The Agouti gene controls the distribution of black pigment. The dominant allele A restricts black pigment to the points of the horse (mane, tail, lower legs and ear rims), as seen, for example, in bays and buckskins. The recessive allele a uniformly distributes black pigment over the entire body.
Breeders interested in producing black horses need to have breeding stock carrying the a allele, in addition to the E allele of the Extension gene. Using results from the red factor and agouti tests, click here for a table of breeding schemes to produce black animals.
Agouti results are reported as:
A/A or A/a
Black pigment distributed in point pattern. The basic color of the horse will be bay or brown in the absence of other modifying genes. A has no effect on red pigment (ee).
a Only recessive allele detected. Black pigment distributed uniformly. The basic color of the horse will be black in the absence of other modifying genes.