Horse Coloration

Coloration in Horses

• Pigment Melanin in Horses

  • Coloration is primarily due to melanin, which exists in two forms:

  • Eumelanin: Responsible for black or non-red colors.

  • Phaeomelanin: Responsible for red colors.

• Interactions of Pigments

  • Various colors and shades arise from the interaction between eumelanin, phaeomelanin, and other modifying genes.

  • All horses can produce red pigment, but not all can produce black pigment.

• Inheritance of Color

  • Having black pigment does not guarantee the horse will be black due to modifying genes.

Basic Colors

• Extension Gene

  • E (dominant): Results in a non-red (black) horse (without modifying genes).

  • e (recessive): Results in a red horse.

  • Genotypes:

  • EE = black horse (cannot produce chestnut)

  • ee = red horse

  • Ee = black horse (can produce chestnut)

• Agouti Gene (A) Gene:

  • Modifies black base color to produce bay.

  • A (dominant): Restricts eumelanin to points, leaving the rest of the body red. (creates bay).

  • a (recessive): Allows full eumelanin expression (creates black).

  • Genotypes:

  • AA = bay horse

  • Aa = bay horse (can produce black foal)

  • aa = black horse

Base Colors

• Chestnut: Varies from reddish-brown to orange-red; no black points.

• Bay: Ranges from light to dark red/brown with black points; may have black overlay.

• Black: Solid black coat; often fades/bleaches in sunlight.

Variations of Base Colors

• Bay Variants: Dark bay, blood bay, brown bay

• Chestnut Variants: Liver chestnut, sorrel, blond/light chestnut

• Black Variants: Non-fading, fading black (fading usually caused by sun exposure)

Other Common Horse Colors

• Gray: Born any color or have black skin; white/mixed hairs develop with age; variations include salt-and-pepper, dapple gray, fleabitten, rose gray.

• Buckskin: Bay with cream gene, resulting in a yellow/cream color with black points.

• Cremello: Chestnut base with two cream genes, resulting in pale cream; typically has blue eyes.

• Dun: Yellow/tan coat with primitive markings and possible stripes on legs and withers.

• Palomino: Chestnut with one cream dilution gene, resulting in golden color with flaxen or white mane/tail.

• Pinto: Large patches of color (brown, white, black). Variants include:

  • Piebald: Black and white spots.

  • Skewbald: White with any color except black.

  • Tovero: Mix of tobiano and overo patterns.

  • Overo: spotting pattern distinct from one another (sharp irregular markings)

  • Paint: Pinto horse with Quarterhorse or Thoroughbred bloodlines.

  • Tobiano: Spotting pattern by rounded markings, white legs, and white across the back between the wither and dock of tail.

• Roan Color: White hairs mixed with the base color; variations include red roan, bay roan, blue roan.

Head Markings

• Bald: White marking from forehead to muzzle, extending to the sides of the face.

• Blaze: Wide stripe along the nose bridge.

• Snip: White spot on the muzzle, between nostrils.

• Star: White spot on the forehead.

• Stripe: Narrow white stripe on the nose bridge.

Leg Markings

• Coronet: Small white band just above the hoof.

• Half Cannon: Marking extending halfway up the leg from the hoof.

• Half Pastern: Marking extending halfway up the pastern from the hoof.

• Sock: Marking extending two-thirds up the leg from the hoof.

• Stocking: Marking extending fully up to the knee or hock from the hoof.

Albinism in Horses

• White Horses: Have a pure white coat from birth; may have brown or blue eyes and pink skin.

• Albinos: Have white coat and non-pigmented eyes (true albinism: rare and lethal).

Genetic Defects in Horses

• Lethal White Syndrome: (Overo Lethal White Syndrome) Genetic disorder caused by an autosomal dominant gene, results in:

  • Lack of pigment and blue eyes.

  • Non-functional colon, leading to colic shortly after birth.

  • Euthanasia is often recommended due to suffering; there is no cure.