IMO looking at the movement of a hunter foal is different then predicting the movement on a dressage foal. Almost all long legged foals are going to have knee action that will subside when they grow into themselves. As they develop and grow their movement will become flatter and this is particularly true at the trot. What you can tell more predictably is the canter, how much impulsion they have and freedom of shoulder, which for a true hunter prospect is far more important then how flat their trot is a 2 months which will most likely not be the same trot you will have as a 3 year old. It is also important to look at BOTH parents of the foal which should certainly give you an idea of what this foal could become.
In my experience top hunter foal prospects can have a lower neck set and also can have a straighter shoulder than a world class dressage prospect foal. The straighter shoulder/lower neck is fine for a second/third level prospect, which is the majority of the dressage market anyway. A fabulous canter is important for both categories though.
Knee action is not all that desirable for the top in dressage, although I recently heard of a breeder who wants to "corner" the dressage market using hackney/Dutch harness horse crosses.
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