Turkeys are curious birds and need to be occupied, like most living things, or they get bored in the confines of even a large pen. So they are provided with bunches of herbs and ears of corn suspended from the ceiling for them to pick at.
In this photo, it is comfrey that they are eating. Comfrey is one of my staple herbs that I use frequently when making topical creams or lotions. Comfrey contains allantoin which causes cells to divide at an increased rate, thus healing bones and wounds more quickly. Comfrey may be used topically -- as a salve or poultice -- on cuts, bruises, abrasions, and burns.
For turkeys, comfrey is pure protein and they seem to love it. They get a bunch about once a week as a supplement and to amuse them with.