Hey, I'm not a horse 'expert' but I did work with them a bit when I worked at the vet clinic... It's really hard to determine if a horse is 'fat' from looking at a photo.. It's kind of the same determination as with dogs, if you can run your hands over their side gently and are able to feel their ribs without having to push down really hard then they aren't over weight.

I found a website for you that goes into much greater depth:

http://www.horses-and-horse-informat...0197trim.shtml

Hopefully that helps