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Key Ideas From Silage Conference Discussed


Key Ideas From Silage Conference Discussed

By Bill Mahanna

I recently spent an informative week attending the 15th International Silage Conference, where I had the opportunity to review research and interact with 250 silage researchers from more than 20 countries.

This conference was hosted by the U.S. Dairy Forage Research Center and the University of Wisconsin-Madison and was held in the U.S. for the first time since its inception in 1970. To conclude the week, the forage research center hosted a post-conference symposium with presentations of cutting-edge research being conducted by several of its scientists.

Following is a summary of research presentations I felt would be of the most interest to Feedstuffs readers


Dr. Frank Mitloehner from the University of California-Davis presented research (Mitloehner et al., 2009) on silage volatile organic compounds (VOCs). VOCs consist of more than 700 reactive gases, some of which contribute to the production of ground-level ozone (smog) by the gas-phase reaction of VOCs and oxides of nitrogen in the presence of sunlight.

The Environmental Protection Agency has instituted ozone standards, and some California dairy producers are currently incurring fines for exceeding air quality standards. In an attempt to educate producers, Mitloehner has trained more than 1,200 California dairy producers on approaches to mitigate VOCs.

The VOC emissions from dairy facilities and waste have been previously researched; however, limited data exist on VOC emissions from silages and total mixed rations (TMRs). This research utilized large samples of silage and TMRs transported to experimental chambers at the University of California-Davis, where sophisticated analytical methods were used to quantify VOCs such as alcohols, volatile fatty acids (VFAs), esters and aldehydes.

Results showed that approximately 120 VOCs were emitted from silages and/or TMRs, with corn and cereal silages being the primary contributors. Alcohol was the dominant VOC, with ethanol being the highest among all emitted alcohol compounds. What is relatively comforting is that ethanol has only a small impact on ozone formation.

VFAs were identified as the secondmost abundant compounds, with acetic acid having the highest concentration, and, again, VFAs represented an insignificant effect on ozone formation.

However, emissions of highly reactive compounds such as alkenes, alkynes, diene compounds and aldehydes were found in relatively high levels and could make a significant contribution to ozone formation. The net effect is that silages may have an air quality impact similar to vehicle emissions.

The practical implication of this research for nutritionists is that any management practice that helps conserve silage nutrients (density, face management, minimal surface area exposure, additive use to reduce yeast growth, etc.) will reward producers with both improved feed quality and a reduction in silage-induced air quality issues.

Air quality legislation may even force the industry to rethink feed delivery and bunk management as it appears that a major source of VOCs includes emissions from the mixer wagon (aeration of VOCs combining with oxides of nitrogen from the truck/tractor) and from feed in the feed bunk (a large surface area increases the volatilization of problematic VOCs).

California may be on the leading edge of regulating ozone emissions, particulate matter and odor, but do not discount these issues affecting other regions in the near future.

Silage porosity

Dr. Brian Holmes from the University of Wisconsin-Madison discussed a renewed emphasis on managing silage porosity (Holmes and Bolsen, 2009). Most density measurements to date have focused on silage dry matter density with recommendations to exceed 15 lb. of dry matter per cubic foot.

However, dry matter density does not account for porosity, which is defined as the voids between solid particles of a material. These voids can be filled fluids or gases and set the rate at which air moves into silage. This subsequently affects the amount of spoilage and/or aerobic stability in ensiled feeds.

It is impractical to attempt to measure silage porosity in the field, so algorithms from composting research have been modified to relate silage porosity to both dry matter and silage bulk density (as-fed density; Holmes, 2009).

Bulk density is affected by the same management practices as dry matter density such as tractor weight, packing time per ton, layer thickness and the height of the storage structure. However, while dry matter density (what traditionally has been measured) may increase with advancing dry matter of the feed, bulk density decreases.

In other words, as forage becomes drier, the porosity increases across similar dry matter densities.

Given that porosity varies widely across a combination of dry matters and bulk densities, University of Wisconsin researchers are recommending that silage producers strive for less than 40% porosity and bulk density compaction in excess of 44 lb./cu. ft. The Table shows the level of commonly measured dry matter density necessary to achieve the recommended porosity and bulk density hurdles.

Chart: Porosity and dry matter density as a function of forage bulk density and dry matter content.


Several presentations and hallway conversations made note of the need for a renewed focus on safety around silage structures. A safe distance to remain from a silage face has been proposed as five times the height of the structure.

It appears that several feed companies have now prohibited nutritionists from taking silage samples directly from the bunker/pile face, instead opting for samples taken from the TMR mixer. This will likely not only improve safety but also serves to reduce sampling errors.

I spend a considerable amount of time in front of silage bunkers/piles, and these safety reminders are important for all who routinely take samples or test silage for densities, particle size or kernel damage.

Sample handling

Research from the Miner Institute by Cotanch et al. (2009) looked at how forage samples should be handled when shipped to analytical labs for mold and yeast determinations. Cotanch et al.’s conclusions were that samples should be shipped in plastic bags and should contain a coolant pack. However, even with coolant packs, after approximately 36 hours, sample temperatures were close to ambient air temperatures.

The Cotanch et al. study points to the importance of proper handling and quick delivery as they concluded that even under the most optimum conditions used in their study, there were dramatic differences in yeast and mold counts between fresh and transported samples.

Silage variability

In the post-conference symposium, Dr. Dave Mertens presented data from a study (Mertens and Berzaghi, 2009a) designed to determine the production effects from changes in silage dry matter.

The basic nutritional premise underlying this experiment was that high-producing cows need to be precisely fed each and every day because of their very narrow dietary range that results from the conflict between high nutrient demand and the need to maintain minimum fiber requirements.

In a separate presentation, Mertens reinforced the idea that the effect of consistent neutral detergent fiber content of the ration should not be taken lightly as it can have upwards of three times the production impact of neutral detergent fiber digestibility (Mertens and Berzaghi, 2009b).

The experiment utilized a diode array near-infrared sensor (HarvestLab, Deere & Co.) to monitor daily changes in forage dry matter and to experimentally induce changes in dry matter to evaluate the effects of single-day changes in feed composition and allowance on milk production.

The ration consisted of the following on a dry matter basis: 27% alfalfa silage, 25% corn silage, 28% high-moisture corn, 10% roasted soybeans, 5% distillers grains, 2.5% of 48% crude protein soybean meal, 1% blood meal and 1.5% mineral/vitamin premix. Treatments consisted of diets with corn silage and/or alfalfa silage dry matter reduced by either 8% or 16%.

Mertens concluded that day-to-day variation in forage dry matter was large, and on-farm rapid methods of analysis with rugged near-infrared instruments can help manage these variations.

Summarized across all treatments, animal data showed that single-day variations in forage composition have an immediate effect on dry matter intake, and for every 2.2 lb. decrease in dry matter intake, 1.8 lb. of milk were lost in each of the following two days.

Most nutritionists would have likely predicted this response to varying forage dry matter, but now, there is solid research data to convince dairy producers in non-arid environments of the importance of monitoring forage dry matter daily and implementing silage face management practices to reduce exposure to rain and snow events.

The Bottom Line

Silage certainly has international research appeal, as demonstrated by the largest attendance yet at the International Silage Conference. It was also encouraging that more than 15 graduate students were in attendance to provide the impetus for future silage research.

This conference solidified my belief that North Americans have much to learn from land resource-limited international colleagues in regards to improving silage management.

International conferences that encourage cross-disciplinary interactions among agricultural engineers, microbiologists and nutritionists are extremely important for the total understanding of the conservation and feeding of fermented feeds.


Cotanch, K., J. Darrah, C. Kent-Dennis, A. Manning, C. Ballard, E. Thomas, R. Schmidt and R. Charley. 2009. Should forage samples be shipped to analytical labs in plastic or paper bags to accurately assess mold and yeast counts? Proceedings of the 15th International Silage Conference. Madison, Wis. p. 221-222.

Holmes, B. 2009. Density and porosity in bunker and pile silos. Available on UW Extension-Forage Resources web site: Density-Porosity3.pdf.

Holmes, B.J., and K.K. Bolsen. 2009. What’s new in silage management? Proceedings of the 15th International Silage Conference. Madison, Wis. p. 61-76.

Mertens, D.R., and P. Berzaghi. 2009a. Adjusting for forage variability via on-farm analysis. Proceedings of the Getting More from Forages Symposium. Madison, Wis. Available at:

Mertens, D.R., and P. Berzaghi. 2009b. Silage quality and dairy production. Proceedings of the 15th International Silage Conference. Madison, Wis. p. 101-114.

Mitloehner, F.M., I.L. Malkina, A. Kumar and P.G. Green. 2009. Volatile organic compounds emitted from dairy silages and other feeds. Proceedings of the 15th International Silage Conference. Madison, Wis. p. 15-26.

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For reproduction permission, contact:

Bill Seglar
Ph: 515-334-6674
Bill Mahanna
Ph: 515-334-6673