Please excuse me for sticking my nose in (since I don't keep livestock), but Scartlet.Dragon is obviously right: hardy, potentially native or other semi-wild breeds of animal will almost certainly be the animals requiring least oversight (but not "no over-sight"). If the preferred animal doesn't get on well with brambles, then mechanically cut. You might need to repeat mechanical cutting, but animals will then gradually win the battle in a confined area.
Stock numbers will also need to be fine-tuned to the grazing potential available throughout the year to minimise the need for supplementary feeding.
Fencing: the larger the animal the more likely they will accept a hedge as their boundary, but, as even I know, goats and sheep will simply see a hedge as something they need to get to the top of !