«MISCONCEPTIONS U. S. GRAIN SORGHUM OF Issue: Palatability Rumor...... Palatability of grain sorghum-based rations is lower than corn-based ...»
P R E FA C E
U. S. Grain Sorghum is considered a high-value ingredient for least-cost feed
formulations around the world.
Its moisture content is lower than many comparable ingredients.
Its palatability is equivalent to corn in grain/soybean-based formulations,
Its utilization by the animal (nutrient availability) is equivalent to corn
when processed appropriately.
It stores easily in warm climates because of its low moisture content.
It breaks little in handling.
It costs less to grind because of its soft kernels.
Its unit cost is lower than many competing ingredients.
It is available year-round at competitive prices.
MISCONCEPTIONSU. S. GRAIN SORGHUM OF Issue: Palatability Rumor...... Palatability of grain sorghum-based rations is lower than corn-based rations.
Fact........ When fed without choice, consumption of sorghum-based rations is equivalent to corn-based rations.
Issue: Nutrient Uptake Rumor...... Utilization by the animal is lower for sorghum-based rations because sorghum nutrients are not as readily available in the gut.
Fact........ When properly processed, uptake in the gut is not significantly differ- ent in sorghum and corn-based rations.
Issue: Tannin Content Rumor...... Grain sorghum is high in tannins.
Fact........ Officially graded U. S. grain sorghum must contain less than 3% of high-tannin varieties. Most shipments contain insignificant levels of high-tannin kernels.
INTRODUCTIONProduction and Export of U.S. Grain Sorghum Grain sorghum was domesticated 3,000 to 5,000 years ago, probably in northern or eastern Africa. Throughout the dry areas of the world, this hardy grass is grown for its seeds, which are used for human and animal food. In the United States, sorghum production is concentrated in the dry states of Nebraska, Kansas, Oklahoma, and Texas (Figure 1). Grain sorghum often is used as a rotation crop with wheat or corn.
The ground is prepared and the hybrid seed is planted in the North American spring season (April–June). Sorghum harvest begins in south Texas in July and moves north, finishing in October or November in Kansas and Nebraska. In most of the major pro- duction areas, grain sorghum is harvested as the cool season begins. Because of the dry climate, much of the grain is harvested with a moisture content low enough to store without high-temperature drying.
Figure 1. Eighty-five percent of all U.
S. Grain Sorghum is grown in these dry states.
2 Physical and Nutritional Characteristics of Grain Sorghum Almost all grain sorghum exported from the U. S. is purchased as U. S. #2. Its average bulk density between 1997 and 1999 was 75.6 kg/hl and its average moisture content was 13.7% (Table 1). Its broken kernel and foreign material content was 4.1% with a dockage content of 0.2%.
Like other cereal grains, sorghum kernels consist of a germ and an endosperm covered by a pericarp (Figure 2). The pericarp contain the fibrous outer layers of the kernel. The germ contains the embryo of the new plant and associated structures. The endosperm is the nutrient storage area for the new plant and contains mostly protein and carbohydrates. U. S. grain sorghum typically contains more protein than corn, but slightly less protein than feed wheats (Table 2). Its carbohydrate content is about the same as wheat or corn, but its energy value is about 4% lower. It is best utilized in the digestive tract of meat animals and poultry when ground to a particle size of 600 microns or smaller.
Figure 2. Internal structure of a grain sorghum kernel.
3 U. S. grain sorghum has a large portion of soft endosperm and, therefore, can be processed easily. When ground to 900 microns, U. S. sorghum requires about 34% of the energy required by U. S. corn. For a 500 micron or smaller particle size, U. S. grain sorghum requires about one-fourth the energy needed for corn. Grinding rates are often much higher for U. S. sorghums than for corn. Pelleting energy, percentage of fines, and pellet durability of U. S. sorghum are equivalent to those of corn.
SEED. U. S. grain sorghums are hybrid varieties developed through multi-milliondollar breeding research programs funded by private seed companies, producer groups, and government entities. A network of seed companies and university evaluators provide grain producers with the latest information on variety trials. The resulting seed is adapted to the dry plains on which U. S. grain sorghum is produced.
SOIL AND CLIMATE. The deep, rich soils of North America provide an excellent terrain for grain sorghum. Because of the dry climate in most of the production areas, U. S. grain sorghum rarely experiences the mold and mycotoxin problems that plague sorghums grown and harvested in wet climates.
INFORMATION. A network of private suppliers, government and academic scientists provide growers with the latest research and technology information on agronomic practices, including tillage, crop protection, fertilization, and mechanization. This information helps the grain sorghum producer make the best use of the fertile soil and dry climates to which U. S. grain sorghums are adapted and assures the efficient production of high-quality grain.
MACHINERY. U. S. grain sorghum is planted, tilled, and harvested mechanically.
During exceptionally wet years, some of the crop is dried in high-temperature grain dryers before storage. Grain sorghum is not as susceptible to breakage after drying as is corn, and even when the grain is high-temperature dried, grain quality is maintained easily. Some sorghum grain is stored on farms, usually in metal bins, and the remainder is stored in commercial grain elevators, which may have either metal or upright concrete bins. Most grain sorghum is cooled quickly after storage and is stored cold, until it is used domestically or moved to export. The cool temperature and low moisture content of most grain sorghum helps managers maintain quality in storage at minimal cost.
4 MARKETING. A massive and sophisticated system of marketing information, official grain inspection, and grain storage and transportation equipment allows sorghum to be moved to the export elevator efficiently. Most sorghum is transported from inland elevators on dedicated grain trains directly to the export elevators or to border transfer points in Texas. Large quantities also are transported by river barge to Louisiana Gulf export elevators.
QUALITY. Throughout the system, grain is sampled to determine quality characteristics. At inland locations, grain in trains and barges bound for export facilities is sampled by trained inspectors who are supervised by federal government inspectors. At export, all grain is inspected by the Federal Grain Inspection Service (FGIS) unless the contract mandates otherwise. Most contracts reference a U. S. grain grade as the basis of quality inspection. The U. S. grain grading system provides a well-known standard that does not vary from year to year with the quality of the crop (Appendix 1).
SUMMARY. The U. S. grain sorghum crop begins with quality-assured seed of varieties developed to provide maximum yield and excellent feeding value. The seed is one component of an agricultural system operated by experienced producers aided by a vast network of private and public sources of information and agricultural inputs. Tillage, fertilization, harvesting, and marketing take place in a mechanized system that provides maximum grain value at minimum cost. The highly capitalized merchandizing and transportation system assures that this value is transferred to the point of export in the most efficient way possible. Thus, importers of U. S. grain sorghum are assured of a product that has high intrinsic value and is delivered to them at minimum cost.
5 STORAGE OF U. S. GRAIN SORGHUM IN
T R O P I C A L C L I M AT E SWhen U. S. grain sorghum arrives at tropical destinations, it often must be stored before processing. Some grain is stored for short periods without the benefit of a protective structure. In dry climates, grain sorghum stores better in unprotected piles than do most grains because of its low initial moisture and ability to withstand light rains with little or no damage. However, outdoor piles provide no protection against rain or wind, and the grain is subject to contamination by insects, birds, and rodents.
Therefore, all grain should be stored inside protective structures such as warehouses, metal bins, or concrete silos, especially in tropical climates. Each storage structure has associated advantages and disadvantages for tropical storage.
6 Causes of Grain Deterioration During grain handling and storage, many factors may contribute to grain quality deterioration.
Mechanical breakage. When mechanical forces encountered in harvesting and transport cause breaks in the pericarp, the nutritious endosperm and germ tissue is exposed to attack by insects and molds. Small pieces of broken kernels and other small particles fill the open spaces between kernels, compacting the area and slowing the dissipation of metabolic heat and moisture out of the grain mass. Although the broken kernels of grain sorghum contain the same nutrients and energy value as the sound kernels, large numbers of cracked or broken kernels facilitate deterioration and should be avoided, if possible.
Leaks. In transport or storage, leaks may allow rain or seawater to contaminate the grain. Areas of moldy grain may result.
Molds. Some of the same molds that thrive in the wet grain caused by leaks are able to grow slowly in warm, dry grain. At the low moisture contents typical of exported U. S. grain sorghum, molds develop so slowly that, for practical purposes, they can be considered dormant as long as the grain is cool. However, when the grain is exposed to the warm, humid air of tropical climates, molds at the grain surface may begin to develop colonies that could affect grain quality if storage is extended.
Grain deterioration often occurs even though the mold that caused the deterioration never is visible. This invisible threat is controlled better if the storage manager understands certain parameters of mold-induced deterioration.
Not all the molds present in the grain are active during storage. Molds of the genera Fusarium and Alternaria, among others, infect the seed before it is harvested. These “field” molds become dormant when the seed dries to below 20% moisture and remain dormant unless the available moisture becomes very high. This may occur if water leaks on the grain or if excessive water is added during processing. In contrast, “storage” molds, mostly members of the genera Aspergillus and Penicillium, are able to develop using the water available in grain containing as little as 13% moisture, depending on temperature. Various species of these molds are able to exploit slightly different moisture and temperature conditions within the grain mass.
The molds commonly found in U. S. grain sorghum occur in all types of grains, regardless of country of origin, in all climatic zones. Mold spores and other reproductive structures are microscopic. They germinate under favorable temperature and moisture conditions to produce a tubular body called a hypha. As hyphae continue to grow, they form a tangled, branched mass called a mycelium. Mycelia are nearly transparent and difficult to observe; though experimental procedures using a microscope allow stained mycelia to be seen on the surface and under the outer layers of stored grain. Under optimum conditions, mature masses of mycelia produce spores.
The spores and other reproductive structures have color, and masses sometimes can be seen with the naked eye, if the deterioration is severe.
7 The first four toxins (DON, T2, zearalenone, and fumonisins) are produced by field fungi before the grain is harvested. Thus, even severe deterioration by storage molds cannot result in the production of these substances. In contrast, aflatoxin is produced by certain Aspergillus molds that can infect seeds either before harvest or during storage. In those rare instances when aflatoxin is observed in U. S. grain, it usually is produced before harvest. This is typically observed in grains other than sorghum.
It is much more likely to be found in grain harvested wet in tropical climates than in grain imported from temperate climates such as the U. S. However, under rare and unusual circumstances, rapid growth of certain strains of certain Aspergillus species in moist grain under high temperatures can cause aflatoxin contamination of the stored grain. Aflatoxicosis can produce liver cancers, reduced feed consumption, poor feed conversion, and many other symptoms depending on the species and age of the animal. To control the risks associated with mycotoxins, many feed millers routinely screen feed ingredients. Quick-test kits are available from several vendors to test for the most common toxins.
Insects. A variety of small insects can infest dry grain sorghum. The genera and species of grain-infesting insects are similar throughout most of the world.
Cosmopolitan beetles likely to be found in stored grain sorghum include the weevils (Sitophilus spp.), the lesser grain borer (Rhyzopertha dominica), the sawtooth grain beetle (Oryzaephilus spp.), flour beetles (Tribolium spp.), and flat or rusty grain beetles (Cryptolestes spp.). A few species of moths, psocids, and mites also inhabit stored grain sorghum. Grain held long-term in the dry tropics also is attacked by indigenous insects such as Trogoderma granarium or Prostephanus truncatus.
Because nearly all importers of U. S. grain sorghum store the grain for less than two months, insect problems seldom are reported.