Mushroom

Mushroom dilution

The Mushroom dilution is a coat colour caused by the red pigment (phaeomelanin) is not produced. This results in red-based horses (chestnut, palomino) appearing as a sepia-tone of brown/light brown. Bay or buckskin horses also lose the red tone in their body hair.

Mushroom is unique to Shetland ponies originating from the UK, and populations/breeds derived from this population. Specifically, genetic testing has detected carriers of the Mushroom in the American Miniature Horse population.

The colour should not be mixed up with the Silver dilution, in which the dark pigment (eumelanin) is not produced. Although silver bay and red-based Mushroom ponies both have light manes and tails, Mushroom ponies are missing the red tint and are distinctly “cooler” in colour tone.

No evidence of eye problems has been found in ponies with the Mushroom dilution.

Inheritance

The Mushroom variant has an autosomal recessive method of inheritance. Carriers of the mutation have no visible difference in coat colour, but has a 50% chance to passing the variant to each foal.

Black horses can be homozygous for the variant without any change in their coat colour, so need to be tested for carrier or homozygous status if coming from lines with Mushroom.

Relevant tests

• P386