Cereal grains are seeds produced by plants of the grass family Gramineae for animal feed and human food. Corn, wheat, and the coarse grains barley, oats, and sorghum are used for animal feed, whereas very little rice or rye are used for animal feed.[1,2] Nutrient composition values for feedstuffs fed to livestock are provided in comprehensive publications1-3,4-1 and in the nutrient requirement publications for each livestock species.[5-8] Book values provide useful estimates of feedstuff nutrient composition. However, nutrient composition of cereal grains may vary from one region or year to the next because of differences in plant genetics or environment (e.g., soil fertility and rainfall). With the continued development of new trait-related and genetically modified grains, it may be prudent to obtain analytical nutrient composition values for current feedstuffs to increase the validity of the data used in diet formulation. Laboratories must be selected with care, however, because the analytical variability between laboratories may be as great or greater than the variability within ingredients. The feeding values of the commonly fed cereal grains are discussed subsequently, excluding rice, which is grown almost exclusively for human consumption.
Corn (Zea mays), also called maize, is native to the American continent and is the most important feed grain in the regions of the world where the soil, temperature, and rainfall are suitable for growth. Corn can produce more energy per acre than any other cereal grain because it has a C4 photosynthetic pathway that utilizes solar energy more efficiently than C3 plants. There are several types of corn, but dent yellow corn is the primary type grown for feed. Corn has the highest metabolizable energy (ME) in Mcal/kg [89% dry matter (DM)] compared with all other grains, with values that range from 3.03 for ruminants to 3.30 and 3.38 for swine and poultry, respectively. The main energy-yielding fraction is the starchy endosperm consisting of amylose (about 25%) and amylopectin (about 75%). Corn contains about 4% oil, of which the fatty acid composition is about 50% linoleic acid.[5,6] Corn hybrids have been developed that have higher contents of oil or lysine (Opaque-2), or a lower content of phytic acid. Feeding low-phytic acid corn hybrids will reduce phosphorus and other mineral excretion in poultry and swine manure.[11,12]
Grain sorghum (Sorghum vulgare) includes several varieties, of which milo is the most important as a feed grain in the United States. Milo is more resistant to heat and drought than most grain crops. It may be grown on a variety of soil types, and is usually grown where the environmental conditions are too harsh for corn. Compared with corn at 100%, the ME feeding value of milo ranges from 96% when ground for nonruminants to 99% when steam flaked for ruminants. A higher tannin content (dark seed color) lowers nutrient digestibility.[1,2] Barley (Hordeum vulgare) is well adapted for growing seasons that are too short for corn production in the cooler regions of United States, Canada, and Europe. There are many types of barley that are grown for livestock feed or to make malt for beer production. Compared with corn, barley contains more protein and amino acids, but is lower in fat and higher in fiber. Barley contains beta-glucans, water-soluble carbohydrates that are poorly digested by poultry and weanling swine.[2'9] Feeding low-phytic acid barley will reduce the excretion of phosphorus and other minerals in poultry and swine manure.[13'14] Compared with corn at 100%, the ME feeding values of barley are 75%, 89%, and 96%, respectively, for poultry, swine, and ruminants.
Wheat (Triticum spp.) is grown primarily for human consumption, and ranks first in world grain production. Wheat is higher in protein and lower in fat than corn. Wheat should not be finely ground for nonruminant diets fed as a meal to avoid sticky diet problems that reduce consumption. Dry- or steam-rolling increases the feeding value for feedlot cattle, although lactic acidosis is more common in cattle fed wheat than corn. Compared with corn at 100%, the ME feeding value of wheat is about 95%, 97%, and 100%, respectively, for poultry, swine, and ruminants.[1,2]
Oats (Avena sativa) are of minor importance as a livestock feed because they are higher in fiber and lower in energy than other grains. The energy yield per acre is also low, making oats less profitable to grow. However, oats have the highest protein content of the grains, and hull-less oat cultivars are available that have a higher energy content than hulled oats. Compared with corn at 100%, the ME feeding values of hulled oats are 75%, 80%, and 87% for poultry, swine, and ruminants, respectively.1-1,21
Rye (Secale cereale) is cold-tolerant and will grow at high altitudes in northern climates. It will also grow in acid soils with low fertility. However, rye is susceptible to ergot infection, and contains pentosans that reduce the feeding value for poultry. Compared with corn at 100%, rye has ME feeding values of 79%, 89%, and 96% for poultry, swine, and ruminants, respectively.1-1,2-1
Triticale, a grain derived by crossing durum wheat and rye, has poor palatability similar to rye, whereas the energy value is closer to that of wheat. Compared with corn at 100%, the ME feeding value is 92% for poultry and swine, and 96% for ruminants.[1,2]
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