I would be sad to see a reining spin in a WD test.
Big can of worms here, but a horse that spins good and fast on the INSIDE hind as his ‘pivot point’ is NOT balanced and set up to go after an errant cow immediately after the spin.
You can see here in this slo-mo video that the spinning horse is on the wrong lead, relative to what is asked in a pirouette.
http://www.youtube.com/watch?v=ePdn2tKW8fg
If you do the ‘reining spin’ as a pirouette, the ‘pivot foot’ is the outside hind. The horse will not spin as fast. However, by setting the spin up as a pirouette, the horse is able to at any point in the spin, leap forward into canter to cover an errant cow. If he’s spinning reining-style, on the ‘wrong lead’, he will have to rebalance himself before he can go forward.
The whole ‘reining spin’ issue was a favorite of reining show-types to discredit Ray Hunt and Tom Dorrance, for ‘teaching the spin wrong’. When asked about why they never did a reining spin the way show horses were trained to, Tom Dorrance replied (paraphrase here) that they pretty much didn’t use that ‘turn’ to control a cow…because it doesn’t control the cow.
A rollback, though, DOES balance the horse for an athletic maneuver, like going to a cow or a jump. A rollback is a GREAT gymnastic exercise, but you can’t start with a fully realized gallop in, rollback and gallop off. A rollback rebalances the horse, teaches him to rock his weight backwards, and especially weight the outside hind leg. If you want a great canter depart from halt or walk, you MUST be able to ask the horse to weight that outside hind, because he strikes off into canter with the outside hind. A canter depart with the horse already taking his weight on a coiled hind end (from balancing back in a rollback), striking off cleanly, makes for a lovely collected canter.
Given a series of ‘western dressage’ tests, I would not ask for a rollback at speed until the higher level tests. I would start with rollback at a walk: done from a halt, backup four or five steps, rollback 90 degrees and walk forward. You might call that turn on the haunches, at that point. (And repeat in the test with another rollback going 90 degrees the other direction.) You’d progress through trot, halt, backup, rollback 90 or 180 degrees, trot; then go to lope, and last eliminate the backup before the rollback.
And with half-pass, I would definitely put it in a test, but again at a higher level test. Lateral work needs to start at leg-yield, proceed through shoulder-in and then get to half-pass.