That's really interesting because the chickens here (mainland Orkney) absolutely love the long clumps of cocksfoot. They graze them right down to lumpy stubble, scratch around the base of those once they're bare, and the free range flock of Hylines where I used to live on one of the Orkney isles would often choose to lay in nests in the middle of a few dense clumps that were still standing.
For seed they seem to like rough meadowgrass the best but I'm not sure how much of that is because the smaller seeds are easy to strip off the more openly structured flowering spike.
Definitely noticed them nibbling on some pollen recently too but I can't remember what plant.