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Considerations for an HYPP N/H Horse

December 10, 2012

When it comes to buying a horse who’s an HYPP carrier, there are some things to consider.

Ask an ExpertQuestion:

I am looking at a horse to purchase. He is HYPP N/H. What special considerations should I look at, as he has never had an episode and is now 6 years old? What are the chances that he will eventually show signs? I am looking at this horse for a 10-year-old rider.


the answer to this question, the American Association of Equine Practitioners consulted Dr. Kerry Beckman.


Possible results of HYPP testing are H/H (double positive), N/H (heterozygous) or N/N (normal).  N/H horses are also referred to as HYPP “carriers,” because they carry the disease in their genes but don’t always exhibit symptoms. Usually, a horse will shows signs of HYPP during the first few years of life, especially when training is intense. However, there are documented cases of horses showing signs of their first HYPP attack late in life. There is no way to predict if a N/H horse will show signs of HYPP during his or her lifetime.

I recommend that all American Quarter Horses be managed as if they have a tendency toward having HYPP attacks. Dietary management is extremely important in the management of affected horses. Dietary adjustments include:

  1. Avoiding high potassium feeds such as alfalfa hay, brome hay, canola oil, soybean meal or oil, and sugar molasses and beet molasses, and replacing them with Timothy or Bermuda grass hay, grains such as oats, corn, wheat and barley, and beet pulp.
  2. Feeding several times a day.
  3. Exercising regularly and/or being allowed frequent access to a large paddock. If an attack has been documented, treatment of the horse with acetazolamide (under veterinary supervision) can also be helpful.

You are wise to investigate the potential health problems of a horse before you purchase him. You may also consider screening the horse for other genetic diseases. AQHA offers a five-panel genetic disease screening test through the University of California-Davis Veterinary Genetics Laboratory.

The test will screen for five potentially fatal genetic diseases often found in Quarter Horses:

  • Glycogen branching enzyme deficiency (GBED);
  • Hereditary equine regional dermal asthenia (HERDA);
  • Hyperkalemic periodic paralysis (HYPP);
  • Malignant hyperthermia (MH); and
  • Polysaccharide storage myopathy (PSSM).

The five-panel test is $85 for AQHA members and $125 for nonmembers. Call AQHA at (806) 376-4811 to secure your test for your horse.

— Dr. Kerry Beckman, member of the American Association of Equine Practitioners