Single-use plastic bags can kill cows and horses if they eat them. Death can be slow or quick. Neither speed is pretty. The best bet is to not let them get loose in the first place. The second best bet is to pick up every one you see around corrals, stalls and pastures.
Source: The Texas Tribune, August 14, 2019. Link. When West got to the pen, the colt had already swallowed the bag, and she could see that he was suffocating. He then bolted, jumping a barb wire fence. West ran after him. But she was too late.
Source: Drovers, March 8, 2013. Link. Complete blockages of the digestive tract can sometimes occur in cattle. Calves are curious and anything moving around the field becomes something to chew on.