The Agouti Explained

With the rising importance of knowing your horse's genotype, many people have been hearing the term "agouti."

The agouti (allele A) is a modifier that regulates the distribution of black pigment. Put simply, it limits the black on a black horse to the points (ears, legs, mane, and tail).

  • A red based horse (see "color recipes") can carry the agouti without showing it, as the agouti does not affect red pigment.

  • A black horse can not carry the agouti without expressing it. True black horses are always "aa"

  • You can not tell whether or not a horse is heterozygous or homozygous for the agouti based on physical appearance - genetic testing is needed.

aa = no agouti

If your horse is "a" (actually shorthand for "aa") then he/she is homozygous recessive for the agouti, but it is easier to understand if I explain it as "NO agouti" (which is technically incorrect, but the easier to picture). Black horses are "aa."

Aa = heterozygous agouti

If a horse is "Aa", then he/she is heterozygous for the agouti and can throw horses with or without the agouti.

AA = homozygous agouti

If a horse is "A" (shorthand for "AA"), the he/she is homozygous for the agouti and will NEVER throw black based horses without the agouti...that means NO blacks, smokey blacks, classic champagnes, blue roans, etc...any black-based foal will have the black limited to the points. So if you have a black mare and you want a foal who is "any color except black", then breed your mare to a stud who is homozygous for the agouti!

Horses homozygous for the agouti:

Westwood Farms - Locust Dale, Virginia 22948 - - 540-825-1300