Roughages are a good, and cheap, source of essential nutrients for dairy cows. One possible way to increase roughage consumption is to add some ground corn to grass silage at ensiling or to feed concentrates on top.
Porter, A. R. and Allen, R. S.
"Dairy Cows Like Ground Corn in Grass Silage,"
Iowa Farm Science: Vol. 9
, Article 3.
Available at: https://lib.dr.iastate.edu/farmscience/vol9/iss4/3