Did you know there are over 100 names for horse color and pattern in the Icelandic language?
Icelandic horses are a colorful bunch, and there are literally hundreds of different colour variations and patterns seen in the breed.
But how did these unique horses get such unique coats and markings? The answer is more complex than it seems.
Base Coats of Icelandic horses
Although many genes influence coat color in horses, they are are all controlled by the interaction of just two ‘ASIP and MC1R’.
Black and red pigments form the building blocks that all coat colors can be built upon. There are only three base coats found in Icelandic (and all) horses.
These are red (chestnut), bay and black.
Chestnut is the most common base coat in Icelandic horses and can be found in four different shades. Even though the genetic makeup of chestnut horses is simple, the variations in different shades are created through complex gene structures.
Liver chestnuts have a chocolate brown body with a mane and tail the same color, flaxen chestnuts are reddish-coloured with a flaxen mane and tail, light chestnuts have a sandy colored body and red chestnuts have a bright almost bronze coloured sheen.
If a brown horse has any black hair at the points, they are not chestnuts. Darker hairs around the eyes can be accepted, but these areas should never be black.
While black is the most common color pigment found in wild animals, it is most seen in the eyes, skin, and extremities. The wild pattern gene causes black pigment to show up only in the dorsal stripe and on points around the body and legs.
Over thousands of years of domestication, the black genetic variety disappeared in wild horses. But the wild gene pattern (which causes bay markings) is still present. In fact, it is even found in the sole surviving wild horse: the Przewalski horse.
Bay horses can range from dark mahogany to sandy, yellow body color but it will always retain the primitive wild gene pattern in its black mane, tail, and legs.
Dark bays/browns can be so dark they are often mistaken as black, while liver chestnuts can be so dark, they appear bay. Even very dark bay horses will always have red hair around the muzzle and eyes, while liver chestnuts can be differentiated from bays because they do not have black points.
A true black horse has an entirely black coat without any areas of red or brown hair. Researchers found that black coats evolved into a more prevalent color when climate change pushed horses into dark forests full of predators 11,000 years ago, helping them survive when other species died out.
Black Icelandic foals are usually born with a blue sheen to their coat, and this will typically shed to normal black by the time they are yearlings.
This coat color is controlled by the E gene. A homozygous black horse (EE) will be born with a very rich black coat that is sometimes called coal black that does not fade in the summer.
Roans and Greys
Some Icelandic horses may appear grey, but genetically grey is not actually a base color at all, but a modifier caused by a mutation of the STX17 gene. That means a grey horse is always born either bay, chestnut or black, and gradually fades as he or she ages.
The genetic modifier responsible for greying possibly developed as a camouflage adaptation for horses living in swamps (like the Camargue horses) to better blend in amongst reflections of the clouds and sun on water.
Roan is also genetically a modifier caused by a mutation on the RnRn gene.
The mutation “covers” specific parts of the horses body with a light dusting of white hairs that are evenly mixed within the base coat. Much like horses that are greying, roans have white hairs in their base coats. However, the action of this mutation is different to the gray modifer, since it places just a certain number of white hairs in the body coat, and this pattern is often uneven or more obvious on areas such as the flanks or around the dock of the tail.Roans are rare amongst Icelandic horses due to their popularity (many are exported) and are nicknamed the coat-changers, because when these horses change their coat, they can appear to be a different colour.
Dilutions and other coat variations
Genetic mutations are responsible for many of the Icelandic breeds unique coat variations, including palomino, buckskin, cremello, perlino, and smokey black. The actual coat colour depends on the number of mutations a horse inherits from its parents, and the horse’s base color underneath.
Sabino is thought to be the first spotting phenotype, and this colour probably appeared in horses during the fifth Century BC in Siberia. Many Icelandic horses are born with white splash markings or have Pinto/Skewbald patterning.
Some genetic mutations responsible for certain colors bring with them undesirable effects. Icelandic horses born with the rare silver dilution pattern can develop multiple congenital ocular abnormalities, and megaloglobus (eyeball enlargement).