I have sour grass all over in my yard, the chickens love to eat the young shoots as well as the flowers. I also have sheep sorrel which they leave alone entirely. They will scratch all around the sheep sorrel looking for the worms that congregate in the roots of the plant.
I had to google "sour grass" to see what it is, and YES - they love it. In fact, we call it"chicky weed" because they love it so much, especially the flowers. I wish they loved all my weeds as much as this one.