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Cold temperatures challenge corn silage production

J.W. Schroeder Published on 31 December 2009
Just when you thought the dairy economic situation was getting some relief, at least with somewhat lower feed costs, thanks in part to some decent corn silage yields, Mother Nature stepped in.

Not that producers were tardy in cutting their corn; a wet spring delayed planting and below-average temperatures slowed the crop’s development during the growing season, so they were waiting for the forage to mature for cutting.

However, just as the silage harvest was in full swing, very cold weather complicated the situation. Not only did much of the Upper Midwest get a hard frost, the temperatures remained cold. This resulted in frozen forage that was too cold for adequate fermentation, setting the stage for potential losses of a valuable feedstuff.

Now the questions are: When will the weather warm enough to start fermentation in the pile? Will the silage become adequately fermented to make silage? Will the silage be any good in the spring? A packed and cold silage pile will be very well-insulated. And, what heat is generated more likely will be lost to the heat of fusion (the amount of heat required to convert a solid at its melting point into a liquid without an increase in temperature).

This is an unstable situation for silage. Unfortunately, the inoculants added to enhance the ensiling process may not work, either, because they need some heat to activate. All may not be lost, however, because inoculants do kill undesirable “bugs,” or microbes, and yeast. Likewise, cold kills and preserves as well (that is why we freeze food for later use).

The recommendations to the manager at this point are simple. With winter here, the cold temperatures offer some advantage for preservation. However, predicting the outcome of this silage next spring is somewhat more difficult. Without adequate fermentation, this refrigerated pile of feed will keep just fine until temperatures rise. As outside temperatures rise, the frozen silage can become very reactive. You will see it begin to heat in the feedbunk, as well as spoiling in the storage bunker. This leads to another concern, the rate of feedout.

Once the silo, bunker or pile is opened, spoilage begins in normal situations. Unfermented silage likely could spoil at a faster rate as oxygen permeates the exposed face of the pile because the silage did not have the benefit of achieving any anaerobic stability of ensiling. The watchword here is monitoring the pile often to adjust its use and exposure of the silage to the air to minimize spoilage losses.

Probing the pile for temperature change can provide clues about fermentation. A normal fermentation would reach about 100 to 110ºF. Less than that means it still is in the freezer. Higher temperatures (120 to 130ºF) are not good and mean undesirable processes related to spoilage are going on.

Another way to determine if fermentation is occurring is to check the pH (alkalinity or acidity). Normal silage should have a pH of about 3.6 to 3.8. If the pH is more than 5, not much fermentation happened. But if the silage still smells normal, it is fine to feed, but treat it like fresh greenchop.

If you are feeding large quantities of a normal silage, don’t make a sudden switch to this stuff. You could have fresh, frozen greenchop, which typically is high in free sugars. You would do well to adapt your cows to this silage during a week-long period. Going “cold turkey” or feeding large amounts overnight could send your cows into subacute ruminal acidosis (digestive upset). Normal silage typically has 1 to 2 percent sugar, but if fermentation did not take place, the sugar content could be 6 percent to 8 percent of the dry matter and contribute to an overload in the cow’s rumen and cause her to go off feed.

Unfortunately, new silage never seems to yield as much milk as silage that has fermented 60, 90 or, even better, 120 days. If you have to use it before it has fermented, you likely will need to make additional dietary adjustments to maintain milk production. Unfortunately, additional ingredients will result in higher feed costs.

If you have a frozen pile of green silage, it will need to be managed in a manner that will reduce eventual losses next spring or you could have a huge pile of slop.

For now, make sure the pile is covered as you normally would. Monitor it closely for changes in temperature, appearance and smell. If you find yourself in a situation of having a large pile of unfermented, or greenchop and frozen silage, having a feed analysis laboratory test for at least total sugar content and pH also would be advisable. Knowing the pH can be very useful information and provides a status of the fermentation. If the pH remains high, you and your nutritionist can manage accordingly and prevent overfeeding the silage.

The challenges just keep coming!  FG

J.W. Schroeder, Dairy Specialist, North Dakota State University