If you have extra 2013 corn silage, keep using it and allow the new silage to ferment for as long as possible. If you are running short or have only one silo to use, try getting 2 to 4 weeks worth of silage made from earlier fields stored in a bag or perhaps a covered pile. This early crop can start fermenting and help provide at least some transition silage to get you through the time when the bulk of your 2014 silage is fermenting. Keep the other forage components of your rations the same during the corn silage transition period to help minimize changes for your cows.
Variation from one year to the next is often large, and many people collect silage samples for a preliminary analysis right away. Even with this preliminary analysis, be sure to collect more samples when you open your new 2014 silage after it has fermented for 3 weeks.
Lastly keep track of silage dry matter changes. During the transition from fresh-cut silage to fermented silage, the dry matter will change, so keep monitoring it closely. Most of these changes occur in the stalk and leaf portion of the silage, while the grain seldom changes in dry matter. As a result, huge shifts in forage to grain ratios and overall ration nutrient concentrations can occur if the actual forage dry matter differs from the dry matter entered at the time the diet was balanced. Tracking forage dry matter and adjusting the ration accordingly can allow your cows to have a lot more ration consistency during the inevitable forage changes that occur.
Source: Penn State Extension