We all know the grazer value is buggy, but this is not really related. Right now, it seems that your animals and the wildlife live in perfect harmony. I think it would be fun to have the predators attempt to slaughter your animals, and haul their corpses off the map. Or eat them right there. Depends on how Toady would want to approach it. Behavior wise, the predators should linger around, trying to home in on a young or injured one that is seperate from the group. Depending on the animal, they would either flee randomly, or huddle around the young, old, and injured, or even attack in pursuit of the predators. You could also install a guard animal. A good example would be a dog, donkey, horse, llama, mule, or even a jabberer. Just a generally agressive and capable creature. Guard animals would attempt to kill anything that comes into their pasture, inadvertantly protecting the herd within. In real life, cattle or sheep, when they feel threatened, they huddle over near their guard animal. Generally a guard animal must be bigger than the majority of the flock or herd. Also, in real life cows don't just sit and starve amid a big field of grass. I think if you assign a pasture they will go directly there and stay there (or wander a bit like goats), but otherwise they will just graze randomly.
removed hay, posters below aren't crazy. I just thought it was a useless bit.