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Testing for genetic diseases before breeding your horse - GBED

Newborn paint foal
Newborn paint foal
Photo by B. Halpenny

Glycogen-Branching Enzyme Deficiency (GBED) is a fatal genetic disease affecting mostly the Quarter Horse breed but is also found in related breeds, the Appaloosa and Paint breeds for example. This disease affects newborn foals and their ability to store sugar molecules. The branched form of glycogen cannot be stored as the foals that are affected lack the enzyme needed to perform this function. The heart, brain and skeletal muscles are all affected and cannot work without the sugars they use for fuel, and late term abortion or death results during or soon after birth.

This disease is an not connected to any sex genes, so it affects males and females equally. It is also a recessive gene so horses can be carriers and pass on affected genes without ever showing the symptoms themselves.

Some foals have lived to be be 18 weeks old, but all foals that have ever been diagnosed with GBED have either died or been euthanized due to the weakness that results. GBED was difficult to diagnose for a time because other diseases that affect foals may have similar symptoms such as:

  • Low body temperature
  • Seizures
  • High respiratory rate and weakness of the muscles used to breathe
  • Contracted tendons in all four legs
  • Overall weakness and the inability of the foal to get up from lying on its side

If you suspect your foal has GBED or to get your horse tested visit the UCDavis Veterinary Genetics Laboratory website and download the form there. The completed form, a fee of $50 and a sample of hair, including the roots, are all that is needed to ensure that your animal can be bred without passing on this disease.


  • K-B.ster 5 years ago

    Love it. Bridget's writing is full of feeling and information.

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