A lot depends on what kind of "scratch" you get.
"Scratch" is a very generic name for a grain that can be tossed on the grown to make a bird "scratch" at the ground. it can be as simple as crack corn or a 15 grain mix. 
For the most part the "scratch:" you will get at the feed mill will be a low protein (9%) high carbohydrate grain mix that is OK to feed as a treat. 
I don't feed any "scratch" till I get my first egg from my pullets/hens and then I feed about 1 cup of "scratch" per 5 large fowl birds.
I feed a 16% protein scratch grain that I mix. Basically it is a 14% all grain pigeon feed with some extras I add in..
The 14% pigeon feed contains grains like ( AUSTRIAN PEAS, CANADIAN PEAS, MAPLE PEAS, MUNG BEANS, VETCH PEAS,  POP CORN,  LINSEED (Flax),  MILLET, GROATS,  BROWN RICE,  SAFFLOWER, BLACK OILED SUNFLOWER SEED,  BUCKWHEAT, WHEAT) 
To the 14% pigeon feed I add BLACK RAPE SEED, HEMP SEED (Whole), GROUND UNSALTED PEANUTS
Chris