Determining Horse Color: A Tutorial

[Raikit]

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I recently had a foal born that had a very interesting color - one that even I had trouble figuring out. ( ) I thought this would be a good opportunity to help the community at large learn some of the finer points of determining a horse's color.

The foal in question:


First things first, what information do we get just from glancing at his foal picture?

1. He is not grey.
   How do we know this?:
   • Look at his face, lower legs, and stomach. He has a lighter mask of foal pangare on his muzzle, lower legs, and under belly. This indicates that he is displaying a foal coat rather than an adult coat. A horse that is grey will be born with an adult coat and will grey with age. Since this foal was born with a foal coat we know that he is not grey.
   • Secondarily, neither of the foal's parents are grey. Grey is a dominant gene and one of the parents must present as grey for the foal to be grey. Since neither parent is grey we know that this foal can not be grey.
2. He has either silver, flaxen, cream, or a combination of those three.
   How do we know this?
   • This foal's mane and tail are a very bright white. A horse that is undiluted will be born with a much darker mane and tail.
   How do we determine which dilution he has?
   • Determining which specific dilution this foal has is a bit more complicated, and largely relies on the foal's genetic heritage. Therefore, while we can tell he has a dilution that affects the mane and tail simply by looking at him we should wait until we consider his pedigree before trying to make a determination as to which dilution he has.
3. He is a double-dilute, meaning he is either double-pearl or cream-pearl.
   How do we know this?
   • This foal's body color - the area that is not covered by foal pangare - is extremely light, almost white. Currently there are only two ways that this super light body color can occur on a foal coat on HWO - a full-body double Lp expression with minimal spotting, or double dilution. As this foal has a small blanket we know that his lightness is not caused by his Lp, therefore he must be a double-dilute.
   • This foal's eye color is a very light, blue-ish grey. This is a good indicator of a doubly diluted coat, but can be misleading.
   How do we determine which dilution he has?
   • Once again, determining exactly which dilution he has will be more difficult than determining that he is a dilute. Again we will save the determination for after we have considered his parents.
4. He has a single copy of the Lp gene.
   How do we know this?
   • The small white blanket over this foal's croup is indicative of the Leopard complex. We know that he only has a single copy of the gene because of the smooth edges on the blanket. If he had two copies the edges would be much more jagged, giving it a lacy appearance.

After all of that, we only know two genes for certain - his grey gene (g+/g+), and his leopard gene (Lp/lp+). So how do we figure out the rest? We start by looking at his parents.

This is the colt's sire, Razz Berry:



Razz is a Silver Smoky Brown Pearl Roan Snowflake. That's a long and really complicated color. Here's how he breaks down genetically:

• Agouti: at/a+
  We know Razz has an at because he is brown. Being brown also means that he can not have an A. Therefore the second allele has to be either at or a+. How do we know what the second allele is? We look at his parents. His sire is Silver Amber Pearl and his dam is Smoky Brown Roan Snowflake. That alone doesn't tell us anything other than what we already know, but take a closer look his sire. He is Silver Amber Pearl, meaning that he is bay-based (A/?), but he has thrown black-based foals. In order to throw black-based foals he must carry a copy of the black agouti allele, making his A/a+. That means he does not have a brown allele, so he could not have thrown a brown gene to Razz. Therefore Razz must have gotten it from his (brown-based) dam. So what did the sire give to Razz? If he'd given Razz his A, Razz would have been bay-based. Since he isn't, we know that Razz's sire passed on his a+, making Razz at/a+.
• Extension: E+/?
  Razz is not chestnut-based, so we know that he needs at least one dominant extension allele. However, he does have chestnut ancestors on both sides of his family. His maternal grand-dam was chestnut, meaning this dam was E+/e. This alone gives Razz a 50% chance of carrying a recessive red allele. So far Razz only has three foals and none of them are red-based, so we can't know for sure if he does or does not carry that recessive allele, leaving it a mystery.
• Champagne: ch+/ch+
  Razz does not display any of the indicators of the champagne gene (most noticeable would be freckled skin around the eyes and muzzle), therefore he is homozygous recessive.
• Cream/Pearl: Cr/prl
  We know Razz has a pearl gene because his sire is double pearl, meaning he will pass pearl to all of his foals. A single copy of pearl will not affect coat color, but Razz is clearly diluted so we know that he must have either another pearl gene or a cream gene. Razz's dam is a single-cream dilute (Cr/n+), so the only thing she could have given him is a cream gene. Therefore we know that Razz inherited pearl from his sire and cream from his mother, making him a cream-pearl dilute.
• Dun: d+/d+
  Razz does not display any indicators of the dun gene (dorsal stripe, leg bars, facial and leg masks, etc), therefore he is homozygous recessive.
• Flaxen: ?/?
  Razz is black-based rather than red-based and has thrown no red-based foals. Since flaxen only affects red-based horses it is impossible to know if Razz does or does not carry it.
• Leopard Complex: Lp/lp+
  Razz has snowflakes and varnishing, so we know he must have at least one copy of the leopard complex. His sire does not display the leopard complex, meaning that he could not have passed it down to Razz so Razz's only copy of Lp came from his dam, making him heterozygous dominant.
• Roan: R/r+
  Razz displays roan, so he must have at least one copy of the roan gene. His sire is not roan, so he could not have passed roan to Razz meaning that Razz's only copy came from his dam and he is heterozygous dominant.
• Silver: Z/z+
  Razz displays silver so he must have at least one copy of the silver gene. His dam does not display silver, so she could have passed silver on to Razz. Therefore Razz is heterozygous dominant for silver.
• Sooty: S+/S+
  Razz does not display any visible sooty.

This is the colt's dam, Eaves:



Eaves is a palomino snowcap - not nearly as complicated as Razz. Either way, here's her breakdown:

• Agouti: ?/?
  Because Eaves is red-based and has only had one foal it is impossible at this point to be entirely sure what agouti alleles she carries. However, we can determine a few things. The first is that she does not carry an A. This is because both of her parents are brown-based and there is nowhere she could have inherited an A from. That means she can have one of three different agouti sets - at/at, at/a+, or a+/a+. As both of her parents are brown it is most likely that she is either at/at or at/a+, but we don't know for sure at this point.
• Extension: e/e
  Eaves is red-based, so we know that she is homozygous recessive for extension.
• Champagne: ch+/ch+
  Eaves does not display any of the indicators of champagne, so she is homozygous recessive.
• Cream/Pearl: Cr/n+
  Eaves is palomino. That means she has one copy of the cream gene on a red-based coat.
• Dun: d+/d+
  Eaves does not display any indicators of the dun gene, so she is homozygous recessive.
• Flaxen: ?/?
  Though Eaves is red-based and flaxen does affect red-based coats, Eaves also has a copy of the cream gene which means that her mane and tail are already bright white. Therefore we would not be able to see the effects of the flaxen gene, even if she does have it, leaving it a mystery.
• Leopard Complex: Lp/Lp
  Eaves displays a snowcap pattern over her croup, meaning that she has two copies of the leopard complex.
• Roan: r+/r+
  Eaves does not display roan, so she is homozygous recessive.
• Silver: z+/z+
  Eaves is red-based, so she would not display silver even if she carried it. However, neither of her parents carried silver meaning that she has nowhere to have inherited it from and therefore she is homozygous recessive.
• Sooty: S+/S+
  Eaves does not display any indicators of sooty.

That's a lot of information. But what does it mean for our foal?

The first thing to do is to rule out things we know that the foal can't be, but what are those?

• The foal can not be bay-based.
  How do we know this?: Neither parent carries the needed A allele for the foal to be bay, therefore the foal can only be brown, black, or chestnut.
• The foal can not be champagne or dun.
  How do we know this?: Neither parent carries champagne or dun, therefore the foal can not have them.
• The foal can not be double pearl.
  How do we know this?: Only one parent carries a copy of pearl. This means that the foal can either be single-cream, single-pearl, double-cream, or cream-pearl but can not carry two copies of pearl. Because we have already determined that the foal is a double dilute we know that he is either double-cream or cream-pearl.

Where do we go from here?

At this point the process starts to involve a lot of guess work and probability. We know that Eaves is e/e, but we don't know if Razz carries a recessive red allele or not. Even so, once the probability is calculated we are left with our foal having a 75% chance to be black-based (so either brown or black), and only a 25% chance to be red-based. Here's how the punnet squares worked out for extension:

	E+	E+	OR	E+	e
e	E+/e	E+/e		E+/e	e/e
e	E+/e	E+/e		E+/e	e/e

And here are the punnet squares for the agouti allele:

	at	at	OR	at	a+	OR	a+	a+
at	at/at	at/at		at/at	at/a+	OR	at/a+	at/a+
a+	at/a+	at/a+		at/a+	a+/a+	OR	a+/a+	a+/a+

The agouti punnet squares show that if the foal is not red-based, then it has a 75% chance of being brown and a 25% chance of being black. Both of these squares together mean that our foal has a very high probability of being brown-based. When we take this data into account, along with the very high probability that the dam carries at least one brown allele, it is relatively safe to conclude that our foal is brown-based.


So he's probably brown-based, but what dilutions does he have?

When we first looked at him we determined that he was a double-dilute. That leaves with a few possibilities:

• Cremello
  
  Cremello foals tend to be almost white in color with just a very slight yellowish tint to their coat. If you compare our foal to the foal above you can see that our boy has more of a light brown-ish gray color to him. Therefore it is pretty safe to say that our boy is not cremello.
• Palomino Pearl
  
  Palomino Pearl foals tend to be a very pale yellow. Our foal is much more gray than yellow, therefore it is fairly safe to say that our boy is not palomino pearl.
• Brown Cream
  
  This color is closer to our foal, but still isn't quite right. It would be a much better match if the foal we're using as a comparison also carried silver. Right now brown cream is a very good possibility.
• Smoky Cream
  
  Once again, this is really close but still not quite right. It gets closer if we add silver but just doesn't seem right.
• Smoky Brown Pearl and Smoky Black Pearl
  
  The foal pictured above is actually our boy's sire, Razz Berry. Razz Berry is a silver smoky brown pearl, and we can see that as a baby he was much more yellow than his son. It is likely that a silver smoky black pearl would also have a somewhat yellow cast to its coat, though unfortunately I do not have any foal pictures floating around to compare with. Looking at Razz's foal picture, it seems more likely that his son is a double-cream rather than a cream-pearl.

So, when we gather all of our data together we can make the following conclusion:

Based on his color profile, our foal is a double-dilute (either double-cream or cream-pearl) with silver on either black or brown. Based on his pedigree the most likely color is Silver Brown Cream.

This conclusion can be re-evaluated when the foal finishes 'blowing out' his foal coat at one year. I will update this post when he reaches that point. The foal has reached his first birthday. Scroll down if you want to find out what his final color is!
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And here is our foal on his first birthday:


Now that we know what his adult coat looks like, what do we know that we didn't know before?

The first thing is that our foal is brown-based. The pale cream areas around his muzzle and underbelly against his main brown color show very clearly that he is brown rather than bay, black, or chestnut. His coloring is also a classic example of double-cream on brown. A pearl-cream would have been much more yellow throughout the body rather than brown. Therefore we know that our boy is Silver Brown Cream.

[Raikit]

Some helpful terms:

Foal coat: The coat that non-grey foals display as newborns. This coat is different from the one they will display as adults, hence the name. They will blow out this coat throughout their first year and will display their full adult color on their first birthday.

Adult coat: The coat that non-grey foals display on their first birthday. This is their base coat, unaffected by sooty, varnish, appaloosa bronzing, or champagne lightening. The aforementioned effects only begin to show after one year of age, making the first birthday the optimal time to determine a horse's base color.

Eye color: Several genes can affect eye color on HWO. The first is tiger eye - a single tiger eye allele will only affect the eye color of a horse that carries the champagne gene, but two copies of tiger eye will affect any horse that carries them. A non-champagne horse with two copies of tiger eye and no other dilutions will have green eyes. A non-champagne horse with two copies of tiger eye and a single cream will have blue eyes.
Champagne horses with a single cream are often born with very light eyes, but their eyes will darken as they age.
Horses that are double-cream or cream-pearl will have very light, blue-ish grey eyes.

Skin color: Skin color can also be affected by several different genes. The first is champagne - a horse with the champagne gene will have pink, freckled skin. Horses that are double-pearl will have pink skin coupled with dark eyes. Horses that are double-cream or cream-pearl will have pink skin with light eyes. Undiluted horses will have black skin.

[Raikit]

Reserving this post in case I want to add anything else.