Coat Colour Tests

Please select one of the following tests for further information:

Red factor
The inheritance of basic horse colours black, bay and chestnut is determined by two different gene loci (the Extension and the Agouti locus). The Extension locus (E) corresponds to the melanocortin-1 receptor gene which accounts for the different melanin types. While the dominant allele E is associated with black pigment (eumelanin) the recessive allele e results in reddish coat colour (pheomelanin). Horses showing some black pigment therefore bear at least one copy of allele E at the Extension locus, either in homozygous (EE) or in heterozygous (Ee) state. Horses lacking black pigment (chestnuts) are reddish in colour and homozygous ee. Depending on the genotype of the mating partner, carriers of the red factor (i.e. animals with gene status Ee or ee) can produce reddish coloured offspring. In contrast, animals that are homozygous EE will never produce red offspring, regardless of the colour of the mate.
Red factor testing can be used to differentiate between black horses carrying Ee and those carrying EE. For further information on the inheritance of colours in horses please visit the section about Agouti testing.
The agouti locus controls the distribution of black pigment: while the dominant allele A confines black pigment to the lower legs, tail, mane and ear rims (e.g. bay horse), the recessive allele a leads to a uniform distribution of black pigment over the entire body (black).
The agouti locus directly interacts with the extension locus (red factor), e.g. horses, which are homozygous ee for red factor are reddish in colour independent of the genetic status at the agouti locus.
Accordingly, the interaction of the extension locus and the agouti will create the following situations:

Phenotype Genetic status Possible progenies
Chestnut aa;ee No bay horse if mated
with blacks
Aa;ee Any coat colour possible
AA;ee No blacks
Bay AA;EE No blacks, no chestnuts
Aa;EE No chestnuts
AA;Ee No blacks
Aa;Ee Any coat colour possible
Black aa;Ee Chestnuts possible
aa;EE Only blacks if mated with blacks
The tobiano pattern is caused by the dominant allele TO at the tobiano locus. Homozygous tobianos (TO/TO) pass on the gene independently of the mating partner’s genotype which results in tobiano spotted offspring, exclusively. In contrast, mating of two heterozygous tobianos (TO/to‘) will result in approximately 25% solid coloured horses (to’/to‘). The underlying genetic mechanisms of this spotting pattern were identified by researchers at the University of Kentucky. A direct PCR based test clearly distinguishes homozygous spotted animals from heterozygous tobianos and therefore enables selective matings according to the breeder’s requirements.
Cream Dilution
Several different genes (e.g. dun, cream, silver dapple and champagne) can dilute the basic coat colour of a horse.
At the cream dilution locus there are two possible allelic states: CCr and C. The semi-dominant allele CCr causes brightening of the basic coat colour which in single dose results in palominos, buckskins or smoky blacks and in double dose causes pale cream colours seen in cremello, perlino or smoky cream horses.
In contrast, the recessive allele C has no influence hair pigmentation. Animals being homozygous for allele C are non-dilute and show basic colours like chestnut, bay or black in the absence of other modifying genes.
Silver dapple
The autosomal dominant silver dapple gene (Z-locus) causes dilution/brightening of black pigment (=eumelanin) in black and bay horses. This effect can be mainly observed in tail, mane and feathering. In addition to brightening black pigmented parts of the body, silver dapple can also cause other characteristic features such as striped hooves, white eyelashes or dapple markings on the body. All these effects are particularly pronounced in young animals and significantly diminish in the course of aging. As the silver dapple gene has no significant effect on reddish pigment (= pheomelanin), chestnut horses can hardly be recognized as carriers from their physical appearance. In breeds such as Icelandic Horse and German Classic Pony, silver dapple is fairly common. Nevertheless, the trait is also known in Quarter Horses, Paints, Appaloosas, Paso Finos, as well as in cold-blooded Belgians, Bretons and Noriker.
The autosomal dominant Grey gene (G) causes premature greying of horses which are born as coloured foals. The progressive loss of pigments usually begins in foals which acquire white hair around the eyes. As the horse ages, more and more white hairs appear throughout the entire body until the animal’s coat becomes more or less white. Due to its autosomal dominant inheritance, heterozygous carriers of the Grey gene as well as homozygous animals become white, albeit in an individual greying process.
Please note: The offered test does not distinguish between homozygous and heterozygous carriers of the Grey gene, but discriminates presence and absence of the Grey gene.
Splashed White
Splashed white horses show a variable white spotting pattern which is characterized by an extremely large blaze, often accompanied by blue eyes and extended white markings at the distal limbs. Some, but not all, splashed white horses are born deaf.
Recent research revealed 3 mutations (SW1, SW2 and SW3) that cause splashed white spotting pattern in horses.
Variant SW1 is found in several breeds, e.g. Quarter and Paint Horse, Trakehner, Miniature Horse, Icelandic Horse and Shetland Pony. Homozygous SW1 splashed horses have been identified, which suggests that this variant is not lethal in homozygous state.
Occurrence of SW2 and the rare SW3 mutation is confined to certain lines of Quarter Horses and Paints. Both mutations are suggested to have a lethal effect in homozygous state. Thus breeding two horses that carry SW2 or SW3 should be avoided due to the risk of generating nonviable embryos.
Horses that carry two or more splashed white mutations or a combination of tobiano or lethal white overo and splashed white may display extensive white markings up to being completely white.
Mushroom describes a dilution effect with autosomal recessive inheritance, which is known almost exclusively in Shetland ponies. Homozygousity for this trait leads to the lightening of reddish pigment (pheomelanin).
In chestnuts, the gene causes a lightened sepia color of the body as well as a flaxen mane and tail. In bay horses milder gene effects are seen with normally pigmented mane and tail and a sepia diluted body due to lack of red pigment.
Mushroom can show similarities to cream and silver dilutions, although these have different genetic background.
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