If you’ve looked at a stallion ad or sale listing recently, you’ve probably seen something like: “Panel N/N.”

For years, that meant a 5-panel test. Today, most Quarter Horse–type horses are tested for eight genetic diseases, not five. Understanding what those tests cover, and how inheritance works, is especially important if you’re breeding.

Let’s break it down.

What Is the Current 8-Panel?

For Quarter Horses and related lines, the commonly tested genetic diseases now include:

1. HYPP – Hyperkalemic Periodic Paralysis
2. HERDA – Hereditary Equine Regional Dermal Asthenia
3. GBED – Glycogen Branching Enzyme Deficiency
4. PSSM1 – Polysaccharide Storage Myopathy Type 1
5. MH – Malignant Hyperthermia
6. MYHM – Myosin-Heavy Chain Myopathy
7. IMM – Immune-Mediated Myositis
8. LWO – Lethal White Overo Syndrome

When a horse is listed as N/N, it means the horse tested negative for the specific disease being referenced. If a seller says “5-panel N/N,” that does not automatically mean the horse has been tested for all eight. It simply means they were tested for the original five.

Clarity matters. Always confirm which diseases were included in the test.

Dominant vs. Recessive: Why It Matters in Breeding

This is where breeding decisions become serious.

Autosomal Recessive Diseases

With recessive conditions, a horse must inherit two copies of the defective gene, one from each parent, to be affected.

If a horse tests:

• N/N → Clear
• N/HRD (or N/GBED, etc.) → Carrier
• HRD/HRD → Affected

Carriers are typically normal and healthy. The risk appears when two carriers are bred together.

If both parents are carriers, there is:

• 25% chance of an affected foal
• 50% chance of a carrier foal
• 25% chance of a clear foal

Recessive diseases in the 8-panel include:

• HERDA
• GBED
• LWO

This is why testing matters. Two healthy-looking horses can produce a severely affected foal if both carry the same recessive mutation.

Autosomal Dominant Diseases

With dominant conditions, a horse only needs one copy of the mutation to be affected.

If a horse tests:

• N/N → Clear
• N/HYPP (or N/PSSM1, etc.) → Affected

There is no “safe carrier” with dominant diseases. If the gene is present, it can express and can be passed to offspring.

Dominant diseases in the 8-panel include:

• HYPP
• PSSM1
• MH
• MYHM
• IMM

Breeding a horse that carries a dominant mutation carries a direct risk of producing affected offspring. Some conditions vary in severity, but the genetic risk remains.

Why Panel Testing Matters for Breeders

If you are breeding horses, panel testing is not optional. It is responsible.

It protects:

• The health of the foal
• The reputation of your program
• Your buyers
• Your long-term bloodlines

Breeding two carriers of a recessive disease is preventable. Ignoring dominant mutations without transparency is avoidable.

Genetic testing allows informed decisions.

Why It Matters in Sale Listings

Even for geldings and performance horses, disclosure matters.

Buyers want to know:

• Whether long-term management is required
• Whether the horse carries breeding potential
• Whether there are risks tied to certain lines

Clear genetic information builds credibility. Avoiding the topic raises questions.

A Balanced Perspective

Genetic testing is not about eliminating bloodlines or creating fear. Many exceptional performance horses carry certain genes. The key is understanding inheritance and breeding thoughtfully.

The goal is not perfection.

The goal is healthy horses and informed decisions.

Final Thoughts

Panel testing is simply information.

Know which diseases were tested.
Understand the difference between dominant and recessive.
Make breeding decisions intentionally.

Clear information protects everyone involved.

And in an industry built on reputation, that matters.