paralysis and death in severe cases.
Hay can have a much higher potassium level than commercial horse feeds or feedstuffs like oats. Feeding large amounts of Triple Crown Growth for growing horses, or Triple Crown Senior, Triple Crown Complete or Legends Performance Pelleted or Maturity for mature horses, with a limited amount of hay, allows for more control over the potassium level of the total diet. Grass hay usually contains a lower potassium level than alfalfa hay so only grass or mixed hay is recommended for HYPP horses. Feed the limited amount of hay twice per day and the horse its feed at least two, or three to four times daily, if possible.
Here are some ways to more safely feed horses that have been diagnosed or suspected of having HYPP by keeping dietary potassium levels low, less than 1.3% (as fed basis). A horse is more prone to an attack two to five hours after a meal, when potassium is at its peak in the bloodstream. Avoid training or working the horse, if possible, during this time.
- For mature horses, feed whole or crimped oats (0.4% potassium) and Triple Crown 12% Supplement (0.6% potassium). Adjust the amount of oats fed to maintain proper body condition. Triple Crown Rice Bran Oil Plus (no potassium) or corn oil (no potassium) can also be safely added to the feeding program.
- If you have not tested your hay, or if the potassium level of your hay is 1.5% or more you need to limit the amount of hay you are feeding to keep dietary potassium levels low. You can contact your local or state extension specialist about testing your hay for potassium content. A test for potassium and several other minerals and nutrients should cost less than $20. Provide Triple Crown Complete (1% potassium), Legends Maturity (1% potassium), or Reliance Hay Stretcher (1% potassium) at 1% of body weight and feed only 0.5% of body weight of hay per day. This would be 10 pounds of feed and 5 pounds of hay for a 1,000 pound horse on a daily basis, which is the minimum amount of feed that should be provided for an inactive horse. For a more active horse, increase the amount of feed but not the amount of hay to keep the total dietary potassium level as low as possible.
- Another method for growing horses is to feed a limited amount of hay and Triple Crown Growth as the main part of the diet. The following table shows the amount of hay and Triple Crown Growth to feed at different ages.
Feeding Guidelines for Growing HYPP Horses (lbs per day)1
| 6 months |
550 |
9.0-11.5 |
3 |
| 12 months |
850 |
11.0-13.0 |
4.5 |
| 18 months |
1100 |
10.0-12.0 |
6 |
| 24 months |
1250 |
9.5-12.5 |
6.5 |
| Example 1: |
|
Feeding a Yearling Horse (850 pounds) Grass Hay and Triple Crown Growth.
11 pounds Triple Crown Growth (1.1% potassium)
4.5 pounds Grass Hay (1.5% potassium)
11 pounds Triple Crown Growth x .011 = .12 pounds potassium< BR > 4.5 pounds Grass Hay x .015 = .07 pounds potassum
|
|
Total Dietary Potassium = .19 pounds or 1.2% dietary potassium (.18 lbs ¸ 15.5 lbs x 100) = 1.2% (as fed basis)
|
| Example 2: |
|
Feeding a Mature Horse (1200 pounds) Triple Crown 12% Supplement, Oats and Grass Hay.
4 pounds of Oats (.4% potassium)
2 pounds of Triple Crown 12% Supplement (0.6% potassium)
14 pounds of Grass Hay (1.3% potassium)
5 pounds of Oats x .004 = .02 pounds potassium
2 pounds of Triple Crown 12% Supplement x .006 = .01 pounds potassium
12 pounds of Grass Hay x .015 = .18 pounds potassium
|
|
Total Dietary Potassium = .21 pounds or 1.1% dietary potassium (as fed basis)
|
| Example 3: |
|
Feeding a Mature Horse (1200 pounds) Triple Crown Complete and Grass Hay.
12 pounds of Triple Crown Complete, Legends Maturity or Reliance Hay Stretcher (1% potassium)
6 pounds of Grass Hay (1.5% potassium)
12 pounds of Triple Crown Complete, Legends Maturity or Reliance Hay Stretcher x .01 = .12 pounds potassium
6 pounds of Grass Hay x .015 = .009 pounds potassium
|
|
Total Dietary Potassium = .21 pounds or 1.2% dietary potassium (as fed basis)
|
| Example 4: |
|
Feeding a Mature Horse (1000 pounds) at Light Activity Triple Crown Low Starch and Grass Hay.
11 pounds of Triple Crown Low Starch (0.75% potassium)< BR > 5 pounds of Grass Hay (1.3% potassium)
11 pounds of Triple Crown Low Starch x .006 = .07 pounds potassium
5 pounds of Grass Hay x .013% = .07 pounds potassium
|
|
Total Dietary Potassium = .14 pounds or 0.9% dietary potassium (as fed basis)
|
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