My cows come running when I show up at the fence with a bowl of apples. Of course, I'm always glad there's a fence, and a hedge of brambles, between us. Cows weigh around a thousand pounds—and that's before they're fully grown and pregnant, as they almost always are. It's not unheard of for people to be trampled by them, especially if they don't follow the simple common-sense rules explained here:
1. Never get between a cow and its calf. Cows are protective creatures and will defend their young if they feel there is a threat. Standing or walking between a cow and its calves is easily avoided by avoiding walking through the middle of a herd of cows if young calves are present. Cows often make this easier for you by moving away from approaching walkers, as long as they see you in good time.
Very good advice, and easy to follow. You should also not let your dog off lead around cows, even if your dog has no more interest in cows than mine, who found it strange I'd toss lovely apples to strange cows when she was perfectly capable of eating them herself.
On the other hand, if the cows are already angry at you for some reason—perhaps they smelled the steak on your breath, or heard you speak disparagingly of the herd—then you should let your dog off lead to fend for herself. She can get away from them much easier than you imagine. (Of course if she's a small terrier, you'd better pick her up and run like hell—they'll be after you both then.)
(Thanks to @Travelwriticus for the link above. If you're not on Twitter, you're probably missing out on many valuable tips, regarding cows and other creatures.)
In other news, I learned today (again, via Twitter) that BBC4 will be airing a new sitcom filmed in the Chilterns, about a group of ramblers with leadership issues. It's called "The Great Outdoors and airs Tuesday. Be sure and watch, for a glimpse of the land I regularly trample.
Not sure there'll be any cows, but it's a safe bet.