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Silage isfodder made from green foliage crops which have been preserved byfermentation to the point ofsouring. It is fed to cattle, sheep and otherruminants.[1] The fermentation and storage process is calledensilage,ensiling, orsilaging. The exact methods vary, depending on available technology, local tradition and prevailing climate.
Silage is usually made fromgrass crops includingmaize,sorghum or othercereals, using the entire green plant (not just the grain). Specific terms may be used for silage made from particular crops:oatlage for oats,haylage foralfalfa (haylage may also refer to high dry matter silage made fromhay).[2]
Using the same technique as the process for makingsauerkraut, 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 ofSologne, nearOrléans. He published a book in 1877 which described the experiences of preserving green crops in silos.[3] Goffart's experience attracted considerable attention.[4] The conditions ofdairy farming in the United States suited the ensiling of green maize fodder, and was soon adopted byNew England farmers. Francis Morris of Maryland prepared the first silage produced in America in 1876.[5] 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.[6]
The modern silage preserved with acid and by preventing contact with air was invented by Finnish academic and professor of chemistryArtturi 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.[7]
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 tomildew. In the US, structures were typically constructed of wooden cylinders 35 to 40 feet (11 to 12 m) in depth.[4]
In the early days of mechanized agriculture (late 1800s), stalks were cut and collected manually using a knife and horsedrawn wagon, and fed into a stationary machine called a "silo filler" that chopped the stalks and blew them up a narrow tube to the top of atower silo.[8]
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The crops most often used for ensilage are the ordinary grasses,clovers,alfalfa,vetches,oats,rye andmaize.[4] Many crops have ensilaging potential, includingpotatoes and variousweeds, notablyspurrey such asSpergula 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 fullflower, and deposited in thesilo on the day of its cutting.[4]
After harvesting, crops are shredded to pieces about 15 mm (1⁄2 in) long. The material is spread in uniform layers over the floor of the silo, and closely packed. When the silo is filled or the stack built, a layer ofstraw or some other dry porous substance may be spread over the surface. In the silo, the pressure of the material, whenchaffed, excludes air from all but the top layer; in the case of the stack, extrapressure is applied by weights to prevent excessive heating.[4]
Forage harvesters collect and chop the plant material, and deposit it in trucks or wagons. These forage harvesters can be eithertractor-drawn or self-propelled. Harvesters blow the chaff into the wagon through a chute at the rear or side of the machine. Chaff may also be emptied into a bagger, which puts the silage into a large plastic bag that is laid out on the ground.
In North America, Australia, northwestern Europe, and New Zealand it is common for silage to be placed in large heaps on the ground, rolled by tractor to push out the air, then covered with plastic sheets that are held down by used tires or tire ring walls. In New Zealand and Northern Europe, 'clamps' made of concrete or old wooden railway ties (sleepers) and built into the side of a bank are sometimes used. The chopped grass can then be dumped in at the top, to be drawn from the bottom in winter. This requires considerable effort to compress the stack in the silo to cure it properly. Again, the pit is covered with plastic sheet and weighed down with tires.
In an alternative method, the cut vegetation is formed into bales using abaler, makingbalage (North America) orsilage bales (UK, Australia, New Zealand). The grass or other forage is cut and partly dried until it contains 30–40% moisture (much drier than bulk silage, but too damp to be stored as dry hay). It is then made into large bales which are wrapped tightly in plastic to exclude air. The plastic may wrap the whole of each cylindrical or cuboid bale, or be wrapped around only the curved sides of a cylindrical bale, leaving the ends uncovered. In this case, the bales are placed tightly end to end on the ground, making a long continuous "sausage" of silage, often at the side of a field. The wrapping may be performed by abale wrapper, while the baled silage is handled using a bale handler or afront-loader, either impaling the bale on a flap, or by using a special grab. The flaps do not hole the bales.
In the UK, baled silage is most often made in round bales about 1.2 m × 1.2 m (4 ft × 4 ft), individually wrapped with four to six layers of "bale wrap plastic" (black, white or green 25-micrometre stretch film). The percentage of dry matter can vary from about 20% dry matter upwards. The continuous "sausage" referred to above is made with a special machine which wraps the bales as they are pushed through a rotating hoop which applies the bale wrap to the outside of the bales (round or square) in a continuous wrap. The machine places the bales on the ground after wrapping by moving forward slowly during the wrapping process.
Haylage sometimes refers to high dry matter silage of around 40% to 60%, typically made fromhay. Horse haylage is usually 60% to 70% dry matter, made in small bales or larger bales.[9]
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.[9]
Silage undergoesanaerobic fermentation, which starts about 48 hours after the silo is filled, and converts sugars to acids. Fermentation is essentially complete after about two weeks.
Before anaerobic fermentation starts, there is an aerobic phase in which the trappedoxygen is consumed. How closely the fodder is packed determines the nature of the resulting silage by regulating thechemical reactions that occur in the stack. When closely packed, the supply of oxygen is limited, and the attendant acidfermentation brings about decomposition of thecarbohydrates present intoacetic,butyric andlactic acids. This product is named sour silage.[10] 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 60–70 °C (140–160 °F), the action ceases and sweet silage results. Thenitrogenous ingredients of the fodder also change: in making sour silage, as much as one-third of thealbuminoids may be converted intoamino andammonium compounds; in making sweet silage, a smaller proportion is changed, but they become lessdigestible.[4] If the fermentation process is poorly managed, sour silage acquires an unpleasant odour due to excess production of ammonia or butyric acid (the latter is responsible for the smell of rancid butter).
In the past, the fermentation was conducted by indigenous microorganisms, but, today,[when?] some bulk silage is inoculated with specific microorganisms to speed fermentation or improve the resulting silage. Silage inoculants contain one or more strains oflactic acid bacteria, and the most common isLactobacillus plantarum. Other bacteria used includeLactobacillus buchneri,Enterococcus faecium andPediococcus species.
Ryegrasses have high sugars and respond to nitrogen fertiliser better than any other grass species. These two qualities have made ryegrass the most popular grass for silage-making for the last sixty years.[timeframe?] There are three ryegrasses in seed form and commonly used: Italian, Perennial and Hybrid.[11]
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 toeutrophication (hypertrophication), the growth ofbacterial oralgal blooms.[12]
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.[13]
Silage must be firmly packed to minimize the oxygen content, lest it spoil.
Silage goes through four major stages in asilo:[14]
Silos are potentially hazardous: deaths may occur in the process of filling and maintaining them, and several safety precautions are necessary.[15] 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 containsnitric oxide (NO), which will react with oxygen (O2) in the air to formnitrogen dioxide (NO2), which is toxic.[16] Lack of oxygen inside the silo can cause asphyxiation. Molds that grow when air reaches cured silage can causeorganic dust toxic syndrome. Collapsing silage from large bunker silos has caused deaths.[17]
Silage itself poses no special danger, and the improvement in legislation to regulate the animal food industry has reduced the problems concerning food-relatedhuman diseases by improvement of the hygienic quality of silage.[18] Milk from cows fed with silage containingclostridial spores could represent a risk in hard cheese production.[19] A special focus has to be directed tozoonotic pathogens likelisteria,mycotoxins,clostridia, andE. coli bacteria as a result of deficient hygiene in silage production and could end up in dairy products.[20]
Ensilage can be substituted forroot crops. Bulk silage is commonly fed todairy cattle, while baled silage tends to be used forbeef cattle,sheep andhorses. The advantages of silage as animal feed are several:
Silage may be used for anaerobic digestion.[24]
Fish silage[25][26] is a method used for conservingby-products from fishing for later use as feed infish farming. This way, the parts of the fish that are not used ashuman food such as fish guts (entrails), fish heads and trimmings are utilized as ingredients in feed pellets.[27][28] The silage is performed by first grinding the remains and mixing it withformic acid, and then storing it in a tank. The acid helps withpreservation as well as further dissolving the residues. Process tanks for fish silage can be aboard ships or on land.[29]
One or more of the preceding sentences incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Ensilage".Encyclopædia Britannica. Vol. 9 (11th ed.). Cambridge University Press. pp. 653–654.The first silage made in America was prepared by Francis Morris ofEllicott City, Maryland, in 1876, by putting whole corn in a trench or pit dug in the ground and covered with earth.[p. 2]
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