Home / Glossary


Acetic Acid
The acid that is present in vinegar. It has a strong ability to prevent the growth of yeasts and molds and so should ideally be present in silages at a reasonable level to prevent heating and spoilage. It is typically produced in silage by lactic acid bacteria. Acetic acid can 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. Acetic acid can also 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”).
Acid Detergent Fiber (ADF)
Chemical analysis of the forage that determines the amount of indigestible cellulose and lignin, which is then used to predict the energy content of the silage. As the ADF increases, the digestible energy decreases.
Aerobic Instability
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 2º C. Most of the heating events seen in silage result from the growth of yeasts (see “Yeasts and Molds”).
Ammonia Nitrogen
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 nitrogen should preferably be <15% of the CP in corn silage, <10% in grass and alfalfa silages and haylages. Excess microbial proteolysis (protein break down) 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).
Anhydrous Ammonia
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 sufficient rates. 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.
Ash Contamination
Ash is the total mineral content of a forage or diet. Silage ash typically comes from the plant’s internal ash, which provides minerals like magnesium, calcium and potassium; or soil contamination, which is characterized by high concentrations of iron, aluminum and silica. Higher ash can indicate excessive soil contamination, which can negatively affect fermentation.
Silage stored in bales. Sometimes called “haylage.”
Degrees Brix (symbol °Bx) is the sugar content of an aqueous solution. One degree Brix is 1 gram of sucrose in 100 grams of solution and represents the strength of the solution as percentage by mass.
Buffered Propionic Acid
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 to 6 lbs./ ton, or 1.8 to 2.7 kg/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.
Butyric Acid
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, or by overcompacting low dry matter forage. 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 purification or decay.
CFU (Colony Forming Unit)
Microorganisms are counted 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. Therefore, the number of colonies seen are counted and multiplied by the dilution and reported as CFU per gram, since the CFU could have been one cell or a clump of many originally.
Crimped Cereal
Grain crimping is a system developed in Finland that enables farmers to harvest, process, store, and preserve the full feed value of their own or locally-grown cereal and protein grains for use as animal feed. The only storage requirement is a clean, airtight clamp where the processed cereal grain can be ensiled. If sealing is not perfect, crimped cereal significantly mold, which is why many farmers choose to use a preservative treatment.
Direct Cut
Used to describe a forage that is cut and harvested at the same time, i.e. the forage is not allowed to sit in a windrow and dry down.
Double-Crop (Bi-Crop) Silage
Bi-cropping combines a spring-sown cereal crop and a spring-sown legume crop.
Dry Matter (DM)
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 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 %. Conversely, moisture content (%) is obtained by: 100 - %DM = % moisture.