I grew a bunch of multi-headed sunflowers last year, not on purpose, that ended up going to seed. I had to fight my local wildlife birds to save a few heads but I waited to make sure the seeds were mostly formed in the head before removing them. Just tossing the head into the run, they didn't have much interest but if you break it up a bit so they can figure out there are seeds in it
led them to tearing up the remaining sunflower heads.
Chickens are funny, they are nervous of new things until they realize they are delicious!