⚠️ Vet’s 2025 Guide to Equine Hyperkalemic Periodic Paralysis (HYPP)

By Dr Duncan Houston BVSc

1. What Is HYPP?

Hyperkalemic Periodic Paralysis (HYPP) is a serious genetic muscle disorder caused by a mutation in the SCN4A gene, which disrupts sodium channels in muscle cells. This leads to episodes of elevated blood potassium, causing muscle over‑excitability or paralysis, sometimes with life‑threatening respiratory or cardiac effects :contentReference[oaicite:3]{index=3}.

2. Genetics & Bloodlines

• HYPP is inherited in an **autosomal dominant** manner—with just one copy of the mutated gene (N/H) causing the disease; two copies (H/H) often result in more frequent and severe episodes :contentReference[oaicite:4]{index=4}.
• First traced back to the Quarter Horse sire **Impressive**, HYPP is most common in **Quarter Horses**, **Paints**, **Appaloosas**, and their crosses :contentReference[oaicite:5]{index=5}.
• Affected bloodlines are now under mining via mandatory **genetic testing** by registries such as AQHA and APHA :contentReference[oaicite:6]{index=6}.

3. Clinical Signs & Triggers

HYPP episodes may present as:

• Muscle twitching or trembling, heaviness in hindquarters, difficulty rising
• Excess sweating, rapid breathing or heart rate, loud respiratory noises if airway muscles are affected
• Weakness to collapse; during episodes horses remain conscious—risking injury :contentReference[oaicite:7]{index=7}.

Common triggers:

• High‑potassium feeds (alfalfa, molasses), stress, fasting then feeding, strenuous exercise, illness, anesthesia, temperature extremes :contentReference[oaicite:8]{index=8}.

4. Diagnosis

• Clinical history and observation of episodes.
• Blood tests during an attack showing elevated potassium.
• Definitive diagnosis via **DNA testing** (mane or tail hair with roots) identifying N/N, N/H, or H/H status :contentReference[oaicite:9]{index=9}.

5. Emergency Management of an Attack

• Encourage light movement—walk slowly to help potassium shift from blood into muscles safely :contentReference[oaicite:10]{index=10}.
• Administer **oral sugar** (corn syrup or glucose) to stimulate insulin release and lower blood potassium :contentReference[oaicite:11]{index=11}.
• Keep the horse calm, in a quiet, dark area.
• Vet intervention may include:
  • IV fluids with dextrose ± calcium gluconate to stabilize muscles
  • Sodium bicarbonate in cases of metabolic acidosis
  • Diuretics like acetazolamide or hydrochlorothiazide for long-term control :contentReference[oaicite:12]{index=12}.

6. Long‑Term Management

• Maintain a **low‑potassium diet**: <1 % of total ration (use mature grass hay, beet pulp, straw-based feeds, grains like oats/barley); avoid alfalfa, molasses, soybean meal :contentReference[oaicite:13]{index=13}.
• Regular light exercise and turnout to promote potassium excretion via urine :contentReference[oaicite:14]{index=14}.
• Provide free‑choice **plain salt** and constant access to fresh water :contentReference[oaicite:15]{index=15}.
• Daily medications such as diuretics may help stabilize potassium :contentReference[oaicite:16]{index=16}.
• Monitor regularly for body condition, recurrence, and adjust protocols as needed.

7. Prognosis & Breeding Considerations

• Heterozygous (N/H) horses can lead full lives with proper care; homozygous (H/H) horses show more severe disease and may not be suitable for breeding :contentReference[oaicite:17]{index=17}.
• Registries prohibit H/H breeding; N/H individuals should only be bred to N/N horses to avoid producing affected colts :contentReference[oaicite:18]{index=18}.
• Genetic testing remains essential in breeding decisions and foal selection.

8. Prevention Strategies

• Test all foals from bloodlines tracing to Impressive.
• Eliminate H/H from breeding programs.
• Adapt feed programs to maintain stable potassium levels (0.6–1.5 %) and limit meals to <33 g K⁺ each :contentReference[oaicite:19]{index=19}.
• Manage stressors: consistent routine, regulated exercise, avoid sudden changes.

9. Ask A Vet Support 🩺

At Ask A Vet, we support owners with:

• Interpreting genetic test results and breeding advice
• Developing low‑potassium nutrition plans
• Emergency protocols and vet‑led follow-ups
• Monitoring medication regimens and behavioral patterns
• Breed‑specific turnout and exercise guidance

Download the Ask A Vet app now to keep your HYPP horse safe, sound, and strong in 2025! ❤️

10. Quick Reference Table

11. Final Thoughts

HYPP is a manageable chronic condition with informed care. Through genetic testing, dietary control, and emergency preparedness, affected horses can live long, healthy lives. Connect with Ask A Vet for tailored support—from nutrition to crisis care—ensuring your horse thrives in 2025 and beyond. ❤️