If you’re wondering what kind of grass is best for grass-fed chickens, the answer is, “green grass.”
What I mean is, lush green grass is loaded with vitamins and is has lots of available nutrients, but as it fades to brown, it becomes more and more useless to chickens. Chickens aren’t ruminants and can’t digest cellulose, so it’s the soft, green, palatable grasses that count.
Lush spring pasture is the best, of course, and that’s easy enough. The trick is providing green grass year-round, or close to it. Cool-season grasses will stay green all winter in mild climates, and warm-season grasses will stay green all summer when the cool-season grasses have all browned off.