I would go with a maximum of 1/2 inch of aged manure, I would not sift out the bedding (shavings) they offer some buffering effect.
The best method for using chicken manure (which is considered a "HOT" manure just as sheep manure is) is to
compost it with the bedding material and other add ins you might have.
My heaps consist of donkey bedding, manure and
urine, hog manure and bedding, chicken manure and bedding, ground
wood chips (I run them through the chipper twice) and grass / garden clippings.
It takes a fresh heap 3 months to finish, at the one month time I add a
mushroom slurry over the top of the heap, If I have any of my preparations ready (see
preparations those go in right after the heap build or as soon as they are ready.
Aged manure is better but do remember it still has any pathogens that were present in it and they are going to be active, not the best for vegetable feeding if there is anyway around using this, but if not, add some fungi spores to mitigate the "bad bugs".
Redhawk