Horses with hyperkalemic periodic paralysis (HYPP) need careful dietary management to reduce or eliminate its characteristic muscle dysfunction attacks. While diet won't eliminate all signs, it can make an affected horse more comfortable and useful, and even save his life.

HYPP is a genetic muscle disorder tracing back to the Quarter Horse stallion Impressive, although not all descendants have the disease. Genetic testing is highly recommended and is almost 100% diagnostic. A horse can show clinical signs even if the problem is inherited from only one parent.

The HYPP genetic defect disrupts the function of tiny gateways in muscle cell membranes called sodium channels. Instead of opening and closing normally, they stay open during an HYPP episode, allowing an uncontrolled flow of sodium ions into cells. Normal functioning of the cells is altered, which results in the signs of HYPP--weakness, muscle twitching, shaking, trembling, and paralysis of muscles in the upper airway. The most severe threat to these horses is death from heart failure.

Potassium is linked to clinical signs, so Judith Reynolds, PhD, PAS, an equine nutritionist at ADM Alliance Nutrition, who has researched feeding HYPP horses, offers this advice: "To reduce episodes, it is important to limit the amount of potassium fed in each meal."

Limiting Potassium

Potassium is almost 100% absorbable, and since potassium is abundant in common horse feeds, horses' bodies are constantly trying to get rid of excess potassium, she explains. So, reducing the amount in the overall diet can be tricky.

When developing a diet for an HYPP horse, a veterinarian and/or nutritionist should be consulted to ensure the diet meets all necessary nutrient requirements while cutting potassium to 1.1% of the total diet. At least three feedings per day, each with less than 33 grams of potassium, should be given, Reynolds advises. This helps avoid a potassium spike in the bloodstream from a large amount of potassium being fed in a single meal.

Non-working horses need 0.3-0.4% potassium in the total diet, and heavy exercise can double the requirement. Pasturing an HYPP horse on low-potassium forages can allow him to meet many of his dietary requirements without potassium spikes. Also, the exercise he gets on pasture can reduce clinical signs. When hay is fed, Reynolds prefers an alfalfa-grass mix. Beet pulp is a good partial forage option, since it contains 0.2-0.3% potassium. Oats, wheat midds, and oat hay are low-potassium feeds, while alfalfa hay, soybean meal, and molasses are high in potassium and must be fed sparingly. Most grass forages, wheat bran, soybean hulls, and stabilized rice bran are medium-potassium feeds. They can be used in diets for HYPP horses as long as the total ration is properly balanced and fed in multiple small meals throughout the day, she says.

Whole oats are an option for horses not sensitive to starch in the diet, she says. Sweet feed should be avoided since the molasses contains a lot of potassium. Feeding fat can provide needed energy without adding potassium to the diet.

When feeding anything to an HYPP horse, including supplements, ask for a fixed formula in which ingredients used remain relatively constant, Reynolds advises. Check labels for sources of potassium. When in doubt or if the potassium content is not listed, call the manufacturer. Avoid supplements with kelp and electrolytes that contain potassium, which includes most products on the market.

Management Tips

  • Salt and water are important for affected horses, since a lack of salt and/or water reduces urination, which is how the horse excretes excess potassium.
  • A horse is more prone to an attack two to five hours after a meal, when potassium is at its peak in the blood, Reynolds says. She advises monitoring the horse and avoiding exercise during this time.
  • The prescription diuretic acetazolamide promotes excretion of excess potassium and is often recommended by veterinarians, especially for young HYPP horses being fed high-protein feeds for growth, since these feeds usually contain more potassium than is recommended for these horses, says Reynolds.

Your veterinarian and/or nutritionist can help you maintain your HYPP horse to avoid clinical signs and episodes associated with this disease. Diet cannot solve all problems associated with HYPP, but proper nutrition can allow some of these horses to lead normal, athletic lives.

More information: See HYPP under Ailments/Syndromes at TheHorse.com, or e-mail Reynolds at Judy_Reynolds@admworld.com.

NORMAL HORSE/HOMOZYGOUS HYPP CROSS
 
n
n

All offspring affected

100% heterozygous (nH)

H
nH
nH
H
nH
nH

 

NORMAL HORSE/HETEROZYGOUS CROSS
 
n
n

50% of offspring affected

50% heterozygous (nH)
50% normal (nn)

n
nn
nn
H
nH
nH

 

TWO HETEROZYGOUS HORSES CROSSED
 
n
H

75% of offspring affected

25% homozygous (HH)
50% heterozygous (nH)
25% normal (nn)

n
nn
nH
H
nH
HH

 

HOMOZYGOUS HYPP/HETEROZYGOUS CROSS
 
H
H

All offspring affected

50% homozygous (HH)
50% heterozygous (nH)

n
nH
nH
H
HH
HH

 

About the Author

Sarah Evers Conrad

Sarah Evers Conrad has a bachelor’s of arts in journalism and equine science from Western Kentucky University. As a lifelong horse lover and equestrian, Conrad started her career at The Horse: Your Guide to Equine Health Care magazine. She has also worked for the United States Equestrian Federation as the managing editor of Equestrian magazine and director of e-communications and served as content manager/travel writer for a Caribbean travel agency. When she isn’t freelancing, Conrad spends her free time enjoying her family, reading, practicing photography, traveling, crocheting, and being around animals in her Lexington, Kentucky, home.

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