10/25/2025
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✨Why every breeder, stallion, and mare owner should 8 panel test their horses ✨
If you’re breeding Quarter Horses, Paints, Appaloosas, or related breeds, 8 panel testing is VERY IMPORTANT!
It’s not just about knowing what color your foal might be or how they’ll perform — it’s about making sure they have the best chance at a healthy happy life.
The 8 panel test checks for eight known genetic conditions found in MANY different horse breeds. Some are fatal, others cause lifelong pain — but all of them can be avoided with a few simple test.
Here’s a quick breakdown of what each one means 👇
🧬 1️⃣ Glycogen Branching Enzyme Deficiency (GBED)
•Inheritance:
Autosomal Recessive (a horse MUST have TWO copies to be affected).
Explanation of Results:
* N/N —Clear, not affected, cannot pass it on.
* N/G — Carrier, not affected, can pass it to 50% of offspring.
* G/G — Affected (fatal).
GBED prevents the body from properly storing sugar (Glycogen), leaving the brain, heart, and muscle too weak to function.
Affected foals are often aborted, stillborn or die by 18 weeks.
💡 About 8-11% of Quarter Horses are carriers.
🧬 2️⃣ Hereditary Equine Regional Dermal Asthenia (HERDA)
•Inheritance: Autosomal Recessive. (A horse MUST have TWO copies to be affected).
Explanation of Results:
* N/N — Clear, not affected, cannot pass it on.
* N/HRD — Carrier, not affected, can pass it on the 50% of offspring.
* HRD/HRD — Affected, will have symptoms, will pass ONE copy to all offspring.
HERDA causes fragile, stretchy skin that tears easily — often noticed when horses are first saddled around age two. There’s no cure and most affected horses are euthanized due to the severity of the lesions.
💡 About 3.5% of Quarter Horses are carriers.
🧬 3️⃣ Hyperkalemic Periodic Paralysis (HYPP)
•Inheritance: Autosomal Dominant (ONE copy can cause symptoms).
Explanation of Results:
* N/N — Clear, not affected, cannot pass it on.
* N/H — Affected (mild to moderate symptoms), will pass it on to 50% of offspring.
* H/H — Affected (often severe), will pass ONE copy to all offspring.
HYPP causes muscle tremors, weakness, and in severe cases, paralysis or sudden death. It originated from the stallion Impressive, so descendants have to be tested in order to register them in AQHA.
💡 About 4.4% of Quarter Horses are affected.
🧬 4️⃣ Malignant Hyperthermia (MH)
•Inheritance: Autosomal Dominant (ONE copy can cause symptoms).
Explanation of Results:
* N/N — Clear, not affected, cannot pass it on.
* N/MH — Affected, has 50% chance of passing it to offspring.
* MH/MH — Severely affected, will pass ONE copy to all offspring.
MH can be triggered by Anesthesia, Stress, or Excitement — leading to dangerously high temperatures, muscle contractions, and irregular heart rhythm. It can be life-threatening, especially when combined with PSSM1 and/or MYHM.
🧬 5️⃣ Polysaccharide Storage Myopathy Type 1 (PSSM1)
•Inheritance: Autosomal Dominant (ONE copy can cause symptoms).
Explanation of Results:
* N/N — Clear, not affected, will not pass it on.
* N/PSSM1 — Affected, likely to have symptoms, has 50% chance of passing it to offspring.
* PSSM1/PSSM1 — Severely affected, will pass ONE copy to all offspring.
PSSM1 causes abnormal sugar storage in muscles, stiffness, tying-up (this can look like colic) , sweating, and reluctance to move. It’s a metabolic muscle disorder that can sometimes be managed with proper diet and exercise — but often times doesn’t work and ends with euthanasia.
💡 About 11% of Quarter Horses are affected.
🧬 6️⃣ Myosin-Heavy Chain Myopathy (MYHM)
•Inheritance: Autosomal Dominant (ONE copy can cause symptoms).
Explanation of Results:
* N/N — Clear, not affected, cannot pass it on.
* N/MY — Affected, may have symptoms, has 50% chance of passing to offspring.
* MY/MY — Likely more severely affected, will pass ONE copy to all offspring.
MYHM can cause two main issues:
•IMM (Immune-Mediated Myositis): rapid muscle wasting after immune triggers
•Non-Exertional Rhabdomyolysis: severe muscle pain unrelated to exercise.
(Immunizations can be a BIG cause of both of these)
Both cause painful muscle breakdown and require long-term management.
💡About 7% of Quarter Horses are affected.
🧬 7️⃣ Equine Juvenile Spinocerebellar Ataxia (EJSCA)
•Inheritance: Autosomal Recessive (A horse MUST have TWO copies to be affected).
Explanation of Results:
* N/N — Clear, not affected, will not pass it on.
* N/EJSCA — Carrier, not affected, has 50% chance of passing it to offspring.
* EJSCA/EJSCA — Affected (fatal).
A newly identified neurological disease (discovered in 2020) seen in Quarter Horses, Paints, Appaloosas and other related breeds. Affected foals develop severe incoordination (Ataxia) with in the first month of life and are unable to stand as the disease progresses. Sadly all cases end in euthanasia.
🧬 8️⃣ Lethal White Overo (LWO)
•Inheritance: Autosomal Recessive. (A horse MUST have TWO copies to be affected)
Explanation of Results:
* N/N — Clear, not affected, cannot pass it on.
* N/LWO — Carrier, not affected (usually has the overo coat pattern), has 50% chance of passing it to offspring.
* LWO/LWO — Affected (fatal).
Foals born with two copies are pure white and have fatal intestinal abnormalities — they cannot pass waste and die shortly after birth. Responsible breeders test before breeding two frame overos together.
📄Why testing matters?
✅ Prevents fatal or painful genetic conditions.
✅ Helps you make smart breeding decisions.
✅ Builds buyer confidence and program credibility.
✅ Protects the reputation and future of your breeding program.
✅ Saves you and your buyers time, money, and heartache.
💬 My honest opinion
As someone who cares deeply about these horses and the future of our AQHA and APHA breeds -
It’s already required that all AQHA and APHA stallions have to be panel tested, but mares are half the equation. Without testing both sides, we’re still taking unnecessary risks.
Some things I’ve had people say to me:
“Today’s clean horses will be tomorrow’s carriers.”
I understand that and we will cross that bridge when it comes.
“Well your stud is a GBED carrier and you require all mares to be at least 6 Panel tested so I’m not breeding to him”
So you would rather breed to a stud that has only been test for 5 instead of the 8 genetic conditions? You would rather chance your foal having possibly 2 copies of MYHM/IMM, EJSCA or LWO? And you don’t care that your mare may carry a genetic condition?
“I don’t want to spend money when I’m trying to make money”
But here’s the truth:
👉 If you’re breeding horses just for the money, you’re in it for the wrong reasons.
Breeding should be about bettering the breed, producing sound, healthy foals, and leaving the next generation stronger than the one before. You should also be doing it because you love it.🐴
💬 Bottom line
8 Panel testing is one of the most important tools we have as breeders. It’s quick, affordable, and could save a foal’s life! Knowledge is power — and the more we know, the better we can breed for soundness, longevity, and quality! 🐴
I’m not saying you shouldn’t breed a stallion or a mare that carries one of the Autosomal Recessive Traits what I’m saying is don’t breed them to another carrier of the same genetic condition. Why would you want those horses to suffer?
📦 If your stallion(s) or mare(s) haven’t been tested yet — now’s the time! Responsible breeding starts with the testing.
