Glossary

The acid that is present in vinegar. It has a strong ability to prevent growth of yeasts and so should ideally be present in silages at a reasonable level to prevent heating and spoilage. It can be produced in silage in a number of ways, mainly by lactic acid bacteria. Acetic acid can be an indicator of a slow, inefficient fermentation driven by heterofermentative lactic acid bacteria. This type of fermentation can result in the production of other products in the silage that can depress intakes and means that energy has been wasted (see "Homofermenters and Heterofermenters" below). However, acetic acid can also be produced efficiently by homofermentative bacteria, from five-carbon sugars (e.g. xylose) and by the anaerobic conversion of lactic acid to acetic acid by Lactobacillus buchneri. In these situations the fermentation is efficient and the potential intake depressing compounds are not produced.

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Lactic acid bacteria can be broadly categorized into two groups based on how they ferment hexose (6-carbon) sugars like glucose and fructose. Homofermentative LAB convert each molecule of 6 carbon sugar into two 3 carbon molecules of lactic acid: Glucose 2 Lactic acid + 2 H2O Fructose 2 Lactic acid + 2 H2O Heterofermentative LAB produce a mixture of end products from 6 carbon sugars: Glucose 1 Lactic acid + 1 Ethanol + 1 CO2 + 1 H2O and 3 Fructose 1 Lactic acid + 1 Acetic acid + 2 Mannitol + 1 CO2 + 1 H2O So, using a mixture of 3 glucose and 3 fructose, the end products of the two types of LAB would be: Homofermenters: 12 Lactic acid + 12 H2O Heterofermenters: 4 Lactic acid + 1 Aectic acid + 3 Ethanol + 2 Mannitol + 4 CO2 + 4 H2O The heterofermentative LAB produce significantly less acid (slower pH drop) and also produce carbon dioxide (loss of dry matter and energy), ethanol (depending on levels it can increase or decrease palatability) and mannitol (decreases palatability).

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Are additives containing bacteria selected to grow quickly and dominate the bacterial population in the silage. Traditional inoculants contain homofermentative LAB, e.g. Lactobacillus plantarum, Pediococcus spp., to increase lactic acid production and so increase the rate of pH drop and decrease the production of acetic and butyric acids. Newer inoculants have been developed containing bacteria proven as aerobic stability enhancers, e.g. Lactobacillus buchneri, either on their own or in combination with the traditional inoculant organisms.

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An isomer of butyric acid, usually present because of the deamination of the amino acid valine by clostridia (though it is also known to be produced by Lactobacillus brevis).

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Lactic acid is the most acidic of the common fermentation acids and so is the main driver of the initial pH drop responsible for "pickling" the crop and the initial ensilage of the crop. It is produced by lactic acid bacteria, which can vary dramatically in efficacy of production and in levels on the forage crops ensiled. Hence, it is important to inoculate a forage crop with high numbers (100,000 CFU/g minimum) of efficient homolactic lactic acid producers if a fast pH drop is required. However, lactic acid has no effect against yeasts and molds, beyond reducing pH, and many common silage yeasts can actually use lactic acid to grow on.

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There is a setting on the forage harvester which allows the operator to set the theoretical length of cut (TLC). General recommendations are to set the TLC to 3/8" -1/2" for alfalfa and grass, 1/2" - 3/4" for corn, but the particle size distribution achieved should always be checked (e.g. using the Pennsylvania State Forage Particle Separator).

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A known mold inhibitor, used to treat many feedstuffs to prevent molding. It can also be produced in the silage, by fermentation of sugars and/ or lactic acid by propionic acid producing bacteria and/ or as a co-product in the conversion of lactic acid to acetic acid by Lactobacillus Buchneri.

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Literally means any fermentation that takes place after the primary fermentation (i.e. after the lactic acid production). However, some use secondary fermentation only to refer to clostridial fermentation in the silage. Others use the term only to describe fermentation of the silage by yeasts and so the onset of aerobic instability. Technically both are correct, provided there has been an initial lactic fermentation.

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The crop after it has been ensiled (e.g. corn silage, pea silage, alfalfa silage).

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Produced by the breakdown of proteins into amino acids, etc. High levels of soluble protein indicate excessive protein degredation and may also be accompanied by high amonia levels and other indicators of a bad fermentation (e.g. the fermentation acid profile).

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These are acids that are produced by microbes in the silage from sugars and other carbohydrate sources. By definition they are volatile, which means that they will volatilize in air, depending on temperature. Thus, lactic acid is NOT a volatile fatty acid, while acetic and propionic and butyric are. Many use the term VFAs incorrectly to include lactic acid. To include lactic, the term "fermentation acids" should be used.

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The process where forage is left in the field to dry down, usually in windrows, to raise the dry matter level in the crop, prior to being chopped and ensiled.

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Forage collected into loose piles, ranging from inches to several feet in height, running along the length of the field in rows, allowing the wind to pass through the forage and help the forage dry down.

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Term generally used for alfalfa or grass silage made at a higher dry matter level (e.g. >30% DM), though the use of the term can vary! Some refer to any grass or alfalfa ensiled material as haylage regardless of DM, in the Midwest, generally haylage is only used for ensiled alfalfa, the makers of Harvestores insist only material made in a Harvestore is haylage.

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The crop prior to ensiling (e.g. forage corn, forage peas, alfalfa forage).

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In order to get an idea of the quality of the silage and the fermentation pattern we take samples and submit them to approved laboratories (e.g. CVAS, Dairyland) for analysis. There are a number of features we can request in the analysis, all of which add to the cost, so it is important to understand what we are looking for from the analysis so that we do not pay for things we do not need. If we have a good, well preserved silage and we are doing the analysis just to show the producer the feeding quality of the silage, then limit the analysis to the "Feed" analysis. This will show things like the dry matter of the silage, pH, fiber and lignin levels, starch, protein levels (including total crude protein, soluble and bound protein) and the derived parameters like net energy figures. If the producer is unhappy with silage quality, then in addition to the above, add ash (shows if there was soil, or possibly slurry, in the forage: take 7 off the ash and the rest is from something other than the plant, e.g. ash at 12%, 12-7 = 5%, which is 100 lb/ton of silage DM of ash coming from soil, or slurry, potentially sources of clostridia [soil] and/ or enterobacteria [slurry]). In addition, have the fermentation analyses done (include 1, 2-propanediol if it is a silage treated with Lactobacillus buchneri) and also consider microbial analyses (usually only if yeasts are the suspected cause)

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Silage that heats on exposure to oxygen suffers from aerobic instability. In research trials the length of time a silage is stable is measured by the time it takes to heat by a specific amount, most commonly 2ºC. As previously mentioned (see "Yeasts and Molds" above) most of the heating events seen in silage result from the growth of yeasts. When determining in the field if a silage is heating, it is important to note and record the ambient temperature on the day the silage was made. It is normal for a silage to increase in temperature by 15 - 20ºF during a good ensiling process. So, if the forage was harvested on days when the temperature averaged 80ºF it would not be abnormal for the silage to be 95-100ºF. However, if the same silage is 120ºF, then it is heating. Just because the silage "steams" as it is removed during feedout in winter does not necessarily mean that it is heating!

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High levels of ammonia nitrogen show that there has been excessive protein degradation, either due to prolonged wilting (the plant will degrade itself lying in the field) or due to microbial activity. Ammonia should preferably be <15% of the CP in corn silage, <10% in grass and alfalfa silages and haylages. Excess microbial proteolysis (protein degradation) could be due to clostridia (look for the butyric acid level also to be high: >1% DM) or due to other proteolytic bacteria (e.g. Enterococcus faecium).

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The addition of anhydrous ammonia to forage raises the pH of the forage and so tends to inhibit all microbial activity. The effect on yeasts and molds is permanent inhibition, provided the product is applied at recommended rates (7 - 10 lb/ ton of forage DM). Lactic acid bacteria, and enterobacteria, will eventually recover and the silage will ferment, though there will be a considerable delay in the fermentation, which can lead to increased dry matter losses. Ammonia is a hazardous gas and needs to be handled with care.

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Produced by mixing propionic acid with a base, e.g. ammonium hydroxide, to produce a salt, e.g. ammonium propionate. In concentrated solution this will be non-corrosive, but as the mixture hits more moisture, either by dilution or in the crop at harvest, the salt dissociates, forming ammonium ions and propionate ions and becomes as acidic as propionic acid. Buffered propionic acid can be effective in preventing aerobic spoilage, as long as it is used at the recommended level (4 - 6 lb/ ton fresh weight) but is not effective as a general acidifier to ensile forage (rates of use would be too high and so cost prohibitive). Low levels of propionic acid can stimulate the production of some mycotoxins.

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The main source of butyric acid in silage is fermentation by clostridia, which are present on the crop in relatively small numbers at harvest. Numbers in the ensiled forage can be dramatically increased by the inclusion of soil, picked up either by cutting the crop too low or during raking or tedding, or on packing tractor wheels in wet conditions. Soil can contain up to 10 billion CFU of clostridia per gram. In addition to producing butyric acid, which can give the silage a very strong, persistent fecal smell, clostridia can also break down proteins, leading to significant loss of protein and the production of biogenic amines, e.g. histamine, putrescine, cadaverine, that can affect herd health and/ or production and produce odors associated with putrification or decay.

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When we count microorganisms we do so by diluting them and then putting the diluted suspension onto agar (jelly) plates, incubating them at the right temperature and then counting the number of colonies, or "spots", on the plate. Each colony may have formed from one cell being on that point on the plate and multiplying up, or could be from a clump or cluster of cells that were stuck together landing on the spot and multiplying. So, we count the number of colonies we see, multiply by the dilution and report the result as CFU per gram, since the CFU could have been one cell or a clump of many originally.

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Used to describe a silage that is cut and harvested at the same time, i.e. the forage is not allowed to sit in a windrow and dry down.

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Once all the moisture is removed from the forage, what is left is the dry matter. Dry matter is measured as a percentage by weighing the fresh forage, drying it in an oven, a microwave oven or using a Koster tester and re-weighing the material when it is dry. The dry matter content is calculated as: Dry Matter (DM) = (Dry weight/ Fresh Weight) x 100 % Moisture content (%) is obtained by: 100 - %DM = % moisture

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Used to describe the process where a forage is put into a storage structure, becomes anaerobic and is acidified by the production of acids due to the action of bacteria either on the crop at harvest or added as an inoculant.

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Primarily produced by the fermentative activity of yeasts, but is also produced by heterofermentative lactic acid bacteria. If the level of ethanol in the silage is relatively low and there are reasonable levels of lactic and acetic acids, the source is probably heterofermentative LAB. If the level is high, the source is probably from yeasts. In any event, look also at the bound protein level (ADICP). If ADICP is greater than 10% of the CP, then there has been heating and the ethanol most likely came from yeasts (Caution! - the ethanol level may be low due to being volatilized because of the heating).

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The rate at which the silage is fed out, generally expressed in term of inches per day that the silage surface is removed. Conventionally it is recommended that feed out rates are a minimum of 6" per day. In practice, feedout rates should be maintained at whatever is necessary to keep the silage stable.

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When the forage is put into the storage system it initially has some oxygen trapped in. This oxygen allows microorganisms to grow aerobically and produce carbon dioxide (respiration): the plant itself also continues to respire. Once the oxygen supply is exhausted the microbes that absolutely need oxygen to grow (obligate aerobes) cease to grow and the plant ceases respiration. Microbes that can grow without oxygen present (anaerobes and facultative anaerobes) begin to grow fermentatively, producing various fermentation products. Yeasts will produce alcohol, lactic acid bacteria will produce predominantly lactic acid, propionic bacteria produce propionic acid, acetogenic bacteria produce acetic acid, clostridia produce butyric acid.

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Both are fungi: yeasts growing as single cell organisms while molds grow as multicellular filaments. Both occur widely in soil and water and on vegetation, increasing in numbers on vegetation as the crop ages or gets damaged (e.g. frost, hail, drought) and during wilting. In addition to being able to grow on free sugars, both yeasts and molds secrete extracellular enzymes which break down the complex plant materials into simple sugars which can then be used for growth. Many of the yeasts found on plant material contain carotenoid (orange to red) pigments to protect them against UV exposure and so can be responsible for some of the colors seen on silage faces. While yeasts can grow aerobically, they can also grow fermentatively (anaerobically), with ethanol being one of the major products. Other products that yeasts can produce in anaerobic growth conditions include n-propanol, iso-pentanol, acetic, propionic, butyric and iso-butyric acids, as well as small amounts of lactic acid. In the presence of air, yeasts will oxidize sugars fully, producing carbon dioxide and water and generating heat. Many yeasts can also use lactic acid for growth, again oxidizing it fully and generating heat. Yeasts are responsible for the vast majority (>95%) of heating silages: a yeast population >100,000 CFU/ gram in the silage will almost certainly mean that the silage will heat as it is exposed to air during feedout. Yeast growth can be inhibited by acetic acid. The conditions normally associated with stable silage, low pH and anaerobic conditions, do not favor growth of molds. Generally they are only a problem where air exposure has occurred, e.g. at the top and on the sides of bunkers or piles, where there have been air leaks into the silage, where packing has been poor (e.g. localized lumps of moldy silage), at surfaces left exposed during filling and at the surface of the silage during feedout. As the silage moves towards the surface, if there are high numbers of yeasts present these can grow on the lactic acid present, raising the pH and the silage temperature, promoting the subsequent growth of molds. Mold growth is undesirable, since the molds will fully oxidize both sugars and lactic acid, and will also break down (hydrolyze) and fully oxidize cellulose and other cell wall components, resulting in huge dry matter and energy losses. In addition, many of the molds commonly found in silages can produce mycotoxins, which can cause significant health and/ or reproductive problems and dramatically reduce performance. Finally, molds produce spores that become airborne when the silage is disturbed and can cause respiratory problems if they are inhaled (both for the cows and for the producer and farm workers). Mold growth can be inhibited by propionic acid.

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