[who_would_fardels_bear]

My understanding is that sometimes children are prone to eat things they ought not of a metallic nature, and it is often determined that they have some mineral deficiency.

If cattle ate mostly grass then they would tend to consume a sufficient amount of minerals. However, if they are mostly being fed corn then I could see where they might have mineral deficiencies which they compensate for by eating whatever iron objects are ready to eat.

[FredZarguna]

When you are harvesting, storing, transporting, and forking tons and tons of feed per day, bailing wire, nails, staples, fasteners, screws, dust, chunks of wood, chips of concrete and what have you just wind up in the feed. It isn't like pica or deficiency disorders where a human consciously ingests non-food items. A cow consuming a hundred pounds of feed a day is completely unaware of it -- unless it happens to puncture her reticulum, rumen or abomasom.

[SgtHooper]

Cattle do not willingly eat metal; it is only by happenstance in the harvested grains.