By-Product Feeds -- Wet Corn Milling
Livestock Update, May 1999
Mark Wahlberg, Extension Animal Scientist, 4-H Livestock, Animal and Poultry Sciences, Virginia Tech
Corn is processed using a wet milling procedure to produce several important products. The most abundant of these is starch, which is further processed to generate sweeteners used mostly in soft drinks. In addition, oil is also separated from the corn in this process. One hundred pounds of dry corn produces 67 pounds of starch and sweeteners, 3.6 pounds of oil, and 29.4 pounds of byproducts or coproducts.
The byproducts consist of the bran (seed coat), germ (center of the grain), gluten (high protein component of corn flour), and other solids (extractives). Major byproducts are corn gluten feed and corn gluten meal. If separated, the meal is about 5.3 pounds of the original 100 pounds of corn. It is high in protein (40 or 60%). Corn germ meal, 3.8% of the original, remains after the oil is extracted and is fairly high in fiber. The solubles, called Condensed Fermented Extractives, composes 7.1% of the corn. It has no fiber, is moderate in protein, and contains lots of minerals, especially Phosphorous. The final component, corn gluten feed, represents 12.2 pounds of the original 100 pounds. It contains the bran and may contain substantial amounts of germ, gluten, and extractives, depending on the processing used by the plant. Consequently, corn gluten feed is not a uniform product.
Quantities of corn processing byproducts have increased dramatically recently. In 1994 gluten feed and meal totaled 397,000 metric tons, while in 1996 the total was 3.5 million metric tons, almost a ten-fold increase. Although not available, more recent figures undoubtedly are even greater. They are used as feed sources by livestock, most often dairy and beef cattle. They can be incorporated into manufactured feeds or purchased as commodity feeds for use as separate ingredients.
Because these feeds are byproducts of wet milling, they can be obtained from the plant in high moisture form. Typically the partial removal of liquid leaves a feed that is moderate in moisture, somewhere in the range of 40 to 60% dry matter. Wet corn gluten feed has a shorter storage period and must be handled in bulk instead of put into bins and moved with an auger. On the other hand, dry corn gluten feed is easily handled and stored. Because it is contains little water the nutrition is more concentrated and it can be transported economically for a longer distance.
Typically the only feed available on the commodity market is corn gluten feed. The other byproducts are either dumped into corn gluten feed or are routed into the feed manufacturing business. Nutritive values to be used as a guide for corn gluten feed (all values on a dry matter basis) are Dry matter=90%, TDN=83%, Crude Protein=25.6%, Crude Fiber=9.7%. It contains around 36% Neutral Detergent Fiber (NDF), but only 1/3 of this is effective fiber, which provides scratch to the rumen like long hay does.
Corn gluten feed is a unique feed, in that it is high in energy but contains little starch. Most of the energy comes from readily digested fiber found in the bran portion of the corn grain. Because the effective fiber is so low, however, it really is not a substitute for forage.
Corn gluten feed is best used as a supplement to forage-based feeding programs. Because it contains little starch it does not reduce the digestibility of the forage portion of the ration like would happen when feeding high starch feeds. High starch grains begin to cause a reduction in forage digestibility when fed at more than 0.5% of body weight of the animal. Thus it truly acts like a supplement rather than as a substitute for forage. It also provides substantial protein, so that protein supplementation from another source is not normally needed when corn gluten feed is fed.
Corn gluten feed can be obtained in wet or dry form, and when dry it is available as either the natural form or as a pellet. Dry corn gluten feed can be light and fluffy, a problem solved by pelleting. It weighs approximately 30 pounds per cubic foot, as compared to shelled corn which is 48 and Soybean meal at 42.