Updated: Jun 22, 2021
#Rough rice, also called paddy rice, is the whole rice grain with the hulls (about 20% of the grain). It is a coarser product than brown rice, which is the rice grain without the hulls but still containing the bran, or polished rice, which is the rice without the bran. Paddy rice is much less used for animal feeding than other grains, as it is often more expensive and less available. Also, it tends to have a lower nutritional value due to its higher fibre content. However, the overall decline in per capita rice consumption, especially in the middle and high-income Asian countries like Korea and Japan, during the later decades of the 20th century has led to a renewed interest in the utilization of rice grain as a livestock feed. Cultivation of feed rice has been encouraged in the 2000s, for instance in Japan, where there are feed varieties of rice (e.g. Momiroman)
Suply / Distribution
Rice originates from Asia, where it has been cultivated since 6500 BC and is now naturalized in most tropical and subtropical regions. Rice grows from 53°N in China to 35°S in Australia. The optimal growing conditions are: an average day-temperature of 20-30°C, with a night temperature over 15°C; fertile, heavy soils; and a pH of 6.5-7. Most varieties ("swamp rice", "lowland rice") must be planted in stagnant water and require 200 mm rainfall/month or an equivalent amount from irrigation, whereas others ("mountain rice" or "upland rice") require less irrigation and 750 mm rainfall in a 3-4 months period and no dessication.
Grinding and dehulling
Rough rice grains are very hard and abrasive and should be ground before they are used as animal feed, particularly for monogastric animals
Forage rice grain is difficult to store in the same way as food rice because the drying process is not suitable for post-harvest storage, due to problems such as high cost and contamination of forage rice grain with food rice in rice processing facilities or country elevators. Ensiling has been proposed as a useful storage method since it does not require drying by heating. It was found that adding moisture, crushing, and adding lactic acid bacteria enhanced lactic acid fermentation, providing high fermentative quality in rice-grain silage. During a long storage period, not only lactic acid but also butyric acid and volatile basic nitrogen increased, however, a lactic acid bacteria additive can inhibit increases in butyric acid and volatile basic nitrogen
Rough rice is relatively poor in protein (7-12% DM) but rich in starch (62-67% DM) so it is mainly used as an energy source. However, compared to other cereal grains, it is particularly rich in fibre (crude fibre 9-15% DM, lignin 5-6% DM) due to the presence of hulls, which tend to limits its use to ruminants or to fattening livestock. The presence of non-starch polysaccharides such as arabinoxylans and β-glucans may also be detrimental in monogastric diets.
Rice bran is the most important rice by-product. The bran fraction contains 14-18% oil. Rice bran that has not been defatted is a useful binder in mixed feeds. Defatted rice bran can be used at higher levels than ordinary rice bran. Rice bran is often adulterated with rice hulls, as it should have a crude fibre content of 10-15% .
Manufacturing and products
After threshing, the rough rice is transported to mills for processing into white rice (polished rice) through a series of operations that free it from the hull, germ and bran. In many countries the processing of rice for local use is still carried out in one-stage mills. The by-product of this simplest form of processing is a mixture of hulls and bran that seldom reaches the market as it is usually returned to the rice grower.
In large-scale mills the rough rice undergoes several processes: cleaning, parboiling, hulling, pearling, polishing and grading. The cleaning process removes all extraneous matter, such as "dead" grains, stones and stalks. For certain varieties it is necessary to parboil (steep) the cleaned rice in hot water for a time to facilitate removal of the hull and improve the keeping quality of the grain. This process also improves the thiamine content of the grain.
There are several methods of removing the hull. After hulling, the germ and outer bran are removed in a set of huller reels and pearling cones in which the waxy cuticle is scoured off by the friction between the high-speed abrasive cone and its casing. The resultant bran meal is propelled through meshes of wirecloth and collected. The milling space between the cone and the casing is adjustable so that the milling rate can be varied by raising or lowering the cone. In most mills the rice passes through several cones, each with a higher milling rate. The bran from the different settings is usually mixed into one product. For a finer appearance, rice from the pearler is passed through polishers. These machines are similar to pearling cones except that they contain a drum covered with strops of hide rather than an abrasive cone. In this process a part of the starchy kernel (endosperm) is removed. If inner bran layers are included, the product is called fine bran, or pollard. The mixture of whole and broken rice from the polishers is separated in sieves and then remixed in proportions corresponding to the standard at which the rice is to be sold.
The percentage of by-products depends on milling rate, type of rice and other factors. The following figures give an approximate idea of the proportions: hulls, 20%; bran, 10%; polishings, 3%; broken rice, 1-17%; polished rice, 50-66%. Rice pollards are a mixture of bran and polishings. Rice mill feed, a mixture of all the by-products obtained in the milling of rice, contains approximately 60% hulls; 35% bran and 5% polishings. The offal obtained from one-stage mills is of similar composition and is often erroneously called "rice bran". Production of rice mill feed in multi-stage mills is somewhat cheaper than separate production of the ingredients.
Rice by-products are available worldwide.
Irrigated rice causes anaerobic fermentation in the soil, subsequently producing large amounts of CH4 (from 6 to 29% of the total amount of anthropogenic CH4 emissions), one of the most important greenhouse gases. Lodging also causes acidification and increases salinity. Specific water demand for rice ranges from 2000 to 3000 l/kg which is slightly higher than other crops such as legumes or wheat.
Rice bran is a good source of B vitamins and is fairly palatable to farm animals. The oil has a marked softening effect on body fat and on the butterfat in milk. With attention to the oil content, rice bran is a valuable feed for all classes of livestock. Rice pollards are used in the same way and with the same limitations as rice bran. It should be noted that rice milling by-products do not follow strict naming conventions. Many products called "rice brans" are mixtures of by-products obtained at different stages of the milling process, resulting in large variations in chemical composition.
Rice hulls are the by-product of rice dehulling. They are used in some countries for poultry litter that can later be fed to ruminants. Numerous publications on uses of rice hulls attest to the many attempts to solve the problem of disposing of this by-product.
Rice originates from Asia where it is known to have been growing since 6500 BC. It was then brought to all tropical regions within centuries. Rice grows from 53°N in China to 35°S in Australia. The optimal growing conditions are: 20-30°C average day-temperature with night temperature over 15°C; fertile, heavy soils, 6.5-7 pH. Most varieties ("swamp rice", "lowland rice") must be planted in stagnant water and require 200 mm rainfall/month or equivalent amount from irrigation, whereas others ("mountain rice" or "upland rice") require less irrigation and 750 mm rainfall on a 3-4 months period and no dessication.
Irrigated rice causes anaerobic fermentation in the soil, subsequently producing high amounts of CH4 (6 to 29% of the total amount of anthropogenic CH4 emissions) one of the most important greenhouse gases (Neue et al., 1993). Lodging also causes acidification and increases salinity. Water specific demand for rice is ranging from 2000 to 3000 l/kg which is slightly higher than other crops like legumes or wheat
Rice hulls can be used in animal feeding in the following ways:
As raw rice hulls. Low-quality roughages like ground rice hulls can be included in small amounts (up to 15%) in high-concentrate diets for feedlot cattle to help furnish bulk, stimulate appetite and decrease incidence of liver abscesses. In areas with a shortage of roughage, ground rice hulls can be used in place of straw or advantageously as a partial replacement for it. The addition of ground rice hulls has been found in some cases to increase the feed intake.
As ammoniated rice hulls. A process developed for making livestock feed from hulls includes the addition of monocalcium phosphate, removal of silica, ammoniation under pressure and toasting. Ammoniated rice hulls have been used in proportions of up to 40% of the total ration for sheep, without digestive or mastication problems.
Together with bran and polishings.
Horses and donkeys
In Australia, ground rice hulls have been used successfully in lower energy horse feeds at 25% inclusion in the pelleted part of the ration.