My opinon is, that if you're riding a piggy pacer or a very pacy tolter that doesn't want to trot, one of the first steps towards tolt is to get the horse to trot.  It is not the only solution, and one *can* find tolt without it, but it's definitely often a help.

So, to get the horse from one extreme of the gait scale (pace) it sure helps to get it to work on the other end of the gait scale (trot) and then work towards stabilizing the horse in the middle of the gait scale (tolt).

The pacy tolter is very stiff through his topline, and on the forehand.  He can be so because he's ewenecked or because he's drooping down with the neck.  Some horses do have the right neck position but are still on the forehand.  So, to get the horse to tolt, you need to free it from it's stiffness and you need to get it towards collection.

Trot can be stiff, but the horses are also often working very fluidly with the back at the trot.  A horse can be just as collected in trot as in tolt, just in a very different way.  A good dressage horse is a beutiful example of a trotting horse with a totally fluid back.  And an Icelandic horse that is trotting on a bit uneven ground is doing very hard work with it's back, if it weren't it would simply fall over the small obstacles the uneven ground probides.  Horses that are hollowing their backs and pacing start to round their backs up a bit when asked to trot, and lengthening the topline, and you are thus then helping the horse to develop/train the muscles in such a way that it's helping the horse getting away from the hollow back.

There are many methods that help you clean up the pacy tolter.  Doing serpentines, getting the horse into basic dressage like sidepassing, doing slight sidepassing (don't know the english name of the exercise, can anyone tell me?) at the tolt, backing and going into tolt from there, going slightly downhill, using halfhalts and using your weight, evening out crookedness etc etc.  That is enough to fill a whole letter, let's just think about this trot-subject here.

One of the things to do, where the trot helps, is to ask the horse to trot and move the horse towards tolt from there.  You do that by doing slight tolt hints, so that your horse even goes in broken trot or very trotty tolt, that is ok, it's going in the right direction then and not pacing.

Also, to work a bit in canter without cross cantering (that is, do the transition trot-canter instead of pacy tolt-canter, that can end in cross cantering).

Because the pacy horses are occasionally so far away from any diagonal movement, it is quite acceptable for them to trot on the forehand in a certain step of the training-phase, just to get them used to some different rhythm of movement.  Here I'm meaning both mentally, and that their body and muscles get used in a different way.  But do not trot them for a long time each ride.

Also, when you're riding a very pacy tolter, it's very hard work for the horse to do a reasonably good tolt.  Then it's good for the horse that you allow it sometimes to relax a bit in walk, and by doing the trot.  Again, not for a long time.  It's also good to warm the horse up in a bit of walk, then a bit of trot, and then start the hard work.

Many pacy tolters are so reluctant to trot that it's hard to do a lot of collection work at the trot, all hints just make them pace again.  But if you can ask the horse to trot, and it bends in the poll at the same time and works a lot from the hind end, then you're certainly doing collection work, and strengthening the hollow back musckles and the hind end of the horse.

Some horses are very very stuck in the pacyness and "not-trot-ness", and many rides don't give results in a more secure trot, then it can be very frustrating to be trying to get trot all the time, and it doesn't serve the purpose anymore.  Then it's better to skip this part and do all the other things possible to get the horse towards tolt.  But, when training, it's good to have as many tools in the toolbox as possible, and if you can get the trot, then that is one extra tool in your toolbox.

One thing to remember too, is that if you're riding a horse that is not willing to trot, but does it when prompted, it can be detrimental to the trot if you forbid the horse to trot for a long time in the training phase.  Then it can be much harder to get the horse to trot again, and
some horses even won't trot again, at least not for riders that are not very experienced.  The horse can get stuck in the raised-neck frame, and doesn't dare to drop the neck enough to be able to trot.

But, if you ride a pacy horse a lot in trot, it gets stuck in the other excess, with the neck down, on the forehand, against the reins.  My opinion is that trot is good but too much trot is bad ; )  No trot can be bad too ; )

I don't think it's really important whether all horses can trot or not.  Some horses have great difficulties doing it, some maybe squeeze out a couple of steps under very abnormal circumstances or training, some maybe don't dare it under rider, some maybe never do it, some piggy-pacers even have to learn to tolt first before being able to trot.  It's more important to wonder whether the horse has some trot that is of use, and can help us and the horse to reach some goal.  If the trot is virtually non-existent, it's not of any use to us or the horse.

My point is, that this helps, but it's just one of many many things that help, and you're never going to get a very pacy horse to tolt simply by getting it to trot, more things have to be done.   Complicated?  Who said the world was simple ; ) ?

On many days, I'm riding just as much when I'm in the cow barn milking, or driving to shop or wherever I can think.  There are few magic tricks that work with every rider and every horse, except thinking, wondering, learning and experimenting.