Here's why:
* Perlino is a double dilution of a base coat color. It requires two copies of the cream gene (CrCr).
* Chestnut horses carry the red base coat color. This means they have at least one copy of the red allele (E).
* The cream gene dilutes red and black pigments. However, it does not create them.
Therefore, a chestnut mare (EE or Ee) cannot pass on the two copies of the cream gene necessary for a perlino foal. Even if the stallion carries the cream gene (Cr), it will only result in a palomino foal (EeCr) if the mare carries the red allele.
To produce a perlino foal, both parents must carry the cream gene. This can be achieved through various combinations, such as:
* Palomino mare (EeCr) x Palomino stallion (EeCr)
* Cream (CrCr) mare x Chestnut (EE or Ee) stallion
* Palomino (EeCr) mare x Cream (CrCr) stallion
While you can't get a perlino from a chestnut mare, there are other exciting color combinations possible with a chestnut mare, like palomino, buckskin, and chestnut roan, depending on the stallion's genes.