But don't young horses buck around and play and jump anyways? I'm not supporting lunging a foal over jumps, but don't they put that sort of strain on their limbs themselves?
I'm kind of iffy on what's ok and what's not, but horses put very similair strain on themselves playing in the pasture, bucking and galloping.
However, a 4 month old filly, no. I really doubt it's putting an enormous strain on her joints, but I'd be terrified of her getting injured out of confusion and lack of proper co-ordination. And those jumps are definitely to high for her size. I don't mind seeing an older youngster put through a chute with a small vertical, most of them WAY overjump it anyway out of playfulness, but at least they have the option to choose a comfortable height, not be forced over something half their size.