ponytug
Super Member
It is a common weed. Just having your pigs disturb the soil would be enough to get it started. A lot of farmers have trouble with it as a weed because it grows so quickly and in many areas it has evolved to be Roundup(tm) resistant.After following your link out, I am having second thoughts about using it as feed. Apparently it can have nitrate levels high enough to be toxic... especially around bloom which is when I've been feeding it. Now I'm not sure how it got here unless as a noxious seed in the grain.
Depending on the feed, I guess it is possible for it to have turned up via feed, but I have seen it growing practically everywhere around the US. It generally isn't the right size seed (they are tiny!) to pass through a combine or harvester, which would screen them out.
Any physical method works well to get rid of it, but then reseeding with something else to help out compete it helps prevent regrowth. Mulching helps shade it out. (Straw bedding for the pigs?)
All the best,
Peter