I have a non PPID gelding with bad teeth who had a resulting impaction colic a few years ago, and I also have a PPID mare. It was incredibly stressful when my gelding was colicking. He was impacted for 5 days and finally, finally passed it. It was then that we discovered he was likely eating less hay than we thought (his weight was not bad but he looked unthrifty) and was not getting near enough fiber. I also had him on Omeprazole after the impaction passed, because he refused to eat as well. It only took 3-4 days on the Omeprazole for him to get his appetite back. I started him on senior grain (high fiber complete, 11.7% NSC) and alfalfa cubes as a source of long stem forage (the ones I get are 9% NSC). Letting him graze, even though he was unable to actually consume the grass, stimulated his appetite a lot. I'd keep trying some soaked hay pellets or cubes, alfalfa if you can get it. I know many people in the UK with PPID horses use fast fibre and/or speedi-beet. Both are low NSC for his Cushing's. The FB group "Equine Cushing's Disease Horses (PPID)" has files saved on it that give full lists of foods and forage in the UK with NSC. I'd keep trying and consulting with your vet. And you're positive he's getting the Omeprazole in him (ie are you using an oral syringe)? It sounds like he's hopefully on the upswing!