Initially there was only one lab who was offering the W20 test. This testing was open for only a short time. You can read the first blog post about the first round of testing called Dominant White 20 DNA Testing Available for a Limited Time. Due to the small timeline of the test being available few people were able to get their horses tested for W20, including myself.
There is now a second lab offering the W20 test, it is currently the only lab who has W20 testing open and available to the public. This lab is called Practical Horse Genetics located in Australia. Sending hair samples to Australia from North America is a bit costly and the shipping does add time. However, once the samples arrive at the lab the testing is quick and the results can be emailed to you. The testing for W20 from the Practical Horse Genetics lab is well worth the time and money for any horse breeder as well as any horse owner who is curious about horse colour genetics.
I sent in hair samples for my mare, aka the Tawny Horse. It seemed from a visual prospective that a positive W20 result was possible. Tawny had white markings matching the described phenotype of small amount of white markings for heterozygous W20: a blaze, partial white lower lip, sock and cornet band on the rear legs. Tawny’s dam had white markings which matched the described phenotype of a larger amount of white markings for homozygous W20: large blaze, white lower lip, chin and white under the jaw, high whites on all four legs and a small white belly spot. The DNA test results were emailed from Practical Horse Genetics and reviled Tawny to be negative for the W20 mutation. The test results are posted below: