Invasive weed ID

[Suby2]

Hope I have added photos OK.

Can anyone identify this plant which is invading our fields? Our two horses seem to pull it out then spit it out so there are loose tufts all over. It was green but has recently turned a rust colour.

 

[Burnttoast]

Compare with toad rush, Juncus bufonius. Safe but apparently not palatable!

 

[Suby2]

Compare with toad rush, Juncus bufonius. Safe but apparently not palatable!

That does seem likely as it likes wet and muddy conditions (very wet and muddy this last winter!!) and turns red as it starts to die with high () temperatures and moisture stress.