Editor's note: The following answer is provided by Limin Kung, Jr., silage expert and faculty member at the University of Delaware. It is part of a presentation he made at the recent Cornell Nutrition Conference.

Q: There is mounting evidence that prolonged storage time of corn silage improves starch digestion and increases protein solubility. What do these findings mean for the average dairy farmer?

A: Although increasing the storage time of corn silage and high-moisture corn (HMC) appears to improve the rumen availability of starch, not all producers have the capability to increase inventory to achieve this because of a limited land base and (or) fixed silo inventory. The added cost of carry-over has also not been thoroughly evaluated. Furthermore, when modeling forage changes in the silo, Buckmaster et al. (1989) reported that emptying a silo in 120 days vs. 360 days reduced DM loss by 6 percent. They concluded that increasing time in the silo results in greater DM loss because of infiltration of air in to the mass. Thus, this factor should be considered when making a decision about storing silage for longer periods of time.

For those producers that can store silage for longer periods of time before feeding, extra precautions must be taken in silos where plastic is used to maintain anaerobic conditions (bunks, pile, and bags). Chances of damage to the plastic increase with time of exposure to UV radiation, animals and general degradation of the plastic. Because silo plastic is permeable to oxygen, prolonged storage ultimately increases the exposure of surface silage to more air. Prolonged storage also means that silages will be fed in warmer weather and prone to more aerobic deterioration. The need for excellent silo management in terms of correct moisture, chop length, density and sealing will also be critical to maintaining silage quality. Use of plastic with low oxygen permeability and the use of additives to improve aerobic stability (e.g. Lactobacillus buchneri) should be considered.

Changes in starch digestion with prolonged storage may explain two phenomena that are commonly observed with lactating cows. First, it is common to hear reports of cows dropping in milk production when switched from "last season's" corn silage to freshly ensiled corn. Some of this "slump" may be attributable to the consumption of large quantities of unfermented sugars, but it may also be due to the fact that freshly ensiled corn silage is much lower in starch digestion than silage fermented for a longer period of time. Second, it is also common to receive reports of cows with laminitis and low fat tests in the spring. This may be a result of the increased availability of starch in corn silage and HMC. Thus, although prolonged storage of silage improves the digestibility of starch, many may find it difficult to adjust diets to compensate for these highly digestible feeds. If this is the case, one suggestion might be to process corn silage and grind corn less for those feeds that will be stored for longer than eight to nine months.

Read the paper that Kung presented at the recent Cornell Nutrition Conference.