HGG Community Forums

The other day on the Facebook discussion group, Ammit explained that horses can have a range of "pigment density" genes. The range extends from 0, meaning nothing that darkens the basic pigment, through 1, 2, 3, and 4. This range includes both sooty and DP, heterozygous and homozygous. So a horse might have a pigment density of 1 and have either 1 sooty allele or 1 DP allele. The sooty will show up on the gene test and so is easy to identify. If the horse looks darker than non sooty without the Ssty, one would assume probably heterozygous DP.

Since your mare is homozygous for sooty, the question you must ask is, is she darker than the average SstySsty chestnut. I would estimate that she might not be, but if you feel she is, she can only be heterozygous DP, since she isn't dark enough to be homozygous for that and sooty both. Breeding her to definitely homozygous DP stallions will be the best way to tell.