My experience with hardware: a coule of years ago, one of our cows went off feed, depressed, lying down a lot, but getting up to move to the shade. Called the vet (got the vet covering for ours that week); he got there within the hour, examined her in the field (tied to a tree). He thought she had a chest tumor (cough, decreased heart rate, slight bloat, fluid in chest bilateral, no temperature). Suggested we send her to VA Tech for a workup (I about fainted, convinced that we'd never see her again if we did that!). Also said we could try giving her a magnet and penicillin (neither of which he had with him, but at least he got there fast and gave me some options).
So, I got a magnet and penicillin, got the cow (and her 1-mo old calf) up into the pen, got the magnet in her (that was interesting!), gave her a shot (my first ever!). As her milk had dried up (that happened VERY fast!), I had to try to bottle-feed her calf (needless to say, the calf did not take kindly to that and just kept trying to nurse her mama).
The next morning, the appetite was back, the milk gradually came back, and all was well. Not bad for a 10-year old cow. We were lucky! Now all of our cows have magnets!
This is an old farm, and every time I got out in any of the pastures I pick up nails, or small pieces of glass, or wire, whatever...never fails...I just keep picking up stuff, especially after a hard rain...stuff keeps coming up out of the soil. And I suspect some stuff comes in the round bales too. Always something out there to pick up.
Hope this helps.
Gale