How Does Breeding Affect Color in Horses?

Modern day knowledge and understanding of genetics is enabling horse breeders to breed for specific colors. The science behind breeding for specific colors is complex, but a simplified way of explaining it is that horses, like all living things, have recessive and dominant genes. Every horse has a basic background color, which can be bay, black, or chestnut. When the basic colors are mixed with white or cream, you get roans, paints, appaloosas and other colors. While it has proven to be impossible to breed for white facial or leg markings, it is possible to breed for white body markings.

  1. Homozygous and Heterozygous Horses

    • Every horse of every breed and color has a pair of genes to produce every possible spotting pattern. The pattern is only present when one of the genes is dominant. In a homozygous horse, both genes for a particular pattern are dominant. A homozygous stallion will produce that particular pattern no matter what color mares with which he is bred. Although he exhibits the pattern, the chances of a heterozygous stallion's offspring having the pattern will depend upon the genes of the mare.

    The White Patterns

    • In tobiano patterns, the white crosses the horse's back between the neck and the croup and all four lower legs are white. The head of a tobiano is solid colored and may or may not have a regular blaze. The white pattern never crosses the horse's back in the overo pattern, which is the opposite of the tobiano, with at least one leg being solidly colored all the way down, and extensive white on the head. Overos also have four recognized patterns, frame, calico, sabino and splashed white. Piebalds and skewbalds can be overo or tobiano or leopard.

    The Cream Gene

    • The cream gene dilutes the basic color. Chestnut is a recessive color and two chestnut genes will produce a chestnut foal. A palomino has one chestnut and one cream gene, and when bred together they may produce palomino or chestnut foals. Cremellos have no chestnut genes and two cream genes, so they are like a double-diluted chestnut. Breeding a chestnut to a cremello will always produce a palomino. Breeding a bay with a bay will most likely produce a bay foal. A buckskin or dun is a bay with a cream gene, while a perlino is a buckskin with a double cream gene.

    Black

    • The black gene is the most unpredictable. Breeding two blacks does not necessarily produce a black foal. If they carry the dilute gene, they can surprise their owners and produce a palomino or buckskin. In some instances, the black can be lightly diluted to produce a dark gray or smoky coloring. A double dilute black gene will result in a smoky cream, with blue eyes and a pink skin.

    White

    • The American Albino breed is not a true albino because it has brown eyes rather than pink eyes. Horses with a lethal white gene can produce a homozygous overo, which will die soon after birth. This is known as lethal white syndrome and horses can be tested prior to breeding to determine if they carry the lethal white gene. No matter what color a horse starts with, if it carries a gray gene, it will turn gray and become lighter with age. This gene can be noted in the Lipizzaner breed, where the foals are born black and start turning gray within a few months.