Prascend is pergolide mesylate, but is manufactured and packaged differently, and typically has more potency than compounded pergolide which is also pergolide mesylate. That potency difference between the two may range from a lot to basically just the same. The stability (shelf life) of Prascend over compounded is superior, but that doesn't mean that you can't thoughtfully use compounded. Purchase just a month's worth in capsule form, and keep in the fridge door. Compounded pergolide is mixed and packaged by a compounding pharmacy. Whether they keep the components on the shelf for a long time, or order in small batches is always a question, too.
An uncontrolled PPID horse is at high risk for IR, so the safe s/s diet is important. Get the PPID controlled, and many, probably most PPID horses will normalize their insulin. But, since PPID is a somewhat predictably unpredictable disease, the level of control of the insulin may vary even if the ACTH is well within normal ranges.
So the diet is one of those - well, that depends. You need to test ACTH, insulin, glucose and leptin, (at least leptin initially) and see how the given horse responds to his PPID treatment.
Linda and Pap Ballou