I'm not sure what the protein content of the actual seed would be. As a feed source though, I would think it much more economical to use it in a fodder system. Or, if you have a large area for your chickens take it out and broadcast spread it with a lawn feeder. You would probably have to keep your girls contained for a few days until it takes hold and starts growing. Alfalfa as a green feed source runs right around 20% protein and drops slightly when dried or turned to silage. Pellets can be slightly higher.
Of course, even better than alfalfa for fodder/pasture would be White Clover. It's protein content runs around 25% and slightly lower when dried or made into silage. As a pasture it does not grow very tall making it ideal for chickens and they find it more palatable than alfalfa.
A word of warning though,, if using clover as a forage for chickens, be sure to use White only or keep others to a very low minimum. Other varieties like red and crimson clovers can contain levels of cyanide that could potentialy harm chickens. My pasture area for my birds is 2 acres of White clover with a sprinkling of alfalfa, red clover and timothy mixed in. The red clover, timothy and alfalfa are remnants of a field originaly planted for dairy cattle and doesn't contain enough red clover to pose a threat to my birds.
