Last Updated on February 22, 2022 by Allison Price
Hyperkalemic Periodic Parlysis (HYPP), a rare genetic disease, can be traced back only to one quarter horse sire named Impressive. This condition affects more than 4% of all quarter horse breeds.
It can also be found in quarter horse breeds. All of them are derived from Impressive. Impressive, a champion halter horse who went on to have a long and successful breeding career, was also a champion halter horse. Impressive was a sire to 2250 foals, many who went on to become champions. In a matter of years, however, many Impressive’s foals began to experience muscle weakness, muscle twitching and complete paralysis. This was the cause of HYPP. This disorder also has other symptoms such as:
- Colic symptoms such as colic, “tying up”, or feeling like you are suffering
- Tingling in the body
- Third eye prolapse
- Loud breathing sounds
- Tolerance is a virtue
- Stiffness in the muscles
The HYPP disorder affects muscle function by interfering with sodium ion channels in the muscles. It can also affect the potassium balance of the blood. The sodium ion channels that supply the muscles cells with their sodium become “leaky” due to this disease. When triggered by fluctuations in potassium in the blood, these cells contract uncontrollably and may even cause paralysis. Paralysis of the muscles controlling breathing and heart function can cause death.
Many people mistake HYPP for “tying up”. This is understandable as tying down resembles HYPP, which has similar painful, continuous muscle cramps. Tying up can happen either after or during strenuous exercise. HYPP symptoms can occur at any time the horse is resting, but are often more noticeable after a stressful event such as transport or illness. HYPP can appear suddenly to horse owners who are not prepared. We do know that HYPP occurs when there is too much potassium in the blood.
Dietary management is an important aspect of caring for a horse with HYPP. Low potassium intakes are strongly associated with HYPP. Research suggests that HYPP horses should receive no more than 1.5% of their total food and that individual meals should not exceed 33g of potassium. This is difficult because hays tend to be higher in potassium than commercial feeds or cereal grains. For HYPP horses, it is best to avoid feedstuffs with higher potassium levels, such as:
- Brome grass
- Kentucky bluegrass
Safe pasture grazing is a common option for HYPP horses. The high water content of the grass will usually compensate for any potassium excess.
Some hays can be considered safer than others, but they can trigger HYPP if they exceed the low potassium threshold. Because hays can vary in their quality and amount of potassium depending on where they were grown, how much rainfall or irrigation was done, the fertility of the soil and other factors, HYPP can be triggered. It is a good idea to have your hay tested for potassium.
Remember that different commercial feeds have different potassium levels. Owners of HYPP horses should check the feed tag and contact the company to verify the potassium levels. Tribute (r-) includes potassium in all of our nutritional values. Some feeds have less than 1% total potassium.
- Kalm ‘N EZ(r) Pellet
- Kalm ‘N EZ(r) GC Plus
- Kalm ‘N EZ(r) Textured
- K Finish(r)
- Wholesome Mixes (tm), Performance
It is not possible to treat HYPP by feeding HYPP horses hays and commercial feeds. It is recommended that you reduce the amount of meals and give your HYPP horse a minimum of four meals per day. Also, it is recommended that you allow your horse to rest between meals for as long as possible. This will reduce the horse’s circulating potassium levels. You will see a decrease in potassium levels and symptoms of HYPP if you eat smaller and more frequently throughout the day.
Genetic testing is the only method to determine if your horse may be a HYPP-carrier. If you suspect your horse of being HYPP, a veterinarian will evaluate him. Your horse may also benefit from other treatments.