Dairy cows fed plenty of silage, properly balanced with a grain mixture, will produce just as well and keep in as good condition as those fed both alfalfa hay and silage as roughage. In other words, apparently cows do not need a dry roughage along with silage.
Cannon, C. Y.; Espe, D. L.; and Hansen, E. N.
"If Hay Mows Are Empty,"
Farm Science Reporter: Vol. 1
, Article 5.
Available at: http://lib.dr.iastate.edu/farmsciencereporter/vol1/iss4/5