We do not seem to get much choice about feeding on buttercups! we do find that they tend to leave the long stringy ones though and we tend to top the field after the cattle have finished feeding to try to get a new start for fresh growth.
Buttercups in abundance here, but they loose their competitive advantage with continued intensive rotational grazing (the cows don't leave many). Ideally they want an earlier Spring grazing round to knock them back, but it didn't happen this year.