There are many ways in which a horse can be 'downhill'.
In most riding sports, it's sufficient if the horse's back is 'level'. This means that the back does not slope downward toward the withers. Some of this depends on the shape of the withers and croup, how well conditioned the horse is, etc. People often will, instead of looking to see if the back slopes downward toward the front of the horse, just look to see if the point of croup is higher than the withers. That's not quite as good as just being able to see if the back slopes down to the front.
The most obvious 'downhilled-ness' is that the horse's hind legs are longer than its forelegs. If you look at the horse from the side, stood on a level surface, you see that the stifle is much higher than the elbow.
ALL horses have the stifle very slightly higher than the elbow. The horse that has longer hind legs than forelegs, has a stifle that is markedly higher than the elbow.
In other words, his hind legs are, literally, longer than his front legs.
A lot of people will tell you that looking at the 'top line' is deceptive, and what you need to do to really tell downhill-ed-ness, is to look at and compare heights of stifle and elbow.
Every different riding sport has an amount of 'not so uphill-ed-ness' that it can work with.
For other riding sports, the amount of 'downhill-ed-ness' described above, would not work. For example, upper level dressage, a person goes into a lot more detail to see if the horse is even some much slighter amount of 'downhill' or even, if he is 'functionally downhill'.
This is a lot more subtle. For example, if a horse has heavy, loaded shoulders and a very small narrow hindquarter, he may have serious problems working at top levels of dressage, even though he passes the 'withers are taller than croup' test, even if he passes the 'stifle not too much higher than elbow' test.
Say he has a very long, heavy, low set neck. He may be 'functionally downhill' when he's in motion. - enough that being an upper level horse would be a really serious strain for him.
So in that sport, they will look a lot more, at how the horse functions in motion, to see if there are much more subtle types of 'not quite enough uphill' or 'not working uphill enough when in motion' are going on.
What is 'acceptable' really, really depends on what sort of work the horse is going to do. I see a great many 'downhill' horses in some horse show classes, and then not in others.
Last edited by slc; 02-08-2011 at 12:04 AM.