Flaxen (color variant)

Flaxen is a genetic trait in which the mane and tail of chestnut-colored horses are noticeably lighter than the body coat color, often a golden blonde shade. Manes and tails can also be a mixture of darker and lighter hairs.^[1] Certain horse breeds such as the Haflinger carry flaxen chestnut coloration as a breed trait. It is seen in chestnut-colored animals of other horse breeds that may not be exclusively chestnut.^[2]

The degree of expression of the trait is highly variable, with some chestnuts being only slightly flaxen while others are more so. Flaxen was once thought to be produced by a recessive allele, based on preliminary studies, proposed as F^f for flaxen.^[3] However, more recently it is thought that it may actually be polygenic, influenced by multiple genes.^[4][1]

Some chestnut horses that do not exhibit much flaxen may nonetheless produce strongly flaxen offspring. Studies on Morgan horses have indicated that the flaxen trait is inherited.^[4][5] One found that flaxen chestnut horses mated with other flaxen chestnut horses consistently produce only flaxen chestnuts, which, if Mendelian inheritance is assumed, would make it a recessive gene.^[5] Flaxen does not affect black or bay horses, only chestnuts. However, as there are examples of flaxen chestnuts born to parents that are black or bay, it may be masked in darker-colored horses but still passed on to their offspring.^[5]