Will horses eat climbing rose bushes and trumpet vines if they have plenty of grass for grazing?

Yes, horses will eat those plants if planted on a fence line. They will not eat them as a primary forage but will graze them from time to time. I don’t think they will bother the climbing rose bushes once they feel the thorns. To my knowledge, rose bushes and trumpet vines are not poisonous to horses. You can make your own decision, but it is probably not a good idea to plant them along your fencerows close enough that the horses can reach them.