Editor’s note: Jerry Weigel is the manager of nutrition and tech service for BASF Plant Science. You can contact him at gerald.weigel@basf.com.

One of the major goals of fermenting corn silage is reducing oxygen and increasing acidity as rapidly and efficiently as possible. This is required so that lactic-acid-based bacteria will proliferate to stabilize and preserve corn silage. The question is, how long should one wait before feeding corn silage? It is often believed that corn silage will be fairly well fermented and ready to be fed just three weeks post ensiling or chopping, but this isn’t the case.

It is important to understand how the final two phases of corn silage fermentation affect corn silage feeding quality. We understand in phase III, or the anaerobic fermentation phase, we should have depleted all the oxygen. The corn silage area should begin anaerobic fermentation about 15-16 days post chopping. As mentioned before, in this phase we want to ensure that the available sugars are converted to lactic acid, as well as some acetic acid, ethanol and a few minor products. In most cases corn silage should complete the active anaerobic fermentation in about a week, but that is just a rule of thumb. The rate and extent of fermentation depends to a large degree on the quantity of lactic acid bacteria. Here, harvest moisture will become a factor, as wetter forages ferment faster than drier ones.

The next stage, the storage phase, lasts a week to 10 days as the silage pH stabilizes. It has previously been thought that microbial and enzymatic activity occur minimally. That is now being revisited even in the presence of optimum pH and may be more important than simply dry matter loss and excessive heating within the storage area.

An interesting paper1 by Ralph Ward, Cumberland Valley Analytical Services, and Mary Beth de Ondarza, Paradox Nutrition, contends that well-preserved corn silage contains more than 3.00 percent lactic acid and less than 3.00 percent acetic acid with a pH of

We also need to understand and realize that the starch in corn silage increases in digestibility over time in storage due to:

  • Glycolic enzyme production due to continued plant respiration
  • Microbial enzyme activity
  • Effect of solubilzation of prolamins by the production of bacterial based ethanol
  • Acid hydrolysis of certain protein

Another paper2 by C. M. Hallard and others reported that digestibility traits generally stabilized between 4 and 6 months but certainly leveled off at 6 months post chopping.

The important questions here are: how much starch is the rumen actually able to utilize, and how should we as nutritionists get the most efficient use of the starch level within the grain fraction? This is one of the reasons many nutritionists are focusing more on Neutral Detergent Fiber utilization than the total starch content of the corn silage. Ration formulation will allow us to alter corn inclusion into the feed while maintaining high Net Energy for Lactation values with greater digestible NDF. This also allows for a safer feed and could very well add to cow comfort as it creates a less challenged rumen.

I am not sure if we would see any increase in protein solubility in corn silage over time, but we do see increases in protein solubility over time with High Moisture Corn (HMC), so be careful when reading the literature on products being evaluated for protein solubility.

The above thoughts are the very reason we need to spend time planning and considering the time-span between chopping/ensiling corn silage and when feed-out starts. This is especially true for the formulating or consulting nutritionist to know. I have been involved with herds that could not maximize milk production due to underestimating nutrient uptake as well as metabolic and feed intake problems when we did not alter our rations due to improved solubilization.

One take home message here is that while it is okay to sample your silage at harvest or ensiling time for protein and moisture, do not use this analysis for ration formulation. Re-analyze your corn silage at feeding time and look for nutrient digestion over time, especially starch digestibility. There are a number of laboratories that can help you with this process.

So the bottom line becomes, how long does corn silage need to be kept in storage prior to feeding? The literature seems to suggest a minimum of 4 months (~120 days); certainly a minimum of 100 days is very realistic for maximum feeding value.

1 Ward, R. & de Ondarza, M.B. (2007). Is Corn Silage Stable After 3 Weeks of Fermentation? Cumberland Valley Analytical Services. Reprinted in the August, 25, 2009 issue of Feedstuff’s p 532.

2 Hallard, C.M., Sapienza, A., Taysom, D. Effect of length of time ensiled on dry matter, starch and digestibility in whole plant corn silage. Journal of Animal Science, Vol 86, E-Supplement.

Source: BASF