Skeletal Atavism TestTM

Skeletal Atavism is a heritable defect leading to abnormal development of the skeleton structure in the foals’ limbs. It is caused by two different mutations. 

Skeletal Atavism TestTM is the genetic test that identifies carriers and the result of the test can be used by owners to prevent the birth of affected foals and to reduce the frequency of the mutations among Shetland ponies and American miniature horses around the world.




Heritable defect leading to incorrect skeletal structure and impaired movements

  • The defect is an abnormal development of the legs, which can occur in both front and hind legs
  • Ulna (next to the radius) and fibula (next to tibia) is developed throughout their full length. Normally, the distal part of these bones should fuse to the radius and tibia respectively as the horse grows
  • This leads to a disturbed growth of adjacent bones, severe angle anomalies and deformation of the front knee and hock
  • Typical characteristics of horses with Skeletal atavism are short legs, a low rectangular shape body, narrow at knees (knock-kneed), cow hocked, clubfoot, toe out and impaired movements
  • The pattern of movement become gradually worse as the foal is growing and in most cases, the horse has to be euthanized within six months


Wanja all

Photograph of foal with Skeletal atavism. Observe the outward bending of the leg and the short distance between hind knee and hock as well as front knee and elbow.






Abnormally long ulna (white arrow) considering the age of the horse. The distal part  of ulna is normally fused to the radius.



Rntgen krum


Photograph of an older horse with the defect. The pattern of movement displayed by the horse was clearly affected.




SA cross

Horses with normal legs may carry one of the mutations that cause Skeletal atavism. Only foals that inherited the mutations from both parents will develop Skeletal atavism. It is therefore very important to never cross two carriers to each other.

Click on the picture to enlarge or click here for a more detailed description about the inheritance of Skeletal atavism.


Important information to owners before you order a test

The identity of the samples sent in for testing must always be verified. There are different methods to achieve this. Read about the options under ”Test your horse”. 

The cost of the test and how to order is found at respective laboratories webpages.


Popular science articles

Diagnostic DNA test for the developmental disorder "Skeletal atavism"




If two carriers are crossed, the risk of getting a foal with Skeletal atavism is 25%.

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Test your horse

The DNA tests are preformed on a hair sample or a cheek swap depending on which laboratory is used. Order sample kits and follow the easy instructions for sampling. 


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Skeletal Atavism TestTM on Facebook

On the Facebook page Horse Skeletal Atavism TestTM you as a horse owner may post a picture of your horse together with the test result.

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Horse Skeletal Atavism Test