Giddy up go

"giddy up go" what is the origin and meaning of this phrase?

It was traditionally said to a horse to urge it to move: no idea why.

DFG

Cpwbpy speech. Get up becomes git up becomes giddy up.

Yes, this phrase might have been used in the Old West, possibly by cowboys if they were driving the chuck wagon or the stage coach. I've never heard of horses being ridden that were urged to get going by this command. You get him or her going most often by lifting the reins, possibly assisted by a litte foot pressure and a change in the rider's posture. That doesn't mean the cowboys did not urge the horse to move vocally, but I don't think that was how the horses were trained. SS