When giving the Vit. E and B Complex, I don't give Polyvisol.
Try making a mash of the birds crumbles and add the Vit. E. and B Complex to that. Warm it up a bit....I've even added 1 drop of vanilla extract just to give it sweet smell. The pullet I'm treating now wouldn't eat her feed in the beginning but gobbled up the warm mash....even with the E and B added.
Yes, prednisone is a script...and it you are fairly certain it's not an injury, then I wouldn't give it. It won't HURT him...and might actually stimulate his appetite. It's an anti-inflammatory, so if there is some sort of inflammatory process going on...for whatever cause...it would help.
For a full size silkie I would give 5 mg twice a day for 5 days and then once a day for a couple of days before stopping it. For the juveniles, I give 2.5mg.