You need to watch out for smaller animal scat, too, not just livestock. Cat feces can carry some real nasties, the name of which escapes me right now, but one of them is why pregnant women shouldn't clean litter pans-they can end up with blind babies. I'm sure dog carry something transmisable through poo, too, I just don't have any facts on that one.
If ksst says the grass is safe, I believe it, even if my cats always throw it back up for some reason; just make sure you have clean grass. (Oh, man, there has to be a Cheech and Chong type joke in that, somewhere. Come to think of it, I've heard that that kind of grass can carry salmonella . . . bummer.)