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Introduction to Cereal Grains

In livestock rations, the cereal grains are one of the primary sources of energy. Cereal grains are the seeds of plants of the grass family. The cereal grains have been bred to increase the starch content of the cereal grain seed. In the U.S., the primary cereal grain fed to livestock is corn. In the U.S., other cereal grains fed to livestock to various degrees include sorghum or milo, coarse grains including barley and oats, wheat, triticale, and rye. Table 4.1 states the total and relative amount of the major cereal grains produced in the U.S. in 2001. The data are estimated data.

In the U.S. commercial market, the majority of the cereal grains are traded on the basis of bushel weight. Grains may also be traded on the basis of ton. A bushel is a set volume; the volume of a Winchester bushel is 2,150 cubic inches. To determine the test weight, the bushel is filled and the weight of the bushel of grain is measured. As the bushel weight increases, the value of the grain also increases. The system is based on the fact that the increase in density is associated with an increase in starch content, a decrease in fiber content, and therefore an increase in energy content. Grains may be valued based on grades. Grades combine bushel weight and quality measures. Examples of factors that influence the grade of the grain include presence of foreign material, antinutritional components, broken or damaged kernels, etc. Grading standards are established by the Federal Grain Inspection Service. The Federal Grain Inspection Service is a division within the United States Department of Agriculture’s Grain Inspectors, Packers, and Stockyards Administration. The following website defines the official grading standards for the grains in the United States: http://www.usda.gov.gipsa/reference-library/standards/standards.htm. Moisture is classified as a non-grade determining factor. However, as moisture influences the quality of a grain moisture levels may influence the final trade value of the grain.

In general, the nutritional values of cereal grains are relatively similar between the grains. Table 5.4 on page 61 in the text describes the average nutrient composition of the major cereal grains. The nutrient compositions are stated on a dry matter basis. In addition, the nutritional value of cereal grains is relatively constant. Examples of the factors that may influence the nutritional value of a cereal grain include the variety of the grain, fertility of the soil, weather, and presence of pests and disease. Figure 4.1 illustrates the general structure of a cereal grain and the primary nutrients associated with each component. The following section will describe the general nutritional value of the cereal grains. The cereal grains are highly digestible. The digestibility of the grain varies by grain species and quality. For example, heat damage will decrease the digestibility of a grain. As expected, the cereal grains are high in nonstructural carbohydrates. The primary carbohydrate in cereal grains is starch. As described, starch is composed of glucose molecules arranged as either amylose or amylopectin. The type of molecule, chain length, and extent of branching varies between the grains. The cereal grains are low in structural carbohydrates. The carbohydrate cellulose is a component of the cell wall of the kernel and the hulls. Lignin is also a component of the hull. The differential carbohydrate content decreases the nutritional value of grains fed with hulls. Generally, the crude protein content for cereal grains is between 8-14% on a dry matter basis. Wheat is one exception. Generally, the crude protein content of wheat is greater than the average range. In terms of protein quality, the proteins, solubility, and amino acid content varies between cereal grains. In general, the cereal grains may be low in lysine, tryptophan, threonine, and methionine. Generally, the amino acid profile of cereal grains can be stated in the following order: oats > barley > wheat > corn > rice > rye > sorghum > millet. The lipid content ranges from less than 1% to greater than 6%. The predominant fatty acids are palmitic, linoleic, and oleic acid. In terms of minerals, the cereal grains are low in Ca and high in P. A portion of the phosphorus may be bound with phytic acid in a phytate complex. For monogastrics, the availability of the bound P is low. In general, the cereal grains contain low amounts of the microminerals. In terms of vitamins, cereal grains are fair sources of vitamin E, low in A and D and most of the B complex vitamins. One exception to the rule is corn. Corn is a good source of carotene, a precursor of vitamin A.

In comparing the nutritional value between the cereal grains, the most important component to compare is the energy content of the cereal grains. Table 5-13 on page 71 of the text describes the relative ME value of each of the grains for ruminants, poultry, and swine. Corn is the standard; set at 100. The energy values of the other cereal grains are stated in comparison to the energy value of corn. The majority of all the cereal grains for all the species have a lower energy value than corn. Crude protein is also used to compare the nutritional value of cereal grains. Table 5-13 on page 71 of the text describes the relative crude protein value of each of the grains for the ruminants, poultry, and swine. Corn is also the standard for the crude protein comparison. Again, corn is set at 100. In contrast to energy value, the other cereal grains have a higher relative crude protein value than corn.

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