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This is a discussion on Colors within the Horse Breeding forums, part of the Horse Breeds, Breeding, and Genetics category

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    06-17-2010, 12:12 PM

How can you tell if the colt will turn grey? All grey horses don't start out grey right?

Can someone explain to me how the genetics of all that work. Is grey not a dominate gene?

And while I'm asking about colors I'd like to know the difference between

Black and brown and even bay (but you can tell that b/c of the black points right?)

Sorrel and chestnut

Pictures please
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    06-17-2010, 12:28 PM
Green Broke
No grey horses start out grey, although some may show signs. Only genetically white horses are born white in colour. Grey is a dominant gene. All grey horses will grey out over time. Variations are caused by base colour and the speed in which they grey out (eg dapple and flea bitten)

Black horses have a dominant black gene and a recessive red (chestnut) gene, but only black shows through. Bay horses are genetically black but the have a gene (agouti gene) that limits the black to the mane, tail and legs so red shows through.

Chestnut horses only produce red pigment (which is recessive) sorrels are only a variation of red, not genetically different.

Brown is an ambiguous term for a very dark bay (black bay) where the agouti gene disperses the black differently making the body, mane and tail look similar to each other.

Pic on the way...
    06-17-2010, 12:36 PM
Green Broke
Bay horse (black + agouti)

Chestnut horse (red)

Sorrel can be a darker or lighter chestnut, depending on where you are from!

A grey foal, he has the grey gene and by the look of his nose he will grey out

A grey horse showing signs of agouti (so black base coat)

Flea bitten grey- this horse shows signs of a red base as the flea bites are red in colour

Also rose grey horses show red base showing through (they have red flecks, like the opposite of roaning)
    06-17-2010, 12:38 PM
Green Broke
Oh and black bay (black + agouti)

Hope all this helped, it can be confusing, you can ask questions of you want :)
    06-17-2010, 02:13 PM
There are some signs that a foal will end up being grey. Sometimes they will have "goggles" around the eyes. Sometimes they will be a rich, deep color... like born solid black, whereas a horse who will stay black is usually born a smokey greyish color. Or a bay being born with black legs is a sign it might grey, where a bay that wont is often born with the greyish color legs.

Brown has At at the agouti locus, where bay is A. A black horse has aa, no dominant A or At. A is dominant over At, so a horse who is AAt would appear bay, but could have brown offspring.
    06-17-2010, 02:35 PM
If a horse is carrying the gray gene (G), he will turn gray. It is a dominant colour that trumps everything but the Cream gene (Cr). Homozygous Cream (CrCr - double dilution gene) is the only thing that covers up gray.

This is a Smoky Cream (black + double cream - E? CrCr) who is also carrying gray, & the bottom is a Smoky Cream who is not carrying gray. The gray gene is hidden, so you cannot tell the difference between the two without genetic testing.

Breeding 2 gray horses who have tested heterozygous for gray (Gg x Gg) will give the resulting foal a 50% chance of being heterozygous gray (Gg), 25% chance of being homozygous gray (GG), & 25% chance of not inheriting gray (gg).

Breeding a heterozygous gray (Gg) to a non-gray horse (gg) will give a 50% chance of inheriting gray.

If either parent is homozygous for gray, the resulting foal will be gray 100% of the time.

Gray foals are born looking like a "normal" colour, & will shed out gray. One good indication of weather your foal will "gray out" is to look at their eyes - if they start getting a gray ring of hair around their eyes, that's one of the first signs that he or she will be gray.
Some pics of gray foals:

All gray horses get lighter as they age, eventually looking white. Here's an example of one gray horse & how she changed throughout her life:

Several months old - she appears chestnut

3 years old - on the right, next to her dam.

20 years old:
    06-17-2010, 03:43 PM
Some genetic terms:

Extension - this gene determines if a horse will appear red or black. A horse that is EE or Ee will be black based. A horse that is ee will be red based (chestnut). (for the record, sorrel & chestnut are genetically the same thing, people just use different terminology)

Various shades of chestnut/sorrel (red chestnut, liver chestnut, flaxen chestnut):


Agouti - this is the bay gene, & is only expressed on horses carrying Extension. It causes the black to only express itself on the points of the horse (legs, tail, tip of the ears, etc). A red based (chestnut) horse can be homozygous for Agouti, but will not express the gene. Brown horses are caused by a form of the Agouti gene called At. This is a form of the gene that is still being researched, however I believe the horse must be black based & homozygous for At in order to be a true brown. Many horses who are said to be black are actually brown.


Seal Brown:

Cream - This is a dillution gene, which lightens the coat colour. One copy of this gene creates palomino on chestnut based horses, buckskin (which is NOT the same as dun) on bay horses, and smoky black on black based horses (they still appear very dark, because cream hides on black horses). Two copies of the gene (double dillution) create cremello on chestnut based horses, perlino on bay based horses, & smoky cream on black based horses. Double dillutes usually have blue eyes.

Palomino & Cremello:

Buckskin & Perlino:

Smoky Black & Smoky Cream:

    06-17-2010, 03:44 PM
Dun - this gene creates "primitive" markings on a horse, such as a dorsal stripe & leg-barring. The most common form is "brown dun", which is often mistaken for buckskin, but is actually the dun gene on a bay or brown horse. Red dun is dun + chestnut, Grulla is dun + black, Dunalino is dun + chestnut + cream, & dunskin is bay + dun + cream.

Brown Dun:


Red Dun:



[it gets much more complicated than this - roan, flaxen, pangere, sooty, silver, champagne, etc. but these are the basics. I can go into explanations of the rest of it if you want.]
    06-18-2010, 03:05 AM
Originally Posted by Quixotic    
If a horse is carrying the gray gene (G), he will turn gray. It is a dominant colour that trumps everything but the Cream gene (Cr). Homozygous Cream (CrCr - double dilution gene) is the only thing that covers up gray.

Actually it trumps ALL, including cream. And palominos often get DARKER before going "white." You may not be able to tell as much on a double dilute, but they still grey out.
    06-18-2010, 03:43 AM
Do they? I've never seen a double dilute carrying gray that I could tell a difference with. The horse in the photo I posted is 7 or 8, & I don't see any signs of him graying out. I know it affects single cream carriers, but it's always been my understanding that double cream pretty much hides it.

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