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Grain Sorghum

In the U.S., grain sorghum is the second most important cereal feed grain. In the U.S., for 2001, the estimated total production of grain sorghum is 514 million bushels. In addition to the grain sorghums, there are also nongrain varieties such as forage sorghums and Sudan grass. In the U.S., the most popular grain sorghum is milo. Sorghum is grown in the Great Plains region of the country. Figure 4.8 illustrates a field of sorghum. In general, compared to other grains, sorghum is a hardier plant, i.e. more heat tolerant, drought tolerant, pest resistant, and tolerant of poorer quality soils. The estimated average yield for sorghum grain is 59.9 bushels per acre.

The sorghum seed grows on the head of the sorghum plant. The head of the plant can be a number of colors including white, yellow, red, and bronze. Compared to the corn plant, the sorghum plant is shorter.

Figure 4.9 illustrates sorghum seeds on the head.

As illustrated, the sorghum seed is exposed and may be susceptible to predation. The sorghum seed is small and hard.

Figure 4.10 illustrates sorghum seed.

The sorghum seed requires processing to achieve maximal nutritional value. Given appropriate processing, the nutritional value of the sorghum grain is similar to the nutritional value of corn grain.

Table 4.3 summarizes the average nutrient composition of sorghum grain.

As an energy source, in comparison to corn, sorghum grain has a lower and more variable starch content. As a protein source, in comparison to corn, sorghum grain has a similar but more variable protein content. The primary protein in sorghum grain is kafirin. Similar to zein in corn grain, kafirin is also a prolamine. Sorghum grains are primarily low in lysine, threonine, and methionine. In terms of mineral and vitamin content, sorghum does not have any distinct characteristics.

There are multiple sorghum grains that have been developed and are in use. One variety is the normal or nonwaxy sorghum grain. A second variety is the waxy sorghum grain. In comparison to the nonwaxy, the waxy grain has shown an improved feeding value. A third variety is the heteroyellow endosperm which has an improved feeding value over the nonyellow. Another variety is the bird-resistant sorghum grain. Bird-resistant sorghum grains are high in tannins. In comparison to the other grain sorghums, the brown bird-resistant sorghum grains have a lower digestibility and resultant animal performance. In general, brown seeds have a higher level of tannin compared to the lighter colored seeds.

The primary antinutritional factor of sorghum grain is tannins. Tannins are polyphenolic compounds. Tannins possess astringent properties that reduce the palatability of the feed. In addition, in the digestive tract, tannins will complex with protein and reduce protein availability and react with enzymes reducing the digestibility of additional nutrients. Selecting sorghum grains high in tannins, gives an advantage in terms of pest resistance but a disadvantage in terms of nutritional value. Processing may improve the nutritional value of sorghum grains high in tannins.

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