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Testing Now Available

Distichiasis & Dwarf-Hydro Testing Form (PDF)   


Note: Only hydrocephalus and dwarfism tests generated by FHH or FHANA will be accepted by FHH.

 This is so that we can verify that the hair tested matches the parentage DNA we have on file.




Distichiasis is a condition in which the eyelashes grow from an abnormal position on the edges of the eyelids. These misplaced lashes can contact the cornea (clear ‘window’ of the front of the eye), leading to irritation and corneal ulcers, which can impact vision.
UC Davis

This gene is fairly common in Friesians and crossbred Friesians. Breeding carries together should be avoided.
Horses that have one copy (carriers) are not affected by the abnormal gene. However, when a copy of this gene is passed by each parent to the offspring, it will be affected! If undetected, distichiasis can cause blindness.
Testing is inexpensive. You may not be able to see the additional lashes, but horses with excessive tearing or squinting should be examined.

The most common treatment for distichiasis
involves the removal of the abnormal eyelashes under general anesthesia. Electrolysis or cryotherapy are used to destroy the lash follicle, to prevent regrowth. Several treatments may be required.







Late in December 2020, DNA testing for distichiasis  became available to FHH, to test horses with Friesian lineage.  FHH is encouraging testing to avoid the of breeding two carriers together, therefore, reducing the number of affected purebred Friesian and part-bred Friesian horses .

Codes on FHH papers:

Starting in 2018, carrier status codes will be added to all FHH pedigrees. For horses being registered FHH, a note advising testing will be added to the registration document, when the carrier status of the horse(s) with Friesian lineage is not known, or when there is risk, due to a known or suspected carrier in the pedigree.

Codes printed on FHH pedigrees are based on current information that was believed to be accurate at the time of printing, but may be subject to change, as information is updated daily.



The meaning of the codes published on our pedigrees

-/-/-   The third negative mark is for distichiasis. Meaning the horse is negative
ds+   Horse is a carrier of distichiasis. Will pass it on the their offspring 50% of the time.
ds++   Affected by distichiasis to some degree and will always pass it on to their offspring.
    Below are the codes for dwarfism and hydrocephalus



Pedigree indicates testing is not necessary.



Tested as NOT a carrier for dwarfism or hydrocephalus.

-/-/- or 3P-   Tested as NOT a carrier for dwarfism or hydrocephalus or distichiasis.



Was tested as a carrier of BOTH dwarfism and hydrocephalus.

dfhy?   75% Chance of being a carrier.
df/hy?   Could be a carrier of dwarfism or hydrocephalus or both.



Was tested as a carrier of dwarfism, but negative for hydrocephalus.



Was tested as a carrier of hydrocephalus, but negative for dwarfism.



Testing is not necessary for dwarfism, tested as a carrier of hydrocephalus.



Testing is not necessary for hydrocephalus, tested as a carrier for dwarfism.

df+*   Likely carrier of dwarfism, may not be verified by testing. (e.g. foals testing positive)



Likely carrier of hydrocephalus, may not be verified by testing. (e.g. foals testing positive)



Suspected to be a carrier of dwarfism.



Suspected to be a carrier of hydrocephalus.



Status is not known. (e.g. bloodlines may be too old or horse has not been tested yet)

If your horse is a carrier of distichiasis:

Being a carrier does not affect the health of your horse!

It is only if you breed this horse, that carrier status matters. 

If your Friesian or part-bred Friesian is a carrier, they can still be used for breeding, but to avoid the risk, the status of all mates with Friesian lineage must be known, before breeding.

If you breed to any horse with Friesian lineage, you will want to have DNA test PROOF that the partner horse is NOT a carrier also.  Be careful of false testing reports. Ask to see the report or call the registry.

If you breed to another carrier parent, the foal has a 1 in 4 (25%) chance of being affected.

Keep in mind that any carrier parent will pass on the genetic mutation to approximately 50% their foals, even if the other parent is clear or regardless of the breed. So, if you plan to breed offspring from carriers back to Friesian lines, they should tested first.

If you have any questions, please call our office at 877-653-1341.



Sorry, we do not know the origin of the photos.

These photos are being used for educational purposes only.










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