Question: Where can I get genetic testing done for color? My promising 2-year-old colt is registered as a palomino, but when he was a yearling his mane and tail started turning dun/brown/black. I have had people tell me he is going gray. I've researched his pedigree and found his sire is listed as a grullo. His dam is a palomino mare and since I've seen her, I know that is her true color. I have not seen the sire, however, and have had no luck finding out if he is, in fact, a gray and not a grullo. I do not want to falsely advertise my horse and would like to determine his true color. What are my options for testing?
Answer: At this point there are very few genetic tests for horse colors, although many breeders are interested, and the next few years may see more and more become available. Rumor has it that a major university laboratory is nearly ready to come out with a test for the gene that causes palomino and buckskin coloring, which will be useful for a number of breeders.
Gray can be superimposed over any color. This can lead to great confusion, not to mention some very strange combinations with various background colors. Palominos and buckskins that go gray can be very strange colors for a few years until the whitening process evens out and they look more like typical light grays. The term grullo is usually used to describe a blue-slate-colored horse with dark points. A horse does not "fade into" grullo, but the color itself may fade over time from exposure to sunlight.
Either a gray or grullo paired with a palomino could produce a wide variety of colors, so it is difficult to narrow the field much without actually looking at the horse in question. If the sire of your horse is indeed grullo, then gray cannot be in the equation as it is a dominant gene-it must be present in at least one parent for a foal to be gray. If your horse is registered as a palomino, passing all the standards, then I suspect that he is most likely some variant on that basic color.
At this point the best strategy is to continue to try to find out if the sire is indeed grullo rather than gray and bide your time until a genetic test for palomino is available.
D. Phillip Sponenberg, DVM, PhD of Virginia-Maryland Regional College of Veterinary Medicine in
Blacksburg, Virginia is the author of Equine Color Genetics.