It is a problem to make cows eat the drier corn silage. Adding wet gluten or wet brewers grain would help if available and economical. Adding 10 to 15 pounds of water to the total mixed ration (TMR) mixer per cow per day can help hold the TMR together (less sorting) and may improve intake.
Mike Hutjens, Extension Dairy Specialist, University of Illinois - Illini DairyNET