Making corn silage seems simple: chop it, pack it, let it ferment, then feed it. However, making high-quality silage, reducing losses and preserving the silage is more complex than that.

Many producers put up silage in piles and have no way to determine losses. In order to save time and/or the expense of covers and preservatives, the losses may be acceptable to them. A lot of good-looking silage is made by just piling it, but it could be made better.

  • One of the best and more recent innovations for improving silage quality is mechanical processing. In this process, the cut silage passes between rollers operating at different speeds, which crush and shear the silage.

    The shearing improves fiber digestibility by increasing the surface area of the corn plant and cob so that rumen microbes can better work on it. Meanwhile, the crushing improves the kernels' starch digestibility by cracking the hard outer covering of the kernel along with crushing the cob and exposing the starch fraction of the corn kernel to the rumen microbes. The silage seems to pack tighter, which makes for less spoilage.

    The improvement in fiber and starch digestibility due to mechanical processing improves the energy content at all stages of maturity but may improve it more in mature plants.

    In processed silage, it's almost impossible to find any traces of cob. In mature corn, we normally find slices of the cob in the bunk but not with processed silage. Mechanical processing allows more of the fiber and kernels to be digested with less waste.

  • Covering a silage pile with plastic greatly reduces waste, but only a comparison of weight-in and weight-out measures, as well as a nutrient analysis, can tell us what's being lost in storage. Most folks determine waste by the depth of the black layer on top.

  • Silage additives are one way to reduce dry matter and nutrient loss. Silage additives aid fermentation. They supply lactic acid-producing organisms, some nutrients required by the bacteria and/or enzymes that increase the amount of carbohydrates available to the organisms. Other types of additives include molasses, ammonia or other non-protein nitrogen (NPN) and propionic acid. Not all increase fermentation but aid in preservation.

    There are more than 200 different silage additives or preservatives available. Some work well, but many don't. They are classified as bacterial inoculants, enzymes, acids and ammonia or NPN.

  • Aerobic stability — the ability of a silage to remain fresh in the silo, pit face or bunk — may not be a concern for producers who feed a lot of silage daily. But for feeders with a large face on the silage pile or smaller feeders, it may be a problem.

When silage is exposed to air, certain yeasts can degrade the lactic acid. This makes the silage less acidic and leads to spoilage. This is more obvious and occurs more frequently in poor-quality silage that hasn't fermented properly. Warm weather and exposure to air also encourages the growth of spoilage organisms.

Buffered propionic acid-based additives applied at cutting at the rate of 2-4 lbs./ton of fresh forages can help to preserve aerobic stability. Preservatives may also be added when feeding. Anhydrous ammonia can be added at ensiling, but it doesn't enhance fermentation and is dangerous to handle. Traditional microbial inoculants may improve fermentation but don't consistently improve aerobic stability.

Fermentation Analysis

If a producer has a problem with his silage, a new forage evaluation tool called fermentation analysis may help pinpoint the problem. The analysis includes an acid profile — lactic, acetic, butyric and propionic acids, ammonia content, pH and total acid content. Comparing the levels to the normal range may help identify problems.

Even small changes in acid content can alter the intake in all classes of animals but may be more dramatic in young calves and finicky eaters. For example, just a 1% level of butyric acid in the silage may cause odors that discourage some animals from eating it readily.

Each of the acids produced during fermentation of silage and haylage have a distinctive smell:

  • acid smell,
  • acetic acid — like vinegar,
  • butyric acid — rotten,
  • propionic acid — sharp, sting in the nose,
  • lactic acid — sweet.

Acetic acid and lactic acid are the predominant acids in good-quality silage or haylage, while propionic and butyric acid levels should be below 1% in the silage.

Good management, good harvesting and packing methods, along with a way to measure and monitor temperature, pH, acid levels and nutrient values to consistently put up high-quality corn silage are essential. It's possible to make “good” silage better with additives, but additives won't cover for poor harvesting and packing methods.

David Wieland is a nutrition consultant specializing in cow/calf, feedlot and horses. Based in Shepherd, MT, he also publishes a subscription newsletter. Contact him at 406/373-5512 or