Agouti effect on red horses?

So I always thought that the agouti gene restricted the expression of black and had no effect at all on red (ee) horses. Then I came across this website which claims that the type of agouti gene the red horse carries is responsible for the different shades of red expressed.

The first half of the page (difference between classic bay, wild bay, and brown) seems to be correct based on what I've read elsewhere, but then the bottom half of the page explains how those different agouti genes modify red horses. Can any of our color experts on here confirm whether or not this is true?

Any owners of red horses who have had them tested for agouti care to share their results?

I know there's a lot of misinformation out there on the 'net, but I'm surprised to find a website that seems to have correct information about the different types of agouti alleles followed by incorrect information about how they affect red horses.

Here's the website: * Homozygous-Horses**|**Internet Equine Directory**|**Agouti (bay) gene Horses Scroll down to "HOW AGOUTI GENES MAY AFFECT RED HORSES"

That's just that person's personal opinion. There is no scientific evidence to show that agouti does or does not affect red.

That looks like purely her own speculation.

Verona, you were correct in the first place. Agouti does not affect red hair because it only modifies the amount of black on a horse. As red horses do not have any black to modify, agouti can't do anything. Until ee horses of different shades are genetically tested and proven to fall into different shade categories depending on the agouti genes they carry, this remains true.

My stud is ee and AA, his full brother is ee Aa. They are the same shade of red sorrel. I have a mare eho is ee Aa and she is liver chestnut, which would seem to be pretty good proof that the theory is probably wrong. However, I expect the mapping of horse alleles will one day soon provide an answer,
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Ok, that's what I was thinking Thanks everyone!

While I think it is an interesting therory that is really all it is. If there was something to it you would see lagit resurch on it since there are a lot of red horses and the Agouti test has been around for some time.

I would say just like black based horses it comes down to several factores including what the horse eats. Just like the picture of my bay mare who is very dark part of the year. Seems to vary based on several things. Not to mention I am not at all convinced that we have any idea of all the things that control color in horses.

Some of the things we do know effect the shade of red include: mealy, smutty, and flaxen genes.

And I agree with nrhareiner - we don't know all the factors and genetics that influence the shades of color.

Take a look at this boy. All the pics are of the same horse at different times.









They are in order from newest to oldest so you can see that it hasn't even been a gradual change but swings back and forth from light to dark going back to spring of 2011. I didn't even factor in winter coat into these pictures either which is another shade.