Although these are good pasture grasses they will not necessarily make good hay. So bear this in mind when you re-seed your paddocks. Herbs are also good for horses and occur naturally in the wild. Good pasture should include dandelion, garlic, sheep's parsley and chicory. To many dandelions or docks will indicate that the pasture has been overgrazed at some time, and these opportunists have filled the void left by the grass.
Buttercups can also be a problem.
If the field is choked with weeds it will need to be ploughed up and re-seeded. However this is quite a drastic measure but with care and hard work pasture can be turned round to become reasonable grazing. With last winter's rain, lots of horse owners are now being faced with badly poached fields. You can improve drainage by keeping ditches and drainage pipes clear. Streams should also be kept free flowing by removing debris.