🧬 Vet’s 2025 Guide to HERDA in Horses (Hereditary Equine Regional Dermal Asthenia)

By Dr Duncan Houston BVSc

1. What Is HERDA?

HERDA, or hereditary equine regional dermal asthenia (also known as hyperelastosis cutis), is a genetic skin disorder affecting collagen integrity—especially in Quarter Horses and related breeds—causing fragile, stretchy skin prone to tearing, particularly along the back and shoulders :contentReference[oaicite:3]{index=3}.

2. Genetics & Inheritance

• Autosomal recessive mutation in the PPIB gene, altering collagen folding :contentReference[oaicite:4]{index=4}.
• Two copies (HRD/HRD) = affected; one copy (N/HRD) = carrier; no copies (N/N) = normal :contentReference[oaicite:5]{index=5}.
• Traceable to Poco Bueno in Quarter Horse bloodlines, especially cutting-horse lines where ~3–4% of horses are carriers, up to ~28% in some subsets :contentReference[oaicite:6]{index=6}.

3. Clinical Signs

Symptoms generally emerge between ages 2–4 when training begins:

• Excessively stretchy skin over withers and back, easily tearing under saddle :contentReference[oaicite:7]{index=7}
• Painful, slow-healing wounds and widespread scarring :contentReference[oaicite:8]{index=8}
• Possible chronic issues such as seromas, hematomas, corneal ulcers, even mild cardiac valve defects :contentReference[oaicite:9]{index=9}.

4. Diagnosis & Testing

• Clinical diagnosis via history and lesion pattern when breaking or saddling begins :contentReference[oaicite:10]{index=10}.
• Definitive diagnosis by genetic testing or skin biopsy—DNA testing is more accurate and identifies carriers :contentReference[oaicite:11]{index=11}.
• Testing performed with mane/tail hair roots or blood—with results N/N, N/HRD, HRD/HRD :contentReference[oaicite:12]{index=12}.

5. No Treatment, Management Only

There’s currently no cure. Management focuses on comfort and wound care:

• Gentle bandaging, protective blankets, stall rest.
• Prompt wound cleaning, topical antimicrobials, frequent vet reviews.
• Most affected horses cannot be ridden and are often euthanized due to quality-of-life concerns :contentReference[oaicite:13]{index=13}.
• One case reported mild signs in adult homozygous—clinical severity may vary :contentReference[oaicite:14]{index=14}.

6. Breeding & Prevention

• Genetic testing is essential for breeding decisions—carriers should not be bred together (25% chance producing affected foal) :contentReference[oaicite:15]{index=15}.
• AQHA and other registries mandate HERDA testing—breeding only clear-to-clear or clear-to-carrier to avoid affected offspring :contentReference[oaicite:16]{index=16}.
• Goal: gradually reduce HERDA frequency in bloodlines and eliminate clinical cases :contentReference[oaicite:17]{index=17}.

7. Welfare & Ethical Considerations

For affected horses, their fragile skin often makes riding impossible. The majority are eventually euthanized between ages 2–4. Decisions should centre on welfare, quality of life, and long-term care costs :contentReference[oaicite:18]{index=18}.

8. Case Studies & Research Insights

Research from UC Davis, Mississippi State and Cornell confirms HERDA’s molecular cause: mutation p.G39R in PPIB that alters collagen cross-linking and tensile strength :contentReference[oaicite:19]{index=19}.

One case of an adult working horse with mild clinical signs suggests variable expression; genetic testing revealed full homozygosity :contentReference[oaicite:20]{index=20}.

9. Ask A Vet Support 🩺

At Ask A Vet, we help with herd-wide genetic testing, breeding advice, wound management plans, and quality-of-life discussions. Download our app for expert support on HERDA and proactive breeding strategies.

10. Quick Reference Table

11. Final Thoughts

HERDA is a serious genetic disorder, but responsible breeding and early detection through genetic testing allow owners to eliminate it from their herd. While there’s no cure, careful management can provide affected horses with comfort. For help with genetic planning, diagnosis, or long-term care, partner with Ask A Vet for expert support. Download our app today for guidance in 2025 and beyond! ❤️