Trabag - Manchado Chestnut Arabian

Ahem, I'm going to say it's 'environmental' just like the French Arabs looking like TBs is 'environmental.... It's one of the reasons AHA was out of WAHO for a long time, they wouldn't accept the South American Arabs as pure.

Actually, there are/were quite a few Arabians that are/were very colored. I don't think it was environmental.

I remember another discussion about this mare and the "pattern". The active theory was that it was something to do with the water. Can't remember the details.

Unless I am mistaken, Manchado means something like "stained", which I think is cute.

Again, my problem with this is that they are not isolated horses producing the foals, so if there is something in the water, why are the foals not popping up more frequently in those areas? It's not like these horses are being fed from private springs or anything.

Yes.

There are several posts on the Manchado pattern on my blog. Trabag is the only Arabian known to display the pattern, but it has occurred in low levels in a number of breeds in Argentina. My personal suspicion is that its presence in Argentina is due to a founder effect, and not "something in the water". I explain that at greater length in the blog posts, and in the chapter on the color in my book (Equine Tapestry).

Manchado overo « The Equine Tapestry
(scrolling down will take you to the start of the topic)

I also included one of the charts on the pattern in a post about an upcoming book release. Again, you'll need to scroll down to find it.

What the New Year will bring « The Equine Tapestry

Subbing!!! This thread about color is amazing!

Its really facinating.
I have known bad cases of ringworm to grow back permanently white and its common for horses that have had skin damage from badly fitting saddles to do the same but the markings on this horse look too extensive for something like that - it would have been literally raw in huge areas.
A copper deficiency can effect a dependant enzyme called tyrosinase that is linked to melanin production and is also linked to albinoism but you'd expect other health problems with that

I agree. Even if it is environmental and whatever causes it only comes out in, say, May, wouldn't you still see more affected foals? Or hear more about older horses changing coat patterns?

I think about how rare you see a blue eyed Arabian pop up - because it's was bred out for so long, it's rare to see a blue eyed purebred Arabian. So maybe this Manchado gene is just highly recessive?
I wonder if they are thinking of doing any more genetic testing on it now that we've come way further advanced in terms of isolating genes, etc.

That does make sense.

The thing that gets me is: a highly recessive gene that has ever only shown up in Argentina and nowhere else in the world as long as horses have existed? That's a bit of a stretch to me...

There are(were?) significant question marks over the purity of at least the Arabians in Argentina at the time though, and at least two of the horses with the pattern have been related to each other. If the mutation appeared in Argentina, supposing it is a mutation, then it would be isolated to horses related to the "case zero", and if they weren't being bred for colour, then the gene could easily be hiding for generations, or even bred out.