Sorry for the confusion. Most people I know and have read about grow for only 6-7-8 days except for major hydroponic operations.
The science out there says by day 8 the protein is slightly higher % and maybe the highest % it ever gets even though the plant mass will continue to increase as the plant grows and you eventually get more total protein because the plant is so large and has roots that have fed on soil nutrients or hydroponic nutrients. But then it is in the plant, cellulose.
Again, it is a very small change in total protein by weight if any in 8-10 days, even when you add minerals or kelp, to the water.
The total weight is decreasing, except for water. Therefore there is less actual feed by dry weight, so the % protein shows higher mostly because there is less total weight.
There is not really a gain or more actual protein by dry weight than there was in the grain. And even if there is, now it is in the plant cellulose not in the grain.
Just know that you are not getting 7 lbs of feed from 1 lb of grain. You are not getting any significant extra protein in the feed in the 1st 7 days.
But Soaked or Spouted grain is easier to digest.
Chickens may get more nutrient out of soaked or 3-4 day sprouted grain overall than the dry whole grain.
Grass is not easier for chickens to get nutrients out of than grain. The info and % of protein gain in fodder and nutrient benefits for ruminants do not apply directly to poultry.
Fodder is more beneficial for ruminants who can get more nutrients out of the grass. If you are raising goats sheep cows horses, 2nd week old fodder is a great way to feed
Chickens are vultures, meat eaters, omnivores, not vegetarians like ruminants with multiple stomachs that ferment and break down plants and cellulose!
I do sprout to 3 days, and sometimes I let it grow to 8 day and longer grass just to give them greens, which is great if your chickens do not get grass or pasture. But if there is an increase in protein or total mass weight of the feed it would be after the 8th day. Then as the plant matures you get more green mass and root mass that is an increase in total grass feed, but not much more protein by percentage. You are basically growing grass hay for them, not increasing protein %.
And if you don't add nutrients then the grains that do sprout are feeding off the nutrients that leech out of the other grains if you are recirculating water. If you drain and rinse you lose a lot of those.
But if you want to spend the $ to buy grain, and give them grass instead, then fodder is fine. You can grow and get more total dry weight in grass eventually than you had in the grain. But it is not 6 lbs more feed, because the plant is mostly water. So if you want more pounds of feed and don't care that it is grass, it makes more sense to plant the grain in the dirt and let it grow to full grass for them if that is possible, then you get more weight and feed. But hens don't like tall grass as much as young short pieces. So you don't really accomplish much even doing that.
I soak a lot of seeds then I feed some wet seeds the 2nd day, I feed some sprouts the next few days, then sometimes let it continue to grow and after 8 days as I tear out and feed a chunk of it a day for the next week as I try to keep the roots from going foul. By the 2nd week, in the tubs I grow it in, that don't have the best drainage, the roots start to go bad. So if I haven't used it all up, I plant it in the ground.
I add minerals to the soak and rinse water which I reuse in other tubs that I grow a variety of grains in, not just one grain. Triticale, Barley, Peas, BOSS and occasionally Lentils or Flax. So I only have to start soaking a new batch after a week for fodder.
When I am not letting them grow to fodder and just making sprouts, I start new small batches ever 2 days as I use them all up in a couple days.