What's in Your New Crop Corn Silage?

As silo structures are opened after harvest, producers can find issues with molds, mycotoxins, and abnormally warm silage. The initial fermentation period in corn silage can progress in as soon as 30 days, after which producers can evaluate the fermentation and nutrient quality of ensiled corn. Producers may also notice that pH and starch digestibility levels continue to change over the following 180 days as silage acids continue to degrade some components of the starch molecules.

Submit a Forage Analysis

A forage analysis is critical to helping livestock producers properly balance rations, minimize purchased feed costs, and prevent animal health issues. However, a forage analysis offers value beyond indicating protein, starch, fiber, or other nutrient levels. Various commercial forage analysis laboratories have expanded testing packages to include fermentation quality analyses, mold and mycotoxin screens, and energy index calculations.

An annual forage analysis can also help you benchmark your forages against other producers and ideal nutrient levels. Since forage quality can vary from year to year based on growing season conditions, searching through a lab's quality data can explain yearly differences in starch or fiber content. Industry benchmarks can be found in the article Corn Silage Production and Management.

Fermentation Quality

The goal of fermentation is to preserve fresh forage as a high-quality feedstuff that can be utilized year-round. When the silo is sealed, oxygen is depleted, and various microorganisms consume soluble sugars to produce end-products that help decrease the pH and prevent the growth of undesirable microorganisms. A well-fermented silage will be odorless or slightly acidic, like mild vinegar, but not in an unpleasant way.

The main end-product produced during fermentation is lactic acid. Lactic acid is a strong acid produced mainly by lactic acid bacteria (LAB). For corn silage, the final pH should range from 3.7 to 4.0 with a concentration of lactic acid around 3% to 6% of the dry matter (Kung et al., 2018).

The second most abundant end-product in corn silage is acetic acid. Acetic acid may range from 1% to 3% of the dry matter (King et al., 2018). The presence of acetic acid is desirable due to its antifungal properties, which prevent the growth of yeasts and molds once the silo is exposed to oxygen during feed out. However, very high concentrations of acetic acid can also make the silage less palatable. The ratio of lactic acid to acetic acid should be around 2.5:1 to 3:1.

Some additional end products that may be seen on a forage analysis report include propionic acid, 1,2-propanediol, butyric acid, and ethanol. Propionic acid also exhibits antifungal properties; some studies are currently investigating the efficacy of using bacteria that specifically produce this compound to enhance the aerobic stability of silages. For corn silage that is not inoculated with a propionic-acid producing LAB, the concentration may be around or less than 0.1% of dry matter.

If silage is inoculated with Lactobacillus buchneri, 1,2-propandiol may be detected at levels between 0.25% to 1.5% of dry matter, although as high as 3% has been observed (Kung et al., 2018). Ethanol may also be present due to various microorganisms converting sugars to this product. For corn silage, ethanol concentrations may range from 1% to 3% of the dry matter. Concentrations above 3% in corn silage are undesirable because they may indicate high numbers of yeasts, which can decrease the aerobic stability of the silage. Additionally, if butyric acid is detected in corn silage, it could indicate that an undesirable Clostridial fermentation has occurred. Ideally, a forage analysis will report "None Detected" (ND) for butyric acid, but producers should expect animal refusal and potential health issues when butyric acid exceeds 0.5-1.0% DM.

The final concentrations of the various end products produced during silage fermentation will vary greatly depending on the dry matter at which the forage was harvested. The free water (i.e., the water not trapped within the cell walls of the plant material) available for microorganisms is crucial for their growth. Studies have shown that as dry matter increases above 40-45% (or moisture decreases below 55-60%) in corn silage, the pH after fermentation increases due to the limited water availability. Additionally, the use of silage additives will influence the final concentrations of fermentation end products. Therefore, it is essential to consider the specific conditions of your forage.

Molds and Mycotoxins

The presence of mycotoxins may indicate the presence of molds. Common mycotoxins that may be detected in corn silage include aflatoxins, trichothecenes, deoxynivalenol, ochratoxin A, zearalenone, and fumonisins (Ogundade et al., 2018). The best defense against mycotoxins is to be proactive during the planting and growing season. There are three steps you can take to try to reduce mycotoxin production in the future:

• Select corn hybrids with high disease resistance. In some scenarios, seed catalogs will list resistance to individual diseases, but you may have to interpret some of the narratives that describe hybrids – terms like "standability" can hint at improved stalk rot resistance
• Manage insect damage to ears. Caterpillar feeding by corn earworm, western bean cutworm, stalk borer, and fall armyworm can damage husks and shanks, leading to infection by mycotoxin-producing mold species.
• Practice good crop rotation and residue management. Though corn silage generally provides a good chance to remove crop residue, disease inoculum can be introduced from neighboring fields. If you or a neighbor produces corn for grain or no-till wheat, harvesting fodder or rotating to a non-host crop may help reduce mycotoxin issues.

You can also prevent secondary growth of molds that may occur during the ensiling process or when feeding out. Ensure that your corn silage is harvested at the correct whole-plant dry matter, packed tightly, and sealed immediately. Additives or inoculants can also be used to prevent mold growth. Ideally, you should have less than 1,000 CFU/g molds in your corn silage (Goeser, 2024). However, some levels of mycotoxins may be unavoidable in your corn silage due to various challenges. Some producers choose to use a mycotoxin binder when feeding corn silage or other forages that contain high levels of mycotoxins. However, the specific binder will depend on what is available in your area and which mycotoxins are present in the silage. There are currently no FDA-approved mycotoxin binders available on the market, which means you must personally review the research that supports the manufacturer's efficacy claims. In most cases, silage that contains high levels of mycotoxins needs to be either fed to non-lactating animal groups or diluted with other forages and feedstuffs.

Shrink Reduction

Forage shrink due to dry matter losses can lead to considerable forage losses if not identified and addressed. Shrink is commonly defined as feed that is lost during harvest, storage, and feedout, and can be calculated by subtracting total feed fed from the starting inventory, then dividing by the starting inventory. An equation is listed below:

Shrink Loss (%) = [(Starting Weight – Total Fed Weight) ÷ Starting Weight] x 100%

For example, if crop management records indicate a farm harvested 3,375 tons of fresh feed, but feed management records indicate they only fed 3,105 tons of ensiled feed, the farm's shrink loss would be 8%. Managers should standardize forage dry matter levels to a consistent number (e.g., 65% moisture, 100% dry matter, etc.) to prevent moisture losses from skewing shrink loss results.

Ultimately, shrink affects the profitability of a crop production enterprise. Recent crop production budgets from the 2025 Penn State Agronomy Guide suggest that corn silage costs approximately $1,082.46 per acre to produce. At an estimated yield of 25 tons per acre (35% dry matter), this crop's production cost is roughly $43.30 per ton.

The best managers accept 10-15% forage shrink as typical, but when shrink levels start to exceed 15-20%, you should ask yourself several questions: Why is my shrink level so high? What can I do to improve it? Who should I rely on to help identify changes in management practices? Shrink can be reduced by:

• Harvesting corn silage at the correct moisture and stage of maturity
• Filling and sealing the silo structure as rapidly as possible
• Providing adequate packing to the silage mass
• Minimizing oxygen exposure at feedout
• Targeting fermentation end-products identified earlier in this text

Producers must understand production costs and shrink losses for corn silage to remain a high-quality, low-cost forage for livestock. Monitoring silage quality with forage analysis reports remains a key component for improving silage quality every single year.

References

Goeser, John. Fungal and Bacterial Count Guidelines* for Agricultural Feeds and Total Mixed Rations. Rock River Laboratory, Mar. 2024, rockriverlab.com/. Accessed 16 Nov. 2025.

Kung, Limin, et al. "Silage Review: Interpretation of Chemical, Microbial, and Organoleptic Components of Silages." Journal of Dairy Science, vol. 101, no. 5, May 2018, pp. 4020–33, doi.org/10.3168/jds.2017-13909.

Ogunade, I. M., et al. "Silage Review: Mycotoxins in Silage: Occurrence, Effects, Prevention, and Mitigation." Journal of Dairy Science, vol. 101, no. 5, May 2018, pp. 4034–59, doi.org/10.3168/jds.2017-13788.