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Hereditary Equine Regional Dermal Asthenia (HERDA)


→ Skin detachment causing severe lesions and ulcerations.

Instructions for ordering:

  1. Enter the information of the first horse for which you want to order the test
  2. Add to cart
  3. Go to cart to check out, or
  4. Enter the information for a second horse
  5. For sample collection follow the instructions here.
  6. You can use this template to send in hair samples.
  7. Please also send the completed order form together with the samples.

For a breeder or veterinarian discount please contact us before ordering.

Any information you include here is optional, but will be included on the certificate of results (except “Additional info”).

Enter the name of your animal
Enter your animal's date/year of birth
Enter the breed name
Enter the registration number if known
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Is there anything else you would like to tell us about your horse? Reason for testing, symptoms etc.?

General Information

  • First symptoms may be seen at the age of 1,5 years after horses are under the saddle.
  • Areas under pressure (saddle, etc.) are particularly affected, and the skin trauma is difficult to heal.
  • Affected horses are usually euthanized due to poor quality of life.
  • Defect in the connective tissue results in skin splitting, tearing and separating from underlying layers.


  • Loose sloughing skin
  • Lesions and ulcerations/cysts especially in dorsal area
  • Slow healing

Inheritance and Genotypes

→ HERDA is an autosomal recessive hereditary disease, meaning that horses with only one copy of the genetic variant (N/herda) are clinically normal carriers while horses with two copies of the genetic variant (herda/herda) are affected.

Genotype: The horse is: Effects:
N/N normal. The horse does not have any copies of the genetic variant causative for HERDA and therefore cannot pass it on to any offspring.
N/herda a carrier. The horse is clinically healthy. The genetic variant causative for HERDA will be passed on to its offspring with a probability of 50%.
herda/herda affected. If the horse lives long enough to reproduce, the genetic variant causative for HERDA will be passed on to all offspring. All offspring will be clinically normal carriers (N/herda).


  • Carriers may be bred to normal animals (N/herda x N/N) without any risk of producing affected offspring. The offspring should also be tested before breeding to determine if they are carriers or normal.
  • Breeding two carriers (N/herda x N/herda) is not recommended due to the possibility of 25% of the offspring being affected.
  • Affected animals (herda/herda) should not be used for breeding.


Tryon RC, White SD, Bannasch DL. Homozygosity mapping approach identifies a missense mutation in equine cyclophilin B (PPIB) associated with HERDA in the American Quarter Horse. Genomics. 2007 Jul;90(1):93-102. DOI: 10.1016/j.ygeno.2007.03.009.

Further information is available at Online Mendelian Inheritance in Animals.

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