It is true that horses would be more likely to eat it if it was pulled up and left in the field to dry, just as they will eat it if it is included in hay. But who would be daft enough to pull it up and leave it lying around? It needs to be burnt.
Pulling it is always preferable to leaving it, even past the rosette stage, to prevent seeds being blown and more plants growing
''Ragwort if pulled out of the ground is undetectable by the horse and could be eaten mistakenly?''
If it hasn't been left on the ground how is there anything there for them eat??????????? Dig up plant and burn. You can put some rock salt in the hole where you've dug it up if you want which kills any remaining roots..........