Answer

By Your Horse

Dressage rider and trainer Claire Lilley says…

Whether your horse is croup-high from conformation or from poor training, she should still be able to achieve a degree of engagement. This will put less weight on her forehand and help her to work in better balance. If she is naturally built croup-high, you’ll be in luck if nature has given her good flexibility in her hindleg joints to compensate. This is often the way with conformation defects – other aspects of the horse make up for it. With proper training, many conformation issues can be overcome, provided they are not too extreme.
The remedy is to build muscle tone with correct schooling. Working your horse on the lunge over single poles on the ground in walk and a steady trot will help strengthen her back and belly muscles, and help her tuck her pelvis under.
It’s important to work her with her nose stretching forwards and down to get her using her belly muscles, which you will see as a line along her stomach. If she has difficulty stretching fully, a chambon may help.
Once she becomes stronger through her back (you will be able to see the back muscles twitching) try riding walk-halt-walk transitions, using your body and legs to hold her rather than the reins so she has to use her back.
Resistance against the reins will prevent her from stepping under. Maintain a steady contact with the bit, without pulling, and close your legs (thighs, knees and calves) when you ask her to halt or half-halt.