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Infobox on Hay
Example of Hay
Origin -
Stowage factor (in m3/t) -
Humidity / moisture <14%
Ventilation -
Risk factors See text

Description / Application

Hay is grass, legumes or other herbaceous plants that have been cut, dried, and stored for use as animal fodder, particularly for grazing livestock such as cattle, horses, goats, and sheep. Hay is also fed to pets such as rabbits and guinea pigs. Pigs may be fed hay, but they do not digest it as efficiently as more fully herbivorous animals.

Hay is fed when or where there is not enough pasture or rangeland on which to graze an animal, when grazing is unavailable due to weather (such as during the winter) or when lush pasture by itself is too rich for the health of the animal. It is also fed during times when an animal is unable to access pasture, such as when animals are kept in a stable or barn.

Commonly used plants for hay include mixtures of grasses such as ryegrass, timothy, brome, fescue, Bermuda grass, orchard grass, and other species, depending on region. Hay may also include legumes, such as alfalfa (lucerne) and clovers (red, white and subterranean). Other pasture forbs are also sometimes a part of the mix, though other than legumes, which ideally are cut pre-bloom, forbs are not necessarily desired. Certain forbs are toxic to some animals.

Oat, barley, and wheat plant materials are occasionally cut green and made into hay for animal fodder; however they are more usually used in the form of straw, a harvest byproduct where the stems and dead leaves are baled after the grain has been harvested and threshed. Straw is used mainly for animal bedding. Although straw is also used as fodder, particularly as a source of dietary fiber, it has lower nutritional value than hay.

It is the leaf and seed material in the hay that determines its quality. Farmers try to harvest hay at the point when the seed heads are not quite ripe and the leaf is at its maximum when the grass is mowed in the field. The cut material is allowed to dry so that the bulk of the moisture is removed but the leafy material is still robust enough to be picked up from the ground by machinery and processed into storage in bales, stacks or pits.

Hay is very sensitive to weather conditions, particularly when it is harvested. In drought conditions, both seed and leaf production are stunted, making hay that has a high ratio of dry coarse stems that have very low nutritional values. If the weather is too wet, the cut hay may spoil in the field before it can be baled. The hay may also develop rot and mould after being baled, creating the potential for toxins to form in the feed, which could make the animals sick. It also has to be stored in a manner to prevent it from getting wet. Mould and spoilage reduce nutritional value and may cause illness in animals.

Poor quality hay is dry, bleached out and coarse-stemmed. Sometimes, hay stored outdoors will look like this on the outside but still be green inside the bale. A dried, bleached or coarse bale is still edible and provides some nutritional value as long as it is dry and not mouldy, dusty, or rotting.

The successful harvest of maximum yields of high-quality hay is entirely dependent on the coincident occurrence of optimum crop, field, and weather conditions. When this occurs, there may be a period of intense activity on the hay farm while harvest proceeds until weather conditions become unfavourable.

Hay or grass is the foundation of the diet for all grazing animals and can provide as much as 100% of the fodder required for an animal. Hay is usually fed to an animal in place of allowing the animal to graze on grasses in a pasture, particularly in the winter or during times when drought or other conditions make pasture unavailable. Animals that can eat hay vary in the types of grasses suitable for consumption, the ways they consume hay, and how they digest it. Therefore, different types of animals require hay that consists of similar plants to what they would eat while grazing, and likewise, plants that are toxic to an animal in pasture are also toxic if they are dried into hay.

Hay production and harvest, colloquially known as "making hay", "haymaking", or "doing hay", involves a multiple step process: cutting, drying or "curing", processing, and storing. Hayfields do not have to be reseeded each year in the way that grain crops are, but regular fertilizing is usually desirable, and overseeding a field every few years helps increase yield.

Methods and the terminology to describe the steps of making hay have varied greatly throughout history, and many regional variations still exist today. However, whether done by hand or by modern mechanized equipment, tall grass and legumes at the proper stage of maturity must be cut, then allowed to dry (preferably by the sun), then raked into long, narrow piles known as windrows. Next, the cured hay is gathered up in some form (usually by some type of baling process) and placed for storage into a haystack or into a barn or shed to protect it from moisture and rot.

During the growing season, which is spring and early summer in temperate climates, grass grows at a fast pace. It is at its greatest nutritive value when all leaves are fully developed and seed or flower heads are just a bit short of full maturity. When growth is at a maximum in the pasture, if judged correctly, the pasture is cut. Hay cut too early will not cure as easily due to high moisture content, plus it will produce a lower yield per acre than longer, more mature grass. But hay cut too late is coarser, lower in resale value and has lost some of its nutrients. There is usually about a two-week "window" of time in which hay is at its ideal stage for harvesting.

Hay can be raked into rows as it is cut, then turned periodically to dry, particularly if a modern swather is used. Or, especially with older equipment or methods, the hay is cut and allowed to lie spread out in the field until it is dry, then raked into rows for processing into bales afterwards. During the drying period, which can take several days, the process is usually sped up by turning the cut hay over with a hay rake or spreading it out with a tedder. If it rains while the hay is drying, turning the windrow can also allow it to dry faster. However, turning the hay too often or too roughly can also cause drying leaf matter to fall off, reducing the nutrients available to animals. Drying can also be sped up by mechanized processes, such as use of a hay conditioner, or by use of chemicals sprayed onto the hay to speed evaporation of moisture, though these are more expensive techniques, not in general use except in areas where there is a combination of modern technology, high prices for hay, and too much rain for hay to dry properly.

Once hay is cut, dried and raked into windrows, it is usually gathered into bales or bundles, then hauled to a central location for storage. In some places, depending on geography, region, climate, and culture, hay is gathered loose and stacked without being baled first.

Hay must be fully dried when baled and kept dry in storage. If hay is baled while too moist or becomes wet while in storage, there is a significant risk of spontaneous combustion. Hay stored outside must be stacked in such a way that moisture contact is minimal. Some stacks are arranged in such a manner that the hay itself "sheds" water when it falls. Other methods of stacking use the first layers or bales of hay as a cover to protect the rest. To completely keep out moisture, outside haystacks can also be covered by tarps, and many round bales are partially wrapped in plastic as part of the baling process. Hay is also stored under a roof when resources permit. It is frequently placed inside sheds, or stacked inside of a barn. On the other hand, care must also be taken that hay is never exposed to any possible source of heat or flame, as dry hay and the dust it produces are highly flammable.

Hay baled before it is fully dry can produce enough heat to start a fire. Farmers have to be careful about moisture levels to avoid spontaneous combustion, which is a leading cause of haystack fires. Heat is produced by the respiration process, which occurs until the moisture content of drying hay drops below 40%. Hay is considered fully dry when it reaches 20% moisture. Combustion problems typically occur within five days to seven days of baling. A bale cooler than 49°C is in little danger, bales between 49 and 60°C need to be removed from a barn or structure and separated so that they can cool off. If the temperature of a bale exceeds more than 60°C, it can combust.

Modern mechanized hay production today is usually performed by a number of machines. While small operations use a tractor to pull various implements for mowing and raking, larger operations use specialized machines such as a mower or a swather, which are designed to cut the hay and arrange it into a windrow in one step. Balers are usually pulled by a tractor, with larger balers requiring more powerful tractors.

Many farmers, particularly those who feed large herds, have moved to balers which produce much larger bales, maximizing the amount of hay which is protected from the elements. Large bales come in two types, round and square. "Large Square" bales, which can weigh up to 1,000 kilograms, can be stacked and are easier to transport on trucks. Round bales, which typically weigh 300 to 400 kilograms are more moisture-resistant, and pack the hay more densely (especially at the center). Round bales are quickly fed with the use of mechanized equipment.

The ratio of volume to surface area makes it possible for many dry-area farmers to leave large bales outside until they are consumed. Wet-area farmers and those in climates with heavy snowfall either stack round bales under a shed or tarp, but have also developed a light but durable plastic wrap that partially encloses bales left outside. The wrap repels moisture, but leaves the ends of the bale exposed so that the hay itself can "breathe" and does not begin to ferment. However, when possible to store round bales under a shed, they last longer and less hay is lost to rot and moisture.

Conditioning of hay has become popular. The basic idea is that it decreases drying time, particularly in humid climates or if rain interferes with haying. Usually, a salt solution is sprayed over the top of the hay (generally alfalfa) that helps to dry the hay. Conditioning can also refer to the rollers inside a swather that crimps the alfalfa to help squeeze out the moisture.

Shipment / Storage

UN NO 1327, classed IMO 4.1, moisture content MUST be advised by the shipper prior to approval. Ignites readily. Liable to spontaneous combustion when wet, damp or contaminated with oil. Refuse for shipment when loose, damp, wet or contaminated with oil. Thus NOT ACCEPTABLE when loose, damp, wet or contaminated with oil.

The provisions of the IMDG Code shall not apply to consignments of compressed baled hay with a moisture content of less than 14% shipped in closed cargo transport units and accompanied by a certificate from the shipper stating that the product does not present any class 4.1, UN 1327, hazard in transport and that its moisture content is less than 14%. With more than 17% moisture hay is NOT ACCEPTABLE.

The packages, including bales, are exempt from labelling provided that they are marked with the appropriate class (e.g. "class 4.2"). Packages, with the exception of bales, shall also display the Proper Shipping Name and the UN number of the substance that they contain in accordance with 5.2.1. In any case, the packages, including bales, are exempt from class marking provided that they are loaded in a cargo transport unit and that they contain goods to which only one UN number has been assigned. The cargo transport units in which the packages, including bales, are loaded shall display any relevant labels, placards and marks in accordance with chapter 5.3.

Risk factors

Consult the IMDG (International Maritime Dangerous Good) Code for transport information.