I've not seen good data of different breeds having significantly different protien requirements. No doubt there is lots of opinions and backyard science on the subject though.
All flock feeds take into account the needs of ducks, turkeys, geese and even game birds. So tend to 20% or more protien. But commercial layers are getting feed at about 17%. Commercially egg growers know where every gram of feed, protien and nutrient is going and how to extract every last cent of value.
But as backyard chook keepers we like to give a bit extra for whatever reason we see fit.
I'm of the opinion also that protien is not a day in day out requirement. 10% protien feed today and 30% protien tomorrow is fine. Nature is good like that. 10% protien for a month and 30% protien for a month might be getting inefficient however.
So im fine feeding a big treat of low protien (15%) layer feed for a day or few while im too busy because it's convenient. Then giving them some gamebird feed (28%) for a day or few as a soaked porridge after. In my mind variety is interesting for my chickens. But God knows what is really going on in their heads.
Anyway.... I've jabbered enough. People forget game bird crumble as a good affordabke protien boost. So it's a good option if you feel the need for extra protien. I've seen it as high as 30%.
