@@FrancisjMcWade thanks for your comment. It’s hard to show on video in detail. We have a lot of crabgrass and it has a thinner blade and a seed head. This has a really wide blade, is brighter green and no seed head at all.
My father in law milked cows for a living. He said that 2 of his cows broke through his fence to get at the Johnson grass growing in the ditches. The Johnson grass was very tall and had seeded out. He lost both cows and the vet told him that Johnson grass is ok but when Johnson grass is seeded out on top that it is a killer. Just make sure that they eat Johnson grass when it is young and not let it go to seed head. He lived on the border of NE Oklahoma and NW Arkansas.
Johnson grass has to have a freeze for that to happen. It produces cyanide after the frost. Which makes it deadly. Johnson grass has received a bad name, but in fact great for cows.