Essentially, what Chris A said. You're camera's automatic-exposure meter is going to treat whatever your camera's exposure meter is pointing at as if it were a middle grey(i.e. 18% grey). As it appears, you metered off the black cows. That's great, but your camera, by default, thinks those black cows (at levels of[probably] 70-80% grey) are 18% grey. It will compensate for what it thinks is a deadly dark shot (the black cows) by overexposing in order to bring out highlights. So, you'll see a lot of highlights in the dark cows, but the rest of the frame, as you notice, is dangerously overexposed.
You could have fixed this for sure by having that front cow hold a grey card in its mouth, off of which you would have exposed that shot perfectly. If you prefer not getting so close to the cows as to put an 18%-grey card in its mouth, you can expose off of something near 18% grey. I would have probably chosen the grass in front of the cows. Greenish shades are often the nearest to 18% as you can get, and I think that deadish grass might have sufficed.
I'm sure this is a difficult shot to meter as there's so much light/dark polarity with the light/dark cows, but if you stick to something in the middle, I think you would have come closer to exposing this shot more to your liking. I'm guessing you either spot-metered or used a center-weighted metering. Maybe if you'd used a full-frame averaging metering, it might have exposed correctly, but I'm not sure, judging by the amount of dark black in the frame.
Edit. As I look at the frame again, I think maybe you would have done really well to meter off
"How-now-brown-cow's" leg/shoulder/breast region. That would have likely exposed him(her) well and gotten a good amount of detail from the grass, the blackish cows and the background.
The way I would have thought of it is like this: "If I meter off the blackest of cows, the rest of the frame will be really bright since the camera thinks this is a really dark shot. Or...If I meter off their white faces, the rest of the frame will be underexposed since the camera thinks this is a really bright shot. I might as well stick with metering off of something in the middle."
Further edit: If your question is a simple technical question about how to meter with your camera, you simply half-click the shutter as you are pointing towards whatever you want to meter, in this case probably brown cow. Then you'll probably click the AE-L button to lock that metering as how you want your camera to expose the frame, then compose your shot and fire the shutter.
Sorry if this is stuff you already know. I really admire your work, Valdore. I just teach "America's future" so I'm kind of stuck in the mode of giving simplistic advice in the hope that it'll stick with someone.