This is a great topic. I suppose grass and pasture in general is basically herbal?
My horses get free choice with old meadow but I think they prefer grass and hay. I have lots of patches of stinging nettles dotted around the field, but these are only eaten when I cut them and they wilt, so I cut only a few at a time. We have numerous Hawthorn trees and Willow yet I do not see Ben the laminitic prone pony help himself, although if he is spending time in his stable, he is happy for me to collect browse. We also have Poplar, Oak, Ash, Hazel as well as a variety of rushes, sedges and mint growing around the pond. This time of year the Yarrow is flowering, and again it can be such a benefit but my horses seem to prefer the grasses and clovers. All of the horses can manage to pick blackberries but leave the wonderful rosehips.
For a few more herbs/spices/therapies I posted a link to some other treatments, often with multiple properties, curcumin/turmeric is known for digestion, skin, joints, altzeimhers, cancer among some of the research done on it's amazing chemical chains.viewtopic.php?f=13&t=2907