HGG Community Forums

DP isn't invisible, it's just not a gene that you can test for - in other words, it won't show up in your horses' gene testing results.

DP stands for Dense Pheomelanin. It's a darkening gene, similar to Sooty (Ssty) but it affects red pigments. Here is a link to the gene guide which will also show some examples:
http://www.huntandjump.com/geneticsguide/?page_id=135

Three of any four darkening alleles (so 1 DP and 2 Sstys for example) can produce Liver Chestnuts and Chocolate Palominos. It will darken other colors such as bays and buckskins, but their listed color name (after gene testing) won't change even if you have three darkening alleles, so you just have to develop an eye for it.

DP only affects red pigment on horses. Black or Grullo or classic champagne horses can carry DP but will never express it.

DP affects all horses with some red pigmentation--so your red based horses like chestnuts, red duns, palominos and golden champagne, but also bay based horses like bay, brown, wild bay, buckskin, Amber champagne, etc. I personally find that the more diluted the base color, the harder it is to see the affect of the gene. I can easily identify it on chestnuts, with a bit more difficulty in palominos, and only with great difficulty and much comparison back and forth on golden Champagnes.

All horses have 4 possible slots for darkening alleles--two for dp or DP, two for S or Ssty or S+. If a horse is chestnut or palomino or red dun and any 3 of those four slots hold a darkening gene, the horse will qualify for the Liver Breeders Club.

DP on bays with no sooty (SS) will make a red bay. DP on wild bays with S Ssty or Ssty Ssty makes very red bays (blood bays) but the expression on wild bays is pretty variable from quite orangey through to that flaming bloody red. DP on Ssty Ssty bays makes a deep dark mahogany brown.

It takes a lot of time just looking at lots of horses to start to recognize DP. Having horses that are color tested helps--you can look at a bunch of chestnuts that are S S and you will notice a few who are significantly darker than others. They probably have DP. Using the horse search and controlling the variable using the base color tab is a fabulous way to teach yourself to see DP.