HYPP in Horses and Muscular Health

Updated July 6, 2024 | By: Dr. Lydia Gray
Chestnut Quarter horse

What is HYPP in Horses?

Hyperkalemic periodic paralysis (HYPP) is a genetic disease affecting Quarter Horses (and Quarter Horse crossbreds), American Paint Horses, and Appaloosas from the Impressive bloodline. This disease causes a dysfunction in how the electrolytes sodium and potassium move in and out of muscle cells.

Genetics and Signs of HYPP in Horses

Horses can have one or two genes for HYPP, and thus can show a varying degree of signs, from mild to severe. Mild signs generally include sweating and twitching in the neck, shoulders, and flank, while more severe signs may consist of muscle trembling and cramping, which can cause the horse to sway, sit, or even go down.

The entire event lasts anywhere from 15 to 60 minutes and horses can die during episodes due to cardiac or respiratory arrest. Due to the risk of personal injury, only experienced adults should ride and handle horses with HYPP.

Supplements That May Lend Support

Horses that suffer from HYPP may benefit from antioxidants such as Vitamin E as well as muscle supplements specifically designed to help muscle cells recover and rebuild.

However, it is very important to maintain a low level of potassium in the diet, so check with a veterinarian before adding any supplement, especially electrolyte, multi-vitamin/mineral, and kelp products.

Plain salt is an excellent alternative to feeding complete electrolyte supplements, which often contain potassium.

Possible Diagnostic Tests for HYPP

Because an imbalance in the blood levels of sodium and potassium can only be seen during an episode, horses related to the Impressive sire that demonstrate muscle tremors, weakness or collapse should be tested for HYPP. This involves having a DNA test of mane or tail hair performed on a horse that either has Impressive in the pedigree or has shown any of the signs described above.

HYPP Treatment Options and Prevention

quarter horse stallion trotting outside
Image courtesy of Alana Harrison Photography.

Prescription Medications Available

The medication most commonly used to prevent HYPP episodes is the human drug acetazolamide, which is a diuretic that helps filter potassium from the blood. If an owner recognizes that an episode is about to occur, they can gently exercise the horse or try feeding something with sugar in order to ward off the attack.

Veterinarians that are present during an episode may give acetazolamide and other medications intravenously.

Management Suggestions & Things to Avoid Feeding Your Horse

HYPP horses should not be given alfalfa hay, brome hay, molasses, soybean meal, or any other feedstuffs - such as electrolytes - that are high in potassium.

Later cuts of timothy or Bermuda grass hay, grass pasture, beet pulp, and grains such as corn, oats, wheat, and barley contain low amounts of potassium and are generally safer to feed.

Feeding multiple small meals throughout the day so that no one meal exceeds 33 grams of potassium is also advised. A veterinarian can further help you design a nutritional program that is complete and balanced yet contains the minimum amount of potassium necessary.

A consistent exercise program - along with regular turnout on grass pasture - is also important in preventing bouts of HYPP.

Video on HYPP Genetics, Testing & Preventing Episodes

In this Ask the Vet video, Dr. Lydia Gray explains this muscular condition, signs of HYPP, plus what to feed and not to feed your horse that's been diagnosed.

SmartPak strongly encourages you to consult your veterinarian regarding specific questions about your horse's health. This information is not intended to diagnose or treat any disease, and is purely educational.