A purebred Spanish horse (Andalusian) comes in several colors. Most of them grey, there are also some bays (brown body with black points on the legs, black mane, and black tail). A very few chestunts are in the books (used to not be allowed). And the dilute colors are becoming more popular.

One of the dominant characteristics of the Spanish horse is his dapple-grey coat. This is one of a few breeds of horses that are born different shades of dark colors and in time turn white (except for bays).

The main reason there are so many grey Spanish horses is that the gene for grey is dominant. Another factor is more significant historically. According one author, since the modern breed originated in the sixteenth century it was influenced by science which at the time was based on Classical Greek thought. This thought process followed the doctrine of humours all creatures were believed to be composed of the four elements of water, fire, air and earth.

In each animal, one element was believed to be predominant and the corresponding qualities would determine the physical form and temperament. Water corresponded with good harvests and thus a “watered down color of grey would determine that the animal would be generous and noble ideal for a king. Fire, or a red color, conferred that the animal would be too irascible and this color was rejected.

Color Genetics Part 1

by Donna DeYoung Copyright 2002 © Skyhorse Kingdom

An article about color genetics, acceptable colors, and breeding for color

Introduction - Acceptable Colors

The purebred Spanish horse is allowed to be registered in Spain only if they are one of three colors* – grey (some version of white, dapple grey, or silver), bay, or black. *And now, also chestnut. [UPDATE 2016 - dilute colors are also allowed] The color grey is called “tordo” in Spanish. The color bay (brown with black points) is called “castaño”. This “castano” has confused a lot of people because it sometimes translates back into English as “chestnut” but it does not mean chestnut to the Spanish! It means bay! Because . . .chestnut is called “alazán.”

The color black is “negro”. The U.S. registry (IALHA) is slightly different from Spain’s registry as they allow horses of most colors to be registered as “Andalusians” – just remember their registry is not as strict and allows crossbreds such as the Lusitano-Spanish horse into the registry as an “Andalusian”.  Lusitanos (the Portuguese-bred horse) can be registered almost any color including chestnut, palomino, buckskin, etc.

About the grey gene

The grey gene is dominant to all other colors. So anytime a horse is born with a grey gene, eventually he will turn some version of grey or white. There is actually a “white” gene that is different from grey.

The grey gene will eventually turn any horse grey whether the horse is born looking bay, chestnut, or even pinto. If he inherited at least one grey gene from either parent, he will turn grey. In the newborn foal it’s possible to look for grey hairs above the eyelashes or in the mane and tail that will give you some indication that the foal has inherited grey.

When a horse has two copies of the grey gene (from his mother and one from his father) he is said to be homozygous for grey. No matter what color horse he is bred to, his foals will always be grey. When a horse has one copy of the gene, he is heterozygous for grey.

Half of the time he will give his grey gene to his foal and the other half of the time he won’t give a grey gene. When the horse does not inherit grey, the other color genes come into play and are allowed to be expressed.

What if the horse isn’t grey?

In the Andalusian breed, when the horse is not grey, they are usually bay or black in color. Occasionally a chestnut (sorrel) will appear. The important thing to remember is that in order to get a bay or black Andalusian, the horse cannot inherit a grey gene. To increase the chances of getting bay or black, it’s best to breed to a bay or to a grey that is known to have produced bays or blacks.

When two bay Andalusians are bred together, there’s no way to get grey. Most likely the resulting offspring will be bay. Sometimes black can occur and sometimes chestnut.

Black in our breed is actually a version of bay. A bay horse already has a black mane, tail, and legs. When a horse inherits a certain type of black gene, the gene acts to “turn off” the brown coloring of the body. The result is a black horse. This is not quite the same as a “true black” as in the Percherons and Friesians. A true black has blue tints in the sunlight. While the other type of black has brown highlights. The type of gene that turns off the brown coloring is recessive, this means the horse must inherit one “turn off brown body color” gene from each parent as well as the bay gene to result in black.

Chestnut is also recessive - the horse must receive a chestnut gene from each parent  in order to be chestnut.

The following diagrams show the way that bays and greys come about. Black and chestnut could occur in the diagrams wherever the color bay shows up. But the genetics are more complex and are not covered in this article.

Here’s a good follow-up detailed article to read:

Color and Genetics Discussion

If you breed two grey horses what color will you get?

It depends. If both horses have been bred for many many years and have NEVER had a bay even when bred to a bay several times – it’s almost 100% certain that they are both homozygous for grey and will always produce grey. On the other hand, if both horses have already produced bay offspring in the past (i.e. they are must be heterozygous for grey) then there is at least a 25% chance for your foal to be bay. The punnet squares show the parents across the top and down the left side. The results are presented as the genes come together.

Note: The grey gene is shown by the capital letter “G”. The no-grey gene is represented by the small caps “g”. GG is homozygous grey, Gg is heterozygous grey, gg is bay.

Diagram A. Two homozygous GG grey horses are bred.

Neither horse carries the gene for bay (they are GG). The resulting offspring are all homozygous GG in genotype and their phenotype (expressed color) is all grey. None of them carry the bay gene.

Diagram B. One homozygous GG grey horse is bred to one heterozygous Gg horse.

Only one carries the gene for bay (Gg). The other is totally dominant for grey (GG). All the offspring will be grey in color (this is the phenotype). 50% of them will carry the bay gene (Gg).

Diagram C. Two heterozygous grey horses are bred. Each carries the bay gene.

There is a 75% chance the resulting offspring will be grey in color. There is a 25% chance the offspring will be bay. Of all the chances, 3 out of 4 times the resulting offspring will at least carry the bay gene. This is probably the most typical cross when breeding greys together and explains why sometimes you get a bay from two parents that most of the time produce grey.

If you breed a grey horse to a bay horse, what color will you get?

It depends. If the grey horse is homozygous for grey, there is 0% chance for getting bay. If the grey horse is heterozygous for grey, your chances go up to 50%. Also, whenever you get bay, you could also get black or chestnut depending on other factors.

Diagram D. A homozygous grey horse (GG) is bred to a bay horse (gg).

Although all the offspring inherited the bay gene, because they all inherited the grey gene as well, 100% will be grey. This is the first generation result and is called “F1”. If you take these F1 offspring and breed them, the bay color will then appear in the coat color– this is called “F2”.

Diagram E. A heterozygous grey horse (Gg) is bred to a bay horse (gg).

50% of the offspring will be grey (heterozygous) and 50% will be bay (or black or chestnut depending on other factors).

Diagram F. Bay bred to bay.

If you breed a bay horse to a bay horse, what color will you get?

Most likely bay. Although sometimes black or chestnut. But never grey.


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