I use to have a horse that would curl his lips back and eat the flowers off the big purple thistles. He had plenty pasture so all I could think he found them sweet enough to tough out the prickliness.
Our pasture here does not have any thistles (goats)
But they come up in the landscape . I leave them to flower but cut them before dispersing seed.I am often barefooted and do not like them in the lawn.