A lot of people worry about the red gene factor in Friesians. As it's well known it's not fatal for a Friesian to be born chestnut (double red factor). They are allowed to be registered with the KFPS. As of now they are not allowed to be advanced from the foalbook, however if a chestnut mare has a black foal, that foal will be allowed to show at the keuring to try to advance out of the foalbook.
The historical red gene carriers include
For about 8 years the KFPS would not approve any stallions that carried the red gene. At this point they are allowing red gene carriers to be approved. As of #483 they have started posting the test results for stallions that carry red, dwarfism and Hydrocephalus genes, but since that time none have been red carriers.
There is a Fire Friesian or Fox Friesian registry that is trying to create a gene pool to expand the number of horses with the red gene. As mentioned it's not fatal, it's just not part of the breed standard for the KFPS for advancement in the registry. If you know your mare or stallion is a carrier you can contact them to have your horse on record as a carrier. Breeding 2 carriers can give a 25% chance of producing a chestnut offspring. but would give a 50% chance of having the offspring be a red gene carrier thus keeping the recessive red gene still available in the population.
If you would like to post your horse here as a carrier I'm happy to do that just PM me with their name, sire and dam's 2 sires and that they are carriers or homozygous (chestnut hair).