If you must utilize this forage and cannot wait several more weeks for quality reasons, cut the plants so as to leave the bottom third of the plants in the field. The bottom third of the plant contains nearly 7 times more nitrate than the middle part. Cutting the plants for silage would be better than utilizing it as hay. Feed grain with the suspect forage. The most common grass in this area is tall fescue.
Tall fescue is a cool season grass which goes dormant in hot dry weather.
Continuous grazing of the plants prevents that natural dormancy from happening and weakens the plants. Broadleaf weed seeds germinate more easily as the grass grows thinner. These weeds further weaken the grass by competing for water and nutrients. That usually means spraying around the end of April, when the grass is thick and lush and you don't think you have a weed problem. Spray for broadleaf winter weeds the end of November.