I would add, however, that where there are cows (and I mean cows-girly cattle) and calves present or where there is a bull with it's harem there is the potential of aggression from the beasts. This will become a likelihood of aggression if you have a dog with you. In these circumstances it is wise to give them the widest possible berth or if you come upon them without warning, a retreat is advised - find another way.
I have walked through herds of dairy cows since childhood (which was quite a long time ago now) without any bother and the only time I've felt any concern with bullocks (remember they're the ones with a couple of bits missing) is when a group galloped happily down hill to investigate (without any real hope of stopping in time !). I have had a bull rise up from rest and begin an angry-looking walk towards me before but a strategic retreat resulted in his satisfaction that he'd made his point.
I DID see a couple with a dog walk straight through a herd of cows with calves resulting in very agitated and aggressive responses from the cows. I was on the point of driving my car (parked up for a cuppa) quickly down to rescue them when they finally twigged and retreated. All was well.
Another time I came across a bull among cows right beside a public footpath, obscured until the last moment by a barn wall. The cows were curious, the bull barely managed to open one eye - and then promptly shut it again.
So we all need to try and read the situation before we're in the middle of it and caution is the better part of valour. Equally it would be nice if farmers all considered the potential for trouble as well