Tiger Eye

Tiger eye is a dilute iris color found in Puerto Rican Paso Fino Horses. In contrast to the brown-colored eyes of most horses, “tiger eye” is characterized by a yellow, amber, or bright orange color. Researchers at the Veterinary Genetics Laboratory investigated the genetic basis of this phenotype and identified two variants in the gene SLC24A5 responsible for tiger eye, named Tiger eye 1 (TE1), in exon 2, and Tiger eye 2 (TE2), in exon 7. The tiger eye phenotype is inherited as a recessive trait. Horses with tiger eye are most frequently homozygous (two copies) for the TE1 variant (TE1/TE1). Some tiger eye horses are compound heterozygous (one copy each) for both variants (TE1/TE2). Horses with the genotype (TE2/TE2) are rare; the one documented case had a very light yellow/blue iris color. Brown-eyed horses can carry one copy of either TE1 or TE2 but they will also have one copy of the normal gene. Unlike the iris color dilution associated with the cream and champagne mutations, there does not appear to be a connection between tiger eye and dilute coat pigmentation. The tiger eye phenotype has been seen on all three non-dilute base coat colors (black, bay, and chestnut) and in both males and females. While to date TE1 and TE2 have only been detected in Puerto Rican Paso Finos, it is possible that these variants may explain lighter eye color in closely related breeds.

Testing for these tiger eye variants allows breeders to identify carriers of tiger eye. Since brown-eyed horses can carry either TE1 or TE2, owners breeding for or against this unique eye color can use this diagnostic tool to inform mating decisions.