I used to breed Polish years ago, and never gave them any kind of special diet. Certainly a higher protein feed would be helpful, but not 28%. At most, 22%, but I personally think 18 to 20% is ideal. Grower feed and even layer feed will have all the nutrients your birds will need, but some greens thrown in with them now and then could be helpful, as well as oyster shell as a supplement if you use grower feed.
What Polish do need is careful monitoring of their crests. You must be very careful when you de-louse them not to get Sevin dust or anything else in their eyes. In the case of Polish, I think Invermectin is probably best for parasite control. You also do not want those crests getting wet or muddy, especially when it is cold out. A covered run is very helpful, but if they do get wet crests during freezing temperatures, the owner needs to intervene and dry them off.
Polish can also be subjected to bullying and even cannibalism by other breeds. If you see evidence that a Polish crest has been pecked at, especially if it has bled, the bird needs to be isolated until it heals. Also, crests make Polish very vulnerable to predators of all kinds, but especially aerial predators.
In most cases, I think it's best to keep Polish away from other breeds, with the exception of bantams. But I have two white crested blacks in with my Dorkings and they do fine together. The main things is prevention of problems and keeping a close eye on them in case problems do arise, because such problem can escalate very quickly.
