Silage

thumb|Silage underneath plastic sheeting is held down by scrap tires. Concrete beneath the silage prevents fermented juice from leaching out.thumb|right|Cattle eating silage

Silage is fodder made from green foliage crops which have been preserved by fermentation to the point of souring. It is fed to cattle, sheep and other ruminants. The fermentation and storage process is called ensilage, ensiling, or silaging. The exact methods vary, depending on available technology, local tradition and prevailing climate.

Silage is usually made from grass crops including maize, sorghum, or other cereals, using the entire green plant (not just the grain). Specific terms may be used for silage made from particular crops: oatlage for oats, haylage for alfalfa (haylage may also refer to high dry-matter silage made from hay).

History

Using the same technique as the process for making sauerkraut, green fodder was preserved for animals in parts of Germany since the start of the 19th century. This gained the attention of French agriculturist Auguste Goffart of Sologne, near Orléans. He published a book in 1877 which described the experiences of preserving green crops in silos. Goffart's experience attracted considerable attention. The favourable results obtained in the US led to the introduction of the system in the United Kingdom, where Thomas Kirby first introduced the process for British dairy herds.

The modern silage preserved with acid and by preventing contact with air was invented by Finnish academic and professor of chemistry Artturi Ilmari Virtanen. Virtanen was awarded the 1945 Nobel prize in chemistry "for his research and inventions in agricultural and nutrition chemistry, especially for his fodder preservation method", practically inventing modern silage.

Early silos were made of stone or concrete either above or below ground, but it is recognized that air may be sufficiently excluded in a tightly pressed stack, though in this case a few inches of the fodder around the sides is generally useless owing to mildew. In the US, structures were typically constructed of wooden cylinders in depth.

Production

thumb|[[MB Trac rolling a silage heap or "clamp" in Victoria, Australia]]

The crops most often used for ensilage are the ordinary grasses, clovers, alfalfa, vetches, oats, rye and maize. Many crops have ensilaging potential, including potatoes and various weeds, notably spurrey such as Spergula arvensis. Silage must be made from plant material with a suitable moisture content: about 50% to 60% depending on the means of storage, the degree of compression, and the amount of water that will be lost in storage, but not exceeding 75%. Weather during harvest need not be as fair and dry as when harvesting for drying. For corn, harvest begins when the whole-plant moisture is at a suitable level, ideally a few days before it is ripe. For pasture-type crops, the grass is mown and allowed to wilt for a day or so until the moisture content drops to a suitable level. Ideally the crop is mowed when in full flower, and deposited in the silo on the day of its cutting.

Handling of wrapped bales is most often with some type of gripper that squeezes the plastic-covered bale between two metal parts to avoid puncturing the plastic. Simple fixed versions are available for round bales which are made of two shaped pipes or tubes spaced apart to slide under the sides of the bale, but when lifted will not let it slip through. Often used on the tractor's loader as an attachment called a bale grabber, they incorporate a trip tipping mechanism which can flip the bales over on to the flat side or end for storage on the thickest plastic layers. If the fodder is unchaffed and loosely packed, or the silo is built gradually, oxidation proceeds more rapidly and the temperature rises; if the mass is compressed when the temperature is , the action ceases and sweet silage results. The nitrogenous ingredients of the fodder also change: in making sour silage, as much as one-third of the albuminoids may be converted into amino and ammonium compounds; in making sweet silage, a smaller proportion is changed, but they become less digestible.

Pollution and waste

The fermentation process of silo or pit silage releases liquid. Silo effluent is corrosive. It can also contaminate water sources unless collected and treated. The high nutrient content can lead to eutrophication (hypertrophication), the growth of bacterial or algal blooms.

Plastic sheeting used for sealing pit or baled silage needs proper disposal, and some areas have recycling schemes for it. Traditionally, farms have burned silage plastics; however odor and smoke concerns have led certain communities to restrict that practice.

Storing silage

Silage must be firmly packed to minimize the oxygen content, lest it spoil.

Silage goes through four major stages in a silo:

Presealing, which, after the first few days after filling a silo, enables some respiration and some dry matter (DM) loss, but stops.
Fermentation, which occurs over a few weeks. pH drops, and there is more DM loss, but hemicellulose is broken down; aerobic respiration stops.
Infiltration, which enables some oxygen infiltration, allowing for limited microbial respiration. Available carbohydrates (CHOs) are lost as heat and gas.
Emptying, which exposes surface, causing additional loss; rate of loss increases.

Safety

Silos are potentially hazardous: deaths may occur in the process of filling and maintaining them, and several safety precautions are necessary. There is a risk of injury by machinery or from falls. When a silo is filled, fine dust particles in the air can become explosive because of their large aggregate surface area. Also, fermentation presents respiratory hazards. The ensiling process produces "silo gas" during the early stages of the fermentation process. Silage gas contains nitric oxide (NO), which will react with oxygen (O<sub>2</sub>) in the air to form nitrogen dioxide (NO<sub>2</sub>), which is toxic. Lack of oxygen inside the silo can cause asphyxiation. Molds that grow when air reaches cured silage can cause organic dust toxic syndrome. Collapsing silage from large bunker silos has caused deaths.

Silage itself poses no special danger, and the improvement in legislation to regulate the animal food industry has reduced the problems concerning food-related human diseases by improvement of the hygienic quality of silage. Milk from cows fed with silage containing clostridial spores could represent a risk in hard cheese production. A special focus has to be directed to zoonotic pathogens like listeria, mycotoxins, clostridia, and E. coli bacteria as a result of deficient hygiene in silage production and could end up in dairy products.

Nutrition

Ensilage can be substituted for root crops. Bulk silage is commonly fed to dairy cattle, while baled silage tends to be used for beef cattle, sheep and horses. The advantages of silage as animal feed are several:

During fermentation, the silage bacteria act on the cellulose and carbohydrates in the forage to produce volatile fatty acids (VFAs), such as acetic, propionic, lactic, and butyric acids. By lowering pH, these produce a hostile environment for competing bacteria that might cause spoilage. The VFAs thus act as natural preservatives, in the same way that the lactic acid in yogurt and cheese increases the preservability of what began as milk, or how vinegar (dilute acetic acid) preserves pickled vegetables. This preservative action is particularly important during winter in temperate regions, when green forage is unavailable.
When silage is prepared under optimal conditions, the modest acidity also has the effect of improving palatability, and provides a dietary contrast for the animal. (However, excessive production of acetic and butyric acids can reduce palatability: the mix of bacteria is ideally chosen so as to maximize lactic acid production.)
Several of the fermenting organisms produce vitamins: for example, lactobacillus species produce folate and vitamin B12.
The fermentation process that produces VFA also yields energy that the bacteria use: some of the energy is released as heat. Silage is thus modestly lower in caloric content than the original forage, in the same way that yogurt has modestly fewer calories than milk. However, this loss of energy is offset by the preservation characteristics and improved digestibility of silage.

Anaerobic digestion

thumb|Anaerobic digester

Silage may be used for anaerobic digestion.

Fish silage

Fish silage is a method used for conserving by-products from fishing for later use as feed in fish farming. This way, the parts of the fish that are not used as human food such as fish guts (entrails), fish heads and trimmings are utilized as ingredients in feed pellets. The silage is performed by first grinding the remains and mixing it with formic acid, and then storing it in a tank. The acid helps with preservation as well as further dissolving the residues. Process tanks for fish silage can be aboard ships or on land.

References

Sources

Making and Feeding Silage, John Murdoch, B.Sc., Ph.D. Published by Dairy Farmer (Books) Limited, Lloyd's Chambers, Ipswich, UK 1961)
Feeding baleage to horses – the ultimate guide – Horsetalk.co.nz
"The Owner-Built Homestead" by Barbara and Ken Kern, New York: Scribner, 1977.