Since corn silage harvesting is currently under way, a review of the processes that are involved in the fermentation of corn silage is probably warranted.
Silage fermentation can be broken down into four phases:
The aerobic phase begins immediately after the corn is chopped. Oxygen trapped in the air spaces of the silage is used up by plant and microorganism respiration which gives off carbon dioxide and water--andheat. Ideally, the temperature should rise somewhat during this phase to 80 to 90oF. During the lag phase which follows, plant cell membranes break down. This sets the stage for the fermentation phase, where anaerobic bacteria which do not use oxygen grow on the sugars in the plant juices, producing acids which reduce the pH of the silage. Bacteria which produce acetic acid are most desirable at the beginning of this process, and as the pH drops, about the third day, lactic acid-forming bacteria take over until the silage is so acid that even they can no longersurvive. At this point, all bacterial activity stops and the silage is now in the stable phase, until the pit is opened and oxygen is againallowed to enter.
If there is too much oxygen during the initial aerobic phase (the pit isn't sealed well, the silage is too dry to pack well, hollow oat stems aren't crushed, the cut is too coarse, etc.) excess heat may be produced, and too much plant material will be broken down and the nutrients lost. Silage temperatures over 100oF will cause browning and loss of palatability. On the other hand, if the silage is too wet (over 72 to 75% moisture), and packed tightly, the silage may run out of oxygen before the temperature reaches 80oF. This temperature is too cool for the desirable acetic acid-producing bacteria but just right for butyric acid formation, which gives silage a putrid odor and the unpleasant taste of rancid butter.
Use of Inoculants
It is difficult to show an economic advantage from the use of silage additives when the use of proper procedures will keep silage losses to as little as 3 to 7%. The economics of using silage additives must consider the cost of the treatment and the value of the silage. Most silages will have a value between $20 and $30 per ton at feeding time, depending on kind and moisture.
With the expense of using inoculants, a silage producer should expect results that are predictable. Unfortunately, results with inoculants have been anything but predictable.
The following table will indicate the percentage increase in feeding value that must be realized, just to pay for the additive, not to mention the cost of application. For example, if an additive costs $2 per ton of ensiled material that is worth $26 per ton, then an increase of 7.7% in feed value would be necessary to pay for the additive.
Example: $ 2.00 x 100 = 7.7%
No additive is generally warranted for corn silage, provided it was harvested under normal weather conditions.
To ensure that a quality silage product is produced, silage producers should follow these recommended steps:
November 5, 1999