Hay is often bound up into bales with plastic twine. Cattle happily eat bits on accident. They used to use wire, but that caused a much more serious problem for the cattle.
CalRobert
Silage uses insane amounts of plastic wrap and then is left in direct sunlight to decay
giantg2
They used to use natural twines like jute, which was better. They really don't eat much of the plastic stuff. The larger pieces of it do kill them (choking, cholic, etc).
kylebenzle
Now we will wrap the bales in 5 to 10 lb of plastic each, so they last longer!